A passive membrane system for on‐line mass spectrometry reagent addition

Abstract

Rationale: Post-separation addition of chemical modifiers in liquid chromatographymass spectrometry is widely used for improving ionization sensitivity and selectivity. This is typically accomplished using a post-column T-junction, which can result in sample dilution and imperfect mixing. We present a passive semi-permeable hollow fiber membrane approach for the addition of chemical modifiers that avoids these issues.Methods: Model compounds were directly infused by flow injection to an electrospray ionization triple quadrupole mass spectrometer after passing through a polydimethylsiloxane hollow fiber membrane. Ionization enhancement reagents were introduced into the flowing stream by membrane permeation from aqueous solutions. Ionization enhancement from volatile acids and bases in positive and negative electrospray ionization was evaluated to assess the feasibility of this approach.Results: The membrane-based apparatus resulted in relative ionization enhancement factors of up to 14Â, depending upon the analyte, reagent, and ionization mode used. Ionization enhancement signal stability is reasonable (relative standard deviation of 5-7%) for extended periods from the same reagent solution, and minimal analyte dilution is observed. A proof-of-concept demonstration of the chromatographic "trifluoroacetic acid fix" strategy is presented.Conclusions: An on-line mass spectrometry ionization reagent addition method with potential post-chromatography reagent addition applications was developed using a hollow fiber polydimethylsiloxane membrane. This approach offers a promising alternative to traditional methods requiring additional hardware such as pumps and T-junctions that can result in sample dilution and imperfect reagent mixing. | INTRODUCTIONThe post-separation infusion of derivatizing reagents and chemical modifiers in liquid chromatography-mass spectrometry (LC/MS) workflows has been widely used to enhance ionization without altering chromatographic performance. This is done because optimal separation solvent systems can be quite different from those needed for efficient ionization. 1,2 Reagents are frequently introduced to the LC eluent via a T-junction, infusing reagent via a second pumping system. Other post-column addition techniques (still utilizing secondary liquid handling pumps) include the use of reaction coils 3 and triaxial electrospray probes. 4 Although analyte ionization is

Online Membrane Sampling for the Mass Spectrometric Analysis of Oil Sands Process Affected Water-Derived Naphthenic Acids in Real-World Samples

“…Given the marginal improvements over the regular acceptor phase, we elected not to incorporate base enhancement into the quantitative method (described below) due to the challenges this presents to online membrane transport experiments described previously [33]. Future work will evaluate the use of a second membrane probe for the introduction of ionizationenhancing agents [34].…”