Isomeric characterization of polychlorinated biphenyls using gas chromatography–Fourier transform infrared/gas chromatography–mass spectrometry

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Abstract
A new technique combining both mass spectrometry and infrared spectroscopy to analyse simultaneously the components from a single gas chromatographic injection has been applied to the quantitative and qualitative characterization (including distinguishing positional isomers) of polychlorinated biphenyl (PCB) mixtures. The sensitivity of vibrational spectroscopy to subtle differences in structure was shown to be highly complementary to gas chromatography–mass spectrometry (GC–MS) for qualitative identification of individual PCB isomers and congeners. A key feature of the infrared apparatus is the provision for low-temperature trapping (approximately 77 K) of the GC effluent for subsequent analysis. This technique produces infrared spectra that resemble normal room-temperature condensed-phase spectra (as opposed to the gas-phase spectra produced by light-pipe gas chromatography—Fourier transform infrared spectroscopy) and leads to lower detection limits (500 pg for 3,3′,4,5-tetrachlorobiphenyl). The GC–MS portion of the instrument provides superior quantitative capabilities with sub-picogram detection limits possible using selective ion monitoring.