Characterization of illicit amphetamines through 13C/12C and 15N/14N isotopic ratio measurements

Introduction: Amphetamine and related drugs are psychostimulants which act by increasing levels of norepinephrine, serotonin and dopamine in the brain. Today, the designer drug 3,4-methylenedioxymethamphetamine (MDMA) is the most common amphetamine on illicit market and it is produced in several clandestine laboratories all over Europe. Aims: Our aim was to discriminate the origin of different seizures through the analysis of: i) impurities due to manufacturing processes, which should be similar for sample belonging to the same batch, and ii) the measurement of natural abundance of stable isotopes 13C/12C and 15N/14N, expressed as δ13 and δ15 and supposed to depend on both chemical and physical processes applied for the synthesis and the origin of precursors used. Data obtained were elaborated through chemometric techniques (cluster analysis and PCA). Methods: Twelve ecstasy tablets were analyzed. After dissolution of MDMA tablets in carbonate buffer and shaking with dichloromethane, the extracts were dried and reconstituted in 50 µl of methanol. Analysis were performed with GC-MS (Agilent Technologies) and with GC-C-IRMS (Thermo Electron). The δ13 and δ15 values were expressed as mean of five consecutive injections of the same extract. Statistical analysis was performed by SPSS 16.0. The data matrix obtained from chemical profiling and isotopic ratio analysis was examined using Pearson’s correlation test to eliminate the redundant variables. The principal component analysis and the hierarchical cluster analysis were used to classify all samples. Results: Large variability in tablets composition was registered, as expected. Several amphetamine-like drugs (AMP, mAMP, MDEA, MBDB) were detected as well as various impurities (lubricants and adulterants), which turned out specific for the synthetic process used in the production. Upon chemometric elaboration, the amphetamine tablets were properly discriminated and clustered in a dendrogram. Conclusions: We investigated a new approach to discriminate the origin of different seizures of illicit amphetamine-like drugs. Chemical variables including impurity profiling and natural abundance of stable carbon and nitrogen isotopes were used. The 15N/14N ratio proved particularly significant, as a specific parameter. The evidence of nitrogen isotopic fractionation can be explained in terms of differences in synthetic pathways, operating conditions and precursors used for the synthesis. Further elaboration of results is progressively updated, as long as new samples are collected for profiling, in order to confirm the usefulness of GC-C-IRMS analysis in the classification of MDMA tablets.