An enzyme derivatized polydimethylsiloxane (PDMS) membrane for use in membrane introduction mass spectrometry (MIMS)

Abstract

Membrane introduction mass spectrometry (MIMS) provides direct measurement of volatile and semivolatile analytes in condensed and gas-phase samples without sample preparation steps. Although MIMS has numerous advantages that include direct, on-line, real-time analysis with low detection limits, current applications of MIMS are predominantly limited to volatile and semivolatile analytes that permeate hydrophobic membranes (e.g., polydimethylsiloxane; PDMS). We report the first enzyme modified PDMS membrane for use with MIMS. This was achieved by immobilizing Candida rugosa lipase directly onto the surface of oxidized PDMS. These surface immobilized enzymes catalyze ester hydrolysis, releasing an alcohol product at the membrane interface that is readily detected. We have successfully used an enzyme modified membrane for the analysis and quantification of low-volatility and hydrophilic esters. We report the quantification of several carboxylic acid esters in dilute aqueous solutions, including a phthalate monoester carboxylate that is not readily detected by conventional MIMS. This new interface demonstrates the potential for extending the range and versatility of MIMS.

Characterization of a condensed‐phase membrane introduction mass spectrometry (CP‐MIMS) interface using a methanol acceptor phase coupled with electrospray ionization for the continuous on‐line quantitation of polar, low‐volatility analytes at trace levels in complex aqueous samples

“…large, highly polar and/or charged species) has been accomplished by chemical derivatization of these analytes before measurement [12,22,23] or strategies that produce volatile fragment molecules from the analyte, including the use of enzymes immobilized on the membrane surface. [24] The on-line performance characteristics of conventional MIMS (favoring relatively volatile analytes) are seriously limited for many molecules of environmental and bio-analytical significance because many such molecules are large, polar and/or charged compounds. A powerful variant on the MIMS approach that can address this limitation is accomplished by using a condensed (liquid) acceptor phase and a suitable direct liquid ionization technique such as electrospray (ESI) or atmospheric pressure chemical ionization (APCI).…”

Membrane introduction mass spectrometry (MIMS): a versatile tool for direct, real‐time chemical measurements

“…semi‐volatile organic compounds, SVOCs), their measurement becomes hindered or impractical by GP‐MIMS, limiting the initial applications of MIMS to gases and VOC analysis. Improvements to extend the capability of GP‐MIMS to sensitive and rapid SVOC measurement have included increasing the volatility of analyte species via chemical derivatization prior to measurement, a variety of membrane heating and desorption strategies, alternate membrane materials including an enzyme modified PDMS membrane developed by our group . In addition, we have developed a novel, coaxially heated, hollow fibre PDMS GP‐MIMS interface that retains all the capabilities for trace level VOC measurements in both air and aqueous samples.…”

“…Improvements to extend the capability of GP-MIMS to sensitive and rapid SVOC measurement have included increasing the volatility of analyte species via chemical derivatization prior to measurement, [18,19] a variety of membrane heating and desorption strategies, [20][21][22][23][24][25][26][27][28] alternate membrane materials [29][30][31] including an enzyme modified PDMS membrane developed by our group. [32] In addition, we have developed a novel, coaxially heated, hollow fibre PDMS GP-MIMS interface that retains all the capabilities for trace level VOC measurements in both air and aqueous samples. By actuating a heating element located in the lumen of the hollow fibre membrane (HFM), this system achieves on-line ppb-pptr detection limits for SVOC analytes.…”

Condensed Phase Membrane Introduction Mass Spectrometry with In Situ Liquid Reagent Chemical Ionization in a Liquid Electron Ionization Source (CP-MIMS-LEI/CI)

“…For soil samples, this method obviated sample cleanup, resulting in remarkably high throughput (15 soil samples per hour) combined with sensitive detection (70 μg/kg detection limit for benzo[a]pyrene from soil). 23 We also have previously used MIMS for phthalate quantitation using enzyme-derivatized PDMS, 34 and for the study of phthalate−particulate interactions. 35 The study presented here demonstrates the use of CP-MIMS for phthalate analysis and extends the capabilities of the technique with respect to both selectivity and sensitivity.…”