Methodology and applications of membrane introduction mass spectrometry

Ahti Antti Tapio Kotiaho, Purdue University

Abstract

The methodology and applications of membrane introduction mass spectrometry, an analytical technique in which a semi-permeable membrane mounted in a probe is used to introduce fluid samples into a mass spectrometer, are described. Different designs of direct insertion membrane probes, built based on the flow-through operation concept, are presented. These devices allow mounting of the membrane within or adjacent to the ion source of a mass spectrometer, an arrangement which gives low detection limits, little memory effect and rapid analysis times. Optimization of parameters which affect the performance of the devices is reported. High probe temperatures and high flow-rates are generally preferred, as a means of maximizing sensitivity. A knowledge of the sample matrix is essential in precise quantitative analysis, because matrix components can change permeation rates and ionization efficiencies. Methods for on-line concentration of samples using a capillary membrane concentration device are also presented as are experiments done with physically and chemically modified membranes. Together with flow injection analysis methods of sampling membrane introduction mass spectrometry is used for on-line quantitative monitoring of dissolved products and off-gases of fermentations of Klebsiella oxytoca and Bacillus polymyxa organism. Membrane introduction mass spectrometry is also used in on-line monitoring of interconversion reactions of the chloramines NH$\sb2$Cl, NHCl$\sb2$ and NCl$\sb3.$ The time persistence of monochloramine in human saliva and stomach fluid is also measured. In addition, this methodology is used in the determination and identification of organic chloramines at sub-ppm levels in water. It is shown that typical aliphatic amines are chlorinated at nitrogen but that aniline is ring chlorinated. The reactions which accompany ozonation of contaminated water are also studied and the pentafluorobenzyl hydroxylamine derivatives of aldehydes are studied by negative chemical ionization using membrane introduction mass spectrometry. Membrane introduction mass spectrometry is also demonstrated to be applicable in air monitoring. Successful gas phase chlorination of benzene and substituted benzenes using protonated monochloramine as chlorination reagent is also presented. The structures of the chlorinated products are studied by collecting sequential product ion mass spectra (MS$\sp3)$ with a pentaquadrupole instrument.

Degree

Ph.D.

Advisors

Cooks, Purdue University.

Subject Area

Analytical chemistry|Environmental science

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