Improving the Confidence of Unknown Compound Identification by First Responder Mobile GC-MS Laboratories in Time-Critical Environmental and Homeland Security Incidents

GC–MS is the tool of choice for the rapid identification of volatile and semivolatile organic compounds. Standard EPA methods cover the identification of over 200 compounds of environmental concern. These methods provide extremely sensitive and accurate identifications of these target compounds based upon their retention time and GC–MS library search match. However, for compounds that are not characterized by these methods, a significant uncertainty can exist for these "unknown" compounds when using GClibrary search routines alone for identification. Misidentification can lead to an expensive and potentially dangerous or fatal incorrect response by first responders and law enforcement. Uncertainties or delays in confident identification also can contribute to high costs and consume valuable public resources.

Recent advances in MS data processing have shown the potential for obtaining accurate formula identification of unknowns by unit resolution MS (1). The application is based upon a novel method for accurate mass and accurate line-shape calibration for unit resolution mass spectrometers that allows both the accurate mass and accurate isotope pattern matching (spectral accuracy) to be used for formula identification, competitive to results obtainable by high-resolution accurate mass instrumentation.

This article presents a new method for increasing the speed and accuracy of unknown identification by GC–MS by utilizing the standard GC–MS library search, combined with confirmation of the result by formula identification on a standard unit resolution single-quadrupole GC–MS instrument. The method is based upon the standard EPA method for volatile organic compound (VOC) analysis (2) (EPA 8260B) and will be designated here as EVOCA (extended VOC analysis).

Experimental

A test solution for evaluating EVOCA was prepared using the standard EPA 8260B protocol utilizing seven surrogate compounds and internal standards. A test solution was created from 73 target compounds of environmental concern and an additional 17 compounds in separate runs, for a total of 90 compounds to evaluate the method.

Figure 1