Chromatography (Gas Chromatography)

Presented By:-

Ruta Satoskar &

Suman Muthu

THE CHROMATOGRAPHIC PROCESS - PARTITIONINGTHE CHROMATOGRAPHIC PROCESS - PARTITIONING

(gas or liquid)MOBILE PHASEMOBILE PHASE

STATIONARY PHASESTATIONARY PHASE

Sampleout

Samplein

(solid or heavy liquid coated onto a solid or support system)

Original Chromatography Experiment

Later

Start: A glass column is filled with powdered limestone (CaCO3).

End: A series of colored bands isseen to form, corresponding to the different pigments in the original plant extract. These bands were later determined to be chlorophylls, xanthophylls and carotenoids.

An EtOH extractof leaf pigments is applied to the top of the column.

EtOH is used to flush the pigments down the column.

Chromatography: (Greek = chroma “color” and graphein “writing” ) Tswett named this new technique chromatography based on the fact that it separated the components of a solution by color.

Common Types of ChromatographyTswett’s technique is based on Liquid Chromatography. There are now several common chromatographic methods. These include:1. Paper Chromatography2. Thin Layer Chromatography (TLC)3. Liquid Chromatography (LC)4. High Pressure Liquid Chromatography (HPLC)5. Ion Chromatography6. Gas Chromatography (GC)

How Does Chromatography Work?In all chromatographic separations, the sample is transported in a mobile phase. The mobile phase can be a gas, a liquid, or a supercritical fluid.

The mobile phase is then forced through a stationary phase held in a column or on a solid surface. The stationary phase needs to be something that does not react with the mobile phase or the sample.

The sample then has the opportunity to interact with the stationary phase as it moves past it. Samples that interact greatly, then appear to move more slowly. Samples that interact weakly, then appear to move more quickly. Because of this difference in rates, the samples can then be separated into their components.

Chromatography is based on a physical equilibrium that results when a solute is transferred between the mobile and a stationary phase.

A

A

A

A

AA

A

AA

A

A

A

K = distribution coefficient or partition ratio K

C S C M

Where CS is the molar concentration of the solute in the stationary phase and CM is the molar concentration in the mobile phase.

Cross Section of Equilibrium in a column.“A” are adsorbed to the stationary phase.“A” are traveling in the mobile phase.

Gas ChromatographyGas Chromatography

• The father of modern The father of modern gas chromatography is gas chromatography is Nobel Prize winner Nobel Prize winner John John Porter Martin,Porter Martin, who also who also developed the first developed the first liquid-gas liquid-gas chromatograph. (1950)chromatograph. (1950)

Gas Chromatography

B.D of G.C.

GAS CHROMATOGRAPHY

Separation of gaseous & volatile substances Simple & efficient in regard to separationGC consists of :- •GSC (gas solid chromatography) •GLC (gas liquid chromatographyGas → M.PSolid / Liquid → S.PGSC not used because of limited no. of S.PGSC principle is ADSORPTION

GLC principle is PARTITION

Sample to be separated is converted into vapour And mixed with gaseous M.PComponent more soluble in the S.P → travels slowerComponent less soluble in the S.P → travels fasterComponents are separated according to their Partition

Coefficient

Criteria for compounds to be analyzed by G.C 1.VOLATILITY.

2.THERMOSTABILITY.

How a Gas Chromatography Machine How a Gas Chromatography Machine WorksWorks

– First, a vaporized sample is injected onto the chromatographic column.

– Second, the sample moves through the column through the flow of inert gas.

– Third, the components are recorded as a sequence of peaks as they leave the column.

Chromatographic SeparationChromatographic Separation

-Deals with both the -Deals with both the stationary phase stationary phase and and the the mobile phasemobile phase. .

• Mobile – inert gas used as carrier.Mobile – inert gas used as carrier.• Stationary – liquid coated on a solid or Stationary – liquid coated on a solid or

a solid within a columna solid within a column..

Chromatographic SeparationChromatographic Separation• Chromatographic SeparationChromatographic Separation

– In the mobile phase, components of the sample In the mobile phase, components of the sample are uniquely drawn to the stationary phase and are uniquely drawn to the stationary phase and thus, enter this phase at different times. thus, enter this phase at different times.

– The parts of the sample are separated within the The parts of the sample are separated within the column.column.

– Compounds used at the stationary phase reach Compounds used at the stationary phase reach the detector at unique times and produce a the detector at unique times and produce a series of peaks along a time sequenceseries of peaks along a time sequence . .

Chromatographic Separation A(continued)Chromatographic Separation A(continued)

– The peaks can then be read and analyzed by The peaks can then be read and analyzed by a forensic scientist to determine the exact a forensic scientist to determine the exact components of the mixture.components of the mixture.

– Retention time is determined by each Retention time is determined by each component reaching the detector at a component reaching the detector at a characteristic time.characteristic time.

Chromatographic AnalysisChromatographic Analysis

– The number of components in a sample is The number of components in a sample is determined by the number of peaks.determined by the number of peaks.

– The amount of a given component in a sample is The amount of a given component in a sample is determined by the area under the peaks. determined by the area under the peaks.

– The identity of components can be determined The identity of components can be determined by the given retention times.by the given retention times.

Peaks and DataPeaks and Data

GRAPHICAL ANALYSIS

PRACTICAL REQUIREMENTS• Carrier gas• Flow regulators & Flow meters• Injection devices• Columns• Temperature control devices• Detectors• Recorders & Integrators

CARRIER GAS

» Hydrogen • Better thermal conductivity• Disadvantage: it reacts with unsaturated compounds

& inflammable» Helium• Excellent thermal conductivity• It is expensive» Nitrogen• Reduced sensitivity• It is inexpensive

Requirements of a carrier gas

InertnessSuitable for the detectorHigh purityEasily available CheapShould not cause the risk of fireShould give best column performance

ADVANTAGES OF G.C

1. Very high resolution power, complex mixtures can be resolved into its components by this method.

2. Very high sensitivity with TCD, detect down to 100 ppm

3. It is a micro method, small sample size is required4. Fast analysis is possible, gas as moving phase-

rapid equilibrium 5. Relatively good precision & accuracy6. Qualitative & quantitative analysis is possible

Disadvantages of G.C.• The samples analysed are limited to those that

are volatile or can be made volatile.• The samples must be thermally stable to prevent

degradation when heated.• Cannot be used to prepare samples for further

analysis once separated.• Problems can be encountered when injecting the

sample

Applications of G.C

• G.C is capable of separating, detecting & partially characterizing the organic compounds , particularly when present in small quantities.

1, Qualitative analysisRt & RV are used for the identification & separation

2, Checking the purity of a compoundCompare the chromatogram of the std. & that of the

sample

Applications of G.C

3, Quantitative analysisIt is necessary to measure the peak area or peak

height of each component

4, Used for analysis of drugs & their metabolites.

The Next Generation in Gas Chromatography