Gas chromatography

Introduction to gas Chromatography
,Principle of gas chromatography
Instrumentation of gas Chromatography
Type of detectors of gas chromatography
Advantages of gas chromatography
Disadvantages of gas chromatography
Applications of gas chromatography

1. GAS CHROMATOGRAPHY By R.PRIYANKA (Regd.No:616233704010) M. Pharmacy 2 nd year Pharmaceutical analysis and quality assurance SrinivasaRao college of pharmacy, P.M.palem , Visakhapatnam

2. Contents Introduction Principle Instrumentation Advantages Disadvantages Applications

3. INTRODUCTION The chromatographic technique requires that a solute undergoes distribution between two phases one of them is fixed (stationary phase) and other one is moving (mobile phase). Gas chromatography is a analytical technique that helps to separate and analyze a mixture of organic vaporizable or volatile compounds without their decomposition.

4. PRINCIPLE The organic compounds are separated due to difference in their partitioning behavior between the mobile gas phase and the stationary phase in the column. In this the mobile phase is a gas and liquid which is coated on the solid support is used as stationary phase. The mixture of components to be separated is converted into vapour and mixed with gaseous mobile phase. the component which is more soluble in the stationary phase travels slower and elute later , which is less soluble in the sp travels faster &elute out first.

5. INSTRUMENTATION The gas chromatography consists of following components. 1.Gas supplying units –carrier gas ,flow regulators & flow meters ,pressure regulators. 2.Sampling units 3.Column 4.Temperature programmer 5.Detectors 6.Recorders

6. Instrumentation Carrier gas (mobile phase) supply: N2, He, H2 Flow control Injector Column Detectors Computer/recorder

7. Carrier gas supply Function: to provide carrier gas to chromatographic column Carrier gas carries sample to column. Tank, needle valve, flow meter, pressure gauge Type of carrier gases → depends on column & detector Capillary columns: H2, He. Packed columns: N2 TCD, ECD: N2 FID: He

8. Carrier gas supply Ideal carrier gases: pure & dry Impure & moisture: harm the column, ↓performance of detectors, adversely affect quantification of trace analysis. Measures: Tubing (gas source → GC)→uncontaminated. Molecular sieve beds → ↓moisture, hydrocarbon, oxygen content.

9. 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

10. Flow control Regulates the carrier gas flow in GC Constant flow of carrier gas → column efficiency & reproducible elution time. Magnitude of carrier gas flow rate depends → type of column Packed column – 10-60ml/min Capillary column – 1-2ml/min

11. Injection port The injection port consists of a septum through which a syringe needle is inserted to inject the sample. The sample is injected into a stream of inert gas usually at an elevated temperature by a micro syringe. The vaporized sample is carried into acolumn packed with the stationary phase. To ensure rapid & complete solute volatilization temp of injector → 30-50 degree celsius>column temp

12. Injection techniques Split Splitless

13. Columns & its types Packed column Capillary( open tubular column) 1 - 4mm ID; 1 - 5 m length Glass/stainless steel coil Packed solid particles either porous/non-porous coated with thin (1 μm) film of liquid 0.1 - 0.5 mm I.D. (ID); 10 - 150 m length  Thin fused-silica.  Inner wall coated with thin (0.1-5 μm) film of liquid (stationary phase)

14. Capillary(open tubular) column 3 layers 1. Polyamide coating – strong water proof barrier 2. Thin fused-silica- minimize chemical reactivity, uniform surface for stationary phase Stationary phase

15. Stationary phase Polymer – inner surface of fused silica layer Thickness, uniformity, chemical nature → influences the separation of components in sample. Mc stationary phase silicon polymer used → poly siloxane

16. Detection Systems The detector is the device located at the end of the column which provides a quantitative measurement of the components of the mixture as they elute in combination with the carrier gas.

17. Types of Detectors in GC To measure the separated analytes as they elute from the column. Universal unit → detect most analytes Thermal conductance detector (TCD) Mass spectrometer (MS)Selective detectors → detect specific substances Flame Ionization Detector (FID) → hydrocarbon Electron capture detector (ECD) → electronegative groups

18. Flame Ionization Detector (FID) Compounds that produce ions when burned in an H2-air flame → organic cation → releases electron → detected by collector electrode → generation of current. Mc detector used for clinical analysis Magnitude of current α mass of carbon material delivered to detector → used for detection & quantification of eluting solutes. Advantages → simple, reliable, sensitive, linearity. Disadvantage – destroy all the sample. Uses → detects hydrocarbon including fatty acids .

19. Types of Gas Chromatography Detectors Non-selective Responds to all compounds present in carrier gas stream except the carrier gas itself Selective Responds to range of compounds with a common physical or chemical characteristic Specific Responds to a single specific compound only Detectors can also be grouped into concentration or mass flow detectors

20. Thermal conductance detector( tcd ) Universal detector → most of the analytes Difference in thermal conductivity between the carrier gas and sample gas causes a voltage output

21. Electron capture detector (ECD) Selective type of detector – electronegative groups- halogens (F, Cl , Br, I), peroxides , quinones, & nitro groups  Principle – reaction b/n electronegative groups & thermal electrons(radioactive source) →Thermal electrons captured on the electrode → If electron capturing compound is present the number of thermal electrons on the electrode (standing current) is decreased. ECD Advantages Highly sensitive Easy to use reliable Selective

22. computer Regulates mobile phase composition, flow rate, column detector temp Electronic signals generated by detectors are recorded in the form of chromato graghic peak at varied function of time Area, height, retention time ,base width of chromato graghic peak is measured to compute analyte concentration of each peak.

23. ADVANTAGES OF G.C Very high resolution power, complex mixtures can be resolved into its components by this method. Very high sensitivity with TCD, detect down to 100 ppm It is a micro method, small sample size is required Fast analysis is possible, gas as moving phaserapid equilibrium

24. Disadvantages of GC Limited to volatile sample. Not suitable for thermally labile samples. Samples be soluble and don’t react with the column. During injection of the gaseous sample proper attention is required.

25. Applications of GC Separation & identification of lipids, carbohydrates & proteins. Separation & identification of amino acids in urine by GC-MS for diagnostic purpose. Measurement of drugs & other metabolites in biological fluids. Used for toxicological analysis of biological fluid by using ECD. Analysis of pesticides in soil, water, food. Forensic analysis of blood and urine alcohol levels by using PEG-SP IN GC.