“Band broadening in space” and the “retention gap” in capillary gas chromatography

Abstract

Peak may be broadened, distorted or even split if the sample components are spread out in the column inlet by large amounts of condensed solvent. This “band broadening in space” occurs during splitless injections with the solvent effect and cold on-column sampling. The features of the band broadening in space are summarized. Peak distortion is often found to be less pronounced than would be expected from the length of the flooded column section. It is assumed that this is due to partial transport of the solvent within the flooded zone by the vapour phase. Minor temperature gradients in the column inlet may greatly influence the peak distortion. The “retention gap” is proposed as a method of eliminating peak distortion caused by band broadening in space. The retention in the colum inlet (the approximate length of the flooded zone) is reduced to accelerate the migration of the spread sample components and to reconcentrate them at the beginning of the regular film of the stationary phase. The peak broadening is reduced by a factor corresponding to the reduction of the film thickness in the retention gap zone compared with the remainder of the column. For the routine analysis of free sterols it is shown that the retention gap completely eliminates the peak distortion and, at the same time, greatly reduces problems caused by by-products of the sample which distrub or degrade the stationary phase in the flooded zone of the column inlet.