Gas chromatography

1. Working and application of
Gas Chromatography
Manoj Lawande
BiSEP Student

2. Chromatography
 Chromatography is a technique for separating mixtures into their components to
analyze, identify, purify and or quantify the mixture of components.
 The components to be separated or distributed between two phases i.e. Stationary
phase and mobile phase.
 The factors effective on this separation process include molecular characteristics related
to adsorption (liquid-solid) and affinity or differences among their molecular weight.
 Basic terminologies :
 Mobile phase: A solvent that flows through the supporting medium.
 Stationary phase: A layer or coating on the supporting medium that interacts with the
analytes.
 Supporting medium: A solid surface on which the stationary phase is bound/coated.

3. Principle of Chromatography
 Physical method of separation that distributes components to separate between
two phases move in a definite direction.
 Substances are separated based on their differential distribution between two
phases.
 Substances will move with the mobile phase at different rate depending upon their
partition or distribution coefficients.

4. Classification of Chromatography
 Based on Mechanism of separation
1. Adsorption chromatography
2. Partition Chromatography
3. Ion-Exchange Chromatography
4. Size-Exclusion Chromatography
 Based on Mobile Phase
1. Liquid chromatography
2. Gas chromatography
3. Super critical fluid chromatography
 Based on the shape of the chromatographic bed
1. Planner chromatography
2. Column chromatography
I. Packed column chromatography
II. Tubular column chromatography

5. Gas Chromatography
 Used for the separation of gaseous and volatile substaces
 Simple and efficient in terms of separation2
 Stationary phase can be both solid as well as liquid while mobile phase is gas.
 GSC works on the principle of adsorption while GLC works on partition principle.
 The van diameter equation relates heigh equivalent to a theoretical plate (HETP) of a
chromatographic column to the various flow and kinetic parameters which cause peak broadening, as
follow:
𝐻𝐸𝑃𝐴 = 𝐴 + 𝐵 ÷ 𝑢 + 𝐶8 + 𝐶𝑚 . 𝑢
Where
HETP= a measure of the resolving power of the column (m)
A= Eddy-diffusion parameter, related to channeling through a non-ideal packing [m]
B= diffusion coefficient of the eluting particles in the longitudinal direction, resulting in dispersion [m2 s -
1]
C= Resistance mass transfer coefficient of the analyte between mobile and stationary phase [s]
u= Linear Velocity [m s -1)

6. Types of Chromatography
 Normal Phase chromatography
 Reverse Phase chromatography
 Hydrophobic interaction chromatography
 Hydrophilic interaction chromatography
 lon - Exchange chromatography
 Fast protein liquid chromatography Size Exclusion chromatography
 Affinity chromatography
 Super critical Fluid chromatography
 Gas chromatography
 Paper chromatography
 Thin Layer chromatography. Etc.

7. Working of Gas Chromatography

8. Key points for Gas Chromatography
 Samples to be separated is converted into vapours and mixed with gaseous mobile
phase.
 Components more soluble in stationary phase or bigger in size travels slower.
 Components more soluble in mobile phase or smaller in size travels faster.
 Components are separated according to their Partition co-efficient.
 For GC analysis/separation, the sample should be thermostable and volatile.
 The number of components in a sample is determined by the number of peaks.
 The amount of a given component in a sample is determined by the area under the
peaks.
 The identity of components can be determined by the given retention times.

9. Applications of Gas Chromatography
 Gas chromatography is capable of separating, detecting and partially
characterizing the organic compounds, particularly when present in small
quantities.
 Qualitative analysis : Retention time and volume are used for identification and
separation
 Checking purity of compounds: Comparison of chromatogram of the sample with
standard chromatogram of compound
 Quantitative analysis : By measuring peak area or peak height
 Used for analysis of drugs and their metabolites.