Classification of Narcotics in Solid Mixtures Using Principal Component Analysis and Raman Spectroscopy

• NCJ Number: 195246
• Journal: Journal of Forensic Sciences Volume: 47 Issue: 2 Dated: March 2002 Pages: 275-284
• Author(s): Alan G. Ryder
• Date Published: 2002
• Length: 10 pages
• Publication Format: Article
• Publication Type: Report (Study/Research)
• Language: English
• Country: United States of America

Annotation

This study examined a wide range of dilutents and narcotics by Raman spectroscopy and determined whether or not simple chemometric methods such as Principal Component Analysis (PCA) could be used to classify samples according to narcotic type.

Abstract

Eighty-five solid samples that consisted of illegal narcotics diluted with several different materials were analyzed by near-infrared (785 nm excitation) Raman spectroscopy. PCA was used to classify the samples according to narcotic type. The best sample discrimination was obtained by using the first derivative of the Raman spectra. Furthermore, restricting the spectral variables for PCA to 2 percent or 3 percent of the original spectral data according to the most intense peaks in the Raman spectrum of the pure narcotic resulted in a rapid discrimination method for classifying samples according to narcotic type. This method allows for the easy discrimination between cocaine, heroin, and MDMA mixtures even when the Raman spectra are complex or very similar. This approach of restricting the spectral variables also decreases the computational time by a factor of 30 compared to the complete spectrum, making the methodology attractive for rapid automatic classification and identification of suspect materials. A spectral database for Raman spectra of narcotic-containing samples is being established with a view toward generating the large datasets required to validate this method as a possible fast screening method. Part of this data base will involve monitoring samples for several years after makeup to investigate the effects of sample aging. The time series of spectra thus produced will serve as the basis for an identification method for the free bases of narcotics. The authors are also continuing to develop stronger models, which will provide unequivocal classification at low narcotic concentrations. 11 figures, 3 tables, and 31 references