Presumptive Field Testing Using Portable Raman Spectroscopy.

摘要

The Las Vegas Metropolitan Police Department (LVMPD) currently utilizes commercially prepared chemical color test kits that officers use to presumptively identify cocaine, methamphetamine, and marijuana in the field. Over the past few years, false positive results have been discovered due to subjectivity of color interpretation and tedious procedures. Recognizing the need to find a more reliable method for presumptive field testing, the LVMPD Forensic Laboratory began investigating the use of Raman spectroscopy. The laboratory used National Institute of Justice funds to research and enhance existing Raman field technology to provide presumptive analysis of controlled substances. Part of the research focused on evaluating the performance of the ReporteR device, manufactured by SciAps, Inc. (previously DeltaNu, Inc.). Research was successful for analyzing methamphetamine and cocaine through the implementation of improvements designed to enhance the ReporteR device. The laboratory also investigated the advantages of algorithm-based fluorescent baseline correction technology by integrating a Raman microscope into the research design. To examine the specificity of the handheld device and validate its accuracy, the laboratory also used the microscope to compare results generated by the ReporteR. Casework evidence samples were analyzed in three distinct phases, comparing the ReporteR to the current chemical-based field test kits. The first phase of testing consisted of solely laboratory-based evaluation of the ReporteR. In the next two phases, narcotics detectives were recruited to perform tests on substances encountered in the field. From the onset of testing until after the enhanced ReporteR was evaluated, methamphetamine field testing accuracy increased 19.4%. Cocaine field testing accuracy increased 26.6% after enhancements. The reliability of the ReporteR was investigated through random re-testing of samples and results were consistent in approximately 87% of instances. Correlation settings and library content were studied and it was found that proper regulation of these factors can decrease erroneous results. Alleviating fluorescence issues of commonly encountered drugs is important to the future of Raman-based field testing. Unlike other techniques, the advantage of algorithm-based fluorescence baseline correction technology is that it could be translated to a portable system. During the third phase, the laboratory used the Raman microscope to determine if a specific patented algorithm would aid in the identification of fluorescing substances (e.g. ecstasy tablets, black tar heroin, and marijuana). Repeatable spectra indicating the presence of cannabinoids in