Street-level classification of illicit heroin using inorganic elements coupled with pattern monitoring

A total of 96 illicit heroin samples seized in 2013-2014 were analyzed by inductively coupled plasma-mass spectrometry (ICP-MS) to determine 16 inorganic elements at parts-per-billion (ppb) level. Of eleven submissions, two or three samples with similar appearance were taken from the same seizure to form related samples. These samples were used to monitor the clustering outcome suggested by principal component analysis (PCA). They provided hints regarding the acceptance of within-seizure variability in-situ. The previously established data pretreatment method (N+4R) did not function well with the present data probably due to the higher concentrations reported for the current samples. With the aid of the above-cited related samples for pattern monitoring, a better outcome was achieved when the pretreatment method was modified to employ solely standardization (S) to optimize the necessary variability for sample classification.