A universal temperature controlled membrane interface for the analysis of volatile and semi-volatile organic compounds

Abstract

A universal temperature controlled membrane interface (TCMI) has been constructed for hollow-fibre membranes. The membrane temperature is controllable in the range -70 to 250 degrees C using an electric heater and a flow of cooled nitrogen or helium gas. Volatile and semi-volatile organic compounds may be detected either by continuous diffusion across the membrane or by in-membrane pre-concentration followed by thermal desorption into the detector. The TCMI interface is demonstrated in combination with mass spectrometry and GC-MS, for the determination of VOCs and SVOCs in aqueous and air samples and for the on-line monitoring of a bioreactor.

A coaxially heated membrane introduction mass spectrometry interface for the rapid and sensitive on‐line measurement of volatile and semi‐volatile organic contaminants in air and water at parts‐per‐trillion levels

“…In all cases, a temperature gradient applied opposite to the analyte concentration gradient results in a greater mass transfer from the sample to the mass spectrometer. We believe that previously reported ‘flow‐over’, thermally assisted strategies that relied on heating the entire membrane interface22, 27, 39 would result in significant losses of analyte desorbed from the exterior of the membrane for two primary reasons. First, as the heating is applied externally, the outside of the membrane will heat up before the interior surface.…”

“…Soni et al . described the use of a low‐power carbon dioxide laser to desorb analyte from a sheet membrane directly into a mass spectrometer source,26 and recently Creaser et al have developed a ‘universal MIMS interface’ that incorporates heating and cooling to facilitate measurements of both VOCs and SVOCs 27. Lauritsen and coworkers report an elegant experimental system with a flow‐through geometry based on stimulated thermal desorption within a chemical ionization plasma that dramatically increases sensitivity for SVOCs and polar compounds while simultaneously decreasing precursor ion fragmentation 28, 29…”

“…Thermal desorption methods have been successful in improving the analytical performance of MIMS for the analysis of SVOCs in air samples 27, 30. By elevating the interface temperature after pre‐loading the membrane with analyte, SVOCs permeate and desorb more rapidly 13.…”

Fast and direct screening of solid materials for their potential liberation of hydrophobic organic compounds using hot cell membrane inlet mass spectrometry

“…To analyze semi‐VOCs (boiling point (bp) above 250°C) using MIMS, various forms of stimulated desorption are needed and the analysis is normally performed using the trap‐and‐release technique12, 13 (T&R‐MIMS). In the T&R‐MIMS technique the analyte is preconcentrated in the membrane, before it is rapidly released either directly into the ion source of the mass spectrometer14–20 or into a hot transfer line leading to the ion source 21–24…”

Fast and direct screening of polyaromatic hydrocarbon (PAH)‐contaminated sand using a miniaturized membrane inlet mass spectrometer (mini‐MIMS)

“…In this technique the sample, liquid or gaseous, is flushed through a cold membrane inlet and, due to preferential partition between the sample matrix and a silicone membrane, the PAHs accumulate in the membrane. After a collection period of 1–20 min the membrane is rapidly heated and the PAHs are released either directly into the ion source of the mass spectrometer15–18 or into a transfer line leading to the ion source 19–22. In one variation of the trap‐and‐release technique a laser was used to assist desorption of PAHs from the membrane 23, 24.…”