High-temperature solid-phase microextraction procedure for the detection of drugs by gas chromatography–mass spectrometry

Abstract

High-temperature headspace solid-phase microextraction (SPME) with simultaneous (“in situ”) derivatisation (acetylation or silylation) is a new sample preparation technique for the screening of illicit drugs in urine and for the confirmation analysis in serum by GC–MS. After extraction of urine with a small portion of an organic solvent mixture (e.g., 2 ml of hexane–ethyl acetate) at pH 9, the organic layer is separated and evaporated to dryness in a small headspace vial. A SPME-fiber (e.g., polyacrylate) doped with acetic anhydride–pyridine (for acetylation) is exposed to the vapour phase for 10 min at 200°C in a blockheater. The SPME fiber is then injected into the GC–MS for thermal desorption and analysis. After addition of perchloric acid and extraction with n-hexane to remove lipids, the serum can be analysed after adjusting to pH 9 as described for urine. Very clean extracts are obtained. The various drugs investigated could be detected and identified in urine by the total ion current technique at the following concentrations: amphetamines (200 μg/l), barbiturates (500 μg/l), benzodiazepines (100 μg/l), benzoylecgonine (150 μg/l), methadone (100 μg/l) and opiates (200 μg/l). In serum all drugs could be detected by the selected ion monitoring technique within their therapeutic range. As compared to liquid–liquid extraction only small amounts of organic solvent are needed and larger amounts of the pertinent analytes could be transferred to the GC column. In contrast to solid-phase extraction (SPE), the SPME-fiber is reusable several times (as there is no contamination by endogenous compounds). The method is time-saving and can be mechanised by the use of a dedicated autosampler.