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572 A · ANALYTICAL CHEMISTRY, VOL. 59, NO. 8, APRIL 15, 1987
tern was in 1980, as described in a paper published early in 1981 (12). Interface of GC/FT-IR/MS instruments When a linked GC/FT-IR/MS system is designed, the first problem that must be addressed is the difference in sample requirements between the three instruments. Whereas gas chromatographs operate at pressures well in excess of 760 torr, which are readily accommodated by common GC/FT-IR lightpipe interfaces, mass spectrometers require sample pressures at least eight orders of magnitude lower (between 10 - 5 and 10~8 torr). In the first report of GC/IR/MS, a packed GC column was used with a jet separator that eliminated much of the carrier gas prior to introduction into the mass spectrometer. Because of the relatively high required carrier flow rates and the inefficiency of packedcolumn GC, this approach was abandoned following the initial feasibility demonstration. Most subsequent studies have employed surface-coated open-tubular (SCOT) columns in conjunction with splitters to reduce the carrier gas flow to the mass spectrometer (18). Thus, in the second published report of GC/IR/MS (18), Hirschfeld and co-workers used a SCOT column linked via a splitter to a quadrupole mass spectrometer and an FT-IR spectrometer in parallel. Because FT-IR is nondestructive, it is obvious that either parallel or serial linkage of this instrument with a gas chromatograph (input) and mass spectrometer (output) is possible. Of course, if the serial arrangement is used, the lightpipe dead volume is interposed between the GC and the mass spectrometer, with the concurrent potential for degrading chromatographic resolution. In fact, this is what is found. In an early report of linkage of G C / F T IR with a Fourier transform mass spectrometer (FT-MS), using a SCOT column for separation and a jet separator (employing helium make-up gas) as an interface, chromatographic resolution was degraded by almost 50% for the longest retained substances in two complex mixture separations (19). Furthermore, in these studies the disparity between the sensitivity of the infrared and mass spectrometers was such that, even in the absence of deleterious chromatographic effects, there was no need to use a serial configuration. Thus for G C / F T - I R / M S systems employing lightpipes, a parallel split interface between the GC and the two spectrometers, routing most of the effluent (95% or more) to the IR spectrometer and the balance to the mass spectrometer, is the method of choice. The rationale is that the full value of GC/IR/MS is realized only when both
