Enhancement of process mass spectrometric analysis of mixtures utilizing parameterization and a zeolite membrane inlet.

摘要

Process mass spectrometry was used for simultaneous quantitation of mixtures of hydrocarbons that included up to four butene isomers and a total of up to six components. Remarkably, even for mixtures containing multiple isomeric compounds, differences in relative intensities of electron ionization mass spectra provided a basis for quantitation. Quantitation accuracy and precision decreased as the number of components in a mixture and the spectral similarity of those components increased. In general, when cis-2-butene and trans-2-butene were present in mixtures, quantitation performance was compromised.; Selection of which ions to monitor (parameterization) was critical to optimum analysis accuracy, precision, and speed for all mixtures tested. An empirical parameterization algorithm based on comparison of reference spectra of mixture components was developed for ion selection. Empirical algorithm parameterizations gave analysis accuracy and precision values statistically equal to, or better than, all-mass parameterizations (using all masses above 1% relative intensity).; A zeolite membrane inlet to the mass spectrometer (MIMS) was tested for its ability to differentiate components. Even when there was little or no difference in the steady-state permeation rates of compounds through the membrane, distinctive time dependence of component approaches to steady state provided a basis for differentiation. Time dependent permeation enrichments were exploited to quantitate binary mixtures of cis-2-butene and 1-butene using dynamic (pulsed sample) MIMS. In this experiment each pure component had a characteristic ion signal phase shift relative to the timing of the pulsing valve, with the more quickly permeating compound (1-butene) having the smaller phase shift. Mixtures of cis-2-butene and 1-butene were found to have ion signal phase shifts that correlated with relative concentration.