Question

Will any gas do in gas-liquid chromatography? Explain.

Describe the chemical reactions in the flame ionization detector.

Answer 1

Chromatography is a method of resolution of mixtures. It depends on the distribution of components between 2 phases 1. stationery 2. mobile. Gas- liquid chromatography is a special form of partition chromatography. Stationeryphase is a non-vaporised liquid like paraffins , applied to an inert solid support like silica.Mobile phase is an indifferent gas like nitrogen, helium as carrier gas. Condition for a carrier gas are - 1. inert & readily available. 2. Should not cause fire or explosion. It consists of cylinder of carrier gas which supplies the gas at const pressure. A flowmeter to measure & regulate the rate of flow of carrier gas. The chromatographic column consisting of thin capillary tube filled with solid support moistened with stationery liquid phase. There is a provision for introducing the sample at the top of the column. Detector arrangements - electrodes are placed adjacent to a flame fuelled by hydrogen & when carbon containing compds exit the column they are fired by the flame. It works only for organic compds due to the ability of carbon to form cations & electrons upon heating generates a current between the electrodes. They have low detection limits but they are unable to generate ions from carbonyl containing carbons.