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Several data reduction procedures have been used for converting isotope ratios, determined using gas chromatography mass spectrometry, into mole ratios for the purpose of quantitating organic compounds. In this report, these procedures are shown to be related under certain limiting approximations of original sample and internal standard isotope ratios. With the understanding that some of the procedures involve approximations, the incorporation of related systematic errors into calculated mole ratio values was investigated. The results indicate that certain data reduction procedures allow quantitation over wider mole ratio ranges and with internal standards which contain a significant quantity of unlabeled impurity.

The use of mass chromatogram peak centroids has been investigated as a means of deconvoluting the spectra of overlapping gas chromatography/mass spectrometry components. The peak centroids have been calculated with a precision of 0.04 scans (sd). This proved sufficient to allow deconvolution of the mass spectra belonging to two chemical components which were eluted 0.48 scans apart. For a more complex chromatography peak, it was possible to deconvolute the spectra of six components which were eluted within a 9 scan window. All the spectra produced by using this deconvolution mechanism agreed well with National Institute of Standards and Technology database spectra.

SummaryOperational characteristics have been determined for fused silica capillary column (FSCC) GC/MS as applied to "extractable" priority pollutants. Chromatographic data show excellent relative retention time (RRT) intralaboratory precision and interlaboratory accuracy when multiple internal standards are employed. Potential chromatographic problems, such as column overload and "double peaking", are addressed. Response factor relative standard deviations (RSD) at 50 ng for most of the extractable priority pollutants over the long term indicated precise determination (i.e. RSD generally < l0"/0). Linearity was demonstrated over two orders of magnitude for FSCC GC/MS analysis of compounds with relatively low and highRF(response factor) values. Potential quantitative problems, such as saturation, are discussed. For certain aromatic priority pollutants interlaboratory RF agreement was obsewed. This was noted as perhaps the most important property of FSCC GC/MS analysis when the multiple internal standard approtach is utilized. Determinations of extractable priority pollutants are directly compared for packed column GUMS and FSCC GC/MS analysis of separate and composited extracts. For !six extracts analyzed in triplicate, the latter configuration was shown to produce more consistent results. In view of the superior analysis logistics of composite extract FSCC GC/MS analysis, this approach was established as the preferred method for the analysis of priority pollutants classified as extractable.

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