Identification of impurities and the statistical classification of methamphetamine using headspace solid phase microextraction and gas chromatography–mass spectrometry

Abstract

The profiling of impurities in methamphetamine (MA) using headspace solid phase microextraction (HS-SPME) and gas chromatography–mass spectrometry (GC–MS) is described. The extraction of the impurities with an SPME fiber was examined under varying conditions. Optimal chromatograms were obtained when a 50 mg MA sample at 85 °C for 30 min was extracted using a fiber coated with divinylbenzene/carboxen/polydimethylsiloxane. MA samples from nine different origins were analyzed under optimized extraction conditions. Compounds related to MA such as benzaldehyde, benzyl alcohol, amphetamine, benzyl methyl ketone, cis- and trans-1,2-dimethyl-3-phenylaziridine, dimethylamphetamine, N-acetylamphetamine, N-acetylmethamphetamine and N-formylmethamphetamine were detected in the chromatograms. Trace amounts of ethanol, diethyl ether and acetic acid were also detected in some of the chromatograms. The numbers and intensities of the peaks detected were different, depending on the sample. After the areas of the eight principal peaks were converted to their square root and logarithm, similarities among the samples were evaluated by Euclidian distance, cosine distance and correlation coefficient. The results showed that a combination of logarithmic conversion and cosine distance was the most suitable for discriminating and classifying the samples. HS-SPME/GC–MS is a simple and effective method for the extraction and identification of impurities. The present method, in combination with an appropriate statistical analysis, would be useful for developing a profile of impurities in MA.