The development of a dual detection system that provides simultaneous structural elucidation and isotopic analyses of forensic samples is described. A gas chromatograph (GC) was coupled to an isotope ratio mass spectrometer (IRMS) in parallel with a single quadrupole mass spectrometer (MS). The modification was achieved by using a low, dead volume x-connector to split the effluent coming from the column so that approximately 10% entered the EI MS and the remaining 90% entered the combustion interface for IRMS. The transfer line that connected the GC to the MS was fabricated to extend the line into the GC oven. Heat tape was tightly wrapped around the extension to maintain a predetermined, constant temperature by use of a manual heat controller. The modified instrumentation was then applied to forensic samples to simultaneously determine the structural elucidation and the isotopic ratios of individual compounds and impurities within the sample.
Illicit drugs are one of the most analyzed forensic samples in federal, state, and private forensic laboratories. Cocaine was analyzed and identification was confirmed using a NIST library. The probability scores from the NIST library for all of the cocaine samples ranged between 52.9% and 77.1%. Several cocaine samples were used to determine if the cocaine could have come from the same source using carbon isotopic analysis. Marijuana was another illicit drug that was analyzed using this instrumentation method. We report the first application of GC-IRMS to individual components of Cannabis sativa L. to discriminate between different sources.
Different manufacturers, or lot numbers, of common household accelerants such as Goof Off, turpentine, charcoal lighter fluid and WD-40 were also analyzed. The analysis of accelerants demonstrated that this modification of instrumentation could be used for not only pure compounds but, also for very complex compounds. IRMS could distinguish between different sources of accelerants by analyzing trace residues remaining after combustion.
To further examine the versatility of this tool, individual amino acids in hair were analyzed. We have shown that it is possible to determine minimally nine individual amino acids within hair samples using a single step derivatization method. In the future, we would like to study single strands of hair and the possibilities of segmenting the hair into sections of monthly growth. The analysis of forensic samples using this modification is virtually unlimited.