chromatogarphy technique

1. GAS CHROMATOGRAPHY

2. Gas Chromatography
Content:
 Introduction
 History
 Basic Term
 Working principle
 Types of GC
 Instrumentation
 Application
 Advantage
 disadvantage

3. Gas Chromatography
“Gas chromatography is a type of chromatography used in chemistry for analyzing and separating
compounds that can be convert to gas without decomposition.”
 Uses of this technique include testing the purity of a Gaseous substance and separating the different
components of a mixture. Sometimes, it may help in identifying the compound. It can also be used to
prepare pure compounds from a mixture.
History:
 German physical chemist Erika Cremer in 1947 together with Austrian graduate student Fritz Prior
developed the theoretical foundations of GC and built the first liquid-gas chromatograph, but her work
was deemed irrelevant and was ignored for a long time.
 English chemists Archer Martin and Richard Synge received a Nobel Prize in 1952 for the invention of
partition chromatography in the 1940s, laying the foundations of gas chromatography.
 The father of modern gas chromatography is Nobel Prize winner John Porter Martin , who also
developed the first liquid-gas chromatograph.

4. Basic Term:
 Mobile Phase: Solvent moving through the Column i.e. inert gas He,N2,Ar,H2.
 Stationery Phase: Substance that stays fixed inside the column i.e. high-boiling liquid that is
adsorbed on a Solid (silicones).
 Eluent: Fluid entering the column
 Eluate: Fluid exiting the column
 Elution: The process of washing out a compound through a column using a suitable solvent.
 Analyte: Mixture whose individual components have to be separated and analyzed.
 Retention Time: retention time (RT) is the interval between the injection of a sample and the
detection of substances in that sample. Or the time required for the solute to pass through a
chromatographic column.
 Retention Factor:
RF = Distance moved by the analyte / Distance moved by Solvent

5. Working Principle of Gas chromatography
 The sample solution injected into the instrument, enters a gas stream which transports the sample
into a separation tube known as the "column." (Helium or nitrogen is used as the so-called carrier
gas.) The various components are separated inside the column.
 The detector measures the quantity of the components that exit the column. To measure a sample
with an unknown concentration, a standard sample with a known concentration is injected into the
instrument.
 The standard sample peak retention time (appearance time) and area are compared to the test
sample to calculate the concentration.

6. Type of Gas Chromatography
On the base of Stationary phase the gas Chromatography has two types:
1. Gas Solid Chromatography
2. Gas Liquid Chromatography
GAS Solid Chromatography: In this, the retention of analytes is due to physical
adsorption. The principle of GSC is Adsorption.
Gas Liquid Chromatography: In this, it separates the ions or molecules that are
dissolved in a solvent. The principle of GLC is Partition.

7. Instrumentation :

8. Components
1. Carrier Gas(cylinder):
 The choice of carrier gas depends on the type of detector that is used and the components
that are to be determined.
 Carrier gases for chromatographs must be of high purity and chemically inert towards the
sample e.g., helium (He), argon (Ar), nitrogen (N2), carbon dioxide (CO2) and hydrogen
(H2).
 The carrier gas system can contain a molecular sieve to remove water or other impurities.
 The Carrier Gas system also contain a molecular sieve to remove water and other impurities.
 p inlet is 10-50psig.
 Flow rate range 20-50ml/mint for Conventional Analytical column.
 Flow rate is 1-5ml/mint for Capillary Column.

9. 2-Sample injection system:
 A sample port is necessary for introducing the sample at the head of the column.
 Modern injection techniques often employ the use of heated sample ports through which the
sample can be injected and vaporized in a near simultaneous fashion.
 A calibrated micro syringe is used to deliver a sample volume in the range of a few microliters
through a rubber septum and into the vaporization chamber.
 The vaporization chamber is typically heated 50 °C above the lowest boiling point of the
sample and subsequently mixed with the carrier gas to transport the sample into the column.

10. 3-Column:
There are two general types of column, packed and capillary.
 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 - 4mm.
 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.

11. 4-Detector:
A detector is a device used in gas chromatography (GC) to detect components of the mixture being eluted off the
chromatography column.
There are two type of detector Destructive and non- destructive:
Destructive: The destructive detectors perform continuous transformation of the column effluent (burning,
evaporation or mixing with reagents) with subsequent measurement of some physical property of the resulting
material.
 Flame ionization detector (FID)
 Flame photometric detector (FPD)
 Nitrogen Phosphorus Detector (NPD)
 Atomic-emission detector (AED)
Non-Destructive: The non-destructive detectors are directly measuring some property of the column eluent
 Thermal conductivity detector, (TCD). Measures the thermal conductivity of the eluent.
 Electron capture detector, (ECD). The most sensitive detector known. Allows for the detection of organic
molecules containing halogen, nitro groups etc.
 Photoionization detector, (PID). Measures the increase in conductivity achieved by ionizing the effluent gas with
UV radiation.
 Olfactometric detector. Assesses the odor activity of the eluent using human assessors.

12. 5-Read out Device:
 This device show the graphical representation on the screen in which on X-axis the retention
time and in y-axis the intensity or concentration time is present.
 The low boiling molecule move faster so their peak is large and high boiling molecule move
slower so they have small peak value.

13. Application
 Gas Chromatography is used for the detection of Natural Substance such as fatty
acid, flavour & Aroma Compound.
 It is used for the detection of food contaminant such as modern pesticides,
Polychlorinated biphenyls, Veterinary drugs, Phthalate and adipate esters,etc.
 Gas Chromatography is used extensively in forensic science. Disciplines as
diverse as solid drug dose identification and quantification, arson investigation,
paint chip analysis, and toxicology cases, employ GC to identify and quantify
various biological specimens and crime-scene evidence.
 Gas chromatography is used in the analysis of: air-borne pollutants, performance-
enhancing drugs in athlete’s urine samples, oil spills , essential oils in perfume
preparation.

14. Advantage
 The major advantage of gas chromatography is its high sensitivity, resolution, and separation ability, which
allows it to separate a wide range of volatile compounds.
 It can be upgraded to a mass spectrometer (MS), which is used to determine the mass-to-charge ratio of ions.
 It comes with a variety of detectors and injectors that can be used for various pharmaceuticals as well as other
applications.
 Gas chromatography can analyze a sample much faster than other chromatographic techniques.
 It is a robust method of separation that gives the superior signal-to-noise ratio.
 It only takes a very small amount of sample to inject, and its detectors are extremely sensitive, allowing it to
detect extremely low concentrations.
 As per the requirement of the molecule, there are different types of GC columns are available in many
diameters and lengths.
 Gas chromatography is easy, automated, and has quick analysis of data which gives comparatively high
precision, accuracy, and reproducible results.
 Operational parameters such as flow rate, temperature, and pressure, etc. are easy to change even during
chromatographic runs.

15. Disadvantage
 The major disadvantage of GC is that only volatile and thermally stable compounds can be
separated using gas chromatography.
 Detectors which are used in the GC are destructive, except for MS.
 Selectivity in HPLC or TLC is also better as a mobile phase can be easily changed. In GC,
you can just modify the temperature of the column and oven, but you cannot change the
mobile phase as it has a constant flow of carrier gas (helium, nitrogen).
 Since hydrogen gas, which is used for flame, is highly flammable, care must be taken when
using it.
 It is impossible to recover individual sample component.