A portable near infrared spectrometer was applied to the presumptive identification of psychotropic drugs based on library searching. Data-treatment methods (mathematical pretreatment and library search algorithm) were examined on the basis of differentiation ability. The optimized mathematical pretreatment was a standard normal variate followed by the 2nd derivative. The correlation coefficient showed the best differentiation ability in the library search algorithms. Optimized data-treatment was effective for minimizing the effect of particle size on identification. The optimized data-treatment methods were validated by the spectra of psychotropic substances (n=120). Identification criteria for the psychotropic drugs were decided on the basis of the results of the validation. As a consequence, 8 out of 11 forensic samples containing psychoactive substances were able to be positively identified. Thus, the portable near infrared spectrometer with optimized data-treatment processing is a useful tool for rapid screening and presumptive identification of seized materials.
"For example, three positional isomers of fluoromethcathinone (Figure 5), which have the same monoisotopic mass and show very similar EI mass spectra [1], gave distinguishable NIR spectra for the three isomers. The highest similarity between the different isomers was 85.8, which was sufficiently low in comparison
with the similarities within the same isomer (≥ 99.6)."
