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
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
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
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
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
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
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
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
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
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
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
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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