Membrane introduction mass spectrometry has been coupled with multivariate calibration for the analysis of volatile organic compound (VOC) mixtures. Three mixtures of increasing complexity were modeled using multivariate calibration methods. Multivariate calibration models built using partial least-squares (PLS) regression were compared with univariate calibration for the analysis of a benzene, toluene, and p-xylene (BTX) mixture and an ethylbenzene and p-xylene (EX) mixture. The univariate and multivariate calibration methods performed similarly for the BTX mixture with prediction errors of <15%. For the isomer EX mixture, the PLS model outperformed the univariate model having prediction errors between 8 and 13% compared to errors of 40% for the univariate model. The third mixture, containing all four analytes (benzene, toluene, ethylbenzene, p-xylene), was modeled using PLS and resulted in calibration relative errors of 6−15% and prediction relative errors of 3−48%. This paper demonstrates the feasibility of using membrane introduction mass spectrometry with multivariate calibration for the analysis of complex VOC mixtures.
A recent analysis of data from nine studies provided convincing evidence that plasma estradiol measurements predict the risk of breast cancer in normal postmenopausal women. However, the median values detected by the various assays used in this study varied by 5-fold. These and other published data in normal postmenopausal women suggest that assays measuring low plasma estradiol concentrations suffer from problems of sensitivity, specificity, and precision. Availability of a practical, low-cost, specific, precise, and ultrasensitive estrogen assay might allow enhanced prediction of the risk of breast cancer and provide an objective means of selecting postmenopausal women for breast cancer prevention. A recombinant cell ultrasensitive bioassay (RCUB) for estrogen was recently validated for use in prepubertal children. We postulated that the RCUB might also prove useful for measurement of postmenopausal levels and designed the present study to examine this possibility. Thirty normal postmenopausal volunteers provided blood samples for measurement of estrogen by RCUB and, for comparison, by RIA. The estrogenic activity measured by RCUB [mean +/- sd, 11.9 +/- 10.9 pmol/liter (SI units, 3.23 +/- 2.96 pg/ml] was significantly lower than estradiol levels measured by RIA [43.7 +/- 44.0 pmol/liter (11.9 +/- 12.0 pg/ml)] in our volunteer subjects (P < 0.00001). Nonetheless, plasma estradiol levels measured by bioassay were significantly correlated with the estrogenic activity measured by RIA (r = 0.84) and by gas chromatography/tandem mass spectrometry (r = 0.85). To obtain biological evidence of the validity of the RCUB, we related plasma estrogen levels to body weight and body mass index and found highly significant correlations (r = 0.54 and r = 0.53, respectively). Surprisingly, 28 of 30 postmenopausal women were found to have estrogen levels in the prepubertal range with the RCUB. The levels detected by RCUB were similar to those previously reported using an ultrasensitive but less practical yeast bioassay. These results provide validation for the RCUB in postmenopausal women and suggest that it might prove useful for selection of women for drug therapy to prevent breast cancer.
The performance of radio frequency-powered glow discharge mass spectrometry (rf-GDMS) has been evaluatedfor the direct analysis of nonconducting samples. The parameters under study are the discharge power, the discharge pressure, the sample versus exit orifice distance, and the effect of cryogenic cooling. Optimum conditions are used to evaluate some analytical figures of merit for the analysis of compacted oxide-based materials. A precision of better than 5% is obtained on all measured species in the discharge, and a semiquantitative analysis delivers results within a factor of 2 from the certified concentrations. Relative sensitivity factors are reported and compared for various matrices. The analytical data demonstrate the potential capabilities of rf-GDMS for direct analysis of various kinds of nonconducting materials.Glow discharge mass spectrometry (GDMS) has developed rapidly in recent years as a technique for the elemental analysis of solid samples. The great majority of that work has used a direct current (dc) glow discharge, although attention is now turning to a radio frequency (rf) discharge. More than two decades ago, Cobum and Kay1 showed that a combination of rf glow discharge sputtering and mass spectrometry allowed elemental analysis of thin surface layers for either conducting or insulating matrices.They reported comparable sensitivities for almost all elements.Studies by Donohue and Harrison,2 who modified a spark source mass spectrometer to power an rf hollow cathode discharge ion source, indicated that similar spectra and sensitivities were obtained for dc and rf discharges, with the latter having the added advantage of sampling insulators directly.
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