Broadening of peaks eluted before the solvent in capillary GC Part 1: The role of solvent trapping

Abstract

In capillary GC the analysis of solutes eluted before the solvent is often precluded because of severe broadening and distortion of the peaks. This problem has three sources: a) most solutes are partially solvent trapped; b) phase soaking broadens peaks eluted shortly before the solvent and c) slow sample transfer from the injector to the column in splitless injection creates broad initial bands which cannot be re-concentrated to narrow bands. The most important (and troublesome) broadening effect is partial solvent trapping. Full solvent trapping of solutes eluted before the solvent only occurs under special conditions. Most solutes are either partially trapped or non-trapped. Partial solvent trapping is mostly of the weak type, broadening the solute bands less than that due to the evaporation time of the solvent at the column inlet. Deformation of peaks eluted before the solvent by solvent trapping can only be avoided by the selection of conditions which create non-trapping. Rapid introduction of the sample into the column is required, which calls for split or on-column injection.