Search

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.

The 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.A 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.An 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.We 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.

Beer is a complex mix of more than 7700 compounds, around 800 of which are volatile. While GC-MS has been actively employed in the analysis of the volatome of beer, this method is challenged by the complex nature of the sample. Herein, we explored the possible of using membrane-inlet mass spectrometry (MIMS) coupled to KNIME to characterize local Danish beers. KNIME stands for Konstanz Information Miner and is a free open-source data processing software which comes with several prebuilt nodes, that, when organized, result in data processing workflows allowing swift analysis of data with outputs that can be visualized in the desired format. KNIME has been shown to be promising in automation of large datasets and requires very little computing power. In fact, most of the computations can be carried out on a regular PC. Herein, we have utilized a KNIME workflow for data visualization of MIMS data to understand the global volatome of beers. Feature identification was not possible as of now but with a combination of MIMS and a KNIME workflow, we were able to distinguish beers from different micro-breweries located in Denmark, laying the foundation for the use of MIMS in future analysis of the beer volatome.

A Membrane Introduction Mass Spectrometry (MIMS) method was developed to differentiate and quantify the different chlorinated and brominated-amines, present in drinking water during chloramination. The representative mass to charge ratios (m/z) of 53, 85, 97, 175 and 131 corresponding to the mass of the parent compounds were selected to monitor NH2Cl, NHCl2, NH2Br, NHBr2 and NHBrCl and the detection limits were found to be 0.034, 0.034, 0.10, 0.12 and 0.36 mg/L as Cl2, respectively. NHCl2, NHBr2 and NHBrCl fragments interfere with the analysis/quantification of NH2Cl and NH2Br via protonation reactions at hot metal surfaces inside the mass spectrometer. To accurately quantify NH2Cl or NH2Br in mixtures of NH2Cl/NHCl2 or NH2Br/NHBr2, the interference from NHCl2 or NHBr2 was subtracted to the signal of the parent compound. If NHBrCl is present, NH2Br and NH2Cl cannot be accurately quantified since the interference from the NHBrCl fragment cannot be distinguished from the signal of the parent compound. Under drinking water conditions, the interference from NHBrCl on NH2Cl was negligible. The different halamines were monitored and quantified for the first time in two surface waters and one seawater that were chloraminated to mimic a realistic disinfection scenario.

The reactivity of [Fe III(tpena)] 2+ (tpena=N,N,N′-tris(2-pyridylmethyl)ethylenediamine-N′-acetate) as a catalyst for oxidation reactions depends on its ratio to the terminal oxidant H 2O 2 and presence or absence of sacrificial substrates. The outcome can be switched between: 1) catalysed H 2O 2 disproportionation, 2) selective catalytic oxidation of methanol or benzyl alcohol to the corresponding aldehyde, or 3) oxidative decomposition of the tpena ligand. A common mechanism is proposed involving homolytic O−O cleavage in the detected transient purple low-spin (S=1/2) [(tpenaH)Fe IIIO−OH] 2+. The resultant iron(IV) oxo and hydroxyl radical both participate in controllable hydrogen-atom transfer (HAT) reactions. Consistent with the presence of a weaker σ-donor carboxylate ligand, the most pronounced difference in the spectroscopic properties of [Fe(OOH)(tpenaH)] 2+ and its conjugate base, [Fe(OO)(tpenaH)] +, compared to non-heme iron(III) peroxide analogues supported by neutral multidentate N-only ligands, are slightly blue-shifted maxima of the visible absorption band assigned to ligand-to-metal charge-transfer (LMCT) transitions and, corroborating this, lower Fe III/Fe II redox potentials for the pro-catalysts.

Rationale Inhaled nanoparticles may cause adverse effects due to inactivation of lung surfactants. We have studied how three different nanoparticles interact with dipalmitoyl-phosphatidylcholine (DPPC), the main component in lung surfactant. Methods DPPC in solution was mixed with a suspension of nanoparticles, both in organic solvent, and allowed to interact for 40 min under conditions partly resembling the alveolar lining. Nanoparticles were isolated by centrifugation, washed, and re-suspended in ethanol/water 1:1 (v/v). The resulting solution was analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) using dihydroxybenzoic acid as matrix. Results The developed methodology was successfully applied for quantitative detection of phospholipid lung surfactant bound to three different types of nanoparticles. Titanium dioxide nanoparticles had a strong affinity for binding of lipid lung surfactant in contrast to pristine and methylated silica nanoparticles. When the concentration of lipid surfactant was raised in the reaction mixture, the titanium dioxide nanoparticles showed an apparently non-linear binding process. Conclusions This work demonstrates that MALDI-TOFMS can be used for direct determination of the binding of surfactant lipids to nanoparticles and represents an important initial step towards a simple and quantitative in vitro method for assessment of interactions of nanoparticles with lung surfactants. Copyright © 2015 John Wiley & Sons, Ltd.

Hitherto analysis of chemicals in the field using mass spectrometry (MS) has been limited to analysis of non-polar and thermally stabile organic compounds using either a direct gas leak or a membrane inlet as MS interface. Recently, Professor R. Graham Cooks’ group demonstrated that miniature mass spectrometers operating at elevated pressures (>0.13 Pa (1 · 10−3 Torr)) can be combined with electrospray ionization (ESI) for analysis of polar as well as thermally labile organic compounds. We present a simple miniaturized ESI unit for analysis of small liquid samples using miniature mass spectrometry. The ESI unit operates without pumps and supplementary sheath gases, which makes it very simple to handle in the field. 20–30 µL of sample solution is simply dropped into a small cavity in the ESI unit, where after the spray is initiated by applying high voltage to it. The miniaturized ESI unit was tested in combination with a miniature mass spectrometer (the Mini 10 developed by Professor R. Graham Cooks, Purd...

RATIONALE Screening of drugs from urine samples can be non-selective or laborous, using either immunological, gas chromatography/mass spectrometry (GC/MS) or liquid chromatography (LC)/MS methods. Therefore, a rapid screening method for selected drugs in urine sample was developed in a proof-of-principle manner, utilizing simple and fast techniques for both sample treatment and sample analysis. METHODS Sample treament of spiked urine samples was performed with microextraction by packed sorbent (MEPS). Five different sorbent materials (C2, C8, C18, M1 (cation exchanger), and Sil (pure silica)) were tested for the MEPS. The sample analysis was performed using a circular microchip with 60 micropillar electrospray ionization (μPESI) tips combined with a mass spectrometer (either a triple-quadrupole or ion-trap mass spectrometer) without any chromatographic step. RESULTS The sample treatment/analysis setup was tested using three drug compounds at a concentration of 1 μM. We found that the C2, C8 and C18 sorbents in combination with 96% alkaline methanol as an eluent worked the best. All compounds were easily detected and identified by MS/MS in spiked urine samples. The whole qualitative analytical procedure was rapid as the sample treatment together with the MS analysis took about 5 min per sample. CONCLUSIONS A rapid screening method for selected drugs from urine samples was developed, providing adequate selectivity and sensitivity, as well as a short total analysis cycle time. This new method can provide a new alternative for screening purposes, as both the extraction and analysis steps could be totally automatized. Copyright © 2011 John Wiley & Sons, Ltd.

We present a very simple electrospray unit, a capillary spray cell, for easy analysis of small (10–50 μL) sample aliquots. The sample, e.g., an unfiltered extract, is injected to a small sample cell, made of alumina and containing a short fused silica capillary mounted in its side. By the application of a 5 kV potential between the sample cell and the entrance orifice of a mass spectrometer with an atmospheric pressure interface, the sample is dragged out of the cell at a rate of a few μL/min and an electrospray is generated at the tip of the silica capillary. The capillary spray cell benefits from a high internal diameter (up to 250 μm) and very easy and inexpensive replacement of the capillary, which makes the sprayer well suited for analysis of unfiltered extracts. We demonstrate the direct analysis of extracts from plants and insects. In quantitative measurements using internal standards, a relatively high sensitivity (low ng/mL) is obtained together with good linearity ( R 2 = 0.998) in the range of 10–1000 ng/mL. The capillary spray cell is also suited for use with field portable mass spectrometers, since no syringe pump or nebulizer gas is needed. Furthermore, the capillary spray cell is easily manufactured by most mechanical workshops.

The progress of an on-surface polymerization process involving alkyl and perfluoroalkyl silanes and siloxanes was monitored in real-time via easy ambient sonic spray ionization mass spectrometry (EASI-MS). When sprayed on surfaces, the organosilicon compounds present in commercially available nanofilm products (NFPs) react by condensation to form a polymeric coating. A NFP for coating of floor materials (NFP-1) and a second NFP for coating tiles and ceramics (NFP-2) were applied to glass, filter paper or cotton surfaces and the progress of the polymerization was monitored by slowly scanning the surface. Via EASI(+)-MS monitoring, significant changes in the composition of hydrolysates and condensates of 1H,1H,2H,2H-perfluorooctyl triisopropoxysilane (NFP-1) and hexadecyl triethoxysilane (NFP-2) were observed over time. The abundances of the hydrolyzed species decreased compared with those of the non-hydrolysed species for both NFP-1 and NFP-2 and the heavier oligomers became relatively more abundant over a period of 15-20 min. A similar tendency favouring the heavier oligomers was observed via EASI(-)-MS. This work illustrates the potential of ambient mass spectrometry for the direct monitoring of polymerization reactions on surfaces.

The use of nanofilm spray products (NFPs) has been associated with a number of severe cases of airway injuries; however, the causative agents are unknown. To identify possible causative agents, 10 products from three different suppliers have been analysed using two mass spectrometric methods: (1) ESI-MS and ESI-MS/MS; (2) GC–MS and GC–MS/MS. The 10 products could be classified into three groups (NFPs 1–3). NFP 1 and NFP 2 contained hydrolysates and condensates of the organo-functionalized silanes 1H,1H,2H,2H-perfluorooctyl triisopropoxysilane and hexadecyl triethoxysilane, respectively. NFP 3 contained non-ionic detergents and abrasive as active ingredients. To verify the fluorosilane solution in NFP 1, a synthetic NFP 1 was prepared by hydrolysis and condensation of 1H,1H,2H,2H-perfluorooctyl triethoxysilane. After about 1 month in acidic 2-propanol substitution of the ethoxy groups with isopropoxy groups had taken place and all silane was converted to disiloxanes, trisiloxanes and tetrasiloxanes.

This paper demonstrates that the active ingredient in many common tablets (anti-depressives, pain relievers, epileptic medicine and anti-histamines) can be recognized directly and without any pretreatment using hot cell membrane inlet mass spectrometry (hot cell MIMS). The tablets were simply placed in a sample vial and then dumped into a small oven heated to approximately 200 °C (the hot cell). The hot cell was interfaced directly to the ion source of an electron ionization mass spectrometer (EI-MS) via a polymer membrane. A few minutes thereafter an EI-MS spectrum of the chemicals desorped from the sample was recorded. Even though the tablets contained a significant number of chemicals (fillers) and often a polymer coating in addition to the active ingredients simple EI-MS spectra were recorded, wherefrom the active ingredient could be recognized by comparison with a standard EI-MS database. Of the eight tablets tested only one tablet, Bio-Melatonin (sleeping disorder), did not give a recognizable EI-MS spectrum. Over a period of 6 months the spectra recorded from the tablets did not change and the active ingredients were always recognized. The reproducibility of signal intensities from characteristic ions following successive injections was high (≈7%) for tablets without surface coating, whereas it varied up to 25% for tablets with a surface coating. Since hot cell MIMS is fully compatible with field portable instruments our results open the possibility of creating a small portable mass spectrometer for use in paramedical vehicles for immediate, on-site identification of medications found near intoxicated patients.

To study the long-term dynamics of trihalomethanes (THMs) in a warm (31–33°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 µg/L for chloroform. The variation of bromodichloromethane was 5–10 µg/L, except during bursts of 1–2 days duration, where the concentration of bromodichloromethane could reach 100 µg/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. Copyright © 2009 John Wiley & Sons, Ltd.

Here, we present emission data on VOCs and particles emitted during simulated use of four commercial nanofilm spray products (NFPs) used for making easy-to-clean or self-cleaning surfaces on floors, ceramic tiles, and windows. The aim was to characterize the emitted VOCs and to provide specific source strength data for VOCs and particles released to the airduring use of the products. Containers with NFP were mounted on a spray-stand inside a closed stainless steel chamber with no air exchange. NFPs were sprayed in amounts corresponding to 1 m2 surface toward a target plate at a distance of 35 cm. Released VOCs were measured by a combination of air sampling on Tenax TA adsorbent followed by thermal desorption GC/MS and GC/FID analysis and real time measurements using a miniature membrane inlet mass spectrometer. Particles were measured using a fast mobility particle sizer and an aerosol particle sizer. A number of VOCs were identified, including small alcohols, ketones and ethers, chlorinated acetones, a perfluorinated silane, limonene, and cyclic siloxanes. The number of generated particles was on the order of 3 x 10(8) to 2 x 10(10) particles/m3 per g sprayed NFP and were dominated by nanosize particles.

This paper presents the first membrane inlet method that can be used together with field portable mass spectrometers for the analysis of semivolatile pharmaceuticals (pethidine, benzophenone, and cocaine) and environmental pollutants (terbutryne and butylated hydroxyl toluene (BHT)) dissolved in organic micro extracts. A microliter of the organic extract is simply injected into a closed hot cell membrane inlet (hc-MIMS), and an electron ionization mass spectrum of the vaporized semivolatile sample molecules can be recorded shortly thereafter. Detection limits at low picomole quantities or low/sub ng/microL concentrations in the extract are demonstrated for solutes in methanol, ethanol, acetone, and toluene. A linear correlation between analyte concentration and signal was found in the range of 1-100 ng/microL, and the relative standard deviation (RSD) was approximately 10%. As a practical example we demonstrate the detection of cocaine in extracts from dried coca leaves. The analysis of organic micro extracts using hc-MIMS represents a considerable extension of the type and complexity of analytes that can be measured using a field portable MIMS system, since it does not require special and field tedious modifications to the standard MIMS system.

We demonstrate that solid materials can be screened directly and without any pretreatment for their potential liberation of chemicals into the surroundings using a hot (150-250 degrees C) sample cell membrane inlet mass spectrometer with electron ionization. Three very different types of solids were tested: polymers (in this context regarded as a solid), tea leaves and pesticide-contaminated soil. From the polymers phthalates and other additives were liberated; from the tea leaves flavor additives and caffeine were liberated; and from the contaminated soil degradation products of 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) were liberated. In all cases we detected characteristic compounds directly from the untreated sample with an analytical turnover of 8-10 samples per hour. Improved selectivity of compounds penetrating the membrane was achieved either by operating the hot cell at different temperatures or by using variations in the time trend of individual ions following insertion of a piece of the solid material into the hot cell.

This historic review of membrane inlet (or membrane introduction) mass spectrometry, MIMS, covers the scientific development of MIMS from initially a method for the analysis of atmospheric gases dissolved in water to a well-established field-portable technique for the analysis of volatile and semi-volatile organic compounds from solid, liquid, and gaseous samples without sample pretreatment. The path to the modern field-portable instruments went through three major research areas: in vivo probes for the analysis of blood gases (1960–1980), on-line monitoring of fermentations (1975–1995), and detection of contaminants in environmental samples (1990 and onwards).

Quantification of a chemical concentration in a pollution plume using a moving membrane-based sensor can be problematic. In many cases, the sensor passes through the plume faster than the time necessary to reach a steady-state signal, which is often used for quantification. Since the exposure time is typically not known, quantification based upon the flow injection analysis principle is also impractical. In this paper, we present a two-dimensional calibration model, exemplified by membrane inlet mass spectrometry, in which the concentration of a chemical can be determined using a simple algorithm. The concentration is given by a calibration factor, which is multiplied by the peak height and divided by the value of a polynomial, calculated at a normalized peak width. The model is demonstrated to give good quantitative estimates of concentrations for exposure times down to approximately 1/10 of the time it takes to reach steady-state diffusion through the membrane. Although the model is demonstrated using membrane inlet mass spectrometry and detection of volatile organic chemicals, it should be generally applicable to many membrane-covered sensors.

A miniaturized membrane inlet mass spectrometer (mini-MIMS; total weight 10 kg everything included) was equipped with a small sample cell using a flat sheet silicone membrane mounted close to the ionizing region of a multipole mass spectrometer. Spiked sand samples were placed in small stainless steel vials and dropped into the heated sample cell (>150°C). A hole in the vial in front of the membrane and above the sand made it possible for the polyaromatic hydrocarbon (PAH) residuals to penetrate the membrane and enter the mass spectrometer as they evaporated from the sample. Using this simple setup we were able to quantitatively (≈10% relative standard deviation (RSD)) detect PAHs with up to five aromatic rings and with detection limits in the low parts-per-million (ppm) range. The vial system solves one of the major difficulties in analysis of larger PAHs using a MIMS. Normally, analysis of PAHs with more than two rings is hampered by a long memory effect due to the sticking of the PAHs to the inlet system, the membrane and surfaces in the vacuum system. By removing the vial from the sample cell within 2 min, we were able to analyze samples at 5–10 min intervals. The preliminary laboratory experiments presented here show much promise with respect to the development of a hand held (

Monitoring CO2 production in systems, where pH is changing with time is hampered by the chemical behavior and pH-dependent volatility of this compound. In this article, we present the first method where the concentration and production rate of dissolved CO2 can be monitored directly, continuously, and quantitatively under conditions where pH changes rapidly (≈2 units in 15 min). The method corrects membrane inlet mass spectrometry (MIMS) measurements of CO2 for pH dependency using on-line pH analysis and an experimentally established calibration model. It is valid within the pH range of 3.5 to 7, despite pH-dependent calibration constants that vary in a non-linear fashion with more than a factor of 3 in this interval. The method made it possible to determine the carbon dioxide production during Lactococcus lactis fermentations, where pH drops up to 3 units during the fermentation. The accuracy was approximately 5%. We used the method to investigate the effect of initial extracellular pH on carbon dioxide production during anarobic glucose fermentation by non-growing Lactocoocus lactis and demonstrated that the carbon dioxide production rate increases considerably, when the initial pH was increased from 6 to 6.8. © 2005 Wiley Periodicals, Inc.

Using fluorescence spectroscopy we detected long trains of macroscopic oscillations in the glycolytic pathway, in whole cell suspensions of Saccharomyces cerevisiae, without addition of cyanide. Such oscillations may be induced if argon or another inert gas is bubbled through the yeast cell suspension. This supports that the synchronizing agent is a volatile compound secreted by the yeast cells, e.g. CO2 and/or acetaldehyde. Our results show that the rate of acetaldehyde removal is not a crucial parameter to the synchronization of the yeast cells. The sample cell was connected to a membrane inlet mass spectrometer (MIMS) for online determination of extracellular non-polar compounds. Oscillations in the secretion of CO2 were detected using the MIMS.

Aims: Staphylococcus xylosus is an important starter culture in the production of flavours from the branched-chain amino acids leucine, valine and isoleucine in fermented meat products. The sensorially most important flavour compounds are the branched-chain aldehydes and acids derived from the corresponding amino acids and this paper intends to perspectivate these flavour compounds in the context of leucine metabolism. Methods and Results: GC and GC/MS analysis combined with stable isotope labelling was used to study leucine catabolism. This amino acid together with valine and isoleucine was used as precursors for the production of branched-chain fatty acids for cell membrane biosynthesis during growth. A 83·3% of the cellular fatty acids were branched. The dominating fatty acid was anteiso-C15:0 that constituted 55% of the fatty acids. A pyridoxal 5′-phosphate and α-ketoacid dependent reaction catalysed the deamination of leucine, valine and isoleucine into their corresponding α-ketoacids. As α-amino group acceptor α-keto-β-methylvaleric acid and α-ketoisovaleric acid was much more efficient than α-ketoglutarate. The sensorially and metabolic key intermediate on the pathway to the branched-chain fatty acids, 3-methylbutanoic acid was produced from leucine at the onset of the stationary growth phase and then, when the growth medium became scarce in leucine, from the oxidation of glucose via pyruvate. Conclusions: This paper demonstrates that the sensorially important branched-chain aldehydes and acids are important intermediates on the metabolic route leading to branched-chain fatty acids for cell membrane biosynthesis. Significance and Impact of the Study: The metabolic information obtained is extremely important in connection with a future biotechnological design of starter cultures for production of fermented meat.

A small fermentor (55 mL) was directly interfaced to a membrane inlet mass spectrometer for continuous on-line monitoring of oxygen and volatile metabolites during batch fermentations of the starter culture Staphylococcus xylosus. Using this technique, we were able to correlate production of the very important flavor compounds 2-methylbutanal, 3-methylbutanal, and 2-methylpropanal with various growth conditions. We found that the aldehydes were present in the culture broth only as transient metabolites. They were produced in the exponential growth phase, reached a maximum concentration when the culture became anaerobic, and then they rapidly disappeared from the culture medium. This general pattern was observed for three different strains of S. xylosus and S. carnosus. Small amounts of inoculum or increased exposure to oxygen were found to favor production of the aldehydes as a result of a longer aerobic growth period. Growing S. xylosus under conditions resembling those in a fermented sausage revealed that NaCl (5%) increased aldehyde production considerably, whereas KNO3 (0.03%) or NaNO2 (0.03%) had little effect. A lowering of pH from 7.2 to 6.0 reduced cell density, but had a minor affect on aldehyde production. © 2004 Wiley Periodicals, Inc.

A complex mixture of methyl-branched alkyl-substituted pyrazines was found in the growth medium of the polymyxin-producing bacterium Paenibacillus polymyxa, and of these, seven are new natural compounds. A total of 19 pyrazine metabolites were identified. The dominant metabolite was 2,5-diisopropylpyrazine as identified using a combination of high-resolution mass spectrometry, (1)H- and (13)C-nuclear magnetic resonance, gas chromatography-mass spectrometry as well as co-elution with an authentic standard. Its biosynthesis was correlated with growth and production was strongly stimulated by valine supplementation. The other pyrazine metabolites, all related pyrazines with either one, two or three alkyl substituents, were identified by means of their mass spectral data and/or co-elution with authentic standards.

The metabolite production of the gram positive bacterium Staphylococcus xylosus when cultivated in a defined medium containing 18 amino acids, 6 vitamins and 2 purines was characterised. Several compounds not previously reported as metabolites of this organism were identified including 2,5-methylpyrazine, 2-phenylethylacetate, 2-methyltetrahydrothiophen-3-one, 3-(methylthio)-propanoic acid and 3-(methylthio)-propanal. The organoleptic metabolites derived from branched-chain amino acid catabolism; 2-methylpropanal from valine, 2-methylbutanal from isoleucine and 3-methylbutanal from leucine were detected at levels ranging from 0.4 to 2.0 μM. The concentrations of the corresponding carboxy acids were 963, 858 and 1486 μM respectively. We demonstrated that α-ketoisocaproic acid was biotransformed to 3-methylbutanal which immediately was oxidised into 3-methylbutanoic acid. Kinetic studies of the conversion of 2-methylpropanal, 2-methylbutanal and 3-methylbutanal into their corresponding acids were also performed and we found K m values of 0.8, 0.9 and 1.6 μM, and V max values of 9.4, 7.1 and 5.9 μmol/min/10 12 CFU, respectively.

This paper describes the use of desorption chemical ionisation membrane inlet mass spectrometry (DCI-MIMS) for the detection of a broad range of common contaminants in water. In addition, we discuss the advantages/disadvantages of two different types of chemical ionisation reagent gases, i-butene (a Broensted acid reagent) and argon (a charge exchange reagent). We found that polyaromatic hydrocarbons was detectable at ppt levels, the estrogenic compounds diethyl phthalate and octylphenol at high ppt levels, steroid hormones at ppb levels, hydrophobic pesticides at low ppb levels, whereas hydrophilic pesticides and bisphenol A were not detectable at all. With the exception of the polyaromatic hydrocarbons and pentachlorophenol, none of the reported compounds have to our knowledge been detected previously by other MIMS systems. In most cases the Broensted acid reagent gave characteristic ions at high mass/charge ratio, whereas the charge exchange reagent gave less characteristic ions at low m/z ratio. However, the sensitivity was generally not as good with the Broensted acid reagent as with the charge exchange reagent, since the Broensted acid reagent, i-butene, gave a large chemical background. Copyright © 2001 John Wiley & Sons, Ltd.

Membrane inlet mass spectrometry has been used for the characterization of halogenated organic compounds produced by the fungus Bjerkandera adusta. Using this technique we obtained electron impact-, chemical ionization-, electron capture negative chemical ionization-mass spectra and tandem mass spectra directly from the growth medium. Through this direct analysis of the samples we identified novel bioconversion products and confirmed recently published data on the production of both chlorinated and brominated methoxybenzaldehyde metabolites. Growth profiles of the culture grown on a defined medium showed that the production of secondary metabolites starts after approximately 6 days and reaches maximal concentrations of 25-250 muM after 15-20 days. Although delayed, the production of secondary metabolites paralleled a depletion of glucose from the medium and stopped shortly after all glucose had been consumed. Experiments in which fluoro- and bromo-labeled 4-methoxybenzaldehydes were added to the medium at day 8 showed biotransformation of these compounds into chloro-3-fluoro-4-methoxy-benzaldehyde and chloro-3-bromo-4-methoxybenzaldehyde, respectively. No dichlorinated products were observed, suggesting that halogenation takes place only at the meta position on the 4-methoxybenzaldehydes. These experiments are the first to bring direct evidence of a halogenation mechanism, where the enzymatic attack takes place directly on the 4-methoxybenzaldehyde intermediates. (c) John Wiley & Sons, Inc.

Ambient air and soil air of spruce forest, beech forest and grassland from Zealand, Denmark, were investigated for volatile chlorinated compounds by adsorbent tube sampling, thermodesorption, cryo-trapping and analysis by high-resolution gas chromatography with electron capture detection. The mean concentration of chloroform in the top soil–air was in the range of 0.4–2.3 ng l−1. Compared to ambient air, the chloroform concentration in the topsoil was 6.7, 4.3 and 4.6 times higher for spruce forest, beech forest and grassland, respectively. For tetrachloromethane, 1,1,1-trichloroethane, trichloroethene and tetrachloroethene, the concentrations were in the same order of magnitude (0.04–1.2 ng l−1). However, the concentration ratios between soil air and ambient air were close to unity. Release studies in the topsoil of the spruce forest showed an increase of the chloroform concentration of approximately 4 times the initial soil air concentration after 38 h, while the concentrations of the other volatile chlorinated compounds investigated remained fairly constant. The observed chloroform concentration profiles and release rates may indicate a biogenic formation of chloroform in the upper soil layer of spruce forests, whereas an anthropogenic origin is suggested for the other chlorinated compounds investigated. From the release study and concentration gradient measurements in the spruce forest soil, chloroform release to the atmosphere was calculated for northern temperate regions. The release was in the range of the annual anthropogenic chloroform emissions, and, therefore, the terrestrial environment can be considered as an important contributor to the atmospheric chloroform input.

We present a novel technique for analyzing volatile organic compounds in air samples using a solid adsorbent together with temperature-programmed desorption and subsequent detection by membrane inlet mass spectrometry (TPD-MIMS). The new system has the advantage of a fast separation of compounds prior to the detection by MIMS. The gaseous sample is simply adsorbed on the adsorbent, which is then rapidly heated from 30 °C to 250 °C at a rate of 50 °C/min. Trapped organic compounds are released from the adsorbent into a helium stream at different temperatures depending on the strength of the interaction between the individual compound and the adsorbent. The helium stream carries the desorbed compounds to a membrane inlet (90 °C) equipped with a thin (25 μm) silicone membrane. The thin membrane and the high temperature of the membrane inlet allows most volatile compounds to diffuse through the membrane into the mass spectrometer in a few seconds. In this fashion we could completely separate many similar volatile compounds, for example toluene from xylene and trichloroethene from tetrachloroethene. Typical detection limits were at low or sub-nanogram levels, the dynamic range was 3 orders of magnitude, and the analysis time for a mixture was about 3–4 minutes. © 1998 John Wiley & Sons, Ltd.

Fluoro-labelled substrates and membrane inlet mass spectrometry (MIMS) was used to test the bioconversion potential of the white-rot fungus Bjerkandera adusta with respect to a production of novel halogenated aromatic compounds. The presence of a fluorine atom on the aromatic ring of possible precursors to the well-known metabolites, 3-chloro-4-methoxybenzaldehyde and 3,5-dichloro-4-methoxybenzaldehyde, did not influence the metabolism and they all gave mixed chloro-fluoro-methoxybenzaldehydes; however, we were unable to produce any new chlorinated compounds. Neither supplementation of anisole, benzaldehyde, veratryl alcohol, the naphthalene analogs nor methyl-substituted benzaldehydes resulted in a production of detectable amounts of the corresponding chlorinated products. Apparently, only hydroxybenzaldehydes and/or methoxybenzaldehydes are chlorinated by the halogenating system. Experiments where an aromatic alcohol, aldehyde, or the analog acid was supplemented gave qualitatively and quantitatively similar membrane inlet mass spectra suggesting that oxidases and reductases maintain a stoichiometric ratio between these compounds. Several cases of hydroxylation and/or methoxylation of the substrates were also observed.

Classification of different cola drinks by membrane inlet mass spectrometry (MIMS) combined with different statistical computing methods is demonstrated. The spectra of cola drinks were measured directly using a single quadrupole mass spectrometer with a hollow fiber membrane inlet in standard MIMS and trap‐and‐release MIMS modes, and the spectra obtained were analyzed by principal component analysis and the mean pairwise difference method, and classified via the k‐NN classifier. The multivariate calculations showed that cola drinks from different manufacturers can easily be differentiated from one another although the spectra of all drinks are usually very alike with minor differences in the abundances of major ion peaks in the range m/z 50–199. The classification of drinks is rapid as a spectrum of one sample can be obtained in a few minutes.

This work focuses on the kinetics of cis -1,2-dichloro-ethylene ( c -DCE) biodegradation at very low concentrations (μg/l range) in an aerobic fixed-film reactor inoculated with a mixed culture of methane-oxidizing bacteria. Analysis of dissolved components (oxygen, methane, c -DCE) were performed by membrane-inlet mass-spectrometry allowing an on-line control of the reactor performance. The c -DCE degradation rate constant k x K s ranged from from 0.1 to 5.5 × 10 −2 m 3 d −1 g −1 x , depending on the c -DCE concentration. However, this degradation rate was underestimated because the amount of active biomass in the biofilm was small (15% to 20% of the total biofilm dry weight). Toxicity effects were observed when the c -DCE initial concentration was above 100 μg/l, leading to a decrease of the c -DCE and methane removal rate. Analysis showed the formation of an intermediate compound subsequent to the c -DCE degradation. Preliminary analysis suggested that it was c -DCE-epoxide. This degradation product or its metabolites seem to be the cause of the deactivation of the cells. However, the toxic effect could be counterbalanced, and the c -DCE degradation rate could be partly sustained if methane was supplied continuously in the reactor so that inactivated cells were replaced. These results are of practical interest for groundwater restoration or for waterworks since concentrations generally encountered in contaminated aquifers are in the μg/l range.

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.

A membrane inlet ion mobility spectrometric method was developed for on-line measurement of ethanol concentration in beer and in yeast fermentation. Main parts of the measurement system are an ion mobility spectrometer, M90, and a custom built membrane inlet. The M90 ion mobility spectrometer is unique in the sense that positive and negative ions are simultaneously measured at 6 different detection channels, 3 for positive ions and 3 for negative ions. The custom built membrane inlet utilized a microporous polypropylene membrane for sample introduction into the M90 instrument. The developed measurement system allowed analysis of ethanol at 0.05% ( v v ) levels, clearly sufficient for the applications reported here. Good signal linearity was observed at positive ion channels 1 and 3 in ethanol concentration range 0.2−10% ( v v ), calculated correlation coefficients were 0.989 and 0.999, respectively. Agreement between the ethanol concentration measured by membrane inlet ion mobility spectrometry and the values declared on the beer bottle labels was good. Reproducibility of signals of the detection channels which gave the best response for ethanol was excellent in ethanol concentration measurement of beer samples, coefficient of variation was 1% for all these channels. Membrane inlet ion mobility spectrometry was also shown to be capable of on-line ethanol measurement, confirmed by membrane inlet mass spectrometry, during yeast fermentations.

A novel procedure to perform a membrane-inlet mass spectrometry experiment is presented, which allows semi-volatile organic compounds to be preconcentrated inside the membrane, before they are thermally released into the ion source. The method uses a standard membrane inlet with a tubular silicone membrane passing straight through the ion source of the mass spectrometer. A long slit in the ion source parallel to the membrane allows electrons from the filament to continuously bombard the membrane surface. The membrane is kept cold by a continuous flow of water or sample solution passing through the inlet. However, during a short interruption of the flow, the membrane is rapidly heated by the electron bombardment and organic compounds dissolved in the membrane are thermally released into the ion source. In this fashion a desorption peak is obtained. Using the areas of the desorption peaks, we have been able to detect semi-volatile, hydrophobic organic compounds (boiling points above 200 °C) in aqueous solution at low and sub parts-per-billion levels. In general, the detection limits were 10–100 times lower than previously published results, where membrane-inlet mass spectrometry has been used for the detection of the same compounds. Good linearity over 3 orders of magnitude was obtained and the standard deviation was 5%.

A sampling system for on-line monitoring of organic compounds of low volatility in complex fermentation media uses membrane inlet mass spectrometry (MIMS). A Syringe pump draws a continuous flow of microfiltered broth from the reactor and circulates it after acidification through a membrane inlet, in which a membrane is the only interface between the sample and the high vacuum of a mass spectrometer. All operations run automatically, i.e., sampling, acidification measurement, and calibration. The on-stream acidification enables MIMS monitoring of carboxylic acids, as they must be undissociated in order to pass the hydrophobic membrane. The performance of the monitoring system was tested by measurements of standard solutions of phenoxyacetic acid (POAA, the sie chain precursor of penicillin-V) as well as on POAA during 200 h penicillin-V fermentation. During the entire fermentation POAA was monitored n low millimolar concentrations with high accuracy and fast response to step changes in POAA concentration. Tandem mass spectrometry (MS/MS) allowed direct identification of peaks in the mass spectrum of the broth that were not accounted for by POAA. These peaks were identified as SO2 and SCO. © 1994 John Wiley & Sons, Inc.

Three different and recently developed desorption ionization techniques, transmission-mode desorption electrospray ionization (TM-DESI), low temperature plasma (LTP) ionization and nano-assisted laser desorption ionization (NALDI), are compared with electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) for the analysis of two nanofilm products (NFPs) for surface coating, which contain hydrolysates and condensates of organo-functionalized silanes. The NFPs were characterized in different states from the liquid phase to the fully formed surface film. The LTP spectra were dominated by the silanes, while the corresponding di-, tri- and tetrasiloxanes were common in ESI, APCI and TM-DESI. This indicates readily condensation of the silanes during the ESI and APCI ionization processes leading to the observed siloxanes. NALDI showed larger siloxane structures than the other techniques, indicating film formation on the NALDI target. Real-time monitoring of the film formation on a glass surface by LTP showed a decreasing abundance of the silanes, while the abundances of the di-, tri and tetrasiloxanes increased significantly within the first 100 s. LTP was superior in showing the non-reacted content of the NFPs, while ESI, APCI and TM-DESI were characterized by artefact formation of siloxanes. NALDI was ideal for showing the siloxane structures of the formed film. The applicabilities of each of the ionization techniques were examined, showing the advantage of utilizing more than one ionization technique for the analysis of reactive species.

The use of a microporous polypropylene membrane for the introduction of aqueous samples into a mass spectrometer in amounts sufficient for the water vapor to be used as reagent gas in chemical ionization (CI) is demonstrated. Solute molecules pass the membrane together with the water and can be analyzed using CI-MS and tandem mass spectrometry (MS-MS). Glow discharge, instead of a filament, is used to ionize the reagent gas, since the high water pressure was found to shorten the filament lifetime to a few hours. The glow discharge was efficient only within a very narrow pressure range, which was controlled simply by adjusting the water flow into the ion source by changing the membrane probe temperature. Using solvent CI with glow discharge, it is possible to measure a broad range of organic compounds with detection limits below 100 ppb and with an accuracy of ±5%. No enrichment of analytes as compared to the water solvent is achieved with the porous membrane and most volatile compounds show similar detection limits. Detection limits and response times were also measured with a silicone membrane introduction system using methane CI. The detection limits using microporous membrane introduction and solvent CI with glow discharge were at least an order of magnitude lower for small polar compounds like alcohols, ketones, aldehydes and acids than with the silicone membrane introduction system, whereas hydrophobic compounds like aromatics and chlorocarbons gave similar results for the two techniques. The response times of the flow injection membrane introduction system were found to be similar for the microporous and the silicone membranes used.

A new technique is described for the direct detection and identification of volatile organic compounds dissolved in organic solvents. The method uses a porous membrane introduction system to a mass spectrometer and is capable of continuous on-line monitoring. The porous polypropylene membrane chosen for this work allows sufficient amounts of the solvent to penetrate into the ion source for chemical ionization (CI) to occur with the vaporized solvent acting as the reagent gas. Solute molecules permeate the membrane together with the solvent and can be analyzed by CI/MS and tandem mass spectrometry (MS/MS)

Summary: The use of a membrane inlet triple quadrupole mass spectrometer revealed indole as an end product in the growth medium of cultures of the cattle parasite Tritrichomonas foetus and the human parasite Trichomonas vaginalis: formation of indole is enhanced in the presence of added tryptophan. Two different clinical isolates of Trich. vaginalis also produce dimethyl disulphide. Electron impact ionization yielded complex fragmentation mixtures, but the facility for analysis of daughter ions enabled unequivocal assignments. Chemical ionization gave [M + 1]+ species, and tandem mass spectrometry produced identification through daughter ions. The method provides a rapid single-step procedure for the characterization of microbial products without the need for preliminary separation and derivatization.

A membrane inlet tandem mass spectrometer is used for easy identification of volatile metabolites in microbial cultures. Filtrates of the cultures are without further purification placed into a measuring cell and introduced via a membrane inlet into a triple-quadrupole mass spectrometer. The samples are analysed with electron impact and chemical ionization mass spectrometry and tandem mass spectrometry. An extra dimension of separation is obtained by utilizing differences in response time due to differences in transport rates through the membrane. The following examples are used to demonstrate the technique. (i) Filtrates from cultures of three parasitic protozoa (trichomonads); two different strains of Trichomonas vaginalis isolated from humans and from Tritrichomonas foetus isolated from cattle were analysed. Indole was found in all samples; dimethyl disulphide was also present in cultures of the two organisms isolated from humans. (ii) The yeast Brettanomyces was grown in the presence of coumaric acid, ferulic acid, vanillic acid or syringic acid and the filtrate analysed for volatile products. In all cases ethyl acetate was found; coumaric acid biotransformation also gave 4-ethylphenol, whereas ferulic acid also gave 4-ethyl-2-methoxyphenol.

In order to detect highly polar organic compounds in water using membrane inlet mass spectrometry (MIMS), we designed a desorption chemical ionization ion source with a tubular polyacrylonitrile membrane positioned in the center of the chemical ionization (Cl) ion plasma. With this system we have for the first time been able to detect dicarboxylic acids (malonic and succinic acid) in aqueous samples with a MIMS system. The dicarboxylic acids were detected with both standard MIMS and trap‐and‐release MIMS methods. The trap‐and‐release MIMS method gave the best signal to noise ratio spectra with detection limits down to 50 mg/L. Although the results presented are very preliminary, they suggest that rapid detection or even on‐line monitoring of this important group of biological metabolites might be possible with a MIMS system.

A flow-through membrane inlet combined with a single quadrupole mass spectrometer has been used for the direct on-line monitoring of biological reactions at the extremely low parts-per-trillion level. Linear signals over at least 4 orders of magnitude were obtained. As an example, on-line monitoring data from the microbial oxygenation of chloroethylenes in pure cultures of the methanotrophic bacteria Methylococcus capsulatus (Bath) are presented

A rapid screening method of styrene and tetrachloroethylene in olive oil based on membrane inlet mass spectrometry has been developed. The presence of these contaminants was identified and monitored on the basis of the mass spectra measured. Detection limits of 100 and 5 ppb were measured for styrene and tetrachloroethylene, respectively. A linear dynamic range of at least 3 orders magnitude was achieved. Fast response times, in the order of 1 min, for the analytes were observed, allowing large sample throughput

Pentachlorophenol (PCP) was used as a model compound to explore the potential of desorption chemical ionization (DCI) in the determination of polychlorinated pesticides using membrane introduction mass spectrometry (MIMS). A direct insertion membrane probe was modified so that a chemical ionization plasma could be established at the membrane surface. Using selected ion monitoring (SIM) in a tandem triple quadrupole mass spectrometer with isobutane chemical ionization (CI), the PCP detection limit under positive chemical ionization is 20 ppb whereas negative CI gives detection limits in the low ppb range. This performance is achieved without any pre-treatment or derivatization of the sample. Negative ion CI gives a signal that is linear over a concentration range of 2–1000 ppb. Comparison of data obtained with low ppb samples of 2,4,6-trichlorophenol, 2,3,4,6-tetrachlorophenol and pentachlorophenol suggests that the sensitivity of this analytical procedure increases with increase in the number of electronegative substituents in the molecule.

Publisher Summary Membrane inlet mass spectrometry (MIMS) is a relatively old technique that was introduced as a method for the continuous monitoring of gases dissolved in water. The main applications of the MIMS technique were in vivo monitoring of blood gases and monitoring of dissolved gases and small organic compounds in fermentors. The application of the MIMS technique was expanded beyond the analysis of gases and small organic compounds in aqueous matrixes. Methods that made it possible to analyze complex organic solutions like gasoline were developed and an interest in the analysis of gaseous samples appeared. Solid analysis is a new application area for the MIMS technique and optimized methods for the analysis of residual volatiles in soil samples are emerging. This chapter provides an overview of the many possibilities of the MIMS technique. Emphasis is on the flexibility of the MIMS technique, when it comes to the analysis of samples having completely different matrixes. The chapter describes methods for the characterization of gaseous samples, characterization of aqueous and organic liquids.

We have studied the peroxidase-oxidase reaction with NADH and O2 as substrates and melatonin as a cofactor in a semibatch reactor. We show for the first time that melatonin is an activator of the reaction catalyzed by enzymes from both plant and animal sources. Furthermore, melatonin promotes oscillatory dynamics in the pH range from 5 to 6. The frequency of the oscillations depends on the pH such that an increase in pH was accompanied by a decrease in frequency. Conversely, an increase in the flow rate of NADH or an increase in the average concentration of NADH resulted in an increase in oscillation frequency. Complex dynamics were not observed with melatonin as a cofactor. These results are discussed in relation to observations of oscillatory dynamics and the function of melatonin and peroxidase in activated neutrophils.

This paper presents the first membrane inlet mass spectrometry system capable of detecting large biomolecules, such as testosterone (Mr 288), testosterone acetate (Mr 330) and α-tocopherol (Mr 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 (Mr 286, vitamin A), cholecalciferol (Mr 384, vitamin D3) and cholesterol (Mr 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.