Portable near-infrared detection to replace color tests in an analytical scheme for forensic drug identification

Abstract

In the ever-changing drug market the popularity and availability of substances is dynamic. In the Netherlands, ketamine and various cathinones have recently seen increased prevalence. It is crucial for law enforcement to quickly obtain an initial indication of the identity of a substance. This first test also serves as quality control for subsequent confirmation with GC–MS analysis. Traditionally, color tests have been used for these purposes. While these tests are quick and inexpensive, they have the disadvantage of reacting only to a few traditional drugs. Suitable color tests are not available for many new psychoactive substances (NPS). Near-infrared (NIR) spectroscopy is a rapid technique that provides a characteristic spectrum for organic compounds. This technique is more versatile than color tests and can adapt more quickly to market changes by incorporating reference spectra into the library. This study demonstrates the feasibility of obtaining a good quality NIR spectrum from a 20 mg sub-sample in a test tube. This was achieved by scanning the test tube through the glass bottom. In the routine analytical scheme, these test tubes were subsequently batchwise analyzed by GC–MS. From the NIR spectra, 84 % true positive and 100 % true negative results were achieved on 516 casework samples, including identification of substances without available color tests like ketamine. Missed false negatives primarily involved new substances absent from the library, emphasizing the need for continuous library updates. NIR’s adaptability to market changes is crucial, allowing the inclusion of new substances as they emerge. This method enhances law enforcement’s ability to make informed decisions, aiding in the indictment process.