Membrane Inlet Mass Spectrometry Research Articles

Assignment of the slowly exchanging substrate water of nature’s water-splitting cofactor

Identifying the two substrate water sites of nature's water-splitting cofactor (Mn4CaO5 cluster) provides important information toward resolving the mechanism of O-O bond formation in Photosystem II (PSII). To this end, we have performed parallel substrate water exchange experiments in the S1 state of native Ca-PSII and biosynthetically substituted Sr-PSII employing Time-Resolved Membrane Inlet Mass Spectrometry (TR-MIMS) and a Time-Resolved 17O-Electron-electron Double resonance detected NMR (TR-17O-EDNMR) approach. TR-MIMS resolves the kinetics for incorporation of the oxygen-isotope label into the substrate sites after addition of H218O to the medium, while the magnetic resonance technique allows, in principle, the characterization of all exchangeable oxygen ligands of the Mn4CaO5 cofactor after mixing with H217O. This unique combination shows i) that the central oxygen bridge (O5) of Ca-PSII core complexes isolated from Thermosynechococcus vestitus has, within experimental conditions, the same rate of exchange as the slowly exchanging substrate water (WS) in the TR-MIMS experiments and ii) that the exchange rates of O5 and WS are both enhanced by Ca2+→Sr2+ substitution in a similar manner. In the context of previous TR-MIMS results, this shows that only O5 fulfills all criteria for being WS. This strongly restricts options for the mechanism of water oxidation.

Biomonitoring: Developing a Beehive Air Volatiles Profile as an Indicator of Environmental Contamination Using a Sustainable In-Field Technique

The wellbeing of the honey bee colonies and the health of humans are connected in numerous ways. Therefore, ensuring the wellbeing of bees is a crucial component of fostering sustainability and ecological harmony. The colony collapse disorder (CCD) phenomenon was first reported in 2006 when the majority of bee colonies in Europe died out, due to an increase in infections, contamination of hives with agrochemical pesticides, and persistent organic pollutants (POPs). Only 6 years after the emergence of CCD, more than 6.5 million premature deaths were reported, as a consequence of persistent human exposure to air pollution. The insect species such as the honey bee Apis mellifera L. and the air matrix inside the beehive can be used as tools in biomonitoring, instead of traditional monitoring methods. This may have advantages in terms of cost-effective bioindicators of the environmental health status, showing the ability to record spatial and temporal pollutant variations. In this study, we present the sustainable in-field usage of the portable membrane inlet mass spectrometry (MIMS) instrument for an instant and effective determination of the level of environmental pollution by analytical identification of hive atmosphere volatile organic compound (VOC) contaminants, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), monocyclic aromatic hydrocarbons (BTEX) compounds, and pesticides. The samples were taken from hives located in urbanized and rural regions, highlighting variations in contamination. The MIMS results were benchmarked against a conventional laboratory sampling technique, such as GC-MS.

Gas equilibrium membrane inlet mass spectrometry (GE-MIMS) for water at high pressure

Abstract. Gas species are widely used as natural or artificial tracers to study fluid dynamics in environmental and geological systems. The recently developed gas equilibrium membrane inlet mass spectrometry (GE-MIMS) method is most useful for accurate and autonomous on-site quantification of dissolved gases in aquatic systems. GE-MIMS works by pumping water through a gas equilibrator module containing a gas headspace, which is separated from the water by a gas-permeable membrane. The partial pressures of the gas species in the headspace equilibrate with the gas concentrations in the water according to Henry's Law and are quantified with a mass spectrometer optimized for low gas consumption (miniRUEDI or similar). However, the fragile membrane structures of the commonly used equilibrator modules break down at water pressures ≳3 bar. These modules are therefore not suitable for use in deep geological systems or other environments with high water pressures. To this end, the SysMoG® MD membrane module (Solexperts AG, Switzerland; “SOMM”) was developed to withstand water pressures of up to 100 bar. Compared to the conventionally used GE-MIMS equilibrator modules, the mechanically robust construction of the SOMM module entails slow and potentially incomplete gas–water equilibration. We tested the gas equilibration efficiency of the SOMM and developed an adapted protocol that allows correct operation of the SOMM for GE-MIMS analysis at high water pressures. This adapted SOMM GE-MIMS technique exhibits a very low gas consumption from the SOMM to maintain the gas–water equilibrium according to Henry's Law and provides the same analytical accuracy and precision as the conventional GE-MIMS technique. The analytical potential of the adapted SOMM GE-MIMS technique was demonstrated in a high-pressure fluid migration experiment in an underground rock laboratory. The new technique overcomes the pressure limitations of conventional gas equilibrators and thereby opens new opportunities for efficient and autonomous on-site quantification of dissolved gases in high-pressure environments, such as in research and monitoring of underground storage of CO2 and waste deposits or in the exploration of natural resources.

Designing a Novel Setup for High-Throughput Investigations of Electrochemical Reactions in Real Time

With the great interest in new electrochemical processes, fast screening of various reaction parameters is highly desirable. For this purpose, differential electrochemical mass spectrometry (DEMS) and membrane-inlet mass spectrometry (MIMS) have been established to enable real-time monitoring of volatile compounds. However, the analysis of non-volatile compounds is commonly limited by the temporal resolution of traditional quantification methods such as NMR, GC-MS, or LC-MS. While ambient ionization mass spectrometry (AIMS) generally enables time-resolved monitoring of non-volatile compounds, electrolyte salts can lead to ionization suppression. The latter can decrease the sensitivity of product detection and the reliability of quantitative data. Therefore, a suitable reaction setup and thorough investigations are needed when utilizing AIMS. Nonetheless, in recent efforts, an electrochemical flow cell was coupled with such a technique to provide a method for on-line monitoring of non-voltile reaction products in aqueous electrolytes. To keep up with the increasing interest in electrosynthesis in organic media, we now present a new setup that is also applicable to non-aqueous media. It pairs a novel and versatile electrochemical cell with an AIMS and DEMS for highly sensitive detection of reaction products. Moreover, various reaction parameters such as electrode material, electrolyte, and temperature can be investigated in high-throughput.Key words: Electrocatalysis, Electrosynthesis, Real-time, On-line monitoring, High-throughput

Low hyporheic denitrification in headwater streams revealed by nutrient injections and in situ gas measurements

Stream networks can retain or remove nutrient pollution, including nitrate from agricultural and urban runoff. However, assessing the location and timing of nutrient uptake remains challenging because of the hydrological and biogeochemical complexity of dynamic stream ecosystems. We used a novel approach to continuously characterize the biological activity in a stream with in situ measurement of dissolved gases by membrane inlet mass spectrometry (MIMS). In a headwater stream in western France, we compared in situ measurements of O2, CO2, N2, and N2O (the main gases associated with respiration, including denitrification) with more traditional laboratory incubations of collected sediment. The in situ measurements showed near-zero denitrification in the stream and the hyporheic zone. However, the laboratory incubations showed a low but present denitrification potential. This demonstrates how denitrification potential is not necessarily expressed in field hydrological and geochemical conditions. In situ measurements are thus crucial to quantify expressed rates of nutrient removal. Broader application of in situ gas measurement based on technologies such as MIMS could enhance our understanding of the spatiotemporal distribution of stream and hyporheic processes and overall nutrient retention at stream network scales.

Multiple highly expressed phosphoenolpyruvate carboxylase genes have divergent enzyme kinetic properties in two C4 grasses.

Phosphoenolpyruvate (PEP) carboxylase (PEPC) catalyses the irreversible carboxylation of PEP with bicarbonate to produce oxaloacetate. This reaction powers the carbon-concentrating mechanism (CCM) in plants that perform C4 photosynthesis. This CCM is generally driven by a single PEPC gene product that is highly expressed in the cytosol of mesophyll cells. We found two C4 grasses, Panicum miliaceum and Echinochloa colona, that each have two highly expressed PEPC genes. We characterized the kinetic properties of the two most abundant PEPCs in E. colona and P. miliaceum to better understand how the enzyme's amino acid structure influences its function. Coding sequences of the two most abundant PEPC proteins in E. colona and P. miliaceum were synthesized by GenScript and were inserted into bacteria expression plasmids. Point mutations resulting in substitutions at conserved amino acid residues (e.g. N-terminal serine and residue 890) were created via site-directed PCR mutagenesis. The kinetic properties of semi-purified plant PEPCs from Escherichia coli were analysed using membrane-inlet mass spectrometry and a spectrophotometric enzyme-coupled reaction. The two most abundant P. miliaceum PEPCs (PmPPC1 and PmPPC2) have similar sequence identities (>95 %), and as a result had similar kinetic properties. The two most abundant E. colona PEPCs (EcPPC1 and EcPPC2) had identities of ~78 % and had significantly different kinetic properties. The PmPPCs and EcPPCs had different responses to allosteric inhibitors and activators, and substitutions at the conserved N-terminal serine and residue 890 resulted in significantly altered responses to allosteric regulators. The two, significantly expressed C4Ppc genes in P. miliaceum were probably the result of genomes combining from two closely related C4Panicum species. We found natural variation in PEPC's sensitivity to allosteric inhibition that seems to bypass the conserved 890 residue, suggesting alternative evolutionary pathways for increased malate tolerance and other kinetic properties.

Mapping Nanocellulose- and Alginate-Based Photosynthetic Cell Factory Scaffolds: Interlinking Porosity, Wet Strength, and Gas Exchange.

To develop efficient solid-state photosynthetic cell factories for sustainable chemical production, we present an interdisciplinary experimental toolbox to investigate and interlink the structure, operative stability, and gas transfer properties of alginate- and nanocellulose-based hydrogel matrices with entrapped wild-type Synechocystis PCC 6803 cyanobacteria. We created a rheological map based on the mechanical performance of the hydrogel matrices. The results highlighted the importance of Ca2+-cross-linking and showed that nanocellulose matrices possess higher yield properties, and alginate matrices possess higher rest properties. We observed higher porosity for nanocellulose-based matrices in a water-swollen state via calorimetric thermoporosimetry and scanning electron microscopy imaging. Finally, by pioneering a gas flux analysis via membrane-inlet mass spectrometry for entrapped cells, we observed that the porosity and rigidity of the matrices are connected to their gas exchange rates over time. Overall, these findings link the dynamic properties of the life-sustaining matrix to the performance of the immobilized cells in tailored solid-state photosynthetic cell factories.

Abrupt and acclimation responses to changing temperature elicit divergent physiological effects in the diatom Phaeodactylum tricornutum.

Growth rates and other biomass traits of phytoplankton are strongly affected by temperature. We hypothesized that resulting phenotypes originate from deviating temperature sensitivities of underlying physiological processes. We used membrane-inlet mass spectrometry to assess photosynthetic and respiratory O2 and CO2 fluxes in response to abrupt temperature changes as well as after acclimation periods in the diatom Phaeodactylum tricornutum. Abrupt temperature changes caused immediate over- or undershoots in most physiological processes, that is, photosynthetic oxygen release ( ), photosynthetic carbon uptake ( ), and respiratory oxygen release ( ). Over acclimation timescales, cells were, however, able to re-adjust their physiology and revert to phenotypic 'sweet spots'. Respiratory CO2 release ( ) was generally inhibited under high temperature and stimulated under low-temperature settings, on abrupt as well as acclimation timescales. Such behavior may help mitochondria to stabilize plastidial ATP : NADPH ratios and thus maximize photosynthetic carbon assimilation.

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

Large volumes of oil sands process-affected waters (OSPW) result from heavy oil extraction in Alberta, Canada. Currently, a toxic legacy of ca. 500 Mm3 is stored in tailings ponds under a zero-discharge policy. OSPW is a complex mixture of suspended and dissolved materials including a wide range of inorganic and organic contaminants. Classically defined naphthenic acids (NAs; CnH2n+ZO2) are one of the primary toxic fractions in OSPW and have therefore been the subject of considerable research interest. Most studies employ considerable sample cleanup followed by liquid chromatography and/or high-resolution mass spectrometry (HRMS) for the characterization of these complex mixtures. However, these strategies can be time- and cost-intensive, limiting the scope of research and adoption for regulatory purposes. Condensed phase membrane introduction mass spectrometry (CP-MIMS) is emerging as a “fit-for-purpose” approach for the analysis of NAs. This technique directly interfaces the mass spectrometer with an aqueous sample using a hydrophobic semi-permeable membrane, requiring only pH adjustment to convert NAs to a membrane-permeable form. Here, we examine the perm-selectivity of classical NAs (O2) relative to their more oxidized counterparts (O3–O7) and heteroatomic (N, S) species collectively termed naphthenic acid fraction compounds (NAFCs). The investigation of 14 model compounds revealed that classically defined NAs are greater than 50-fold more membrane permeable than their oxidized/heteroatomic analogs. HRMS analysis of real OSPW extracts with and without membrane clean-up further supported selectivity towards the toxic O2 class of NAs, with >85% of the overall signal intensity attributable to O2 NAs in the membrane permeate despite as little as 34.7 ± 0.6% O2 NAs observed in the directly infused mixture. The information collected with HRMS is leveraged to refine our method for analysis of NAs at unit mass resolution. This new method is applied to 28 archived real-world samples containing NAs/NAFCs from constructed wetlands, OSPW, and environmental monitoring campaigns. Concentrations ranged from 0–25 mg/L O2 NAs and the results measured by CP-MIMS (unit mass) and SPE-HRMS (Orbitrap) showed good agreement (slope = 0.80; R2 = 0.76).

Temperature sensitivity of carbon concentrating mechanisms in the diatom Phaeodactylum tricornutum

Marine diatoms are key primary producers across diverse habitats in the global ocean. Diatoms rely on a biophysical carbon concentrating mechanism (CCM) to supply high concentrations of CO2 around their carboxylating enzyme, RuBisCO. The necessity and energetic cost of the CCM are likely to be highly sensitive to temperature, as temperature impacts CO2 concentration, diffusivity, and the kinetics of CCM components. Here, we used membrane inlet mass spectrometry (MIMS) and modeling to capture temperature regulation of the CCM in the diatom Phaeodactylum tricornutum (Pt). We found that enhanced carbon fixation rates by Pt at elevated temperatures were accompanied by increased CCM activity capable of maintaining RuBisCO close to CO2 saturation but that the mechanism varied. At 10 and 18 °C, diffusion of CO2 into the cell, driven by Pt’s ‘chloroplast pump’ was the major inorganic carbon source. However, at 18 °C, upregulation of the chloroplast pump enhanced (while retaining the proportion of) both diffusive CO2 and active HCO3− uptake into the cytosol, and significantly increased chloroplast HCO3− concentrations. In contrast, at 25 °C, compared to 18 °C, the chloroplast pump had only a slight increase in activity. While diffusive uptake of CO2 into the cell remained constant, active HCO3− uptake across the cell membrane increased resulting in Pt depending equally on both CO2 and HCO3− as inorganic carbon sources. Despite changes in the CCM, the overall rate of active carbon transport remained double that of carbon fixation across all temperatures tested. The implication of the energetic cost of the Pt CCM in response to increasing temperatures was discussed.

New experimental approaches enabling the continuous monitoring of gas species in hydrothermal fluids

Hot thermal fluids flow through the Earth's crust and carry valuable information about the deep subsurface. The monitoring of natural tracers transported in geothermal fluids, such as gases or ions, are relevant to better understand the geological processes in the Earth's subsurface and their relation to deep fluid dynamics. Recently developed technologies (e.g., portable gas-equilibrium membrane-inlet mass spectrometry) allow for the continuous monitoring of gas species at a much higher temporal resolution than the sampling procedures commonly used, based on a few individual samples. However, the monitoring of gas species from hot thermal fluids still poses experimental challenges tied to unwanted water vapor condensation in the headspace of the separation module, which irremediably leads to clogging (e.g., of the connecting capillaries) and failure of the detection device. In this contribution, we present two new experimental methods that provide suitable technical conditions to measure gases, even in high temperature geothermal fluids, using a portable gas analyzer. Two sites with different thermal water temperatures (first one ranging from 50 °C to 65 °C and second one close to boiling temperature) were selected. The first method was deployed on the thermal waters of Lavey-les-Bains (Vaud, Switzerland), for which we report results from October 2021. The second method was used in Beppu (Oita Prefecture, Japan), for which we report results from April 2018. Our results show that at both sites, our methods allow for continuous measurements of gas species (N2, Ar, O2, Kr, He, CH4, CO2 and H2) in thermal waters. Furthermore, they show that the variability of gas emanation from the two sites can only be adequately described by measurements with high temporal resolution, which both methods allow.

Kinetic and mechanistic study of the effect of Cu(II) on monochloramine stability in bromide-containing waters

Naturally occurring bromide can reduce the stability of monochloramine (NH2Cl) by forming brominated halamines, the most abundant being bromochloramine (NHBrCl). Cu(II) is found in drinking water distribution systems from copper pipes leaching or added as a biocide. This study showed that Cu(II) can catalyse the decay of NHBrCl (proved by Membrane Introduction Mass Spectrometry) during the chloramination process. 11 % of the total oxidant (chloramines, bromamines and NHBrCl) was consumed during chloramination in bromide-containing waters at pH 6.5 after 6 h, while the presence of Cu(II) remarkably accelerated the total oxidant decay with 65 % consumption. Higher bromide concentrations and lower pH led to an increasing total oxidant decomposition. This was primarily ascribed to the higher formation of NHBrCl and its further catalytic degradation from Cu(II) under these conditions. The nitrogen by-products in the presence of bromide and Cu(II) were identified. Nitrogen gas and ammonia were shown to be the main degradation products and a mechanism involving NHBrCl decomposition is proposed. It was also verified that Cu(II) enhanced the disinfectant decay in the absence/presence of bromide when natural organic matter was present. These findings can provide useful information to water utilities to better manage and maintain the stability of disinfectant residual allowing safe distribution of drinking water over a wide geographical area.

MIMS as a Low-Impact Tool to Identify Pathogens in Water

Bacteria produce many kinds of volatile compounds throughout their lifecycle. Identifying these volatile compounds can help to understand bacterial interactions with the host and/or other surrounding pathogens of the same or different species. Some commonly used techniques to detect these volatile compounds are GC and/or LC coupled to mass spectrometric techniques. However, these methods can sometimes become challenging owing to tedious sample preparation steps. Thus, identifying an easier method to detect these volatile compounds was investigated in the present study. Here, Membrane-inlet mass spectrometry (MIMS) provided a facile low-impact alternative to the existing strategies. MIMS was able to differentiate between the pathogenic and nonpathogenic bacterial strains, implying that it can be used as a bioprocess monitoring tool to analyze water samples from either water treatment plants or biotechnological industries.

Monitoring microplastic-contaminant sorption processes in real-time using membrane introduction mass spectrometry.

Microplastics are environmentally ubiquitous and their role in the fate and distribution of trace contaminants is of emerging concern. We report the first use of membrane introduction mass spectrometry to directly monitor the rate and extent of microplastic-contaminant sorption. Target contaminant (naphthalene, anthracene, pyrene, and nonylphenol) sorption behaviours were examined at nanomolar concentrations with four plastic types: low density polyethylene (LDPE), high density polyethylene (HDPE), polypropylene (PP), and polystyrene (PS). Under the conditions employed here, short-term sorption kinetics were assessed using on-line mass spectrometry for up to one hour. Subsequent sorption was followed by periodically measuring contaminant concentrations for up to three weeks. Short-term sorption followed first order kinetics with rate constants that scaled with hydrophobicity for the homologous series of polycyclic aromatic hydrocarbons (PAHs). Sorption rate constants on LDPE for equimolar solutions of naphthalene, anthracene, and pyrene were 0.5, 2.0, and 2.2 h-1, respectively, while nonylphenol did not sorb to pristine plastics over this time period. Similar trends among contaminants were observed for other pristine plastics with 4- to 10-fold faster sorption rates associated with LDPE when compared to PS and PP. Sorption was largely complete after three weeks, with the percent analyte sorbed ranging from 40-100% across various microplastic-contaminant combinations. Photo-oxidative ageing of LDPE had little effect on PAH sorption. However, a marked increase in nonylphenol sorption was consistent with increased hydrogen-bonding interactions. This work provides kinetic insights into surface interactions and describes a powerful experimental platform to directly observe contaminant sorption behaviours in complex samples under a variety of environmentally relevant conditions.

Aqueous naphthenic acids and polycyclic aromatic hydrocarbons in a meso-scale spill tank affected by diluted bitumen analyzed directly by membrane introduction mass spectrometry

With the increasing use of unconventional, heavy crude oils there is growing interest in potential impacts of a diluted bitumen (DB) spill in marine and freshwater environments. DB has the potential to release several toxic, trace organic contaminants to the water column. Here, the aqueous concentrations and compositions of two classes of organic contaminants, naphthenic acids (NAs) and polycyclic aromatic hydrocarbons (PAHs), are followed over 8 weeks after a simulated spill of DB (10 L) into a freshwater mesocosm (1200 L) with river sediment (2.4 kg). These complex samples contain biogenic dissolved organic matter, inorganic ions, petroleum contaminants, suspended sediments, and oil droplets. We report the first use of condensed phase membrane introduction mass spectrometry (CP-MIMS) as a direct sampling platform in a complex multi-phase mesocosm spill tank study to measure trace aqueous phase contaminants with little to no sample preparation (dilution and/or pH adjustment). CP-MIMS provides complementary strengths to conventional analytical approaches (e.g., gas- or liquid chromatography mass spectrometry) by allowing the entire sample series to be screened quickly. Trace NAs are measured as carboxylates ([M-H]-) using electrospray ionization and PAHs are detected as radical cations (M+•) using liquid electron ionization coupled to a triple quadrupole mass spectrometer. The DB-affected mesocosm exhibits NA concentrations from 0.3 to 1.2 mg/L, which rise quickly over the first 2 – 5 days , then decrease slowly over the remainder of the study period. The NA profile (measured as the full scan in negative-electrospray ionization at nominal mass resolution) shifts to lower m/z with weathering, a process followed by principal component analysis of the normalized mass spectra. We couple CP-MIMS with high-resolution mass spectrometry to follow changes in molecular speciation over time, which reveals a concomitant shift from classical ‘O2’ naphthenic acids to more oxidized analogues. Concentrations of PAHs and alkylated analogues (C1 – C4) in the DB-affected water range from 0 to 5 μg/L. Changes in PAH concentrations depend on ring number and degree of alkylation, with small and/or lightly alkylated (C0 – C2) PAH concentrations rising to a maximum in the first 4 – 8 days (100 – 200 h) before slowly decaying over the remainder of the study period. Larger and heavily alkylated (C3 – C4) PAH concentrations generally rise slower, with some species remaining below the detection limit throughout the study period (e.g., C20H12 class including benzo[a]pyrene). In contrast, a control mesocosm (without oil) exhibited NA concentrations below 0.05 mg/L and PAHs were below detection limit. Capitalizing on the rapid analytical workflow of CP-MIMS, we also investigate the impacts of sample filtration at the time of sampling (on NA and PAH data) and sample storage time (on NA data only).

A Rapid Method for Detecting Normal or Modified Plant and Algal Carbonic Anhydrase Activity Using Saccharomyces cerevisiae.

In recent years, researchers have attempted to improve photosynthesis by introducing components from cyanobacterial and algal CO2-concentrating mechanisms (CCMs) into terrestrial C3 plants. For these attempts to succeed, we need to understand the CCM components in more detail, especially carbonic anhydrase (CA) and bicarbonate (HCO3−) transporters. Heterologous complementation systems capable of detecting carbonic anhydrase activity (i.e., catalysis of the pH-dependent interconversion between CO2 and HCO3−) or active HCO3− transport can be of great value in the process of introducing CCM components into terrestrial C3 plants. In this study, we generated a Saccharomyces cerevisiae CA knock-out (ΔNCE103 or ΔCA) that has a high-CO2-dependent phenotype (5% (v/v) CO2 in air). CAs produce HCO3− for anaplerotic pathways in S. cerevisiae; therefore, the unavailability of HCO3− for neutral lipid biosynthesis is a limitation for the growth of ΔCA in ambient levels of CO2 (0.04% (v/v) CO2 in air).  ΔCA can be complemented for growth at ambient levels of CO2 by expressing a CA from human red blood cells. ΔCA was also successfully complemented for growth at ambient levels of CO2 through the expression of CAs from Chlamydomonas reinhardtii and Arabidopsis thaliana. The ΔCA strain is also useful for investigating the activity of modified CAs, allowing for quick screening of modified CAs before putting them into the plants. CA activity in the complemented ΔCA strains can be probed using the Wilbur–Anderson assay and by isotope exchange membrane-inlet mass spectrometry (MIMS). Other potential uses for this new ΔCA-based screening system are also discussed.

An experimental laboratory reactor for quantitative kinetic studies of disinfection byproduct formation using membrane inlet mass spectrometry.

RationaleThe type and quantity of environmentally problematic disinfection byproducts (DBPs) produced during chlorination of water depend on the natural organic matter and organic contaminants that raw water contains, and on the operational conditions of the drinking water treatment process. There is a need for a fast and quantitative method that determines which DBPs are produced and monitors the chemical dynamics during a drinking water treatment.MethodsA small experimental chemical reactor (50 mL) was mounted directly onto the membrane inlet interface of a membrane inlet mass spectrometer (MIMS). In this setup, the membrane was the only separation between the reaction mixture in the chemical reactor and the open ion source of the mass spectrometer 2 cm away. Water samples to be chlorinated were placed in the reactor and the chlorination reaction was initiated by injection of hypochlorite. The formation of intermediates and products was monitored using either full‐scan mass spectra or selected ion monitoring of relevant ions.ResultsAn algorithm for analyte quantification was successfully developed for analysis of the complex mixtures of phenol (a model for waterborne organic compounds), chlorinated intermediates and trihalomethane products which simultaneously pass the membrane into the mass spectrometer. The algorithm is based upon the combined use of standard addition and an internal standard, and all analytes could be quantified at nanomolar concentrations corresponding to realistic water treatment conditions. Experiments carried out in the temperature range 15–60°C showed that the reaction dynamics change with operational parameters, for example in tap versus deionized water.ConclusionsWe have successfully shown that an experimental laboratory reactor directly interfaced with a MIMS can be used for quantitative monitoring of the chemical dynamics during a water treatment. This technique could provide rapid assistance in the optimization of operating parameters for minimizing DBP production.

Membrane inlet mass spectrometry method for food intake impact assessment on specific volatile organic compounds in exhaled breath

This research work describes the development of a novel bioanalytical method for the assessment of food impact on selected exhaled breath volatile organic compounds (VOCs) using a fast and portable screening VOC prototype sensor based on membrane inlet mass spectrometry (MIMS). Method and sensor prototype functionality was verified by obtaining good response times, linearity in the examined concentration ranges, and sensitivity and repeatability for several breath VOCs—acetone, ethanol, n-pentane, and isoprene. A new VOC sensor prototype was also proven to be sensitive enough for selected breath VOC quantification with limits of detection at low part per billion (ppb) levels—5 ppb for n-pentane, 10 ppb for acetone and ethanol, and 25 ppb for isoprene. Food impact assessment was accomplished by tracking the levels of acetone, ethanol, n-pentane, and isoprene in exhaled breath samples collected from 50 healthy participants before the meal and 60 min and 120 min after the meal. For acetone, isoprene, and n-pentane, a larger impact was noticed 120 min after the meal, while for ethanol, it was after 60 min. Obtained VOC levels were in the expected concentration ranges. Mean values at all time points were ~ 500–900 ppb for acetone and ~ 400–600 ppb for ethanol. Most of the results for n-pentane were below 5 ppb, but the mean value for those which were detected was ~ 30 ppb. Along with samples, data about participants’ lifestyle were collected via a short questionnaire, which were compared against obtained VOC levels in order to reveal some significant correlations between habits of participants and their breath VOC levels.Graphical abstractPortable MS: monitoring of food impact on the levels of selected VOCs from exhaled breath

The Influence of the Vietnam Offshore Current and Kuroshio Intrusion on Net Community Production in the Oligotrophic South China Sea in Summer

AbstractIn summer, the Vietnam Offshore Current (VOC) and the Kuroshio intrusion are two important processes inducing considerable environmental fluctuations in the surface water of the South China Sea (SCS). Net community production (NCP) is an important proxy of the biological pump strength and can be estimated based on the dissolved oxygen to argon ratio (O2/Ar) in the mixed layer. To quantify the influence of the VOC and Kuroshio intrusion on NCP in the oligotrophic SCS, we obtained continuous measurements of O2/Ar in the upper mixed layer using membrane inlet mass spectrometry (MIMS) in the northeastern SCS in summer 2017. Average NCP was 2.6 ± 1.5 mmol C m−2 d−1 in Phase 1 (from 13 to 20 July), 5.3 ± 1.7 mmol C m−2 d−1 in Phase 2 (from 20 to 25 July), and 13.9 ± 2.3 mmol C m−2 d−1 in Phase 3 (from 30 July to 9 August). Data from the region influenced by vertical mixing were excluded. A strong correlation between the surface dissolved inorganic nitrogen (DIN) and NCP was obtained, indicating that DIN was an essential factor controlling NCP in the SCS surface water. During our sampling, the Kuroshio intruded into the northeastern SCS in a loop pattern through the Luzon Strait, approximately halving the surface DIN concentration and reducing NCP by 36%. In addition, the VOC drove Vietnam coastal upwelled water to extend northeastward, causing an increase of 140% in the surface DIN concentration and an associated elevation of 160% in NCP in the northeastern SCS.

Brominated trihalamines in chlorinated seawaters: Quantification of tribromamine and identification of bromochloramines by Membrane Introduction Mass Spectrometry

During chlorination of seawater, the presence of bromide and ammonia alters the speciation of the oxidant and lead to the formation of chlorinated and brominated amines. This can affect the effectiveness of the disinfection treatment and the formation of disinfection by-products released to the environment. In this study, a Membrane Introduction Mass Spectrometry (MIMS) analytical method was developed to differentiate brominated trihalamines (i.e. tribromamine NBr3, dibromochloramine NBr2Cl and bromodichloramine NBrCl2) in synthetic and natural chlorinated seawater. A mass-to-charge ratio of m/z = 253 corresponding to the parent ion was used for the quantification of NBr3 in absence of organic matter and the signal of the fragment at m/z = 177 was chosen in presence of high concentration of organic matter. Limits of detection were 0.23 μM (49 μg Cl2/L) and 0.18 μM (38 μg Cl2/L) for m/z 253 and m/z 177, respectively. Both NBr2Cl and NBrCl2 were monitored in chlorinated seawaters with their respective parent ion at m/z = 207 and m/z = 163 but were not quantified. MIMS results also showed that reaction of brominated trihalamines with natural organic matter (NOM) was a minor pathway for 1–2 mg C/L compared to their auto-decomposition in natural or synthetic seawater. Overall, MIMS was able to unambiguously differentiate and monitor brominated trihalamines for the first time in chlorinated seawater, which was not possible by using UV measurement, titration and colorimetric methods.