Gas chromatography in combination with electron-ionization mass spectrometry (GC-MS) plays an important role in the analysis of forensic compounds. A high quality and comprehensive reference mass spectral library can provide a fast and reliable technique aiding in the forensic-related compound identification without the need for certified samples at the time of measurement. The most challenging part of building such a library is evaluation of spectra by experts. In this work we describe methods optimized to assist this procedure.<br/>First, each new mass spectrum was compared with spectra of similar compounds in the NIST17 and 5 other available mass spectral libraries using the improved hybrid search method. Then the structure similarity search and the MS Interpreter program were used to assess the consistency of chemical structure and spectra. Product ions that were not explained or were assigned unreasonable mechanisms were manually examined. Low quality spectra such as missing peaks, spurious peaks not attributable to the compound structure, and incorrect mass assignments (often from incorrect rounding of mass values) were filtered out by manual inspection. For example, for 2 spectra of Cocaine (A and B in Fig.), we used hybrid and structure similarity search, and compared with the spectrum of a similar compound Propylbenzoylecgonine (C in Fig.). The peak of m/z 106 in spectrum A is incorrect (shift up by 1 mass unit), so this spectrum was rejected. However, spectrum B with the peak of correct m/z 105 was confirmed, so it was accepted.<br/>To date, more than 3,500 mass spectra of forensic compounds have been evaluated in this study. Over 2,500 high quality spectra were added to the NIST mass spectral library for reliable identification forensic compounds.

New evaluation methods for building a seized-drug electron ionization mass spectral library

2019 Fall National Meeting

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