Modern FT-IR systems provide rapid analysis of samples with very little effort, putting the technique on par with the dilute and shoot simplicity of the GC/MS.
According to the Scientific Working Group for the Analysis of Seized Drugs (SWGDRUG), infrared spectroscopy is a Category A Technique for drug identification. However, it is underutilized in many forensic laboratories owing largely to the ambiguous results it can produce when analyzing seized drug samples that are mixtures. These results can be difficult for forensic scientists to confidently support when giving expert testimony. Most labs rely heavily on gas chromatography coupled to mass spectrometry (GC/MS) and are confident in the results it provides, but GC/MS may not be adequate in all cases to support a drug’s identification.
This article will present the capabilities of infrared spectroscopy for use by forensic scientists involved in seized drug analysis. It will cover the role Fourier Transform Infrared (FT-IR) spectroscopy plays in forensic drug analysis as a complementary technique to GC/MS. Of key importance to the capabilities of modern FT-IR spectrometers is the use of simple ATR sampling and mixture searching algorithms to rapidly screen and identify seized drugs.
A basic need of any law enforcement agency is to positively identify controlled substances in seized drug samples to support legal proceedings and get convictions. The mission of the Scientific Working Group for the Analysis of Seized Drugs (SWGDRUG) is to recommend minimum standards for forensic examination of seized drugs and seek their international acceptance. The recommendations are intended to assist forensic analysts and managers in the development of analytical techniques, protocols, and policies in an effort to ensure consistent professional practice among the forensic community. Recent changes to the wording of the 5th Edition of the SWGDRUG recommendations published in January 2010 will impact forensic scientists with respect to education, quality control practices, and the use of data from analytical techniques for drug identification.
Currently, there are many common material identification techniques in routine use by crime labs, which are categorized by the updated SWGDRUG recommendations according to their discriminating power (Table 1). Category A techniques have the highest discriminating power and Category C techniques have the lowest. Screening techniques fall under Category C and commonly include quick colorimetric tests, melting point analysis, and solubility in specific solvents. Category B includes intermediate techniques of analysis such as microcrystalline tests or extraction and/or derivitization for gas chromatographic analysis. Finally, Category A techniques are confirmatory techniques like MS, IR, and Raman spectroscopic analysis.