Organic impurity preconcentration by a multimembrane inlet system of a mass spectrometer

Abstract

Using an inlet system comprising a series of membranes sequentially operating in a nonstationary flow regime, it is possible to increase the concentration of an organic impurity in a sample immediately before introduction into a mass spectrometer. The degree of preconcentration calculated in the approximation of a small response time of the membranes is proportional to (k _j /k _m )^N, where k _j and k _m are the membrane permeabilities for the impurity and matrix, respectively, and N is the number of membranes. For a butane admixture in air, the calculated relative effect for an inlet using two membranes instead of one is ∼40, while the experimental verification using 0.1-mm-thick poly(dimethylsiloxane) membranes showed an increase in the degree of preconcentration by a factor of ∼14. It is possible to approach the theoretical value by decreasing the time of impurity diffusion through the membrane at the expense of reduced membrane thickness. It is expected that multimembrane inlet systems will be especially effective in environmental monitoring, where a high sensitivity of the analysis is required with respect to toxic organic substances possessing k _j /k _m ratios much greater as compared to that of butane.