Title Gas Chromatography MSA.pdf ✅

AAFFCC t trraai inni inngg GGaasseessLLaabb MSA 1 Abu Qir Fertilizers Chemical Sector Gases Lab training program Prepared by: Dr.Chemist: Mohamed Said Abdel Aal November 2008
AAFFCC t trraai inni inngg GGaasseessLLaabb MSA 2 Contents Introduction.............................................................(3) Instrumental components...........................................(5) Sample injection port..........................................(5) Columns...........................................................(6) Detectors..........................................................(9) AFC G.C instruments..............................................(14)
AAFFCC t trraai inni inngg GGaasseessLLaabb MSA 3 Introduction Gas chromatography is the technique of choice for separation of thermally stable and volatile organic and inorganic compounds. It may subdivided into: ➢ Gas – liquid chromatography (GLC) accomplishes the separation by partitioning the components of a chemical mixture between a moving (mobile) gas phase and a stationary liquid phase. ➢ Gas –solid chromatography (GSC) uses a solid adsorbent as the stationary phase. Gas chromatography - specifically gas-liquid chromatography - involves a sample being vapourised and injected onto the head of the chromatographic column. The sample is transported through the column by the flow of inert, gaseous mobile phase. The column itself contains a liquid stationary phase which is adsorbed onto the surface of an inert solid. Have a look at this schematic diagram of a gas chromatograph: A typical gas chromatograph consists of: 1. Pressure regulator (flow controller) 2. Sample injection port 3. Stationary support column 4. Stationary phase (embedded within column) 5. Detector 6. Signal recorder All the following conditions should be achieved for a typical analysis: ➢ constant flow of carrier gas. ➢ the introduction of sample vapor into the flowing gas stream. ➢ appropriate length of stationary phase
AAFFCC t trraai inni inngg GGaasseessLLaabb MSA 4 ➢ Maintaining the column at the appropriate temperature. ➢ Detecting sample components as they eluted from the column. ➢ readable proportional to the amount of each component. Carrier gas The purpose of the carrier gas is to transport the sample through the column to the detector. The carrier gas must be chemically inert. Commonly used gases include nitrogen, helium, argon, and carbon dioxide. The choice of carrier gas is often dependant upon the type of detector which is used. The carrier gas system also contains a molecular sieve to remove water and other impurities. Take Care :: ➢ Selecting the proper carrier gas is very important because it affects both column and detector performance. ➢ The purity of the carrier gas should be at least 99.99% ➢ Impurities such as oxygen or water can cause column and detector deterioration.
AAFFCC t trraai inni inngg GGaasseessLLaabb MSA 5 Instrumental components Sample injection port For optimum column efficiency, the sample should not be too large, and should be introduced onto the column as a "plug" of vapour - slow injection of large samples causes band broadening and loss of resolution. The most common injection method is where a microsyringe is used to inject sample through a rubber septum into a flash vapouriser port at the head of the column. The temperature of the sample port is usually about 50C higher than the boiling point of the least volatile component of the sample. For packed columns, sample size ranges from tenths of a microliter up to 20 microliters. Capillary columns, on the other hand, need much less sample, typically around 10-3 L. For capillary GC, split/splitless injection is used. Have a look at this diagram of a split/splitless injector. The injector can be used in one of two modes; split or splitless. The injector contains a heated chamber containing a glass liner into which the sample is injected through the septum. The carrier gas enters the chamber and can leave by three routes (when the injector is in split mode). The sample vapourises to form a mixture of carrier gas, vapourised solvent and vapourised solutes. A proportion of this mixture passes onto the column, but most exits through the split outlet. The septum purge outlet prevents septum bleed components from entering the column. Automatic sampler : The automatic sampler are machine reproducible more precise than skilled chromatographer.