Direct mass spectrometry has grown significantly due to wide applicability, relative ease of use, and high sample throughput. However, many current direct mass spectrometry methods are largely based on ambient ionization techniques that can suffer from matrix effects and poor selectivity. A strategy that addresses these shortcomings is condensed phase membrane introduction mass spectrometry-liquid electron ionization utilizing in situ liquid reagent chemical ionization (CP-MIMS-LEI/CI).In CP-MIMS measurements, a semipermeable hollow fibre polydimethylsiloxane membrane probe is directly immersed into a complex sample. Neutral, hydrophobic analytes permeating the membrane are entrained by a continuously flowing liquid acceptor phase (nL/min) to an LEI/CI source, where the liquid is nebulized, followed by analyte vaporization and ionization. This study marks the first intentional exploitation of the liquid CP-MIMS acceptor phase as an in situ means of providing liquid chemical ionization (CI) reagents for improved analyte sensitivity and selectivity (CP-MIMS-LEI/CI). Acetonitrile and diethyl ether were used as a combination acceptor phase/CI proton transfer reagent system for the direct analysis of dialkyl phthalates. Using isotopically labeled reagents, the gas phase ionization mechanism was found to involve reagent autoprotonation, followed by proton transfer to dialkyl phthalates. A demonstration of the applicability of CP-MIMS-LEI/CI for rapid and sensitive screening of bis(2-ethylhexyl) phthalate in house dust samples is presented. The detection limit in house dust (6 mg/kg) is comparable to that obtained by conventional analyses, but without time-consuming sample work up or chromatographic separation steps.

Benzophenone-3 (2-hydroxy-4-methoxybenzophenone) is present in many sunscreens/cosmetics due to its UV-filtering properties and has consequently been observed in recreational waters. There are growing concerns about endocrine disruption in aquatic organisms and broader impacts in freshwater and marine systems. Therefore, there is value in cost-effective, sensitive techniques that allow for high-density, spatiotemporal data to protect environmental health and inform public policy. Condensed-phase membrane introduction mass spectrometry coupled with liquid electron ionization with in situ chemical ionization (CP-MIMS-LEI/CI) is a novel direct tandem MS technique that fulfills these criteria and was applied for the direct measurement of benzophenone-3 in environmental water samples without any sample preparation. We report results that are sensitive (20 ng/L detection limit), reproducible (11% interday variability), and comparable to those of liquid chromatography tandem mass spectrometry (LC–MS/MS) for environmental samples (n = 4; 12–24% different). CP-MIMS-LEI/CI was applied to samples (n = 33) from the Cowichan River and Cowichan Lake (British Columbia, Canada), an important fish-bearing system significant to First Nations culture, salmonid production, and recreation. The quantitative analysis afforded by CP-MIMS-LEI/CI enabled geospatial benzophenone-3 analysis, identifying elevated concentrations (>180 ng/L) associated with local recreational activity. LC–MS/MS measurements for samples from two locations suggest a correlation between the number of swimmers and benzophenone-3 concentrations (R 2 = 0.88 and 0.94).