Identifying PCP and four PCP analogs using the gold chloride microcrystalline test followed by raman microspectroscopy and chemometrics

Matthew Quinn; Thomas Brettell; Monica Joshi; Jennifer Bonetti; Lawrence Quarino

doi:10.1016/j.forsciint.2019.110135

Identifying PCP and four PCP analogs using the gold chloride microcrystalline test followed by raman microspectroscopy and chemometrics

Forensic Sci Int. 2020 Feb:307:110135. doi: 10.1016/j.forsciint.2019.110135. Epub 2019 Dec 30.

Authors

Matthew Quinn¹, Thomas Brettell², Monica Joshi³, Jennifer Bonetti⁴, Lawrence Quarino⁵

Affiliations

¹ Department of Chemical and Physical Science, Forensic Science Program, Cedar Crest College, 100 College Drive, Allentown, PA 18104, United States. Electronic address: mattquin@pa.gov.
² Department of Chemical and Physical Science, Forensic Science Program, Cedar Crest College, 100 College Drive, Allentown, PA 18104, United States. Electronic address: tabrette@cedarcrest.edu.
³ Department of Chemistry, West Chester University, 750 S. Church St., Schmucker Science South, West Chester, PA 19383, United States. Electronic address: mjoshi@wcupa.edu.
⁴ Virginia Department of Forensic Science, Eastern Laboratory, 830 Southampton Ave, Suite 400, Norfolk, VA 23510, United States. Electronic address: jennifer.bonetti@dfs.virginia.gov.
⁵ Department of Chemical and Physical Science, Forensic Science Program, Cedar Crest College, 100 College Drive, Allentown, PA 18104, United States. Electronic address: laquarin@cedarcrest.edu.

PMID: 31923853
DOI: 10.1016/j.forsciint.2019.110135

Abstract

Identifying drug analogs can be a vexing problem for forensic scientists particularly in today's evolving drug market. This study proposes a method that utilizes microcrystalline tests, Raman microspectroscopy, and chemometrics to help solve this problem. In the present case, the method described was used to clearly differentiate and identify phencyclidine (PCP) and four of its analogs, namely tenocyclidine (TCP), rolicyclidine (PCPy), 3-methoxy phencyclidine (3-MeO PCP), and 4-methoxy phencyclidine (4-MeO PCP). Microcrystals were grown from each drug with gold chloride and examined using polarized light microscopy. Morphological and optical properties such as shape, habit, time of growth, color, retardation colors, type/angle of extinction, and sign of elongation were observed and documented to characterize each microcrystal. Analysis with a Raman microscope was able to provide structural information on the microcrystals. Objective analysis of the microcrystal spectra was done by employing chemometrics. A training set of Raman shifts was compiled and transformed with principal component analysis (PCA) followed by linear discriminant analysis (LDA). The training set was validated by leave-one-out cross validation (LOOCV) and subsequently ran against a separately-compiled test set. Mahalanobis distances between test samples and the clusters of training samples in LDA space were calculated to empirically demonstrate the applicability of this drug analysis technique. From the results of this study, a drug analysis protocol was developed for analysts to use for the identification of PCP, TCP, PCPy, 3-MeO PCP, and 4-MeO PCP and to serve as a model for drug analogs in general.

Keywords: Chemometrics; Drug analogs; Microcrystalline tests; Phencyclidine; Raman microspectroscopy.