Chapter 1 - Introduction

Abstract

The chapter introduces the analytical technique, gas chromatography. When a gas is employed as the mobile phase, either a liquid or a solid can be utilized as the stationary phase. These processes are “gas-liquid chromatography” (GLC) and “gas-solid chromatography” (GSC), respectively but the term “gas chromatography” (GC) is applied to both the processes. In the process of gas chromatography, a thin film of the stationary phase is confined to the column that is continuously swept by a stream of mobile phase (i.e., carrier gas). The two extremes in GC column types are packed columns and open tubular columns. Packed columns are typically 2–5 m long; 1–5 mm in internal diameter (ID); and are filled with an “inert” granular support, each particle of which is coated with the stationary phase. Micropacked columns are a smaller version of the packed column, usually having IDs of less than 1 mm and smaller packing granules. The length of a packed column is practically limited by the pressure drop generated by the resistance it offers to gas flow. There are three general types of open tubular columns: (1) wall-coated open tubular (WCOT) column, (2) porous layer open tubular (PLOT) columns, and (3) SCOT (support coated open tubular) columns. During its passage through the column, a chromatographing solute spends a fractional part of its total transit time in the stationary liquid phase and the remainder in the mobile gas phase. Its apportionment between the two phases is reflected by the distribution constant Kc, defined as the ratio of the weights of solute per unit volumes of the stationary and mobile phases.