Gas Chromatography. Presented By Mr. Venkateswarlu Mpharm KTPC

Transcription

1 Gas Chromatography

2 Gas Chromatography Presented By Mr. Venkateswarlu Mpharm KTPC

3 What is Gas Chromatography? It is also known as Gas-Liquid Chromatography (GLC)

4 GAS CHROMATOGRAPHY Separation of gaseous & volatile substances Simple & efficient in regard to separation GC consists of GSC (gas solid chromatography) GLC (gas liquid chromatography Gas M.P Solid / Liquid S.P GSC not used because of limited no. of S.P GSC principle is ADSORPTION GLC principle is PARTITION

5 Sample to be separated is converted into vapour And mixed with gaseous M.P Component more soluble in the S.P travels slower Component less soluble in the S.P travels faster Components are separated according to their Partition Co-efficient Criteria for compounds to be analyzed by G.C 1.VOLATILITY: 2.THERMOSTABILITY:

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

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8 The Next Generation in Gas Chromatography

9 How a Gas Chromatography Machine Works 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.

10 Chromatographic Separation Deals with both the stationary phase and the mobile phase. Mobile inert gas used as carrier. Stationary liquid coated on a solid or a solid within a column.

11 Chromatographic Separation Chromatographic Separation In the mobile phase, components of the sample are uniquely drawn to the stationary phase and thus, enter this phase at different times. The parts of the sample are separated within the column. Compounds used at the stationary phase reach the detector at unique times and produce a series of peaks along a time sequence.

12 Chromatographic Separation (continued) The peaks can then be read and analyzed by a forensic scientist to determine the exact components of the mixture. Retention time is determined by each component reaching the detector at a characteristic time.

13 Chromatographic Analysis 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.

14 Peaks and Data

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

22 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

23 Requirements of a carrier gas Inertness Suitable for the detector High purity Easily available Cheap Should not cause the risk of fire Should give best column performance

24 Flow regulators & Flow meters deliver the gas with uniform pressure/flow rate flow meters:- Rota meter & Soap bubble flow meter Rota meter placed before column inlet it has a glass tube with a float held on to a spring. the level of the float is determined by the flow rate of carrier gas

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26 Soap Bubble Meter Similar to Rota meter & instead of a float, soap bubble formed indicates the flow rate

27 Injection Devices Gases can be introduced into the column by valve devices liquids can be injected through loop or septum devices

28 COLUMNS Important part of GC Made up of glass or stainless steel Glass column- inert, highly fragile COLUMNS can be classified Depending on its use 1. Analytical column meters length & 3-6 mm d.m 2. Preparative column 3-6 meters length, 6-9mm d.m

29 Depending on its nature 1.Packed column: columns are available in a packed manner S.P for GLC: polyethylene glycol, esters, amides, hydrocarbons, polysiloxanes 2.Open tubular or Capillary column or Golay column Long capillary tubing M in length Uniform & narrow d.m of cm Made up of stainless steel & form of a coil Disadvantage: more sample cannot loaded

30 3.SCOT columns (Support coated open tubular column Improved version of Golay / Capillary columns, have small sample capacity Made by depositing a micron size porous layer of supporting material on the inner wall of the capillary column Then coated with a thin film of liquid phase

31 Columns Packed Capillary

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34 Equilibration of the column Before introduction of the sample Column is attached to instrument & desired flow rate by flow regulators Set desired temp. Conditioning is achieved by passing carrier gas for 24 hours

35 Temperature Control Devices Preheaters: convert sample into its vapour form, present along with injecting devices Thermostatically controlled oven: temperature maintenance in a column is highly essential for efficient separation. Two types of operations Isothermal programming:- Linear programming:- this method is efficient for separation of complex mixtures

36 Temp (deg C) Instrumentation - Oven Temperature Control Isothermal Gradient Time (min)

37 DETECTORS Heart of the apparatus The requirements of an ideal detector are- Applicability to wide range of samples Rapidity High sensitivity Linearity Response should be unaffected by temperature, flow rate Non destructive Simple & inexpensive

38 1.Thermal Conductivity Detector (Katharometer, Hot Wire Detector) Measures the changes of thermal conductivity due to the sample ( g). Sample can be recovered.

39 Flow Flow Thermal Conductivity Basics The TCD is a nondestructive, concentration sensing detector. A heated filament is cooled by the flow of carrier gas. When the carrier gas is contaminated by sample, the cooling effect of the gas changes. The difference in cooling is used to generate the detector signal.

40 Thermal Conductivity Detector When a separated compound elutes from the column, the thermal conductivity of the mixture of carrier gas and compound gas is lowered. The filament in the sample column becomes hotter than the control column. The imbalance between control and sample filament temperature is measured by a simple gadget and a signal is recorded

41 Measures heat loss from a hot filament e filament heated to const T when only carrier gas flows heat loss to metal block is constant, filament T remains constant. when an analyte species flows past the filament generally thermal conductivity goes down, T of filament will rise. (resistance of the filament will rise).

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43 Relative Thermal Conductivity Compound Relative Thermal Conductivity Carbon Tetrachloride 0.05 Benzene 0.11 Hexane 0.12 Argon 0.12 Methanol 0.13 Nitrogen 0.17 Helium 1.00 Hydrogen 1.28

44 Advantages of Katharometer Linearity is good Applicable to most compounds Non destructive Simple & inexpensive Disadvantages Low sensitivity Affected by fluctuations in temperature and flow rate Biological samples cannot be analyzed

45 FID

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