Evaluation method for linking methamphetamine seizures using stable carbon and nitrogen isotopic compositions: a complementary study with impurity profiling.

Drug profiling, extraction of physical and/or chemical profiles from abused drug samples, is useful for inferring and characterizing links between samples originating from the same and different seizures, and supports drug crime investigations. We describe an evaluation method for linking methamphetamine (MA) seizures using stable carbon and nitrogen isotopic compositions concurrently with gas chromatographic impurity profiling, which is one of the major methods of drug profiling. Several sets of MA seized in Japan, whose investigative information indicated linkages, were analyzed. The impurity profile of each set of seizures was quite similar and hierarchical cluster analysis showed a sample classification that was relatively consistent with the investigative information. The stable carbon and nitrogen isotopic compositions of the MA seizures varied between -29.40 and -24.90 (delta(13)C) and -2.29 and 5.94 (delta(15)N), respectively. In the delta(13)C-delta(15)N graph, MA seizures were classified into seven groups, probably reflecting different origins. The size of the cluster in the isotopic-composition graph was determined by pooled standard deviations (s(p)), the pooled estimates of measurement uncertainty. The sizes of the clusters were less than 6s(p) and the linkages between the MA seizures from the isotopic compositions were consistent with the impurity profiling and investigative information. The results showed that complementary use of stable-isotopic compositions with impurity profiling provides useful information for evaluating the links between seizures.