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AUTOMATED MEASUREMENTS OF INFRARED SPECTRA OF CHROMATOGRAPHICALLY SEPARATED FRACTIONS
Citation:
Griffiths, P. AUTOMATED MEASUREMENTS OF INFRARED SPECTRA OF CHROMATOGRAPHICALLY SEPARATED FRACTIONS. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/4-79/064.
Description:
The rapid identification of trace organic pollutants in water presents one of the more severe problems for environmental analytical chemists today. Spectroscopic identifications of chromatographically separated fractions, preferably without trapping each sample, yields more certain identification of each peak. To optimize the sensitivity of infrared measurements of gas chromatographic effluents, the optimal dimensions for the light-pipe gas cells were first calculated. The transmittance of light-pipes with these optimized dimensions is so high that the signal-to-noise ratio of the single-beam interferograms measured using a mercury cadmium telluride photodetector is limited by digitization noise. To get around this problem, the application of dual-beam Fourier transform infrared spectroscopy was tested and the sensitivity of measurements was four times greater than the single beam measurement. Detection limits of less than 1 ppb were observed when this system was applied to trace organics in water. SCOT columns and shorter light pipes were expected to produce detection limits below 10 ng. The application of dual-beam FT-IR spectroscopy to the online indentification of peaks eluting from a high performance liquid chromatograph was investigated. Typical detection limits in excess of 10 micro g were found, which are too great for general analytical work. Spectra of submicrogram quantities were measured in preliminary work with a system based on diffuse reflectance measurements of deposited solutes on KCl powder. The sensitivity of techniques for the in situ identification of species on specially prepared thin-layer chromatographic plates was improved by the application of programmed multiple development. Detection limits of 100 ng could be achieved in less than 5 seconds data acquisition time, and limits of 10 ng could be achieved after extended signal-averaging.