Focus compatible solvents would make a hyphenated system much simpler. GC/IR/MS. If two coupled instruments are good, three must be better. Combined gas chromatography/infrared spectrometry/mass spectrometry (GC/IR/MS) makes it possible to obtain a greater number of exact structural identifications. The idea is to search for the unknown in both the IR and MS data bases and to make positive identifications by coincidence between the two. And the combined data generated by the three instruments provide more complete structural information, even in instances when an exact identification is not achieved. At the Pittsburgh Conference, C. L. Wilkins presented a paper on "New Approaches to Direct Linked GC/ FTIR/MS," coauthored by G. N. Giss, R. L. White, G. M. Brissey, and E. Onyiriuka. Two instrumental systems have been used in Wilkins's work to date. In the first, a GC is connected in parallel to an IR spectrometer and a conventional (non-FT) MS instrument via a stainless steel transfer line and a 99:1 splitter (99 parts to the IR, one part to the MS). In an alternate (serial) configuration, the GC was interfaced to the light pipe of the IR stage by a fused silica transfer line. The effluent, after exiting from the light pipe, was directed to an FT-MS instrument via stainless steel glasslined tubing. The conventional MS needed 2.7 s to obtain a spectrum at a resolution of about 1000. "This kind of scan time is on the edge of what's going to be acceptable with high-performance chromatography where narrow peaks are obtained," said Wilkins. The F T - M S instrument, on the other
hand, which obtains information on all masses simultaneously, required only about 25 ms per spectrum at a resolution of 1000. Wilkins reports excellent GC/IR/ MS results for major mixture components. For one sample of peppermint oil, for instance, 7 of 29 separated components were correctly identified via joint library search methods. Four out of five major components (greater than 5% of the sample) were correctly identified. For compounds in the 1-5% concentration range, however, 3 out of 10 were correctly identified. Components comprising less than about 0.5% of the sample did not yield spectra with high enough S/N ratios to be useful for library searching. According to Wilkins, one of the chief difficulties in GC/IR/MS involves the need for greater sensitivity (particularly in the IR stage) for the identification of such minor components. One other significant problem in GC/IR/MS, said Wilkins, is that of spectral data bases. "First," said Wilkins, "the quality of the data bases is highly variable. Second, the cost of expanding the data base is significant and there is considerable difference of opinion about how important it is to expand data bases, considering the expense. I happen to think it's very important." Stuart A. Borman
References (1) Erickson, Mitchell D. Appl. Spectrosc. Rev. 1979, 75(2), 261-325. (2) de Haseth, James A. "Fourier Transform Infrared Spectrometry," in "Fourier, Hadamard, and Hubert Transforms in Chemistry"; Marshall, Alan, G., Ed.; Plenum: New York, 1982. (3) Kuehl, Donald T.; Griffiths, Peter R. Anal. Chem. 1980,52,1394-99.
Participants at the 1982 Pittsburgh Conference symposium, "State of the Art of the Hyphenated Technique, " included (standing, left to right) G. L. Carlson (presiding), C. A. Cody, P. R. Griffiths, and (seated, left to right) C. L. Wilkins and T. Hirschfeld
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ANALYTICAL CHEMISTRY, VOL. 54, NO. 8, JULY 1982 · 905 A
