Gas Chromatography-Mass Spectrometer (GC/MS): In Scientific Evidence, Even 'Gold Standard' Techniques Have Limitations

There is an emerging view that there are two types of forensic science: “junk” science such as forensic odontology (bitemark analysis) and “real” science such as nuclear DNA typing. The 2009 National Research Council report contributed to the emergence of this view. On the one hand, the report was sharply critical of techniques such as bitemark analysis. On the other hand, the report had high praise for techniques such as the DNA typing identification technique and gas chromatography/mass spectrometry (GC/MS) as an elemental analysis methodology. The courts are becoming increasingly skeptical about “junk” science techniques. In some instances, they are excluding testimony based on such techniques. In other cases, they are severely restricting the wording of the opinions based on such techniques that experts may testify to. However, in the case of “real” science, the courts tend to assume reliability. In particular, the courts have come to view nuclear DNA typing and GC/MS analysis as the “gold standards” of forensic science. The courts routinely admit testimony about nuclear DNA typing, and one court has gone to the length of declaring that GC/MS analysis is “nearly infallible.” However, the 2016 President’s Council of Advisors on Science and Technology report raised questions about one “gold standard,” DNA analysis. The PCAST report questioned the validity of the traditional methods of analyzing mixed DNA samples. The report faulted those methods as unduly subjective. In addition, many commentators have challenged the validity of Low Copy Number (LCN) testing of minute or “touch” DNA samples. Although the New York have admitted testimony about LCN analysis, many other courts have barred such testimony. The thesis of this article is that like nuclear DNA testing, GC/MS analysis has important limitations. The article explains that when GC/MS is used in drug testing, the court must inquire as to the mode of analysis: full scan, selective ion reliance, or selective ion monitoring. The article adds that when GC/MS is employed to identify ignitable liquids in arson investigations, the court should inquire as to the condition of the sample tested: Has it been subjected to weathering, microbial degradation, or pyrolysis? It is certainly justifiable to subject “junk” science to more intense scrutiny. However, the courts should not naively assume that GC/MS is “nearly infallible.” In forensic science, even “gold standard” techniques have significant limitations.