GASSCHROMATOGRAPHY, ADVANCED STUDY OF THE FOLLOWING AND THEIR APPLICATIONS, INTRODUCTION, THEORY, COLUMN OPERATION,INSTRUMENTATION AND DETECTION,APPLICATIONS AND ADVANTAGES OF GC,PRINCIPLE OF SEPARATION IN GC, HOW GC MECHINE WORKS? COLUMN, DETECTORS.

Gas-liquid chromatography (often just called gas
chromatography) is a powerful tool in analysis.
Prof. p. Ravisankar
Vignan Pharmacy college
Valdlamudi
Guntur Dist.
Andhra Pradesh
India.
banuman35@gmail.com
00919059994000
GAS CHROMATOGRAPHY

Chromatograph(or)
Chromatogram
Column
( A separation Technique)
Injection port
Gas separator (or) Aerograph.
Gas chromatography (GC) is most widely used analytical method for the separation of
volatile and semi-volatile organic compounds without decomposition
Small amounts of sample For ex.1ml
of air 1µl (microlitre) uL; 1/1000 of a
mL)the solutions either Liquids in
solids in solution
The compounds are separated primarily based on the relative(differences in their) volatilities
What is gas chromatography?
Genarates a written record of analysis

All forms of chromatography involve a stationary phase and a mobile phase. In all the other
forms of chromatography you will meet at this level, the mobile phase is a liquid. In gas-
liquid chromatography, the mobile phase is a gas such as helium and the stationary phase is
a high boiling point liquid absorbed onto a solid.
Introduction

From the column, the separated solutes pass
through a detector where they are sensed
generating an electronic signal. The signal is
then amplified and normally displayed on a
strip chart recorder. The trace plotted on the
recorder is called a "Chromatogram".
It is a plot of the detector response in millivolts
as a function of time.
Time is the Abscissa(horizontal or X-axis)
And
millivolts the Ordinate.(y- coordinate(vertical
axis)

Gas Chromatograph Components
Flame
Ionization
Detector
Column
Oven
Injection Port
front view

One milligram in a kg is 1 ppm (by mass). One
liter . so 1 mg/L is 1 ppm
One ppb represents one microgram of
something per liter of water (ug/l), or one
microgram of something per kilogram of soil
(ug/kg).
GC
with a TCD the components can continue on to another detector after
passing through the TCD; thus it is considered a non-destructive detector
(this can be useful for further analysis.

What are advantages of GC?
The GC is one of popular instrument used in the world
Several advantages include
High resolution.
High speed.
High sensitivity
The GC is robust, flexible, and user-friendly.
Most importantly, it has the best value in the market..
High resolution :Many compounds can be resolved nicely
for ex: Gasoline has been resolved in to over 300 different peaks complex
sample of Petroleum. (complex mixture can be resolved in constituents)
The term resolution refers to well separated two peaks
are from each other.
If two peaks are so close together that you can’t tell when one peak
begins and the other ends the resolution is poor; you can also say that
the separation is poor.
If you can clearly identify two different peaks- the resolution is good.
The longer and more narrow the column, the better the resolution.
Increasing the carrier gas flow rate and/or the temperature will send
the vapours through the column faster, which will lower the retention
time and worsen the resolution. Lowering the temperature
and/or flow rate increases retention times and broadens the peaks.

Analyze in a matter of minutes and few compounds can
analysis in a matter of few seconds also possible.
we see both rapid analysis as well as high sensitivity.(detectability) even
Providing selective(identification)
For ex a 2 1/2 min of separation 3 common pesticides
Methyl parathion, Malathion, Ethion at pg levels. Pg 10-12 grams means these are
parts per billion. (One trillionth of a gram )This is a very good ex of both the high speed as
well as a very sensitive detection.
.
Methyl parathion
Malathion
Ethion

: It gives good precision and accuracy. (free from errors)
Accuracy just means we do quantitative analysis we get a very good results write
answer, good quantitative results. (possible or actual deviation from the exact
answer(exactness).
GC is also a very easy technique compare to some very well known .
most widely used instruments in the world todayGC and liquid chromatography together just been the premier techniques for Trace analysis
of organic and inorganic compounds.
All the work which has been done by
Air pollution
and water pollution
and food safety
we hv. to analyze for pesticides toxic chemicals founds in Food and food products all of
these things are done by routinely daily and rapidly by gc and or liquid chromatography.
In essential role of chromatography is the QC and foods, and drugs control in raw material
and finished products ensuring the safety of the people. we are so dependent on the world
today on chemicals synthetic chemicals made by chemist.
Primarily pesticides very good for agriculture and very harmful for humans. So
Chromatography is the best separation technique for quantitative trace analysis of toxic
chemicals.

1. GC the samples must be volatile.
Allow to heat the samples up to 3000 and 3500C at that point we must generate
Vapors that can be easily carried by the carrier gas.
2. Dirty samples require cleanup. dirty samples Duran,
waste water Extracts of many things.
and these samples normally contaminate the system and
may even Plug up the column and destroy the column and these case often times
we will extracts with the Solvents to take off the imp components.
3. Another limitation is we must use another instrument for ex a Mass spectrometer
for conformation
Typically we use the retention time of standards of un knows to decide what the
peak can be.
but Legally in the us the retention times are not considered a conformation. A MS
is need for conformation if necessary.,
and finally of course some training/ and some experience is necessary in order to
get good results.
Samples for GC:
They can be gases
Almost every gas has been analyzed liquids and some solids
solids are Usually dissolved in a low boiling solvents and analyzed.
Molecular wt. has been done easily from Molecular weight 2 hydrogen, up to over 800
(2 to~800).
But we must be honest also limitations….

In exceptional cases simple hydrocarbons MW up to 1200 have been separated.
Samples can be organic and inorganic
But most of the things in GC are organic compounds.
Inorganic would be water or gases.
The samples always must be volatile but you cant do rocks , sticks or stones and
You can’t also do proteins, peptides and biological molecules those are better done
by liquid chromatography.
For Quantitative analysis peak area is proportional to the concentration
I would like to show u some data here
this is a very simple sample of hydrocarbons
Decane,(C10H22)undecane(C11H24) ,dodecane(C12H26), tridecane(C13H28)
which would blended up volumetrically and
Using density is calculated mass in grams this is determined by GC plus 1 SD
and results and relative error is less than 1% in this case. This is a simple sample
Done by flame ionization to gather with aid of computer typical very high accuracy
One can obtain.
Quantitative analysis is the major advantages of GC.

GASSCHROMATOGRAPHY, ADVANCED STUDY OF THE FOLLOWING AND THEIR APPLICATIONS, INTRODUCTION, THEORY, COLUMN OPERATION,INSTRUMENTATION AND DETECTION,APPLICATIONS AND ADVANTAGES OF GC,PRINCIPLE OF SEPARATION IN GC, HOW GC MECHINE WORKS? COLUMN, DETECTORS.

Chromatography
Introduction:
The term chromatography is derived from a Greek words
Chromatos= meaning colour.
Graphos = written.
Initially used for analysis of coloured compounds now due to vast
Developments it is also applied to colourless compounts.
Chromatography is the separation technique of a mixture of compounds
(solutes) into separate components By using a stationary phase and a
mobile phase so it is easier to identify (qualitative) and measure the
amount (quantitate) of the various sample components.
Chromatography makes use of 2 phases. The mobile phase and the stationary phase.
Mobile phase refers to the mixture of analyte while stationary phase consists of fixed solid or
Liquid medium. The mobile phase run over the stationary phase and the mixture gets distributed
b/n these 2 phases resulting in the separation of analyte/solute. Finally separated analyte is
Identified qualitatively or quantitatively by Massspectrometry,IR,NMR.
The technique for GC is similar to that of column Chromatography except
that the liquid mobile phasein the column chromatography is replaced by
a moving gas.

History
– Russian botanist and physical
chemist Scientist Mikhail
Semenovich Tswett is credited
for the discovery of chromatography
in the early 1900’s (1903).
– Germangraduate student Fritz Prior is
credited for developing
solid state gas chromatography
(1947).
– However the foundation of the GSC
was laid down by Damkohler and
Thiele in 1943.

Mikhail Tswett, Erika Cremer, A.J.P. Martin og Richard L. M. Synge

• Modern GC was invented in 1952 by Martin
and James.
• The father of modern gas chromatography is
Nobel Prize winner(1952) John Porter
Martin,Synge who also developed the first
liquid-gas chromatograph. (1950).
• The gas chromatography technique was first
carried out in Austria in 1944 by the
chemist Erika Cremer, who used a solid
stationary phase.
• Griffin and George (London, UK) probably
manufactured the first commercial GC
system in 1954, and several
companies, including Perkin
Elmer, Fisher/Gulf, Barber
Coleman, Podbelniak (all U.S.-based) and
Pye Unicam (UK), followed shortly in 1955
and 1956.
• Harold McNair was lucky to be around in the
beginning of gas chromatography (GC).
Harold heard about it in 1956, made his first
injections in 1957, and he is still working
with it today.
• Dr. R. Gohlke had introduced the first GC–
mass spectrometry (MS) experiment in 1959
using a packed column Harold McNair

H C H
H
H
H H
O3.
Bonding electrons are not shared evenly.
The end of the bond with electrons becomes partially negative.
The end of the bondwithout electrons becomes partially positive.
Polar
Polar compound
Non-polar compound
Polar compounds are soluble in polar solvents.
Non-polar compounds are soluble in non-polar solvents.
Basic rule in organic chemistry is that “like dissolves like rule .” Thus the polar
solvent water dissolves the polar solute ethanol but not the hydrocarbon octane. The
nonpolar solvent benzene will dissolve octane but not ethanol. Polar stationary phases will
retain polar solutes and pass those that are nonpolar. The order of emergence is reversed
with nonpolar stationary phases.

Principle:
5 Principle 1.Adsorption in GSC 2.Partition of molecules between gas (mobile phase)
and liquid (stationary phase) in GLC (gas) MOBILE PHASE Sample in Sample out
STATIONARY PHASE (solid or heavy liquid coated onto a solid or support system)
Packing material
The most popular packing material is silica gel.
It is believed that silanol radicals ( -Si-OH ) on the surface of silica gel
act as the active site and the sample is separated.
Si
Si
Si
the surface of silica gel

Gas-liquid chromatography (often just called gas chromatography)
Depending upon the nature of stationary phase used gas chromatography
is divided in to 2 types.
1.Gas liquid chromatography (GLC) or (VPC) or (GC): Principle of separation is PARTITION.
In this technique an inert porous solid is coated by a high boiling viscus liquid or
Non volatile liquid(carbowax 200m(1500C)Applications –CHO,>C=0,PEG(2000C)
Alcohols,pestisides, poly siloxane(2500C)steroids,glycols,pestisides, Silicon rubber gum(300-
3500C maximum temp.)Alkaloids,vitamines,gums,fattyacids.,or polymer .The inert solid
support which acts as a stationary phase ,then this chromatography Is termed as GLC (or)
(VPC) vapour-phase chromatography .
Separation is based on the relative volatilities.
Commonly used support for liquid phase is Diatomaceous earth (or) Kieselguhr.supports may
be either firebrick materials such as (chromosorb-p ,Anakrom- ABS)
Generally this technique is most widely used.
Gas-solid chromatography the solid adsorbent is used as a stationary phase , it is termed as
GSC.
In this technique the components of the mixture get distributed between the
gas and the solid phase due to differences in their adsorptive behavior.
This technique is mainly used for the separation of gases and it is rarely used.
The common adsorbants are Zeolite, activated alumina, carbon, Granular silica gel etc.
It has few applications because
-The active gases get retained on the solid surfaces.
-Reproduction of surface area is difficult.
2. Gas solidchromatography (GSC): In GSC the principle of separation is ADSORPTION

In gas chromatography, the basis for separation is the distribution of solutes
between two phases. One of these phases is a stationary bed of large surface area
(stationary phase) and the other is a gas (mobile phase) which percolates through
the stationary phase. If the stationary phase is a solid adsorbent, then it is known as
gas- solid chromatography (GSC).
Here, the adsorptive properties of the stationary phase are
responsible for separating solutes, primarily gases. Common solid stationary phases
are silica gel, molecular sieves, porous polymers, alumina and charcoal. In case, the
stationary phase is liquid, it is called gas- liquid chromatography(GLC). The liquid is
spread (coated) as thin film over an inert support. The basis of separation is the
partitioning of the solutes in and out of the liquid film. There is a wide range of the
liquid phases with usuable temperatures up to 400ºC. This makes GLC the most
versatile and the selective form of chromatography. It is used for analysis of gases,
liquids and solids.

X = Amount of gas
m = Amount of liquid
C = Concentration of liquid gas
K = Constant.
The principle of GC is similar to the Column chromatography,HPLC as well as TLC
with the following differences.
1. In GC the separation of mixture of components occurs b/n gas mobile phase
and liquid stationary phase where as in other chromatographic techniques
it occurs b/n liquid mobile phase and a solid stationary phase.
2. The concentration of solute(sample) of components in the carrier gas is entirely
a function of vapour pressure of the carrier gas.
3. In GC the column is placed in an oven whose temperature can be controlled
where as in other chromatographic techniques temperature programming is not
essential.

Mover ever principle of GC is also similar to the principle of fractional distillation.
Where in the components of the mixture are separated depending up on the differences
In their boiling points. The GC is used on micro scale and the fractional distillation
on the large scale basis.
After the known volume of sample to be analyzed has been injected in to the injection
Port which is maintained at temp. higher than the boiling point of the sample.
In the column the partitioning of the sample components occurs in between the carrier gas
And the high boiling liquid in accordance with the equilibrium law.
The partitioning properties of sample components differs from one another.
The components that have greater tendency to get dissolved in the liquid stationary phase
Move slowly through the column while negligible solubility move rapidly. Hence the
Components are carried along the column at different rates and at different retention times.

Basic Chromatography Theory
A GC separation, like extraction, involves a partitioning of solutes between phases. In the case
of GC, one phase in stationary and the other is mobile. The more a solute is partitioned in the
mobile phase, the more it moves; in other words, the partitioning between the stationary and
mobile phases affects the time required for a solute to travel through the instrument.
A solute that interacts very little with the stationary phase (via van der Waals forces such as
dispersion, dipole-dipole interactions, etc.) moves relatively quickly through the column. Such a
solute is not retained by the stationary phase material.
A solute with strong interactions with the stationary phase is retained by that phase; such a
solute will take longer to travel through the column.
This is essentially the same for all types of chromatography (thin layer, paper, liquid-
liquid, etc). Gas chromatography is more precisely described as gas-liquid chromatography.

Distribution of analytes between phases
The distribution of analytes between phases can often be described quite simply. An analyte is
in equilibrium between the two phases;
Amobile A stationary
The equilibrium constant, K, is termed the partition coefficient; defined as the molar
concentration of analyte in the stationary phase divided by the molar concentration of the
Diatomaceous earth which is a very porous rock)

The process where a substance divides itself between two immiscible solvents
because it is more soluble in one than the other is known as partition. Now, you
might reasonably argue that a gas such as helium can't really be described as a
"solvent". But the term partition is still used in gas-liquid chromatography.
You can say that a substance partitions itself
between the liquid stationary phase and the
gas. Any molecule in the substance spends
some of its time dissolved in the liquid and
some of its time carried along with the gas

when a mixture is introduced into the hot column, a component that does not dissolve in the
liquid would be vaporized by the heat and carried straight though the capillary column at the
same speed as the helium gas which is called the carrier gas. A compound of the mixture
that dissolves in the liquid called the stationary phase and has less interactions with the gas
phase would remain near the start of the column and move through it with difficulty.
Consequently, different compounds are separated within the column because they move
through it at different rates, depending of the partition between the stationary phase and
the mobile carrier gas.

Principle of searation in Gas liquid chromatography:
 The principle of separation in GLC is Partition.
 Gas is used as mobile phase.
 Liquid which is coated on to a solid support is used as stationary phase.
 The mixture of components to be separated is converted to vapor and mixed with
Gaseous mobile phase.
 The component which is more soluble in the stationary phase travels slower and eluted later.
 The component which is less soluble in the stationary phase travels faster and eluted out first.
 No two components has the same partition co-efficient for a fixed combination of
Stationary phase, mobile phase and other conditions.
 Hence the components are separated according to their partition co-efficients.
 Partition co-efficient is the ratio of solubility of a substance distance between two immiscible
liquids at a constant temperature.
2 important criteria for compounds
To be analysed by GC are
Volatility: unless a compound is volatile,
It cannot be mixed with mobile phase.
Hence volatility is important.
Thermostability: All the compounds will
Not be in the form of vapour. The solid
And liquid samples convert them to a vapour
Form higher temparature is required. That’s
Why compounds have to be thermostable.4m
mm

Theory of gas chromatography:
The column efficiency (or) performance is usually measured in terms of No. of Theoretical
Plates as well as HETP.( Hight equivalent to theoretical plates).
Plate theory was initially developed
According to plate theory The vapors come in ,they partition in to the stationary phase and
red Stationary phase ,Vapours come to equilibrium with moving gas stage and come back again
in the series of steps adsorbing- disrobing ,adsorbing disorbing each of the steps is called
a theoretical plate . (Parallel layers of discrete and Continuous horizontal plates)
Theoritical plate is an imaginary or hypothetical unit of a column and they do not really
Exist.They help to understand the functioning of the column and serve to measure the
Column efficiency.
A theoretical plate can also be called as a functional unit of the column.
The efficiency of the column can be increased by increasing the no. of theoretical plates.
The no of theoretical plates can be calculated (determined) by using the formula:
the chromatographic column is contains a large number of separate layers, called theoretical
plates
No of theoretical plates also known as column efficiency.
HETP

It is important to remember that the plates do not really exist
Measuring column efficiency, either by stating the number of theoretical
plates in a column, N (the more plates the better), or by stating the plate height;
the Height Equivalent to a Theoretical Plate (the smaller the better).
2
Where
N = Number of theoretical plates
tR = Retention time.
W = Peak width obtained upon drawing tangents from 2/3rd height of the peak
up to the base line.
W

The main reason why different compounds can be separated this way is the
interaction of the compound with the stationary phase“(like-dissolves-like”-rule). The
stronger the interaction is the longer the compound remains attached to the
stationary phase, and the more time it takes to go through the column (=longer
retention time).

Theory of Operation
• Velocity of a compound through the column
depends upon affinity for the stationary phase
Area under curve is
______ of compound
adsorbed to stationary
phase
Gas phase concentration
Carrier gas
mass

How does peak look ..lets look at the peak.
you see here Selectivity and efficiency is imp. In the case of the peak
What are the desired characteristics of how peak look like…
If the response is distinguished from all other responses the method is said to be selective.
selectivity obtained by choosing optimal columns and setting chromatographic
Conditions such as mobile phase composition, column temparature
and detector wavelength.
Who will decide this one efficiency of the detector selectivity of the detector and
Also the partition ratio.
the sharpness of the peak is an
indication of how good, or
efficient a column is. The plate
number depends on column length
: the longer the column,
the larger the plate number. Therefore,
the plate height term has been introduced
to measure how efficiently column has
been packed, h = L/N .
The lower the plate height and the
higher the plate number, the more
efficient the chromatographic column.

Scheme of a chromatogram
tR Total retention time of the compound (in the whole
chromatographic system)
t’R Adjusted retention time of the compound (retention time in the
stationary phase)
tM "Dead time" (retention time in the mobile phase)
W0,5 Peak width at half height
h Height of a signal
This yields in following equation: tR = t’R + tM

What influences the separation?
1. Polarity of the stationary phase
Polar compounds interact strongly with a polar stationary phase, hence have a longer retention
time than non-polar columns. Chiral stationary phases based on amino acid
derivatives, cyclodextrins, chiral silanes, etc are capable to separate enantiomers, because one
form is slightly stronger bonded than the other one, often due to steric effects.
2. Temperature
The higher the temperature, the more of the compound is in the gas phase. It does interact
less with the stationary phase, hence the retention time is shorter, but the quality of
separation deteriorates.
3. Carrier gas flow
If the carrier gas flow is high, the molecules do not have a chance to interact with the
stationary phase. The result is the same as above.
4. Column length
The longer the column is the better the separation usually is. The trade-off is that the retention
time increases proportionally to the column length. There is also a significant broadening of
peaks observed, because of increased back diffusion inside the column.
5. Amount of material injected
If too much of the sample is injected, the peaks show a significant tailing, which causes a
poorer separation. Most detectors are relatively sensitive and do not need a lot of material
(see below).
6. Conclusion
High temperatures and high flow rates decrease the retention time, but also deteriorate the
quality of the separation.

(average velocity of the mobile phase)

it is ideal to have the bands of the individual components as narrow as possible. This is to say
that it is best to have each component occupying as little space as possible within the
column:
From this figure it can be seen that a better separation between narrow bands of
components is ideal for easier collection of the individual samples.
H is the height equivalent of a theoretical plate4 (HETP) and u is the velocity (flow
rate) of the mobile phase.
The lower the resulting value of H is, the greater the efficiency of the procedure.
So, ideally, a scientist will want to minimize all three terms in order to minimize H.

The following figure helps in visualizing
Eddy diffusion:
The A factor is determined by a phenomenon called Eddy
Diffusion. This is also called the multi-path term
. Solute molecules will take different paths through the
stationary phase at random. This will cause broadening of the
solute band, because different paths are of different lengths
In the figure, particle B will be eluted before particle C, and both
will be eluted before particle A. Since it is improbable for all
particles of one compound to find the shortest path, there will be
fractions of the component that will behave like particles A, B, and
C. This leads to the broadening of the band. There is little a
scientist can do to minimize the Eddy Diffusion factor, can be
decreased by using smaller particle size(particle size should be
optimum) Shape and manner of packing,Column diameter.
very smaller size particles also increase the pressure drop leading to disturbance in linear
gas velocity that’s why decrease the column efficiency.
Generally Eddy diffusion can be minimized by using small particles of uniform size
and smaller diameter columns.
columns should be 1/8inch inner diameter and particle size up to 100-200 mesh range
are used for good resolution. as
granular bed of the
packing particles

The A term is loosely affected by the flow rate of the mobile phase, and sometimes the
affect of the flow rate is negligible.
B/u is called the longitudinal diffusion term, and is caused by the components' natural
migration from a place of high concentration (the center of the band) to a place of lower
concentration (either side of the band) within the column. Diffusion occurs because molecules
in a place of high concentration will tend to spread out to areas of lower concentration to
achieve equilibrium.
B - Molecular diffusion( Longitudinal diffusion)

. Longitudinal diffusion is a chief cause of band broadening in Gas Chromatography, as
the diffusion rates of gaseous species are much higher than those of liquids.
The magnitude of the term B/u can be minimized by increasing the flow rate of the
mobile phase. Increasing the velocity of the mobile phase does not allow the
components in the column to reach equilibrium, and so will hamper(restrict the
activity or free movement) of longitudinal diffusion.
Hence the molecular diffusion can be decreased by using the optimum linear gas
velocity (flow rate) And using high molecular weight carrier gas eg: Nitrogen, argon
than hydrogen or helium.
At time zero in the figure above, the particles of a compound are generally localized in a
narrow band within the separating column. If the mobile phase flow rate is too small or if the
system is left at rest, the particles begin to separate from one another. This causes a spread in
the concentration distribution of that compound within the column, thus bringing about band
broadening for the band of that particular compound. As the time that the system is left still
approaches infinity, the compound reaches complete concentration equilibrium throughout
the entire column.
B - Longitudinal diffusion
The concentration of analyte is less at the edges of the band than at the center. Analyte
diffuses out from the center to the edges. This causes band broadening. If the velocity of the
mobile phase is high then the analyte spends less time on the column, which decreases the
effects of longitudinal diffusion.

. Nonequilibrium or mass transfer: The analyte takes a certain amount of time to equilibrate
between the stationary and mobile phase. If the velocity of the mobile phase is high, and the
analyte has a strong affinity for the stationary phase, then the analyte in the mobile phase will
move ahead of the analyte in the stationary phase. The band of analyte is broadened. The higher
the velocity of mobile phase, the worse the broadening becomes.
The flow rate of the mobile phase should not be increased in excess, however, as the term Cu is
maximized when u is increased. Cu is referred to as the mass transfer term. Mass transfer refers
to when particles are so strongly adhered to the stationary phase that the mobile phase passes
over them without carrying them along. This results is particles of a component being left
behind. Since it is likely that more than a single particle of any given compound will undergo
this occurrence, band broadening results. This results in a phenomenon called tailing, in which
a fraction a component lags behind a more concentrated frontal band. Non-equilibrium effects
can be caused by two phenomena: laminar flow and turbulent flow. Laminar flow occurs in
tubular capillaries, and so is most prominent in Capillary Electrophoresis. Turbulent flow occurs
as a result of particles becoming overwhelmed by the stationary phase and is more common
in column chromatography.

In the above figure, particles of the adsorbent solid become occupied by particles of the
sample. If too many particles of the adsorbent are occupied, particle A will have nothing
hindering it from flowing through the column. So, the particles of a single compound
separate from one another. Also, as the mobile phase moves through the column, particles
of the sample leave the stationary phase and migrate with the mobile phase. However, if the
flow rate of the mobile phase is too high, many of the sample particles are unable to leave
the stationary phase and so get left behind. These occurrences result in band broadening, as
the individual particles of a single compound become less closely packed. The high flow rate
of the mobile phase makes it more difficult for the components within the column to reach
equilibrium between the stationary and mobile phase. It is for this reason that the Cu term
is also called the non-equilibrium factor. Minimization of this factor can be achieved by
decreasing the flow rate of the mobile phase. Decreasing the flow rate of the mobile phase
gives sample components more time to leave the stationary phase and move with the
mobile phase, thus reaching equilibrium.
By observing the Van Deemter equation, it can be deduced that an ideal mobile phase flow
rate must be determined to yield the best (lowest) value of H. Decreasing the flow rate too
much will result in an increase of the longitudinal diffusion factor B/u, while exceedingly
increasing the flow rate will increase the significance of the mass transfer term Cu. So, H can
be minimized to a finite limit depending on the various parameters involved in the
chromatography being performed.

van Deemter profile for hydrogen, helium, and nitrogen carrier gases.
The curves were generated by plotting the Height Equivalent to a Theoretical Plate
(H.E.T.P., the length of the column divided by the total number of theoretical plates)
against the column's average linear velocity. The lowest point on the curve indicates
the carrier gas velocity at which the highest column efficiency is reached.
Hydrogen is the fastest carrier gas (upto : 40cm/sec.) and exhibits the flattest van Deemter
profile. Helium is the next best choice (uopt: 20cm/sec.). The head pressures at optimum
flow rates are similar for hydrogen and helium because hydrogen has half the viscosity and
double the linear velocity of helium. Nitrogen's performance is inferior for capillary
columns and is usually not recommended because of the slow optimum linear velocity
(uopt: 12cm/sec.) and steep van Deemter profile.

Van Deemter plots
A plot of plate height vs. average linear
velocity of mobile phase.
Such plots are of considerable use in
determining the optimum mobile phase flow
rate.
The van-Deemter-equation demonstrates the
dependence of getting sharp peaks (low HETP)
from the following terms:
small particle’s diameter (particle size),
small column’s diameter,
small film thickness of the stationary phase.

When HETP is plotted against u we get
Hyperbola with minimum HETP.
This minimum is the optimum flow rate (u)
At which column efficiency is maximum.
This graph represents the van deemter curve
Which is a hyperbola with minimum HETP.
It shows that the affects of
A,B,C on the relation ship b/n HETP
And the gas flow rate.
Minimum HETP indicates max. efficiency of
The column.
Hence the ideal flow rate
Corresponding to the minimum value of
HETP is used.
Such plots are of considerable use in determining the optimum mobile phase flow rate.
A- Eddy diffusion
C-Resistance to mass transfer
B- Molecular diffusion

2.Symmetry Factor:
Apart form the the N and HETP another term used to measure the column efficiency or
Column performance is symmetry factor(S) of a peak.
H1/20
It is given by the following equation S = --------------
2A
S = Symmetry factor
H = Peak width at 1/20th level of its height.
A = Distance between the perpendicular dropped from the maximum peak height
upto 1/20th peak height.
When the symmetry factory of a peak is equal to 1 it implies that the peak is reasonably
Symmetrical.
Hence peak height may be used for the calculation of chromatogram.
However, when the symmetry factor of peak is less or greater than 1, then
Fronting( is due to saturation of stationary phase and can be avoid by using less
Quantity of sample)
or tailing of the peak( is due to more active adsorption sites and can be
eliminated by support pretreatment,more polar mobile phased increasing
the amount of liquid phase) may be seen.

Asymmetry factor:
A chromatograhic peak should be symmetrical about centre and peak should be like an
Isosceles triange.
But in practice due to some factors peak is not symmetrical and shows tailing and fronting .
Asymmetry factor (0. 95 to 1.05) can be calculated by using the formula
b
AF = ---------- b and a calculated at 5% or 10% of the peak height.
a

D = Distance b/n the 2 consecutive peak maxima
W1 +W2 = peak widths of peak 1 and peak 2.
When R = 1. 98% resolution is achieve.
R= ≥ 99.7% resolution is achieved.

Where N is no. of theoretical plates.
α=Solvent efficiency
R =Resolution
K’2 =partition ration of second peak.
=
Adjusted retention time(T’R)
-----------------------------------------
Retention time in Air

Interaction forces:
Forces that help to carry out the separation process in GC
a)Debye forces: Debye or induced dipole forces are the minor forces that result from the
interaction of 2 molecules i.e. Induced dipole in in one molecule and dipole in another
molecule.
b) Orientation forces: These forces are the result of interaction between 2 permanent
dipoles.
c)Specific interaction forces: These forces are the resultant of the variations that are made
to occur in the immediate dipoles of any two interacting species.
d)Non Polar forces: These forces are the resultant of the variations that are made to occur
in the immediate dipoles of any two interacting species.
4.Partition Ratio (K)
™Partition ratio is the ratio of total concentration or amount of solute in the column
or stationary phase(t’R) to the total concentration or amount of solute in the gas or
mobile phase
Amount of solute in column t’R
K = ---------------------------------------- K = -----------
Amount of solute in gas tM
Partition ratio is the resultant effect of combination forces i.e., Debyforces ,orientation forces, specific interaction forces and non polar
Forces.
It depends upon the temp.of column ,nature of components of solute and liquid phase as well as
On the quantity of liquid phase in the column.

Retention Time (tR)
The retention time is the total time that a compound spends in both the mobile
phase and stationary phase. Retention time is generally reported in minutes.
Dead Time (tm)
The dead time is the time a non-retained compound spends in the mobile phase
which is also the amount of time the non-retained compound spends in the column.
Dead time is generally reported in minutes.
Adjusted Retention Time (tR
'
)
The adjusted retention time is the time a compound spends in the stationary phase.
The adjusted retention time is the difference between the dead time and the
retention time for a compound.

Capacity Factor (or Partition Ratio) (k'
)
The capacity factor is the ratio of the mass of the compound in the stationary phase
relative to the mass of the compound in the mobile phase. The capacity factor is a
unit less measure of the column's retention of a compound.
Phase Ratio (ß)
The phase ratio relates the column diameter and film thickness of the stationary
phase. The phase ratio is unitless and constant for a particular column and
represent the volume ratioß.
Distribution Constant (KD)
The distribution constant is a ratio of the concentration of a compound in the
stationary phase relative to the concentration of the compound in the mobile phase.
The distribution constant is constant for a certain compound, stationary phase, and
column temperature.

Selectivity (or Separation Factor) (alpha)
The selectivity is a ratio of the capacity factors of two peaks. The selectivity is
always equal to or greater than one. If the selectivity equals one the two
compounds cannot be separated. The higher the selectivity, the more separation
between two compounds or peaks.
Linear Velocity (u)
The linear velocity is the speed at which the carrier gas or mobile phase travels
through the column. The linear velocity is generally expressed in centimeters per
second.

Efficiency
The efficiency is related to the number of compounds that can separated by the
column. The efficiency is expressed as the number of theoretical plates (N,
unitless) or as the height equivalent to a theoretical plate (HETP, generally in
millimeters). The efficiency increases as the height equivalent to a theoretical plate
decreases, thus more compounds can be separated by the column. The efficiency
increases as the number of theoretical plates increases, thus the column's ability to
separate two closely eluting peaks increases.

The oven is used for maintaining the precise temparature control around the
Column. Hence the oven should be free from the influence of changing
Ambient temparature and should have adequate air flow system.
To guard against sample deposition After long use,narrow glass or metal inserts are
provided in the injection port. The sample deposition on inserts can be taken out
periodically for cleaning purpose

A typical GC system used is shown below
(a gas chromatograph)
Carrier gas: He (common), N2, H2
Pinlet 10-50 psig
Flow = 25-150 mL/min packed column
Flow = 1-25 mL/min open tubular column
Column: 2-50 m coiled stainless steel/glass/Teflon
Oven: 0-400 °C ~ average boiling point of sample
Accurate to <1 °C
Detectors: FID, TCD, ECD, (MS)

How separation works on the column
One of three things might happen to a particular molecule in the mixture injected into the
column:
It may condense on the stationary phase.
It may dissolve in the liquid on the surface of the stationary phase.
It may remain in the gas phase.
None of these things is necessarily permanent.
A compound with a boiling point higher than the temperature of the column will obviously tend
to condense at the start of the column. However, some of it will evaporate again in the same
way that water evaporates on a warm day - even though the temperature is well below 100°C.
The chances are that it will then condense again a little further along the column.
Similarly, some molecules may dissolve in the liquid stationary phase Some compounds will be
more soluble in the liquid than others. The more soluble ones will spend more of their time
absorbed into the stationary phase; the less soluble ones will spend more of their time in the
gas.
The process where a substance divides itself between two immiscible solvents because it is
more soluble in one than the other is known as partition. Now, you might reasonably argue that
a gas such as helium can't really be described as a "solvent". But the term partition is still used
in gas-liquid chromatography.
You can say that a substance partitions itself between the liquid stationary phase and the gas.
Any molecule in the substance spends some of its time dissolved in the liquid and some of its
time carried along with the gas.

A compound with a boiling point higher than the temperature of the column will obviously
tend to condense at the start of the column. However, some of it will evaporate again in the
same way that water evaporates on a warm day - even though the temperature is well below
100°C. The chances are that it will then condense again a little further along the column.
Similarly, some molecules may dissolve in the liquid stationary phase Some compounds will
be more soluble in the liquid than others. The more soluble ones will spend more of their
time absorbed into the stationary phase; the less soluble ones will spend more of their time
in the gas.
The process where a substance divides itself between two immiscible solvents because it is
more soluble in one than the other is known as partition. Now, you might reasonably argue
that a gas such as helium can't really be described as a "solvent". But the term partition is
still used in gas-liquid chromatography.
You can say that a substance partitions itself between the liquid stationary phase and the gas.
Any molecule in the substance spends some of its time dissolved in the liquid and some of its
time carried along with the gas.

Retention time
The time taken for a particular compound to travel through the column to the detector
is known as its retention time. This time is measured from the time at which the sample
is injected to the point at which the display shows a maximum peak height for that
compound.
Different compounds have different retention times. For a particular compound, the
retention time will vary depending on:
the boiling point of the compound. A compound which boils at a temperature higher
than the column temperature is going to spend nearly all of its time condensed as a
liquid at the beginning of the column. So high boiling point means a long retention time.
the solubility in the liquid phase. The more soluble a compound is in the liquid
phase, the less time it will spend being carried along by the gas. High solubility in the
liquid phase means a high retention time.

the temperature of the column. A higher temperature will tend to excite molecules into the gas
phase - either because they evaporate more readily, or because they are so energetic that the
attractions of the liquid no longer hold them. A high column temperature shortens retention
times for everything in the column.
For a given sample and column, there isn't much you can do about the boiling points of the
compounds or their solubility in the liquid phase - but you do have control over the
temperature.
The lower the temperature of the column, the better the separation you will get - but it could
take a very long time to get the compounds through which are condensing at the beginning of
the column!
On the other hand, using a high temperature, everything will pass through the column much
more quickly - but less well separated out. If everything passed through in a very short
time, there isn't going to be much space between their peaks on the chromatogram.
The answer is to start with the column relatively cool, and then gradually and very regularly
increase the temperature.
At the beginning, compounds which spend most of their time in the gas phase will pass quickly
through the column and be detected. Increasing the temperature a bit will encourage the
slightly "stickier" compounds through. Increasing the temperature still more will force the very
"sticky" molecules off the stationary phase and through the column.

It should be inert and available at low cost
High purity
Easily available
Less risk of explosion or fire hazards
Pressure:
-Inlet  10 to 50 psi
-packed column  25 to 150 mL/min.
- capillary column  1 to 25 mL/min

CARRIER GAS:
The choice of carrier gas determines the efficiency of chromatographic separation.
The main purpose of the carrier gas is to transport sample components through the column.
Most commonly used carrier gases are Hydrogen, Helium, Nitrogen and Argon.
1. It should be chemically inert and should not interact with sample and stationary phase.
2. It should be suitable for the detector to be utilized and the type of sample analyzed.
3. Easily available.
4. It should be readily available, cheap, and of high purity.
5. It should not cause the risk of fire or explosion hazard.
6. It should give best column performance consistent with the required speed of analysis.
Hydrogen: It has a better thermal conductivity, low density.
It is useful in TCD,FID. The disadvantage is that it reacts with unsaturated compounds and
It is inflammable.
Helium: It is also has excellent thermal conductivity, but it is expensive. It is very good
Carrier gas when used with TCD.
Nitrogen: It is inexpensive but has reduced sensitivity.
Argon: For electron capture detector argon is used as carrier gas. However, argon is not
Readily available in India.

• Impurities in the carrier gas such as air water vapor and trace
gaseous hydrocarbons can cause sample reaction, column
character and affect the detector performance.
• The carrier gas system should contains a molecular sieve and
filter, drier and absorbing tubes to remove water(moisture) and
other gases impurities.
• These gases are available in pressurized tanks. pressure regulators
and flow meters are required to control the flow rate of the gas.
• The gases are supplied from the high pressure gas cylinder , being
stored at pressure up to 300 psi (pounds per sq. inch).
• carrier gas should be better then 99.99% moles % is desirable and
99.999% is often used.

Soap bubble flow meter
Aqueous
solution of
soap or
detergent 68
A soap bubble meter is an accurate
device for reproducing the rate of the
carrier gas. formed indicates the flow
rate.
Glass tube with a inlet tube at the bottom.
Rubber bulb-----store soap solution
When the bulb is gently pressed of soap
solution is converted into a bubble by the
pressure of a carrier gas &travel.
The time required for the soap film to move between
Two graduations on the burette is then measured and
Converted to flow rate.
Soap bubble meter and flow meters
As carrier gases are stored under high pressure
flow regulators are used to deliver gas
With uniform pressure or flow rate.
Flow meters are used to measure the flow rate of carrier gas.
They are soap bubble meter and Rotameter.
Burette
Gas from
column
Gas exit

Sample injection port
 Calibrated Micro syringes are used to inject liquid
sample
 Sample must be introduced as a vapor
in the smallest possible volume and minimum of
time with out decomposition.
 Liquid samples, 1-10 microliters in the volume
are usually injected by a micro syringe through a
self sealing silicone rubber septum.
 The most accurate and precise method for
gas samples used a calibrated sample loop
(0.5-10 ml) and a multiport rotary valve.
 Smaller the sample better the peak shape.

Sample injection port
For optimum column efficiency, the sample should not be too
large, and should be introduced onto the column as a "plug" of
vapour - slow injection of large samples causes band
broadening and loss of resolution. The most common injection
method is where a micro syringe is used to inject sample
through a rubber septum into a flash vaporiser port at the
head of the column. The temperature of the sample port is
usually about 50°C higher than the boiling point of the least
volatile component of the sample. For packed
columns, sample size ranges from tenths of a microliter up to
20 microliters. Capillary columns, on the other hand, need
much less sample, typically around 10-3 mL. For capillary
GC, split/splitless injection is used. Have a look at this diagram
of a split/splitless injector; The injector can be used in one of
two modes; split or splitless. The injector contains a heated
chamber containing a glass liner into which the sample is
injected through the septum. The carrier gas enters the
chamber and can leave by three routes (when the injector is in
split mode). The sample vapourises to form a mixture of
carrier gas, vapourised solvent and vapourised solutes. A
proportion of this mixture passes onto the column, but most
exits through the split outlet. The septum purge outlet
prevents septum bleed components from entering the column.

Split: The inlet is continuously purged with vent gas as some flow ratio to the column flow (at
this lab, we use 60:1). This means the flow through the column is of the total flow. This results
in most of the injected solution being vented rather than deposited on the column, which in
turn gives a tight, spatially limited band of analyte on the column.
Split injection typically gives the best chromatography (highest theoretical plates).
Most of the sample is lost, so split injection is not used when absolute sensitivity is required.
However, this does give 1-2 orders of magnitude of dynamic range in instrument response
without changing any actual detector parameters (simply by splitting or not).
Split less: The split vent is closed during the actual injection. Some time after the injection (for
example, one minute), the split vent is opened to purge excess solvent. This technique allows a
greater amount of the injected sample to be deposited on the column.
Split less injection gives a greater response for a given solution than split since most of the
sample is actually deposited (rather than vented).
Split less injection gives the most precise quantitative results, but the chromatographic
resolution may be less than with split injection.
The instrument parameters needed to produce that maximum resolution are compound
specific. This means that each analysis must be optimized to achieve maximum resolution.
Pulsed Splitless: Pulsed splitless is similar to splitless injection, but during the vent closed
portion of the timing cycle, the column flow is pulsed to a relatively high rate. This a relatively
new technique that combines the advantages of split (better chromatographic resolution) and
splitless (better quantitative results and greater response).

a. Gas samples: The sample gas can also be injected at the top of the column by means
of a hypodermic syringe. The Hamilton Teflon coated gas syringe is particularly
suitable.
Generally gases are introduced by typical hex port gas sampling valve which is also
Installed on the gas chromatograph.
b. Liquid sample:
Liquid samples are most conveniently introduced by means of micro syringe which
are different sizes.
Liquids can be injected through loop or septum devices. Generally high quality silicone
Rubber septum through which sample solution is injected.
The rubber is made up of good quality silicone rubber which can with stand high temp.
c. Solid samples:
Solid samples are dissolved in a suitable volatile solvent and inject like a liquid sample
and they are injected through a septum.

For packed columns, sample size ranges from tenths of a microliter up to 20 microliters.
Capillary columns, on the other hand, need much less sample, typically around 10-3 mL. For
capillary GC, split/splitless injection is used.

Ovens:
The oven is maintaining the precise
temperature around the column.
Hence the column oven should be free from
influence of changing ambient
Temperature(temp. of the surroundings ) and
free and should have well designed
and adequate air flow system.
The column temperature
The temperature of the column can be varied
from about 50°C to 250°C. It is cooler than the
injector oven, so that some components of the
mixture may condense at the beginning of the
column.
In some cases, as you will see below, the
column starts off at a low temperature and
then is made steadily hotter under computer
control as the analysis proceeds.

Column temperature and temperature program
Column selection
A gas chromatography oven, open to show a capillary column
The column(s) in a GC are contained in an oven, the temperature of which is precisely
controlled electronically. (When discussing the "temperature of the column," an analyst is
technically referring to the temperature of the column oven. The distinction, however, is not
important and will not subsequently be made in this article.)
The rate at which a sample passes through the column is directly proportional to the
temperature of the column. The higher the column temperature, the faster the sample moves
through the column. However, the faster a sample moves through the column, the less it
interacts with the stationary phase, and the less the analytes are separated.
In general, the column temperature is selected to compromise between the length of the
analysis and the level of separation.
A method which holds the column at the same temperature for the entire analysis is called
"isothermal." Most methods, however, increase the column temperature during the analysis,
the initial temperature, rate of temperature increase (the temperature "ramp") and final
temperature is called the "temperature program."
A temperature program allows analytes that elute early in the analysis to separate adequately,

Column temperature
For precise work, column temperature must be controlled to within tenths of a
degree. The optimum column temperature is dependant upon the boiling point of
the sample. As a rule of thumb, a temperature slightly above the average boiling
point of the sample results in an elution time of 2 - 30 minutes. Minimal
temperatures give good resolution, but increase elution times. If a sample has a
wide boiling range, then temperature programming can be useful. The column
temperature is increased (either continuously or in steps) as separation proceeds.
The rate at which a sample passes through the column is directly proportional to the
temperature of the column. The higher the column temperature, the faster the sample moves
through the column. However, the faster a sample moves through the column, the less it
interacts with the stationary phase, and the less the analytes are separated.
In general, the column temperature is selected to compromise between the length of the
analysis and the level of separation.
A method which holds the column at the same temperature for the entire analysis is called
"isothermal." Most methods, however, increase the column temperature during the
analysis, the initial temperature, rate of temperature increase (the temperature "ramp") and
final temperature is called the "temperature program

How a Gas Chromatography Machine Works:
• How does this column and system separate things.(How does GC work?
• How does the column work? What happens inside the column? How do
the compounds move through the column? Why do some compounds
stay in the column longer than others? How does the sample get into the
column? These are some of the most basic questions asked about gas
chromatography.
• This shows us a schematic of a GC packed column.
• There are 2 columns:
• Packed columns and capillary.
• In this packed column we have are 2 phases.
• mobile phase which is moving stationary phase which is not moving.
• Mobile phase also called a carrier gas typically it is He some times H2 and
some times Nitrogen.
• It is now possible to separate hundreds of components of a mixture in a
single chromatographic experiment.

How does this column and system separate things.(How does GC work?)
This shows us a schematic of a GC packed column.
There are 2 types of columns.
Packed columns large sample capacity
preparative work
Good packed column will have 1000 to3000 plates/m.
capillary columns.(opentubular column)
Packed column-3m in length.
Capillary column- 50-150 METER LENGTH
liquid stationary 1 Micron thickness.
higher efficiency smaller sample size
analytical applications .
Good capilary column range from 1000 to 4000
plates/m. More no of plates better separation.
diameter

What are guard columns?
Guard columns are short lengths of deactivated, uncoated fused silica or metal tubing
placed between the injection port and the analytical column. They protect and
prolong the lifetime of an analytical column .
Why use a guard column?
Capillary gas chromatography (GC) guard columns protect analytical columns in
several ways. Guard columns trap non-volatile residues, preventing them from
collecting at the head of the analytical column. These non-volatile residues may be
very high molecular weight organic compounds, inorganic salts, or particulates.
If these contaminants enter the analytical column, they can cause adsorption of
active compounds, loss of resolution, and poor peak symmetry
A guard column can
protect your analytical column and
ensure reproducible analyses.

A guard column or retention gap are the same
thing, but they serve different purposes. Both
are 1-10 meters of deactivated fused silica
tubing attached to the front of the column .
Deactivated fused silica tubing does not
contain any stationary phase; however, the
surface is deactivated to minimize solute
interactions. A suitable union is used to attach
the tubing to the column. In most cases, the
diameter of the retention gap or guard
column should be the same as the column.
Guard columns are used when samples contain non-volatile residues that may
contaminate a column. The non-volatile residues deposit in the guard column and not in
the column. This greatly reduces the interaction between the residues and the sample
since the guard column does not retain the solutes (because guard column contains no
stationary phase). Also, the residues do not coat the stationary phase which often results
in poor peak shapes. Periodic cutting or trimming of the guard column is usually required
upon a build-up of residues. Guard columns are often 5-10 meters in length to allow
substantial trimming before the entire guard column has to replaced. The onset of peak
shape problems is the usual indicator that the guard column needs trimming or changing.

Unions
There are a variety of unions that can be used
to connect fused silica tubing. Stainless
steel, stainless steel-glass combinations, glass
press-fit and quick connectors are some of the
more common types.
All mobile phases, samples and additives should be filtered through a .45µm syringe filter.
It is recommended that guard columns are packed with the same stationary phase as the
analytical column to be protected. (Eliminate the possibility of any loss of performance or
selectivity.)
Pump seals and rotor seals should be replaced on a routine basis.
A guard column provides saturation of your mobile phase with silica by “bleeding” silica
into the mobile phase instead of from the analytical column. This can be achieved without
the loss of resolution or performance by using a Guard Column. When the guard column is
destroyed, replace it with another cartridge in minutes.
According to most experts, a guard column can increase the usable life of your columns by
a factor of four. You will save money and valuable time. Another source of problems are
compounds that irreversibly bond to the stationary phase and are often injected into
analytical columns. These compounds cause permanent damage to columns that are not
protected by a guard column. Shifting of retention time and loss of resolution often results.

85
Coated with 30 micro meters
Thick adsorbant such as diatomaceous earth.
Which consists of singled -celled sea -plant skeletons.
Then this adsorbant is treated with liquid stationary phase.
SCOT columns
are capable of
holding a
greater volume
of stationary
phase than a
WCOT column
due to its
greater sample
capacity, WCOT
columns still
have greater
column
efficiencies.
modern WCOT
columns are
made of
glass, but T316
stainless
steel, aluminum
, copper
(capillary tube whose walls
are coated with liquid
stationary phase)
(the inner wall of the capillary is lined with a thin layer of support
material such as diatomaceous earth, onto which the stationary
phase has been adsorbed).
More efficient
Than scot columns

Columns:
There are two general types of column, packed and capillary (also known as open tubular).
Packed columns contain a finely divided, inert, solid support material (commonly based
on diatomaceous earth) coated with liquid stationary phase. Most packed columns are 1.5
- 10m in length and have an internal diameter of 2 – 4 mm.
Capillary columns have an internal diameter of a few tenths of a millimeter. They can be
one of two types; wall-coated open tubular (WCOT) or support-coated open
tubular (SCOT). Wall-coated columns consist of a capillary tube whose walls are coated
with liquid stationary phase. In support-coated columns, the inner wall of the capillary is
lined with a thin layer of support material such as diatomaceous earth, onto which the
stationary phase has been adsorbed. SCOT columns are generally less efficient than WCOT
columns. Both types of capillary column are more efficient than packed columns

In 1979, a new type of WCOT column was devised - the Fused Silica Open
Tubular (FSOT) column
These have much thinner walls than the glass capillary columns, and are given
strength by the polyimide coating. These columns are flexible and can be wound into
coils. They have the advantages of physical strength, flexibility and low reactivity.

One of the most popular types of capillary
columns is a special WCOT column called the
fused-silica wall-coated (FSWC) open tubular
column.
The walls of the fused-silica columns are
drawn from purified silica containing minimal
metal oxides. These columns are much
thinner than glass columns, with diameters as
small as 0.1 mm and lengths as long as 100
m. To protect the column, a polyimide
coating is applied to the outside of the tubing
and bent into coils to fit inside the thermo-
statted oven of the gas chromatography
unit. The FSWC columns are commercially
available and currently replacing older
columns due to increased chemical
inertness, greater column efficiency and
smaller sampling size requirements. It is
possible to achieve up to 400,000 theoretical
plates with a 100 m WCOT column, yet the
world record for the largest number of
theoretical plates is over 2 million plates for
1.3 km section of column.
Computer Generated Image of a FSWC column (specialized to withstand extreme heat)

For example, the FSWC column is designed specially for blood alcohol analysis. It produces
fast run times with baseline resolution of key components in under 3 minutes. Moreover, it
displays enhanced resolutions of ethanol and acetone peaks, which helps with determining
the BAC levels. This particular column is known as Zebron-BAC and it made with polyimide
coating on the outside and the inner layer is made of fused silica and the inner diameter
ranges from .18 mm to .25 mm. There are also many other Zebron brand columns designed
for other purposes.
Another example of a Zebron GC column is known as the Zebron-inferno. Its outer layer is
coated with a special type of polyimide that is designed to withstand high temperatures. It
contains an extra layer inside. It can withstand up to 430 °C to be exact and it is designed to
provide true boiling point separation of hydrocarbons distillation methods. Moreover, it is
also used for acidic and basic samples.

The common liquid phases for Gas chromatography:
Liquid stationary phase Maxium temerature Applications
Squalane(C30H62).
High molecular wt.
hydrocarbon used for non
polar hydrocarbons)
140-150 Hydrocarbons.
Corbowax 200
Carbowax 20M(PEG)
150oC
200-250
Aldehydes, ketones.
Alcohols,aromatics,pesticides
,ketones
Poly siloxane 250oC Steroids,pesticides,Glycols.
Polyethylene glycol(PEG)
(more effective for polar
comounds)
200-250oC Alcohols,pesticides etc.
Silicon rubber gum(SE-30) 300-350oC. Alkaloids,alcohols, gases
fatty acids,gums,bile and
urinary compounds,vitamins,
Sugars,pesticides,

Stationary Phases:
Stationary phase in GC is the main factor determining the selectivity and retention
of solutes.
There are three types of stationary phases used in GC:
Solid adsorbents
Liquids coated on solid supports
Bonded-phase supports
1.) Gas-solid chromatography (GSC)
- same material is used as both the stationary phase and support material
- common adsorbents include:
 alumina
molecular sieve (crystalline aluminosilicates [zeolites] and clay)
 silica
 active carbon
Magnified Pores in activated carbon

Gas-solid chromatography (GSC):
advantages:
- long column lifetimes
- ability to retain and separate some compounds not easily resolved by other GC
methods
 geometrical isomers
 permanent gases
disadvantage:
- very strong retention of low volatility or polar solutes
- catalytic changes that can occur on GSC supports
- GSC supports have a range of chemical and physical environments
 different strength retention sites
 non-symmetrical peaks
 variable retention times

2.) Gas-liquid chromatography (GLC)
- stationary phase is some liquid coated on a solid support
- over 400 liquid stationary phases available for GLC
 many stationary phases are very similar in terms of their retention properties
- material range from polymers (polysiloxanes, polyesters, polyethylene glycols) to
fluorocarbons, molten salts and liquid crystals
Based on polarity, of the 400 phases available only 6-12 are needed for most
separations. The routinely recommended phases are listed below:
Name
Chemical nature of
polysiloxane
Max.
temp.
McReynolds’ constants
x’ y’ z’ m’ s’
SE-30 Dimethyl 350 14 53 44 64 41
Dexsil300 Carborane-dimethyl 450 43 64 111 151 101
OV-17 50% Phenyl methyl 375 119 158 162 243 202
OV-210 50% Trifluoropropyl 270 146 238 358 468 310
OV-225 25% Cyanopropyl-
25% phenyl
250 238 369 338 492 386
Silar-SCP 50% Cyanopropyl-
50% phenyl
275 319 495 446 637 531
SP-2340 75% Cyanopropyl 275 520 757 659 942 804
OV-275 Dicyanoallyl 250 629 872 763 1106 849
McReynolds’ constants based on retention of 5 standard “probe” analytes
– Benzene, n-butanol, 2-pentanone, nitropropanone, pyridine
Higher the number the
higher the absorption.

Preparing a stationary phase for GLC:
- slurry of the desired liquid phase and solvent is made with a solid support
solid support is usually diatomaceous earth (fossilized shells of
ancient aquatic algae (diatoms), silica-based material)
- solvent is evaporated off, coating the liquid stationary phase on the support
- the resulting material is then packed into the column
disadvantage:
- liquid may slowly bleed off with time
 especially if high temperatures are used
 contribute to background
 change characteristics of the column with time

3.) Bonded-Phase Gas chromatography
- covalently attach stationary phase to the solid support material
- avoids column bleeding in GLC
- bonded phases are prepared by reacting the desired phase with the surface of a silica-
based support
reactions form an Si-O-Si bond between the stationary phase and support
or
reactions form an Si-C-C-Si bond between the stationary phase and support
- many bonded phases exist, but most separations can be formed with the following
commonly recommended bonded-phases:
 Dimethylpolysiloxane
 Methyl(phenyl)polysiloxane
 Polyethylene glycol (Carbowax 20M)
 Trifluoropropylpolysiloxane
 Cyanopropylpolysiloxane
advantages:
- more stable than coated liquid phases
- can be placed on support with thinner and more uniform thickness than
liquid phases
Si
CH3
CH3
O
n
Si
CH3
CH3
O
n
Si
C6H5
C6H5
O
m
C CHO O
H
H
H
H
H
n

HO-CH2-CH2-(O-CH2-CH2)n-OH
polyethylene glycol
(Polar)
(intermediate polarity)
(non-polar)
Polydiphyl siloxane
Polyalkyline glycol
Poly bis cyano propyl siloxane (very polar non-bonded phase upto 250oC.

Solid Phase:
The main function of the solid phase is to provide mechanical support to the liquid phase.
The commonly used solid phases include: Diatomaceous earth or Kieselguhr
commonly abailable as dicalite,calite,sterchamol etc.
Firebrick coated with metalic silver or gold commercially available as
Chromosorb P ,, chromosorb W, Kieselguhr ,Anakrom ABS.
Others include glass beads,unglazed tiles, porous polymers, sand etc.
The criteria for an ideal support include:
1. It should have large surface area
2. It should be chemically inert i.e., it should not react with the liquid phase as well as with
the body of the column.
3. It should be thermostable.
4. It should be a poor adsorbent.
5. It should get uniformly wet with the liquid phase.
6. It should be strong enough to prevent the fractionating of the column.

Liquid phase:
Many liquid phases are available of gas chromatography columns. Choice depends upon
the trial/error basis.
The requirements for a good liquid phases are
1. It should be non-volatile
2. It should have low volatility i.e., should be stable at the operating temarature.
3. It should be chemically inert.
4. It should possess low vapour pressure at column temperature.
5. I t should have high decomposition temperatures.
Liquid phases are classified as:
Very polar liquids: Glycerols,glycols, Polyphenols.
Polar liquids: Alcohols, ketones, esters.
Intermediate polar liquids: Aldehydes, ketons, esters.
Low polar liquids: Aromatic hydrocarbons, chloroform, dicloromethane.
For getting very good results…………..
The liquid phase should be chemically and structurally similar to the slolute(sample)
i.e.,
The polar liquid phase for polar solute
The non-polar liquid phase for non-polar solute.

3,6,12 foot length
packed with a solid
support like
Diatomaceous earth
Supports may be
either fire brick
derived materials like
Chromosorb –p ;
Anakrom ABS etc.
packed columns can only achieve about 50% of the efficiency of a comparable WCOT
column.
Due to the difficulty of packing the tubing uniformly, these types of columns have a
larger diameter than open tubular columns and have a limited range of length.
The diatomaceous earth packing is deactivated over time due to the semi-permanent
adsorption of impurities within the column.
In contrast, FSWC open tubular columns are manufactured to be virtually free of these
adsorption problems.
1.6 to 9.5 mm in
Diameter.
Capilary columns have
Tubing coiled in to an
Open spiral ,
A basket-coil or
Flat pancake shape.

Column temperature
For precise work, column temperature must be controlled to within tenths of a degree.
The optimum column temperature is dependant upon the boiling point of the sample. As
a rule of thumb, a temperature slightly above the average boiling point of the sample
results in an elution time of 2 - 30 minutes. Minimal temperatures give good
resolution, but increase elution times. If a sample has a wide boiling range, then
temperature programming can be useful. The column temperature is increased (either
continuously or in steps) as separation proceeds.
The column efficiency can be improved by variation in temperature, low liquid
phase, loading, narrow particle size distribution and tight packing. The length of the
column can be, as deemed necessary, from a fraction of an inch (capillary column) to
several hundreds of feet.
For a given species, the ratio of the times spent in the moving and stationary regions is
equal to the ratio of its concentrations in these regions, known as the partition
coefficient.

Packed columns are made of a glass or a metal tubing which is densely packed with a solid
support like diatomaceous earth. Due to the difficulty of packing the tubing
uniformly, these types of columns have a larger diameter than open tubular columns and
have a limited range of length. As a result, packed columns can only achieve about 50% of
the efficiency of a comparable WCOT column. Furthermore, the diatomaceous earth
packing is deactivated over time due to the semi-permanent adsorption of impurities within
the column. In contrast, FSWC open tubular columns are manufactured to be virtually free
of these adsorption problems.

Temperature Control
• Isothermal • Gradient
0
40
80
120
160
200
240
0 10 20 30 40 50 60
Time (min)
Temp(degC)
Instrumentation - Oven

The best detector must have a high sensitivity
to traces, good stability, and satisfactory
response to a wide variety of substances.
Detectors are classified as integral or
differential, and destructive or non-
destructive.
The integral detector measures the total
amount of the component .The differential
detector measures some property related to
the concentration of the resolved components
In case of the destructive detector, the sample
is destroyed in the process of detection, such
as the case of the flame ionization detector
(FID). The thermal conductivity differential
detector (TCD) is the most widely utilized non-
destructive detector. Fast scanning mass

Detectors:
The detector senses the presence of the individual components as they
Leave(elute) the column. The detector out put after amplification is traced
on a recorder.
As peaks at intervals on the chromatograph.
The duration of the intervals is usually a single second or even less than that.
Hence the detector is considered to be the brain of the gas chromatograph.
The most desirable criteria for a gas chromatographic detectors are:
1.It should be highly sensitive towards wide range of compounds.
2. It should produce uniform and linear responses towards wide range of vaporized
solute particles.
3. It should be stable during operation conditions.
4. It should have concentration reproducibility.
5.It should be easy to operate.
Generally gas chromatography detectors are about 4-5 orders of magnitude more
sensitive than the liquid chromatography detectors.

generally different detectors gives different types of selectivity.
Non-selective detector- It responds to a wide range of compounds except the carrier gas.
Selective detector - it responds to a group of compounds with similar physical or
chemical properties.
Specific detector -specific detector responds to a single chemical compound. .
In general detectors may be divided in to 2types.(detectors in chromatography operated in
2 ways. Respond either to the concentration of solute or the mass flow rate.
1. Concentration dependent detectors:
The signal from a concentration dependant detector is related to the
concentration of solute reaching detector, and usually these detectors do not destroy
the sample.
Dilution of response with make-up gas lowers the response.
Ex: Thermal conductivity detector (TCD)
Electron capture detector (ECD)
Argon ionization detector (AID)
Helium ionization detector (HID)

2. Mass flow dependant detectors usually destroy the sample, and the signal is related to the
rate of solute particles enter the detector. The response of a mass flow dependant detector is
un affected by make-up gas.
In differential detectors that responds to the mass flow rate, the peak area is directly
proportional to the total mass and there is no dependency on the flow rate of the mobile
phase.
. These detectors are suitable for quantitative analysis.
EX:- Flame ionization detector.(FID)
Flame Photometric detector (FPD)
Nitrogen phosphorous detector(NPD)
Depending upon the reason for operation chromatography may be
Preparative chromatography = separation of components of a given
mixture for future use. This chromatography is also known as
purification process.
Analytical chromatography = It can work even with minute
concentrations of the sample mixture and measures the components
of given mixture. Therefore it is used for quantitative estimation of
analytes.

Detectors may be non-destructive, whereby sensing does not alter the nature of the
solutes, as in the case of light absorption, so they may be collected for further use.
Destructive detectors, on the other hand, destroy the solutes. Detectors include not
only the component that senses the solutes but also those that perform the associated
transduction, electronic amplification, and final readout.

To obtain optimal separations, sharp, symmetrical chromatographic peaks must be
obtained. This means that band broadening must be limited. It is also beneficial to
measure the efficiency of the column.

Column efficiency
The efficiency of a column is reported as the number of theoretical plates (plate
number), N, a concept Martin borrowed from his experience with fractional distillation:
where tr is the retention time measured from the instant of injection and w is the peak
width obtained by drawing tangents to the sides of the Gaussian curve at the inflection
points and extrapolating the tangents to intercept the baseline.
The plate number depends on the length of the column. The extreme value of
106 plates was obtained with an open tubular gas chromatographic column 1.6
kilometres (1 mile) long. A more appropriate parameter for measuring efficiency
is the height equivalent to a theoretical plate (or plate height), HETP
(or h), which is L/N, L being the length of the column. Efficient columns have
small h values (see below Theoretical considerations: Plate height).
HETP = L/N ( Efficiencyresolution: Column efficiency).

There are many detectors which can be used in gas chromatography. Different
detectors will give different types of selectivity. A non-selective detector responds to all
compounds except the carrier gas, a selective detector responds to a range of
compounds with a common physical or chemical property and aspecific
detector responds to a single chemical compound. Detectors can also be grouped
into concentration dependant detectors and mass flow dependant detectors. The signal
from a concentration dependant detector is related to the concentration of solute in
the detector, and does not usually destroy the sample Dilution of with make-up gas will
lower the detectors response. Mass flow dependant detectors usually destroy the
sample, and the signal is related to the rate at which solute molecules enter the
detector. The response of a mass flow dependant detector is unaffected by make-up
gas. Have a look at this tabular summary of common GC detectors:

Type of Detector Applicable Samples Detection Limit
Mass Spectrometer
(MS)
Tunable for any sample .25 to 100 pg
Flame Ionization (FID) Hydrocarbons 1 pg/s
Thermal Conductivity
(TCD)
Universal 500 pg/ml
Electron-Capture
(ECD)
Halogenated
hydrocarbons
5 fg/s
Atomic Emission
(AED)
Element-selective 1 pg
Chemiluminescence
(CS)
Oxidizing reagent Dark current of
PMT
Photoionization (PID) Vapor and gaseous
Compounds
.002 to .02 µg/L
Typical gas chromatography detectors and their detection limits

Detector Type Support gases Selectivity Detectability Dynamic range
Flame ionization (FID) Mass flow Hydrogen and air Most organic cpds. 100 pg 107
Thermal conductivity
(TCD)
Concentration Reference Universal 1 ng 107
Electron capture (ECD) Concentration Make-up
Halides, nitrates,
nitriles, peroxides,
anhydrides,
organometallics
50 fg 105
Nitrogen-phosphorus Mass flow Hydrogen and air Nitrogen, phosphorus 10 pg 106
Flame photometric (FPD) Mass flow
Hydrogen and air
possibly oxygen
Sulphur, phosphorus,
tin, boron, arsenic,
germanium, selenium,
chromium
100 pg 103
Photo-ionization (PID) Concentration Make-up
Aliphatics, aromatics,
ketones, esters,
aldehydes, amines,
heterocyclics,
organosulphurs, some
organometallics
2 pg 107
Hall electrolytic
conductivity
Mass flow Hydrogen, oxygen
Halide, nitrogen,
nitrosamine, sulphur

Thermal conductivity detector (TCD),KATHAROMETER (OR)
Hot wire detector:
Thermal conductivity detector is the one of the oldest detector still using because of
Simplicity of system and it is widely used. Data’s are available over the years.
It is simple inexpensive, non-selective, accurate, non destructive of the sample.
The TCD is based on the changes in thermal conductivity of the gas stream..
Thermal conductivity of the most of the compounds is lesser than the commonly used carrier
gases (He, H) because the thermal conductivity of He is about 6 to 10 times greater than most
organic compounds.
When He is used as a carrier gas the presence of small amounts of organic materials causes
A relatively large decrease in thermal conductivity of the column effects. As a result of the
decrease in conductivity.
The detector undergoes a marked rise in temperature.
Since detector response depends upon the difference in thermal conduction of the carrier gas
and sample, a large difference is essential. An increase in temp. of the detector causes a
change In the resistance of wire or thermistor and this resistance gives a measure of the
thermal conductivity of the gas.

TCD consists of a temperature controlled metal block into which 2 cylindrical chambers
Or cavities are present.
Both chambers consists of filaments(thermistors,resistance wires) made up of platinum,
tungsten or alloys.
The filaments constitute of the reference(R) and the sensing (S) elements.
Both these filaments are connected to the arms of the Wheatstone bridge arrangement.
At the given temp. when carrier gas alone is flow through the both cylindrical chambers the
Resistance of the both the filaments are thermal equilibrium (they are constant).
As long as the composition of the gas does not change the rate of heat loss from the filaments
Will not alter.
Once the effluent passes through (s) the temp. of the filament (s) changes .
Because of thermal conductivities of sample and the carrier gas are different.
The differences result in heat loss form the filament eventually changes in the resistance
Of (s).This resistance changes are send by the Wheatstone bridge arrangement.
The bridge then produces a measurable voltage change that is amplified and signaled to the
Recorder which is recorded on the chromatogram.

Widge balance
ameter
Excitation voltage
Unbalanced
Voltage.
Same carrier
Gas is passing
Through the
Detectors.
Initially what
To do is widge
Balance with the
By varying these
Potentiomenr
I will balance the
Bridge.
When ever the elution peak comes out side gases comes detector out
Put change there is a thermal conductivity is changed I will get a
Unbalanced voltage recorded on the recorder.
We can have 4 detectors in one block itsef.
Amlifier and
recorder
Battery
(direct current source)

) Thermal Conductivity Detector (TCD)
- katherometer or hot-wire detector- first universal detector developed for GC
Process
- measures a bulk property of the mobile phase leaving the column.
- measures ability to conduct heat away from a hot-wire (i.e., thermal conductivity)
- thermal conductivity changes with presence of other components in the mobile phase

Disadvantages:
An oven is essential for the working of detector to attain column temp.
The detectors are relatively insensitive i.e., sensitivity is only about 10-6 to 10-8.
Advantages:
The detectors are simple in construction having no moving parts and are inexensive.
They give accurate results.
They are durable and possess long life.
They are non- selective hence known as universal detectors.
Use of wheatstone bridge increases the sensitivity of the detector.
It does not result in the destruction of the sample.
Linear response range is about 3 orders of magnitude.
The filament resistances supplies a measure of the thermal conductivity of the gas. Hence
By measuring the filament resistance, the changes in the effluent stream can be monitored.

As the name suggests, analysis involves the detection of
ions. The source of these ions is a (tiny)small hydrogen-
air flame. Sometimes hydrogen-oxygen flames are used
due to an ability to increase detection
sensitivity, however for most analysis, the use of
compressed breathable air is sufficient. Column
effluents are led into the flame wherein ionisation of
compounds may takes place.
In order to detect these ions, two electrodes are used to
provide a potential difference. The positive electrode
doubles as the nozzle head where the flame is
produced. The other, negative electrode is positioned
above the flame. The ions thus are attracted to the
collector plate and upon hitting the plate, induce a
current.
When only carrier gas passes through the flame, its
molecules are ionised and the resulting ionisation
current after amplification is fed to the sutable recorder.
This current is measured with a high-impedance
picoammeter and fed into an integrator.
A FID is sensitive to almost all the organic compounds
But insensitive to noble
gases,oxygen,N,CO,C02,water,H2S,S02,CS2 and Nitrogen

The eluent exits the GC column (A) and enters the FID detector’s oven (B). The oven is
needed to make sure that as soon as the eluent exits the column, it does not come out of
the gaseous phase and deposit on the interface between the column and FID. This
deposition would result in loss of effluent and errors in detection. As the eluent travels up
the FID, it is first mixed with the hydrogen fuel (C) and then with the oxidant (D). The
eluent/fuel/oxidant mixture continues to travel up to the nozzle head where a positive bias
voltage exists (E). This positive bias helps to repel the reduced carbon ions created by the
flame (F) pyrolyzing the eluent. The ions are repelled up toward the collector plates (G)
which are connected to a very sensitive ammeter, which detects the ions hitting the plates,
then feeds that signal (H) to an amplifier, integrator, and display system.
FIDs are best for detecting hydrocarbons and other easily flammable components.
n FID essentially can only detect components which can be burned. Other components may
be ionized by simply passing through the FID's flame, but they tend not to create enough
signal to rise above the noise of the detector.

The effluent from the column is mixed with hydrogen and
air, and ignited. Organic compounds burning in the flame
produce ions and electrons which can conduct electricity
through the flame. A large electrical potential is applied
at the burner tip, and a collector electrode is located
above the flame. (mixture burns at the tip
Ions and the free electrons are in the formed ) The
current resulting from the pyrolysis of any organic
compounds is measured. FIDs are mass sensitive rather
than concentration sensitive; this gives the advantage
that changes in mobile phase flow rate do not affect the
detector's response. The FID is a useful general detector
for the analysis of organic compounds; it has high
sensitivity, a large linear response range, and low noise. It
is also robust and easy to use, but unfortunately, it
destroys the. Positive ions and electrons are produced in
the flame when organic substances are present. The ions
are collected at electrodes and produce a small,
measurable current. The flame-ionization detector is
highly sensitive to hydrocarbons, but it will not detect
carrier gases, such as nitrogen, or highly oxidized
materials, such as carbon dioxide, carbon
monoxide, sulfur dioxide, and water
Parrlar or
cylendrical
½ cm 1cm above the tip
Hydrogen
Tip.
This was the restince
Across the gap and
Causes a current to flow.
mounted
This ensures that
Make current flow only
Ionized materials enters
The external resister
is sensed voltage dropped
Amplified and displayed on
The detector.
Platinum jet
-ve electrode.

advantages:
- universal detector for organics
-doesn’t respond to common inorganic compounds.
- mobile phase impurities not detected.
- carrier gases not detected.
- limit of detection: FID is 1000x better than TCD.
- linear and dynamic range better than TCD
disadvantage:
- destructive detector.
Flame ionization detector
Hydrocarbon groups are enter the flame and a complex process takes place which
+ve ly charged carbon species and electrons are formed. Now the current is greatly
Increased .
This FID responds only to the substances only for ionized
To the substances that produced charged the ions that is burned in H2 flame.
organic compounds the response is proportional to the no. of oxidisable carbon
atoms. This is basic principle of falme ionization detector.

The electron-capture detector, a stream of electrons from a radioactive source is produced in
a potential field. Materials in the gas stream containing atoms of certain types capture
electrons from the stream and measurably reduce the current. The most important of the
capturing atoms are the halogens—fluorine, chlorine, bromine, and iodine. This type of
detector, therefore, is particularly useful with chlorinated pesticides. Certain elements will
emit light of distinctive wavelength when excited in a flame.

The Flame Thermocouple Detector
The "flame thermocouple detector" was the
next detector to be reported which was
developed by Scott and was, in fact, the
forerunner to the flame ionization detector
FID. A diagram of the flame thermocouple is
shown.bellow

3.) Nitrogen-Phosphorus Detector (NPD)
- used for detecting nitrogen- or phosphorus containing compounds
- also known as alkali flame ionization detector or thermionic detector
Process
- same basic principal as FID
- measures production of ions when a solute
is burned in a flame
- ions are collected at an electrode to
create a current
- contains a small amount of alkali metal
vapor in the flame
- enhances the formation of ions from
nitrogen- and phosphorus- containing compounds
Alkali Bead

Flame photometric detector:
The flame photometric detector measures the intensity of light with a photometric o circuit.
Solute species containing halogens, sulphur, or phosphorus can be burned to produce ionic
species containing these elements and the ions sensed by electrochemical means.
It is a selective detector. It uses the luminous emissions of S or P from the effluent in a low
temp. hydrogen flame. These emissions are Serves as a analytical information i.e.,s pecific
For compounds containing these atoms. The intensity for band is recorded photometrically.
The detector consists of combustion chamber that houses flame. H2 as fuel, air or oxygen
to Support combustion. A thermal filter for the separation of UV and visible rays emitted by
The flame.
An interchangeable optical filter for the selection of S,P an insulated Photomultiplier tube
(PMT) and chimney as exhaust for combustion products.
Applications:
For the detection of heavy metals like Iron, chromium, selenium, strontium, tin etc. in
Organometallic compounds.
For the analysis of pesticides, coal, hydrogenated products as well as air and water
Pollutions.

Electron capture detector:
Invented by Dr.J.E.Lovelock in the late 1950s.
It is one of the most sensitive detectors used in GC.
It is specifically used for trace amounts of halaogen containing
Compounds like pesticides,polychlorinated biphenyls.
ECD contains a radioactive β-emitter for the generation of electrons.
This detector functions in 2 modes DC and pulsed mode.
DC mode: constant DC potential is applied b/n 2 electrodes.

The separation of the sample air is accomplished using gas chromatography. Tiny porous
beads, sometimes coated with a liquid, interact with the mixture of molecules impeding
there movement either because of their size or their solubility. In our case, this separation
column is divided into two parts. When the chemicals of interest move onto the second
column, the first column's flow is reversed to clean heavier compounds off before the
next injection. This is called "backflushing".
Detection of the halocompounds is by an electron capture detector. A radioactive foil of
nickel-63 is inside the pin-in-cup detector. The beta decay (an electron) ionizes the carrier
gas forming an electron cloud. Periodically a large positive pulse is applied to the center
electrode. This causes the free electrons to move to the electrode where they are
measured as a tiny current. When a molecule containing halogen atoms, which has the
property of enhanced affinity for electrons, enters the detector, it readily attracts and
holds a free electron. The background current is thus reduced. In due time the electron
capture molecules are flushed out of the detector and the current returns to its previous
level.
The measure of the dip in the current curve is a measure of the amount of chemical
present. By periodically injecting gas mixtures containing known quantities of the
chemical of interest, calibration of the detector is accomplished.
Recording of the inverted current produces a curve called a "chromatogram".

Advantages: It is highly sensitive in its response.
Sensitivity is 10-13 g.
It is 1 million times more sensitive than TCD and about 10,000times more sensitive
Than FID.
It is non-desturctive. i.e., lt does not alter the sample significantly.
It is highly sensitive for the detection of compounds like Halogens(Cl,Br,I), Quinones,
Peroxides,nitrites,nitro and phosphorous compounds, organometallic compounds.
Disadvantages:
It is least sensitive for compounds whose molecules have negligible affinity for electrons.
It is insensitive to functional groups like alcohols, amines and hydrocarbons.
Linear response is limited to 2 orders of magnitude.
The carrier gas used should be in absolutely pure form like pure nitrogen or mixture of
Pure methane-argon.
The temperature limitations of the detector is 2200C.
Applications:
Analysis of halogenated compounds.
Analysis of environmental pollutants.
Detection and quantitative determination of chlorinated insecticides.

Electron-capture Detectors
Electron-capture detectors (ECD) are highly selective detectors commonly used for
detecting environmental samples as the device selectively detects organic
compounds with moieties such as halogens, peroxides, quinones and nitro groups
and gives little to no response for all other compounds. Therefore, this method is
best suited in applications where traces quantities of chemicals such as pesticides
are to be detected and other chromatographic methods are unfeasible.
The simplest form of ECD involves gaseous electrons from a radioactive ? emitter in
an electric field. As the analyte leaves the GC column, it is passed over this ?
emitter, which typically consists of nickle-63 or tritium. The electrons from the ?
emitter ionize the nitrogen carrier gas and cause it to release a burst of
electrons. In the absence of organic compounds, a constant standing current is
maintained between two electrodes. With the addition of organic compounds with
electronegative functional groups, the current decreases significantly as the
functional groups capture the electrons.
The advantages of ECDs are the high selectivity and sensitivity towards certain
organic species with electronegative functional groups. However, the detector has
a limited signal range and is potentially dangerous owing to its radioactivity. In
addition, the signal-to-noise ratio is limited by radioactive decay and the presence
of O2 within the detector.

Electron Capture Detector (ECD)
- radioactive decay-based detector
- selective for compounds containing electronegative atoms, such as halogens
Principle of Operation
- based on the capture of electrons by
electronegative atoms in a molecule
- electrons are produced by ionization of the
carrier gas with a radioactive source
3H or 63Ni
- in absence of solute, steady stream of
these electrons is produced
- electrons go to collector electrode where
they produce a current
- compounds with electronegative atoms
capture electrons, reducing current
Advantages:
- useful for environmental testing
detection of chlorinated pesticides or herbicides
detection of polynuclear aromatic carcinogens
detection of organometallic compounds
- selective for halogen- (I, Br, Cl, F), nitro-, and sulfur-containing compounds
- detects polynuclear aromatic compounds, anhydrides and conjugated
carbonyl compounds.
Disadvantages: Could be affected by the flow rate.
e-
e-
e-
e-
e-
He
He
He
He
He+
He+
He+He+
He+
e-
e-
He
He
He
He
He+
He+
He+He+
He+

Atomic Emission Detectors
Atomic emission detectors (AED), one of the newest addition to the gas
chromatographer's arsenal, are element-selective detectors that utilize plasma, which is
a partially ionized gas, to atomize all of the elements of a sample and excite their
characteristic atomic emission spectra. AED is an extremely powerful alternative that
has a wider applicability due to its based on the detection of atomic emissions.There are
three ways of generating plasma: microwave-induced plasma (MIP), inductively coupled
plasma (ICP) or direct current plasma (DCP). MIP is the most commonly employed form
and is used with a positionable diode array to simultaneously monitor the atomic
emission spectra of several elements.
Instrumentation
The components of the Atomic emission detectors include 1) an interface for the
incoming capillary GC column to induce plasma chamber,2) a microwave chamber, 3) a
cooling system, 4) a diffration grating that associated optics, and 5) a position adjustable
photodiode array interfaced to a computer

Schematic of atomic emission detector

1. Mass Spectrometer (GC/MS)
Many GC instruments are coupled with a mass spectrometer, which is a very good
combination. The GC separates the compounds from each other, while the mass spectrometer
helps to identify them based on their fragmentation pattern.
2. Flame Ionization Detector (FID)
The detector is very sensitive towards organic molecules (10-12 g/s, linear range: 106 –
107), but relative insensitive to a few small molecules e.g. N2, NOx, H2S, CO, CO2, H2O. If
proper amounts of hydrogen/air are mixed, the combustion does not afford any ions. If other
components are introduced that contain carbon atoms cations are produced in the effluent
stream. The more carbon atoms are in the molecule, the more fragments are formed and the
more sensitive the detector is for this compound (-- > response factor). However, due to the
fact that the sample is burnt (pyrolysis), this technique is not suitable for preparative GC. In
addition, several gases are usually required to operate a FID: hydrogen, oxygen (compressed
air), and carrier gas

3. Thermal Conductivity Detector (TCD)
This detector is less sensitive than the FID (10-5-10-6g/s, linear range: 103-104), but is well
suited for preparative applications, because the sample is not destroyed. It is based on the
comparison of two gas streams, one containing only the carrier gas, the other one the carrier
gas and the compound. Naturally, a carrier gas with a high thermal conductivity e.g. helium
or hydrogen is used in order to maximize the temperature difference (and therefore the
difference in resistance) between two thin tungsten wires. The large surface-to-mass ratio
permits a fast equilibration to a steady state. The temperature difference between the
reference cell and the sample cell filaments is monitored by a Wheatstone bridge circuit.
4. Electron Capture Detector (ECD)
The detector consists of a cavity that contains two electrodes and a radiation source that
emits b-radiation (e.g. 63Ni, 3H). The collision between electrons and the carrier gas
(methane plus an inert gas) produces a plasma containing electrons and positive ions. If a
compound is present that contains electronegative atoms, those electrons are “captured”
and negative ions are formed, and the rate of electron collection decreases. The detector is
extremely selective for compounds with atoms of high electron affinity (10-14 g/s), but has a
relatively small linear range (~102-103). This detector is frequently used in the analysis of
chlorinated compounds e.g. pesticides, polychlorinated biphenyls, which show are very high
sensitivity.

Submultiples Multiples
Value Symbol Name Value Symbol Name
10−1 g dg decigram 101 g dag decagram
10−2 g cg centigram 102 g hg
hectogra
m
10−3 g mg milligram 103 g kg kilogram
10−6 g µg
microgra
m (mcg)
106 g Mg
megagra
m (tonne)
10−9 g ng nanogram 109 g Gg gigagram
10−12 g pg picogram 1012 g Tg teragram
10−15 g fg
femtogra
m
1015 g Pg petagram
10−18 g ag attogram 1018 g Eg exagram
10−21 g zg
zeptogra
m
1021 g Zg zettagram
10−24 g yg
yoctogra
m
1024 g Yg yottagram

GASSCHROMATOGRAPHY, ADVANCED STUDY OF THE FOLLOWING AND THEIR APPLICATIONS, INTRODUCTION, THEORY, COLUMN OPERATION,INSTRUMENTATION AND DETECTION,APPLICATIONS AND ADVANTAGES OF GC,PRINCIPLE OF SEPARATION IN GC, HOW GC MECHINE WORKS? COLUMN, DETECTORS.

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GASSCHROMATOGRAPHY, ADVANCED STUDY OF THE FOLLOWING AND THEIR APPLICATIONS, INTRODUCTION, THEORY, COLUMN OPERATION,INSTRUMENTATION AND DETECTION,APPLICATIONS AND ADVANTAGES OF GC,PRINCIPLE OF SEPARATION IN GC, HOW GC MECHINE WORKS? COLUMN, DETECTORS.