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SIMPLE AND EASY DISCUSSION ABOUT GAS CHROMATOGRAPHY

SIMPLE AND EASY DISCUSSION ABOUT GAS CHROMATOGRAPHY

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  • 1.  Introduction It is one of the separation technique Gas is used as the mobile phase, solid or liquid are used as the stationary phase Solid is not mostly used, liquid stationary phase is used GSC is not widely used GSC: principle is adsorption GLC: principle is partitionPRINCIPLE: Partition, the liquid coated on solid support then used as stationary phase The components are separated according to the solubilities More soluble in stationary phase: elute latter Less soluble in stationary phase: elute first The components are separated according to partition coefficient
  • 2. REQUIREMENT FOR COMPOUND ANALYSED BY GLC:1. Volatility: the compound possible to convert volatile state then only it is mixed with mobile phase2. Thermo stability: All the compounds convert into vaporised state by using high temperature then only used, so at high temperature the compound is stableREQUIREMENTS: Carrier gas Flow regulator Injection device Column Temperature control device Detectors Recorders
  • 3. CARRIER GAS: Mostly used inert gases for mobile phase Eg: hydrogen , helium, nitrogen and argon Hydrogen: Thermal conductivity is more, low density, very useful in case of thermal conductivity and flame ionisation detector Disadvantage: it reacts with unsaturated compounds
  • 4. HELIUM: Advantage: Thermal conductivity is more. Disadvantage: ExpensiveREQUIREMENTS OF CARRIER GAS Inertness Suitable to detector High purity Easily available and cheap Less risk of explosion or fire hazardsFLOW REGULATORS AND FLOW METERS: The carrier gas supplied at high pressure so to use flow regulator, to regulate the pressure Flow meter to regulate the flow rate of the gas Eg: rotameter, soap bubble flow meter
  • 5. Rotameter: It is appearing like glass tube containing spring Fixed before the column inlet To pass the gas The spring is floated then measure the flow rateSoap bubble meter: Instead of spring to use soap solution To pass the gas solution soap bubble is form then it travels particular pressureINJECTION DEVICE: To use gas, liquid or solid samples Gases are introduced by using valve devices Liquid are introduced by using septum device Solid: dissolve in particular solvent then introduced in to column
  • 6. COLUMNS: Important part of the instrument Made of glass or stainless steel Two types1. Depending on its use: Analytical column, Preparative column2. Depending on its nature: Packed column, open tubular or capillary columnANALYTICAL COLUMN: Length:1-1.5m, diameter: 3-6mm To use only small quantity of samplePREPARATIVE COLUMN: Length: 3-6m, Diameter: 6-9 mm To use large amount of samples. Possible to loaded
  • 7. PACKED COLUMN: Commercially available Available in polar and non polar nature Eg: polydimethyl.siloxane, poly siloxane, poly alkylene glycol, polyethylene glycol Temperature range 60-320ºCCAPILLARY COLUMN: Made of capillary tubing of 30-90m in length Diameter(internal)0.025-0.075cm Made of stainless steel in the form of coil The inner wall is coated with stationary phase liquid of a thin film 0.5-1µ These have least resistance to the flow of carrier gasSCOT COLUMN:Support coated open tubular column
  • 8.  It is improved type of capillary column The supporting material is micron size in porus layer The the lliquid stationary phase is coated so to get more sample holdingPREHEATERS: For GC to convert the sample in to vaporised state The preheaters are present along with injection deviceTHERMOSTATICALLY CONTROLLED OVEN: To keep the column in thermostatically controlled oven by maintaining the temperature only to get equal distribution between the solutes in mobile phase Column is kept at high temperature oven The columns are highly accurate and it maintains temperature to 0.1ºC
  • 9.  Two types of operations are possible:1. Isothermal programming: to maintain the same temperature up to the process2. Linear programming: the oven is heated linearly over a period of time. To fix the temperature initially 150ºC but at the end of process it becomes 200ºCDETECTORS: To detect the component after separation mainly to detect the component present in the carrier gas Applicable to wide range of sample High sensitivity Rapid response Linearity Not to destructive the sample Simple to maintain In expensive
  • 10. THERMAL CONDUCTIVITY DETECTOR[KATHAROMETER]Principle: to measure the thermal conductivity difference between carrier gas and that ofkatharometerMethod: It consist of two platinum wirs Both connected to wheatstone bridge One side pass only carrier gas other side to pass eluent from column The two platinum wires heated electrically To maintain temperature and electrical resistance To measure the baseline The compound eluted from column to get electrical resistance It is amplified and recorded Hydrogen and helium is most widely used carrier gas good thermal conductivityAdvantage: It is used for wide range of compounds, good linearity and simple
  • 11. KATHAROMETER
  • 12. Disadvantage: Low sensitivity, affected by fluctuation in temperature and flow rateresponse is only relative Biological samples cant be analysedFLAME IONISATION DETECTOR: The ionisation detectors are based upon the electrical conductivity of carrier gas At normal temperature and pressure gasses act as insulators, but become conductive if ions are presentCarrier gas: Hydrogen if used any other carrier gas to mix with hydrogen then use itAdvantage: Extremly sensitive Stable, organic compounds mostly used, linearity is excellent To pass the carrier gas from the column If only hydrogen or carrier gas no ionisation Produce electrical pulse Compound is present ionisation takes place
  • 13. ARGON IONISATION DETECTOR: Argon atoms are excited by using alpha , beta particles Meta stable state --------- pass carrier gas with effulent-------------argon are ionised------- then produce electrical pulse Argon treated with Radium.D or tririum, it goes to metastable state-------pass the carrier gas--- ionised, electric current pulseApplications: Qualitative: to identify the compounds, to check the purity, identification of impurities Quantitative: %purity, Direct comparison method Calibration curve method Internal standard method

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