Delicate polydimethylsiloxane hollow fibre membrane interfaces for condensed phase membrane introduction mass spectrometry (CP‐MIMS)

Abstract

Delicate PDMS HFM CP-MIMS interfaces were developed and used for the direct, on-line detection of low volatility, polar analytes in complex aqueous samples. Composite PDMS HFM interfaces yielded the best overall analytical performance improvements, and were used to demonstrate the direct measurement of naphthenic acids in complex aqueous samples.

Condensed Phase Membrane Introduction Mass Spectrometry with Direct Electron Ionization: On-line Measurement of PAHs in Complex Aqueous Samples

“…The lowest measured concentrations demonstrated S/N ratios of ≥3, defining the measured limit of linearity and detection limits for the current system. It is expected that further reductions of detection limits are possible by reducing the acceptor phase flow rate, or by utilizing a 'stopped-flow' CP-MIMS approach [5][6][7][8]. The signal response times, limited by membrane permeation kinetics, ranged from 2.8 min for naphthalene to 4.7 min for pyrene, consistent with an increase in molar volume and subsequent decrease in diffusion coefficients.…”

“…Nonetheless, this experiment demonstrates the feasibility of the technique as a direct, continuous monitoring strategy for free PAH concentrations at trace levels in heterogeneous and complex samples. Membrane transport kinetics are limited by HFM wall thickness, and thinner PDMS membranes enable faster analytical response times and greater temporal resolution [8].…”

“…Analyte permeation characteristics provide a degree of discrimination at the membrane level, but the use of selective ionization approaches (e.g., chemical ionization, CI) as well as employing unique m/z or tandem mass spectrometry (MS/MS) allows for the rapid, simultaneous resolution of co-permeating analytes. The membrane also rejects bulk matrix components that may result in ionization suppression, increasing the sensitivity over 'dilute-and-shoot' approaches [5][6][7][8].…”

“…CP-MIMS is emerging as a viable approach for the on-line monitoring of low volatility analytes in complex aqueous samples. Most research has used membranes (predominantly PDMS) coupled with direct API sources such as electrospray (ESI) [5,6,8,12], sonic spray ionization (SSI) [13], and atmospheric pressure chemical ionization (APCI) [3,14].…”

“…The CP-MIMS probes used for this work were constructed using 2 cm lengths of 170 μm thick (0.64 mm o.d., 0.30 mm i.d.) PDMS hollow fiber membrane (HFM) stock, unless otherwise noted, mounted on a 'J-Probe' type MIMS interface, whose construction details have been previously described [7,8]. For the multi-PAH detection demonstration presented ( Figure 5), a thin (500 nm) supported PDMS membrane equipped 'J-Probe' interface was used, constructed as described elsewhere [8].…”