ABSTRACT

Since the mid-1980s the most frequently used technique in the bioanalysis of drugs has been high-performance liquid chromatography (HPLC). Prior to this the technique of choice was capillary gas—liquid chromatography (GLC). The reason for the rapid and dominant emergence of HPLC is fairly straightforward. In GLC it is a necessity that the analyte of interest can be volatilised as the separation is carried out in the gas phase, with the key factor for separation being the difference between analytes of their relative affinities for a gaseous mobile phase and a liquid stationary phase. Often, to facilitate this process, derivatisation of the analyte to a more volatile form is required. For example, acids would frequently need to be modified chemically to their more volatile ester forms prior to the chromatographic process. This requirement often led to assay procedures being complicated and not easy for the inexperienced operator to perform. In addition to this, GLC usually operates at 46considerably elevated temperatures and a further consideration is therefore the thermal stability of the analyte(s) of interest.