Spectroscopy for the Quantitative Analysis of ... Analytical Chemistry Laboratory, Chemical Technology Division, Argonne National Laboratory, 9700 South Cass ...
Evaluation of Gas Chromatography/Matrix Isolation-Infrared Spectroscopy for the Quantitative Analysis of Environmental Samples JOHN F. SCHNEIDER,* KEN R. SCHNEIDER, STEPHANIE E. SPIRO, DOUGLAS R. BIERMA, and LOUIS F. SYTSMA Analytical Chemistry Laboratory, Chemical Technology Division, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439
Gas chromatography/matrix isolation-infrared spectrometry (GC/MIIR) is being applied to many analyses previously done only by gas chromatography/mass spectrometry (GC/MS). Qualitatively, the infrared spectra of matrix-isolated compounds contain much information about their structure. The information obtained from the infrared spectrum is complementary to the information obtained from mass spectrometry. The technique of GC/MI-IR should also be useful as a quantitative detector. In this study, semivolatile priority pollutant mixtures were analyzed quantitatively by GC/MI-IR. Results were compared with results obtained by GC/MS. Calibration curves were obtained on the GC/
MI-IR for several semivolatile priority pollutants to measure the precision and linearity of this technique. The results indicated that GC/ MI-IR, in its current form, is only suitable for semiquantitative work. Index Headings: Infrared; Instrumentation; GC/MI-IR; Analytical methods.
INTRODUCTION G a s c h r o m a t o g r a p h y / m a t r i x i s o l a t i o n - i n f r a r e d spect r o s c o p y ( G C / M I - I R ) was d e v e l o p e d a t A r g o n n e N a t i o n al L a b o r a t o r y ( A N L ) b y R e e d y a n d c o - w o r k e r s T M a n d h a s b e e n s h o w n to b e a v e r y u s e f u l q u a l i t a t i v e a n a l y t i c a l
Received 27 October 1990; revision received 10 December 1990. * Author to whom correspondence should be sent.
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V o l u m e 4 5 , N u m b e r 4, 1991
0003-7028/91/4504-056652.00/0
© 1991 Societyfor AppliedSpectroscopy
APPLIED
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techniqueP -23The components eluting off the GC column are trapped in a narrow (~0.3 mm) strip of frozen argon. Trapping the sample in a small area and focusing the IR beam on the spot with parabolic mirrors give GC/MI-IR detection limits of 0.1 to 5 ng, which is in the same range as quadrupole gas chromatography/mass spectroscopy (GC/MS). Thus, GC/MI-IR is an attractive candidate for quantitative determination of semivolatile priority pollutants in environmental samples. The IR spectra of matrix-isolated compounds contain very sharp absorption peaks. Because of the high-quality spectra, the MI-IR technique is well suited for the identification of targeted compounds with known matrixisolated IR spectra; even when other compounds coelute, identifications can usually be made. The information obtained from the IR spectrum complements the information obtained from GC/MS. The combination is a very powerful tool for elucidating the structure of unknown compounds, especially isomers and other compounds that yield similar mass spectra. 23 Figures 1-3 illustrate the utility of GC/MI-IR for distinguishing among isomers. The sharp absorption peaks are well suited to computerized library searching. The GC/light pipe-IR technique has poorer limits of detection 24-27but also produces high-quality spectra. The
GC/cryogenic trapping-IR technique, 2s recently introduced commercially, has very good sensitivity but yields condensed-phase spectra which lack the sharp absorption peaks characteristic of vapor-phase and matrix-isolated spectra. The broad-banded spectra produced by this technique may make positive identification of compounds more difficult, particularly when coeluting compounds complicate the spectrum. Hence, GC/MI-IR appears to be the best GC/IR technique for the low-level detection and positive identification of pollutants in environmental samples, especially for isomers or coeluting compounds. The utility of GC/MI-IR for determining dioxins at picogram levels has been demonstrated, z3-1s Our GC/MI-IR system has been interfaced with a mass spectrometer. The resulting system is very useful in the qualitative analysis of unknown compounds. The ability to obtain quantitative information from GC/MI-IR would be useful in confirming quantitative results obtained by GC/MS. The ability of GC/MI-IR to produce reliable quantitative data is examined in this paper. We sought to evaluate our GC/MI-IR instrument for quantitative analysis of two samples spiked with semivolatile priority pollutants. To this end, we compared the results obtained by GC/MI-IR with those from GC/MS and obtained calibration curves with the GC/MI-IR. APPLIED SPECTROSCOPY
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Phase Sensitive IR Reconstructed Chromatogram
EXPERIMENTAL Our GC/MI-IR is a Mattson Instruments Model 3800 Cryolect. The interferometer is a Mattson Cygnus 100 equipped with a mercury-cadmium-telluride (MCT) detector. Our GC/MI-IR instrument is also equipped with a Hewlett-Packard 5970 Mass Selective Detector (MSD). The MI-IR and MSD are in parallel after a post-column split of the GC effluent (1:1). Infrared spectra were collected at 4 wavenumber resolution. Generally, 32 scans were coadded to obtain both sample and background single-beam spectra. Spectra were generated by ratioing sample and background single-beam spectra. Infrared chromatograms were generated with the use of the Phase Sensitive Infrared Reconstruction (PSIR) algorithm supplied with the Mattson Cryolect software. Disk resolution of 0.01 min was used, with 2 scans coadded per data point. Solutions of standard priority pollutants were obtained from Supelco. Neat priority pollutant standards were obtained from the U.S. Environmental Protection Agency. Dilutions were made with Burdick and Jackson ultrapure dichloromethane. Water samples spiked with
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