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1、Gas Chromatography,Mobile phase: Inert gas such as N2 or He. Stationary phase: May be solid (GSC) or Non volatile liquid at operating temperature over inert support (GLC). Mixture: Mixture components must be: 1- Volatile: Volatile material usually have molecular weight not exceed 400 500 Dalton. 2-
2、Thermo stable.,Instruments: 1- Gas Tank. 2- Flow meter. 3- Injector system for sample application. 4- Column and oven. 5- Detector. 6- Amplifier and Recorder.,stationary phase: GSC: 1- Silica gel. 2- Charcoal (Activated). 3- Molecular sieves (synthetic inorganic materials).,GLC: Liquid or low meltin
3、g solid coating an inert support. e.g. of supports: 1- Chromosorb. 2- Celite. 3- Glass beeds. 4- Teflon e.g. of liquids or low-melting solids: Each liquid have a maximum operating Temperature. Silicon gum rubber (higher than 250 C). Paraffin oil (250 C). Polyethylene glycol (up to 250 C).,Column: 1-
4、 Packed Columns: 2-6 mm id and 1-3 meters in length. 2- Capillary Column: 0.2 0.5 mm id and 10-100 meters in length. Some columns may reach up to 300 meters.,Types of capillary columns:,1-Wall Coated Open tubular (WCOT): Used in GLC, the stationary liquid coats the column wall. 2-Support Coated Open
5、 tubular (SCOT): The inert support is fused to the column wall by special machine then the stationary liquid coat the support. It is used in GLC. 3-Porous layer Open tubular (PLOT): The stationary solid is bonded to the wall of the column. Not commercially produced. 4-Micro-Packed Columns: The colum
6、ns are coiled and packed with the desired support with stationary liquid or solid stationary phase under pressure and vibrations.,Capillary Columns give mush better resolution but their sample capacity is much lower than the packed columns (about 1/10 or less).,Operating Temperature: Operating Tempe
7、rature can be looked at as the polarity of mobile phase in case of adsorption chromatography. Very low temp: Tailing of peaks. Very high temp: No separation of peaks. Temperature programming: Allows starting the process at low temperature and gradually increasing the temperature till reach the maxim
8、um required temperature. Column bleeding: Elution of the liquid stationary phase itself if very high temperature is used (exceed maximum operating temperature).,Conditioning of Columns: Means heating the column before use at a temperature 25-50 0C above the normal working temperature. However, that
9、must not exceed the maximum operating temperature. The mobile phase is allowed to flow during the conditioning but the column outlet must be disconnected from the detector. Conditioning aims to clean the column from any impurities.,Detectors: They are used to indicate the presence and measure the am
10、ount of the components in the column effluent. Examples of the commonly used detectors are: 1- Thermal Conductivity Detector (TCD). 2- Flame Ionization Detector (FID). 3- Electron Capture Detector (ECD).,Sample Introduction Sample introduction will affect the separation, accuracy and precision of th
11、e results. The method of sample application will depends mainly on the nature of the sample. Gaseous samples: They are introduced using special valves. Liquid Samples: Include liquids, liquids or solids in suitable solvents. They are introduced by injection via septum seal.,Capillary column have low
12、 capacity so we have to apply very small amount of samples. This can be achieved by: 1- Dilution of sample with solvent: This will lead to problem due to large amount of solvents that may affect separation and quantitation. 2- Injection of very small amount of more concentrated solution: That leads
13、to increase the error in measurements. 3- Using modified injectors that allow splitting of samples: Only part of the injected sample go to the column and the rest of the sample go to vent. The split ratio to give good results is usually 1: 100.,Head Space Sampling: The sample is contained in sealed
14、vial and maintained at constant temperature for about 20 min. so equilibrium will be achieved between gas and liquid states. The vapour phase is then allowed to enter the column.,Derivatization of non volatile samples:,Non volatile samples containing acidic hydrogen can be converted into more volati
15、le more thermally stable derivatives as: 1- Silylation: This is the most widely used method. Alkylsilyl group will replace the acidic hydrogen. pyridine R-OH+Cl-SiMe3 R-O-SiMe3 + HCl (TMS) Trimethylchlorosilane,2- Acylation: COCF3 R-OH + O R-O-COCF3 COCF3 (TFAA) Trifluoroaceticanhydride 3- Alkylatio
16、n: RCOOH + BF3/MeOH RCOOMe Boron trifluoride,Peak symmetry:,Good system must result in a symmetric peaks with narrow base. Asymmetry ratio (As) can be calculated: b As = - a Where a and b should by measured at10% height of the peak. As for good peak will be 0.9- 1.1.,The peak shape also can be predicted by calculation of the Tailing factor (T): W T= -
