Enhanced Chemical Analysis Using Parallel Column Gas Chromatography with Single-Detector Time-of-Flight Mass Spectrometry and Chemometric Analysis

Abstract

A parallel gas chromatographic instrument with time-of-flight mass spectrometric detection (GC/TOF-MS) is reported. An injected sample is first split between two GC columns that provide complementary separations. The effluent from the two columns is recombined prior to detection with a single TOF-MS. Switching from single to parallel columns increases the chemical selectivity of a GC/TOF-MS data set without increasing analysis time, by doubling the number of peaks, or features, in the chromatographic dimension. The resulting analyzer can be used to reduce analysis times for partially resolved peaks. Simulations compare the quantitative precision of parallel- and single-column instruments using the generalized rank annihilation method (GRAM). Results indicate that a parallel column GC/TOF-MS should substantially improve the chemical selectivity and quantitative precision of the analysis relative to a single-column instrument. For a column at half its peak capacity, for example, a single-column instrument met the target precision less than 75% of the time, while a parallel-column instrument achieved 95% success. Parallel-column analyses of methyl tert-butyl ether (MTBE) and benzene in gasoline samples were also performed to support the simulation studies. An objective chromatographic standardization technique corrected for retention time shifts before GRAM was applied. Although MTBE and benzene were poorly resolved in the 40-s runs, chemometric techniques successfully quantitated them.