Comprehensive two-dimensional gas chromatography applied to illicit drug analysis

Multidimensional gas chromatography (MDGC), and especially its latest incarnation-comprehensive two-dimensional gas chromatography (GC x GC)-have proved advantageous over and above classic one-dimensional gas chromatography (1D GC) in many areas of analysis by offering improved peak capacity, often enhanced sensitivity and, especially in the case of GC x GC, the unique feature of 'structured' chromatograms. This article reviews recent advances in MDGC and GC x GC in drug analysis with special focus on ecstasy, heroin and cocaine profiling. Although 1D GC is still the method of choice for drug profiling in most laboratories because of its simplicity and instrument availability, GC x GC is a tempting proposition for this purpose because of its ability to generate a higher net information content. Effluent refocusing due to the modulation (compression) process, combined with the separation on two 'orthogonal' columns, results in more components being well resolved and therefore being analytically and statistically useful to the profile. The spread of the components in the two-dimensional plots is strongly dependent on the extent of retention 'orthogonality' (i.e. the extent to which the two phases possess different or independent retention mechanisms towards sample constituents) between the two columns. The benefits of 'information-driven' drug profiling, where more points of reference are usually required for sample differentiation, are discussed. In addition, several limitations in application of MDGC in drug profiling, including data acquisition rate, column temperature limit, column phase orthogonality and chiral separation, are considered and discussed. Although the review focuses on the articles published in the last decade, a brief chronological preview of the profiling methods used throughout the last three decades is given.