Analytical Applications of Membranes

Abstract

Roles of membranes in analytical chemistry range from creating potentials in ion‐selective electrodes to catalyzing protein digestion before mass spectrometry. This article focuses on membrane‐based analyte extraction and also briefly discusses recent catalytic membranes that facilitate analyte derivatization or digestion. Membrane‐based liquid‐liquid extraction avoids mixing and subsequent collection of the two phases and the recent development of hollow‐fiber microextraction is particularly attractive for small‐volume, potentially‐automated analyses. Microdialysis sampling is now a widespread tool for analyte collection from a variety of tissues, while membrane introduction mass spectrometry combined with miniaturized mass spectrometers facilitates remote or portable environmental analyses. Derivatization of membranes affords adsorptive materials for solid‐phase extraction. In particular, growth of functionalized polymer brushes in pores yields membrane adsorbers that capture tagged proteins. Moreover, simple methods for enzyme adsorption in porous membranes give reactors that catalyze rapid proteolysis for mass spectrometry. In addition to their history in ion‐selective electrodes and filtration, future membranes will play a significant role in sample purification and derivatization because they provide convenient methods for rapidly concentrating or modifying small‐volume samples.

Mass Spectrometry in the Home and Garden

“…Membranes offer advantages of high sensitivity (with restricted analytes) although recent work has explored ways to lift some of these limitations [8]. Membranes offer many other benefits, especially when examining samples from complex matrices where they allow derivatization and pH adjustment [9, 10]. Examples of applications of membrane introduction include in situ analysis of contaminants in ocean water [11, 12], direct analysis of human breath [13], intravenous blood sampling [14], and on-line monitoring of bioreactors [15].…”