Comparison and classification of methamphetamine seized in Japan and Thailand using gas chromatography with liquid-liquid extraction and solid-phase microextraction.

Abstract Methamphetamine (MA) is one of the most frequently abused drugs worldwide. The aim of this study is to improve the analytical method for profiling MA impurity in order to compare and classify MA crystals seized in different countries and to investigate the relationships between seizures. To compare MA samples seized in Japan and Thailand, the following analytical method was adopted. A 50 mg sample of MA·HCl was dissolved in 1 ml of buffer solution (four parts 0.1 M phosphate buffer, pH 7.0, and one part 10% Na 2 CO 3 ), impurities were extracted with 0.5 ml of ethyl acetate containing four internal standards ( n -decane, n -pentadecane, n -eicosane and n -octacosane) and analyzed by gas chromatography with a flame ionization detector on a DB-5 capillary column (0.32 mm i.d. × 30 m, film thickness 1.0 μm). Fourteen characteristic peaks on chromatograms were selected for the comparison and classification of samples, and the data were evaluated by the Euclidean distance of the relative peak areas after logarithmic transformation. Sixty-nine samples seized in Japan and 42 seized in Thailand were analyzed. The samples were classified into four groups roughly by cluster analysis. In addition, when it was difficult to compare samples that had fewer impurities on chromatograms obtained from liquid–liquid extraction (LLE), solid-phase microextraction (SPME) was effective. Because many characteristic peaks were detected using SPME, SPME made it easy to compare samples of high purity. The combination of LLE and SPME was useful for impurity profiling of MA samples seized in different countries.