Membrane Inlet Mass Spectrometry System Research Articles

Methodology for exposing avian embryos to quantified levels of airborne aromatic compounds associated with crude oil spills

Oil spills on birds and other organisms have focused primarily on direct effects of oil exposure through ingestion or direct body fouling. Little is known of indirect effects of airborne volatiles from spilled oil, especially on vulnerable developing embryos within the bird egg. Here a technique is described for exposing bird embryos in the egg to quantifiable amounts of airborne volatile toxicants from Deepwater Horizon crude oil. A novel membrane inlet mass spectrometry system was used to measure major classes of airborne oil-derived toxicants and correlate these exposures with biological endpoints. Exposure induced a reduction in platelet number and increase in osmolality of the blood of embryos of the chicken (Gallus gallus). Additionally, expression of cytochrome P4501A, a protein biomarker of oil exposure, occurred in renal, pulmonary, hepatic and vascular tissues. These data confirm that this system for generating and measuring airborne volatiles can be used for future in-depth analysis of the toxicity of volatile organic compounds in birds and potentially other terrestrial organisms.

Fast and sensitive method for detecting volatile species in liquids.

This paper presents a novel apparatus for extracting volatile species from liquids using a "sniffer-chip." By ultrafast transfer of the volatile species through a perforated and hydrophobic membrane into an inert carrier gas stream, the sniffer-chip is able to transport the species directly to a mass spectrometer through a narrow capillary without the use of differential pumping. This method inherits features from differential electrochemical mass spectrometry (DEMS) and membrane inlet mass spectrometry (MIMS), but brings the best of both worlds, i.e., the fast time-response of a DEMS system and the high sensitivity of a MIMS system. In this paper, the concept of the sniffer-chip is thoroughly explained and it is shown how it can be used to quantify hydrogen and oxygen evolution on a polycrystalline platinum thin film in situ at absolute faradaic currents down to ∼30 nA. To benchmark the capabilities of this method, a CO-stripping experiment is performed on a polycrystalline platinum thin film, illustrating how the sniffer-chip system is capable of making a quantitative in situ measurement of <1% of a monolayer of surface adsorbed CO being electrochemically stripped off an electrode at a potential scan-rate of 50 mV s(-1).

A membrane inlet mass spectrometry system for noble gases at natural abundances in gas and water samples

Noble gases dissolved in groundwater can reveal paleotemperatures, recharge conditions, and precise travel times. The collection and analysis of noble gas samples are cumbersome, involving noble gas purification, cryogenic separation and static mass spectrometry. A quicker and more efficient sample analysis method is required for introduced tracer studies and laboratory experiments. A Noble Gas Membrane Inlet Mass Spectrometry (NG-MIMS) system was developed to measure noble gases at natural abundances in gas and water samples. The NG-MIMS system consists of a membrane inlet, a dry-ice water trap, a carbon-dioxide trap, two getters, a gate valve, a turbomolecular pump and a quadrupole mass spectrometer equipped with an electron multiplier. Noble gases isotopes (4)He, (22)Ne, (38)Ar, (84)Kr and (132)Xe are measured every 10 s. The NG-MIMS system can reproduce measurements made on a traditional noble gas mass spectrometer system with precisions of 2%, 8%, 1%, 1% and 3% for He, Ne, Ar, Kr and Xe, respectively. Noble gas concentrations measured in an artificial recharge pond were used to monitor an introduced xenon tracer and to reconstruct temperature variations to within 2 °C. Additional experiments demonstrated the capability to measure noble gases in gas and in water samples, in real time. The NG-MIMS system is capable of providing analyses sufficiently accurate and precise for introduced noble gas tracers at managed aquifer recharge facilities, groundwater fingerprinting based on excess air and noble gas recharge temperature, and field and laboratory studies investigating ebullition and diffusive exchange.

Oil-in-Water Monitoring Using Membrane Inlet Mass Spectrometry

A membrane inlet mass spectrometry (MIMS) system has been used for detection and analysis of two types of North Sea crude oil. The system was installed on-field on the Flotta Oil Terminal (Orkney, UK). It consisted of a quadrupole mass spectrometer (QMS) connected to the capillary probe with a silicone-based membrane. The produced mass spectra and calibration plots from the MIMS instrument showed the capability to measure levels of individual hydrocarbons within crude oil in seawater. The generated mass spectra from the field tests also showed the ability to distinguish between different types of oil and to determine concentrations of toxic hydrocarbons in oil (e.g., benzene, toluene, and xylene (BTX)). The performance of the instrument at different temperatures of seawater and oil droplet sizes was also investigated. The results showed that the QMS-based MIMS system has a potential to complement existing oil-in-water (OiW) monitors by being able to detect different oil types and specific hydrocarbon concentrations with high accuracy, which are currently not supported in commercially available OiW monitors.

Online measurement of denitrification rates in aquifer samples by an approach coupling an automated sampling and calibration unit to a membrane inlet mass spectrometry system

Aquifers within agricultural catchments are characterised by high spatial heterogeneity of their denitrification potential. Therefore, simple but sophisticated methods for measuring denitrification rates within the groundwater are crucial for predicting and managing N-fluxes within these anthropogenic ecosystems. Here, a newly developed automated online (15)N-tracer system is presented for measuring (N(2)+N(2)O) production due to denitrification in aquifer samples. The system consists of a self-developed sampler which automatically supplies sample aliquots to a membrane-inlet mass spectrometer. The developed system has been evaluated by a (15)N-nitrate tracer incubation experiment using samples (sulphidic and non-sulphidic) from the aquifer of the Fuhrberger Feld in northern Germany. It is shown that the membrane-inlet mass spectrometry (MIMS) system successfully enabled nearly unattended measurement of (N(2)+N(2)O) production within a range of 10 to 3300 µg N L(-1) over 7 days of incubation. The automated online approach provided results in good agreement with simultaneous measurements obtained with the well-established offline approach using isotope ratio mass spectrometry (IRMS). In addition, three different (15)N-aided mathematical approaches have been evaluated for their suitability to analyse the MIMS raw data under the given experimental conditions. Two approaches, which rely on the measurement of (28)N(2), (29)N(2) and (30)N(2), exhibit the best reliability in the case of a clear (15) N enrichment of evolved denitrification gases. The third approach, which uses only the ratio of (29)N(2)/(28)N(2), overestimates the concentration of labelled denitrification products under these conditions. By contrast, at low (15)N enrichments and low fractions of denitrified gas, the latter approach is on a par with the other two approaches. Finally, it can be concluded that the newly developed system represents a comprehensive and simply applicable tool for the determination of denitrification in aquifers.

Design of a novel flat-plate photobioreactor system for green algal hydrogen production

Some green microalgae have the ability to harness sunlight to photosynthetically produce molecular hydrogen from water. This renewable, carbon-neutral process has the additional benefit of sequestering carbon dioxide and accumulating biomass during the algal growth phase. We document the details of a novel one-litre vertical flat-plate photobioreactor that has been designed to facilitate green algal hydrogen production at the laboratory scale. Coherent, non-heating illumination is provided by a panel of cool-white light-emitting diodes. The reactor body consists of two compartments constructed from transparent polymethyl methacrylate sheets. The primary compartment holds the algal culture, which is agitated by means of a recirculating gas-lift. The secondary compartment is used to control the temperature of the system and the wavelength of radiation. The reactor is fitted with probe sensors that monitor the pH, dissolved oxygen, temperature and optical thickness of the algal culture. A membrane-inlet mass spectrometry system has been developed and incorporated into the reactor for dissolved hydrogen measurement and collection. The reactor is hydrogen-tight, modular and fully autoclaveable.

Denitrification enzyme activity and potential of subsoils under grazed grasslands assayed by membrane inlet mass spectrometer

The importance of subsoil denitrification on the fate of agriculturally derived nitrate (NO 3) leached to groundwater is crucial for budgeting N in an ecosystem and for identifying areas where the risk of excess NO 3 is reduced. However, the high atmospheric background of di-nitrogen (N 2) causes difficulties in assessing denitrification enzyme activity (DEA) and denitrification potential (DP) in soils directly. Here, we apply Membrane Inlet Mass Spectrometry (MIMS) technique to investigate indirectly DEA and DP in soils by measuring N 2/Ar ratio changes in headspace water over soil. Soils were collected from 0–10, 15–25 and 60–70 cm depths of a grazed ryegrass and grass–clover. The samples were amended with helium-flushed deionized water containing ranges of NO 3 and carbon (glucose-C) and were incubated for six hours in the dark at 21 °C. The peaks for N 2/Ar ratio, declined with increasing soil depth, indicating a reduced substrate requirements to initiate DEA en-masse (15–30 mg NO 3-N alone or with 60–120 mg glucose-C, kg −1 soil). The dissolved N 2O concentrations were very small (0.004–0.269 μg N kg −1 soil) but responded well to the added N and C, showing a reduction in DEA with soil depth. In three separate studies, only subsoils were incubated for 3 days at 12 °C with 20–30 mg NO 3-N ± 40–60 mg glucose-C, kg −1 soil. Denitrification capacity (DC, NO 3 only treatment) was not statistically different to the control (no amendment) within a land use (0.03–0.05 vs. 0.07–0.22 mg N kg −1 soil d −1), the highest being in ryegrass subsoils receiving groundwater. The DP was significantly ( P < 0.0001) higher in subsoils under ryegrass than under grass–clover (0.50–0.71 vs. 1.15 mg N kg −1 soil d −1). The rates of DP (NO 3 + glucose-C) increased significantly ( P < 0.0001) in unsaturated and saturated subsoils (0.92 and 2.19 mg N kg −1 soil d −1, respectively) of grass–clover, due to the higher reductive state resulting from the 10 day pre-incubation. Available C accelerated denitrification in soils and superseded the temporary elevation in oxidative state due to NO 3 addition. The substrates load differences between the land uses regulated the degree of denitrification rates. Results suggest that both dissolved N 2O measured by gas chromatography and N 2/Ar ratio measured by MIMS to indirectly determine DEA, and the latter to quantify total DC/DP in soils can be used. However, interference of oxygen in the MIMS system should be considered if available C is added or is naturally elevated in soil or groundwater.

On‐line monitoring of the dynamics of trihalomethane concentrations in a warm public swimming pool using an unsupervised membrane inlet mass spectrometry system with off‐site real‐time surveillance

To study the long-term dynamics of trihalomethanes (THMs) in a warm (31-33 degrees C) public swimming pool, we built a robust membrane inlet mass spectrometer that could perform unsupervised, on-site monitoring of the concentration of these compounds with off-site, real-time surveillance. The instrument was installed in a technical room below the pool and operated continuously for more than a year practically only interrupted for filament replacements every 6-8 weeks. One to two days after a filament replacement, the instrument stabilized and kept its calibration until shortly before the next filament burnout. The on-line monitoring of THMs revealed a daily rhythm in the concentrations of chloroform and bromodichloromethane. They increased during the pool's closing hours and decreased during opening hours with the minimum concentration being approximately half of the maximum. Over the 1 year monitoring period, the variation in the maximum registered daily concentration was 30-100 microg/L for chloroform. The variation of bromodichloromethane was 5-10 microg/L, except during bursts of 1-2 days duration, where the concentration of bromodichloromethane could reach 100 microg/L. The burst in bromodichloromethane concentration was directly correlated with salt addition (sodium chloride) to the pool water for use in the pool's electrolytic in-line chlorination system. A correlation between THM removal from the pool water and the operation of a strong water jet system was also found.

Dissolved gas measurements in oceanic waters made by membrane inlet mass spectrometry

A method is presented for the shipboard analysis of dissolved gases (O2, CO2, Ar, N2, H2S, dimethylsulfide) in oceanic waters using membrane inlet mass spectrometry (MIMS). Gases are extracted from seawater across a semipermeable membrane into the ion source of the mass spectrometer. The method can be used to simultaneously measure both major and trace gases in seawater samples in near real-time. In the case of DMS, low nmol L−1 detection limits can be achieved without any concentration step. Multiple calibration and method comparison exercises conducted in the subarctic Pacific Ocean show that the MIMS method provides gas measurements that are consistent with those obtained by standard techniques, with precision of replicate samples ranging from less than 1% to approximately 5% coefficient of variation (CV). To illustrate the usefulness of the MIMS approach, depth profiles are presented for O2, CO2, N2, and DMS at various coastal and open ocean stations in the subarctic Pacific. In addition to these discrete gas measurements, the MIMS system has also been used to continuously monitor gas concentrations along underway transects. High frequency gas measurements of O2, CO2, and DMS made along two coastal transects reveal a high degree of spatial and temporal variability in gas concentrations, likely resulting from the interplay of various biological, chemical, and physical forcings. The underway MIMS data provide insight into the biogeochemical controls on gas cycling in dynamic marine waters.

Direct detection of large fat-soluble biomolecules in solution using membrane inlet mass spectrometry and desorption chemical ionization.

This paper presents the first membrane inlet mass spectrometry system capable of detecting large biomolecules, such as testosterone (M(r) 288), testosterone acetate (M(r) 330) and alpha-tocopherol (M(r) 430, vitamin E). The result was obtained using a home-made chemical ionization ion source with a thermostated tubular silicone membrane mounted right in the centre of a methane CI plasma. The liquid sample was flushed through the inside of the membrane for a period of 20-25 min, where the analyte diffused into the membrane. Following this trapping period the analyte was released from the membrane into the mass spectrometer by the combined action of heat radiation from the filament and charge transfer from the chemical ionization plasma. As a result of this stimulated desorption a good desorption peak was obtained as the analyte vaporized out of the membrane. Retinol (M(r) 286, vitamin A), cholecalciferol (M(r) 384, vitamin D3) and cholesterol (M(r) 386) were also detected. However, these compounds (all containing a long hydrocarbon chain and being aliphatic alcohols) did not give a protonated molecule. They gave a series of cluster ions with the dominant located 20 mass units below the molecular ion. The detection limits of the new desorption chemical ionization MIMS technique were at low or sub-micromolar concentrations (high ppb levels) and the reproducibility was within 20%, when the area of the desorption peak was used for quantitation.

Time- and concentration-dependent relative peak intensities observed in electron impact membrane inlet mass spectra

This paper demonstrates that membrane inlet mass spectrometry (MIMS) experiments in some cases can result in electron impact mass spectra where the relative peak intensities change both with time and concentration of the sample. The phenomenon was observed both for phenoxyacetic acid (POAA), a highly polar compound with low volatility, and for the highly volatile chloroethylenes vinyl chloride (VC), 1,1- and 1,2-dichloroethylene (DCE) and trichlororethylene (TCE), exemplified here by VC. Following step changes in concentration some of the fragments were observed to have transient patterns deviating from the molecular ion and from most of the fragment ions. Moreover, the relative peak intensities of these fragment ions at steady state were observed to depend on sample concentration. The unusual behaviour of the ions could be explained by a model for the MIMS system, which takes into account the possibility of a surface-catalysed decomposition of the primary molecules (POAA and VC) inside the vacuum system. In the POAA experiments the response patterns for m/ z 94 deviated from the other major ions and it was assumed that POAA dissociated into phenol by interaction with the surfaces. In the VC experiments the masses and the isotope patterns for the deviating ions indicate that HCl and Cl 2 were produced. On the basis of the model of molecule/surface interactions in vacuum systems, we predict that surface-catalysed dissociation of labile molecules can distort both MIMS transients and spectra, whenever the analyte flow into the vacuum system is comparable to the rate of dissociation of analytes. This condition will typically be fulfilled with signals close to the detection limit.