This still remains a great challenge for analytical chemists and may rely on identification of different target compounds. In the case of precursor drug administration, the parent compounds are usually detectable only for a short time, before being fully metabolised or decomposed. For this reason parent compounds can rarely be used for differentiating. Specific metabolites are usually detectable for a much longer time. Their use as target compounds for differentiating has found little application however, since all metabolites are not extracted together with MA and AM and are additionally fully converted to AM or MA after a certain time post administration. Enantiomeric profiles for methamphetamine and/or amphetamine, metabolically formed from precursors have been described for some medicaments and have been used successfully for differentiating between illicit intake and intake of precursors. Thus a reliable method for the quantitative determination of AM/MA enantiomers is essential for differentiation (Kraemer and Mauer, 2002; Musshof, 2000).
A great number of research efforts have focussed on the separation of AM/MA enantiomers particularly from urine or blood matrices. These have been extensively reviewed (e.g. Kraemer and Mauer, 1998; Musshof, 2000). The majority of the methods employed involved enantiomer separation by chromatography, either by HPLC or GC on chiral stationary phases,with or without prior derivatisation with achiral reagents, or by GC on achiral stationary phases, after derivatisation with chiral reagents to the corresponding diastereomers. Detection was commonly by MS to ensure high selectivity and sensitivity. In terms of sample treatment for analyte extraction and concentration, conventional liquid-liquid extraction protocols (Kraemer and Mauer, 1998), solid phase extraction (SPE) on cartridges (Peters et al., 2002) and solid-phase microextraction (SPME - Nagasawa et al., 1996) have been commonly applied. The proposed methods varied in terms of sensitivity, reliability, sample preparation times and analysis times and adaptability to high throughput format.
The current trend in the determination of MA/AM enantiomers is towards the substitution of chiral GC/MS protocols by runs on achiral columns of MA/AM diastereomers. This is because MA/AM diastereomerisation has been shown in several cases to improve resolution, to shorten the retention times of analytes and to enhance the response of the detector, i.e. to improve sensitivity (Kraemer and Mauer, 1998; Peters et al., 2002). Furthermore achiral columns are commonly less expensive compared to chiral columns. Different chiral derivatisation reagents have been applied successfully in MA/AM diastereomerisation (Kraemer and Mauer, 1998; Musshof et al., 2002; Peters et al., 2002; Wang, 2005). Recent advances in the field involve a fast SPME-based approach, where absorption and derivatisation are accomplished in a single step by adding the derivatising chiral reagent directly into the urine sample matrix (Wang, 2005) and the application of automated headspace solid-phase dynamic extraction (SPDE) coupled with GC/MS, for the determination of amphetamines and synthetic designer drugs in hair samples (Musshof et al., 2002). The later technique is an innovative GC/MS approach to the enantiomeric determination of amphetamines and will be discussed further.
Headspace SPDE constitutes an alternative extraction and concentration method for volatile and semi-volatile organic compounds contained in liquid or gaseous samples. Headspace SPDE is a further development of headspace SPME. In fact, SPDE was developed