Membrane introduction mass spectrometry

An overview of membrane introduction mass spectrometry (MIMS) is presented and comparisons are made with other direct sample introduction techniques. Special attention is given to the unique advantages and the limitations of newer variants on the MIMS technique, including affinity MIMS, reverse-phase and trap MIMS. The salient features of the interfaces used in MIMS are summarized and the various membrane materials commonly used are delineated. The applicability of MIMS is illustrated via discussion of

1. (i) bioreactor monitoring (represented by yeast fermentation),

2. (ii) environmental monitoring (illustrated by analysis of contaminated ground water samples) and

3. (iii) on-line chemical reaction monitoring (exemplified by the photolysis of aryl esters).

The applicability of MIMS to the analysis of environmental samples, including complex mixtures in water, air and soil, is noted.     

Comparison of different methods for the determination of volatile organic compounds in water samples

The aim of this work was to compare the characteristics of three methods, membrane inlet mass spectrometry (MIMS), purge-and-trap gas chromatography-mass spectrometry (P&T) and static headspace gas chromatography (HSGC), for the determination of volatile organic compounds in water samples as used in routine analysis. The characteristics examined included linear dynamic ranges, detection limits of selected environmentally hazardous volatile organic compounds (e.g. toluene, benzene and trichloroethene) in water, required analysis time and reproducibility of the analytical methods. The MIMS and P&T methods had the lowest detection limits for all the tested compounds, ranging from 0.1 to 5 mug 1(-1). Linear dynamic ranges using the MIMS method were about four orders of magnitude and using the P&T method about two orders of magnitude. Detection limits of the HSGC method were 10-100 times higher than those of the other two methods, but the linear dynamic ranges were larger, even up to six orders of magnitude. The analysis time per sample was shortest for the MIMS method, from 5 to 10 min, and ranged around from 35 to 45 min for the HSGC and P&T methods. The reproducibilities of the methods were of the same order of magnitude, in the range of 1-13%. Agreement between the analytical results obtained for spiked samples and for environmental water samples by the three different methods was very good.     

Biodegradation studies of 4-fluorobenzoic acid and 4-fluorocinnamic acid: an evaluation of membrane inlet mass spectrometry as an alternative to high performance liquid chromatography and ion chromatography

The biodegradation of 4-fluorobenzoic acid (4-FBA) and 4-fluorocinnamic acid (4-FCA) has been monitored by membrane inlet mass spectrometry (MIMS) using a hollow-fibre silicone membrane. A novel in-membrane pre-concentration/thermal desorption (IMP-MIMS) technique was employed for MIMS analysis using an oven temperature profile that allowed semi-volatile organic compounds to be accumulated in the membrane and then released by rapid heating. Air drying of the membrane between the analyte pre-concentration and thermal desorption stages improved mass spectrometric performance by removing residual water from the membrane. The concentrations of 4-FBA and 4-FCA determined by MIMS compare well with data obtained by high performance liquid chromatography (HPLC). Stoichiometric amounts of fluoride were monitored using ion chromatography (IC). Intermediates in the biodegradation pathway were identified by liquid chromatography/mass spectrometry (LC/MS). These data establish the potential of MIMS as an alternative to chromatographic methods for monitoring the biodegradation of semi-volatile organic compounds.     

On-line monitoring of continuous beer fermentation process using automatic membrane inlet mass spectrometric system

A fully automatic membrane inlet mass spectrometric (MIMS) on-line instrumentation for the analysis of aroma compounds in continuous beer fermentation processes was constructed and tested. The instrumentation includes automatic filtration of the sample stream, flushing of all tubing between samples and pH control. The calibration standards can be measured periodically. The instrumentation has also an extra sample line that can be used for off-line sample collection or it can be connected to another on-line method. Detection limits for ethanol, acetic acid and eight organic beer aroma compounds were from μg l⁻¹ to low mg l⁻¹ levels and the standard deviations were less than 3.4%. The method has a good repeatability and linearity in the measurement range. Response times are shorter than or equal to 3 min for all compounds except for ethyl caproate, which has a response time of 8 min. In beer aroma compound analysis a good agreement between MIMS and static headspace gas chromatographic (HSGC) measurements was found. The effects of different matrix compounds commonly present in the fermentation media on the MIMS response to acetaldehyde, ethyl acetate and ethanol were studied. Addition of yeast did not have any effect on the MIMS response of ethanol or ethyl acetate. Sugars, glucose and xylose, increased the MIMS response of all studied analytes only slightly, whereas salts, ammonium chloride, ammonium nitrate and sodium chloride, increased the MIMS response of all three studied compounds prominently. The system was used for on-line monitoring of continuous beer fermentation with immobilised yeast. The results show that with MIMS it is possible to monitor the changes in the continuous process as well as delays in the two-phase process.     

A membrane introduction flame ionization/electron capture detection (MIFID/ECD) system for the rapid, real-time screening of volatile disinfection byproducts and hydrocarbon contaminants in water

Described is a system that employs an online membrane introduction (MI) interface coupled with parallel flame ionization and electron capture detectors (FID/ECD). We report the use of a MIFID/ECD system as an online method to detect total volatile organic halides (ΣVOXs) and volatile organic compounds (ΣVOCs) as aggregate parameters in environmental water samples at sub parts-per-billion levels without the need for sample handling or analyte pre-concentration. The instrument provides rapid screening and real-time monitoring capabilities of important classes of water contaminants in a simple system without the vacuum requirements of MS detectors. Furthermore, the MIFID/ECD instrument was successfully employed as a real-time reaction monitor for the photodegradation of toluene by an advanced oxidation process and the formation of volatile disinfection byproducts in the chlorination of natural waters. The results of these experiments compare favorably to those obtained using membrane introduction mass spectrometry (MIMS).     

Detection of volatile organic sulfur compounds in water by headspace gas chromatography and membrane inlet mass spectrometry

Two gas chromatographic methods, GC-FID (flame ionization detection) and GC-ELCD (electrolytic conductivity detector) are compared in tlie analysis of volatile organic sulfur compounds (VOSCs) in water samples with a membrane inlet mass spectrometry (MIMS) technique. Carbon disulfide, ethanethiol, dimethyl sulfide, ethyl-methyl sulfide, thiophene, and dimethyl disulfide were used as test compounds. Linear dynamic ranges were found to be two decades with the GC-ELCD method and four decades with the GC-FID and MIMS methods. Detection limits were at low (μg/1 levels with the two gas chromatographic methods and clearly below μg/1 level with the MIMS method. Analysis of one sample takes 40 min with the gas chromatographic methods and five minutes with the MIMS method. The selectivity was good, especially with the GC-ELCD and the MIMS method. In addition, quantitative results obtained with spiked water samples by the three methods are compared.     

Membrane introduction mass spectrometry for monitoring complexation equilibria of beta-cyclodextrin with substituted benzenes

Membrane introduction mass spectrometry (MIMS) was used to monitor complexation reactions between beta-cyclodextrin (CD) and a series of benzene derivatives in aqueous solution. The equilibrium constants for benzene, chlorobenzene, bromobenzene, iodobenzene, toluene, cyanobenzene and nitrobenzene were determined. The suitability of MIMS for monitoring complexation reactions of organic compounds with host molecules was demonstrated. Structure-activity relationship analysis shows that the inclusion phenomena are driven by a variety of chemical forces, of which hydrophobicity is predominant for non-polar compounds, but not the only factor for more polar ones.     

Membrane-introduction mass spectrometry (MIMS)

Membrane-introduction mass spectrometry (MIMS) for chemical analysis involves directly sampling analytes in gaseous, liquid and solid samples through a semi-permeable membrane coupled to a mass spectrometer, yielding selective and sensitive quantitation. Because MIMS is an on-line technique, in which samples can be continuously flowed over a membrane interface, it can yield analytical results in real time without the need for sample clean-up and chromatographic separation. This review highlights trends and developments in MIMS over the past decade and describes recent studies that pertain to its use for on-site, in-situ and in-vivo chemical analysis. We report on advancements in instrumentation, including membrane materials, interface configurations and ionization techniques that have extended the range of analytes amenable to MIMS.We summarize the progress made in the miniaturization of mass spectrometers that have resulted in field-portable systems and review recent applications of continuous mobile monitoring and on-site environmental monitoring to yield both temporally and spatially resolved quantitative and semi-quantitative data. Finally, we describe recent work involving the use of MIMS for in-vivo chemical analysis.     

A coaxially heated membrane introduction mass spectrometry interface for the rapid and sensitive on-line measurement of volatile and semi-volatile organic contaminants in air and water at parts-per-trillion levels

A coaxially heated membrane introduction mass spectrometry (MIMS) sampling interface is presented that demonstrates improved on-line performance for the direct measurement of semi-volatile organic compounds (SVOCs) in air and water samples at parts-per-trillion levels. The device is based on a polydimethylsiloxane (PDMS) capillary hollow fibre membrane (HFM) in a pneumatically assisted "flow-over" configuration that is resistively heated on the membrane interior via a coaxial nichrome wire, establishing a thermal gradient counter to the analyte concentration gradient. This arrangement allows for continuous and/or pulsed heating modes, affording excellent sensitivity for the on-line measurement of SVOCs while retaining sensitivity for volatile organic compounds (VOCs). In addition, the signal response time for SVOCs is reduced substantially over conventional "flow-over" MIMS interfaces. Separation and quantitation of analytes are achieved using quadrupole ion trap tandem mass spectrometry.     

Membrane Introduction Mass Spectrometry (MIMS): A Versatile Tool for Direct,Real‐Time Chemical Measurements

Membrane introduction mass spectrometry (MIMS) is a direct, continuous, on‐line measurement technique. It utilizes a membrane to semi‐selectively transfer analyte mixtures from a sample to a mass spectrometer, rejecting the bulk of the sample matrix, which can be a gas, liquid or solid/slurry. Analyte selectivity and sensitivity are affected by optimizations at the membrane, ionization and the mass spectrometer levels. MIMS can be roughly classified by the acceptor phase that entrains analyte(s) to the mass spectrometer after membrane transport, either a gaseous acceptor phase (GP‐MIMS) or condensed acceptor phase (CP‐MIMS). The aim of this article is to provide an introduction to MIMS as a technique and to explore current variants, recent developments and modern applications, emphasizing examples from our group, the Applied Environmental Research Laboratories as well as selected work from others in this emerging area. Also provided is a synopsis of current and future directions for this versatile analytical technique. Copyright © 2014 John Wiley & Sons, Ltd.     

Improving the selectivity of non-polar alkanes, alkenes, and aromatic hydrocarbon compounds by the application of acetonitrile as a Cl reagent

The selective enhancement of membrane introduction mass spectrometry for non-polar alkanes, alkenes, and aromatic hydrocarbon compounds by the application of acetonitrile as a chemical ionization reagent was investigated. Acetonitrile Cl is able to produce specific fragment ions for many of the compounds test and this can be used to identify and quantify the parent neutrals. This method provided relatively high detection limits of the test compounds. This method could potentially be useful for analytical applications such as the detection of non-polar hydrocarbons for environmental studies if CH₃CN Cl/MIMS is coupled with a preconcentration method.     

Characterization of a mini membrane inlet mass spectrometer for on-site detection of contaminants in both aqueous and liquid organic samples

A mini membrane inlet mass spectrometer (mini-MIMS) of a total weight of 12 kg was constructed using a miniature Multipole mass spectrometer, a small vacuum system and a flexible flat sheet membrane inlet, where the exposed membrane area can be changed by a factor of 80. The variable membrane area together with the possibility of operating the Multipole at pressures up to 1 x 10(-3) Torr made it possible to test the system with three microporous membranes (cellulose, polyether sulfone and polypropylene) normally not compatible with standard electron ionization MIMS systems and a standard non-porous polydimethylsiloxane membrane. We found that the hydrophilic cellulose and polyether sulfone membranes had selectivity characteristics opposite to those of the standard silicone membrane. They demonstrated preferential detection of hydrophilic compounds in hydrophobic organic solvents, whereas the silicone membrane preferentially detects hydrophobic organic compounds in aqueous solution. Using the cellulose membrane, organic contaminants and water could be detected in organic solvents at 10-100 ppm levels by weight, the relative high detection limits primarily caused by interference from a high chemical background from the solvent. When being used with the standard silicone membrane the mini-MIMS behaved just like most standard MIMS systems with detection limits of volatile organic compounds in water at concentrations just below 1 ppm. The hydrophobic microporous polypropylene membrane was not found to be useful with the mini-MIMS.     

固相微萃取-气相色谱联用技术在环境分析中的应用

本文综述了近5年来固相微萃取-气相色谱(SPME-GC)联用技术在环境分析中的应用进展.具体介绍了它在多环芳烃、苯系物、酚类化合物、农药、杂环化合物以及其他有机挥发物分析中的应用.引用文献158篇.     

Membrane inlet mass spectrometry of volatile organohalogen compounds in drinking water.

The analysis of organic pollutants in drinking water is a topic of wide interest, reflecting on public health and life quality. Many different methodologies have been developed and are currently employed in this context, but they often require a time-consuming sample pre-treatment. This step affects the recovery of the highly volatile compounds. Trace analysis of volatile organic pollutants in water can be performed 'on-line' by membrane inlet mass spectrometry (MIMS). In MIMS, the sample is separated from the vacuum of the mass spectrometer by a thin polymeric hollow-fibre membrane. Gases and organic volatile compounds diffuse and concentrate from the sample into the hollow-fibre membrane, and from there into the mass spectrometer. The main advantages of the technique are that no pre-treatment of samples before analysis is needed and that it has fast response times and on-line monitoring capabilities. This paper reports the set-up of the analytical conditions for the analysis of volatile organohalogen compounds (chloroform, bromoform, bromodichloromethane, chlorodibromomethane, tetrachloroethylene, trichloroethylene, 1,1,1-trichloroethane, and carbon tetrachloride). Linearity of response, repeatability, detection limits, and spectra quality are evaluated.     

An enzyme derivatized polydimethylsiloxane (PDMS) membrane for use in membrane introduction mass spectrometry (MIMS)

Membrane introduction mass spectrometry (MIMS) provides direct measurement of volatile and semivolatile analytes in condensed and gas-phase samples without sample preparation steps. Although MIMS has numerous advantages that include direct, on-line, real-time analysis with low detection limits, current applications of MIMS are predominantly limited to volatile and semivolatile analytes that permeate hydrophobic membranes (e.g., polydimethylsiloxane; PDMS). We report the first enzyme modified PDMS membrane for use with MIMS. This was achieved by immobilizing Candida rugosa lipase directly onto the surface of oxidized PDMS. These surface immobilized enzymes catalyze ester hydrolysis, releasing an alcohol product at the membrane interface that is readily detected. We have successfully used an enzyme modified membrane for the analysis and quantification of low-volatility and hydrophilic esters. We report the quantification of several carboxylic acid esters in dilute aqueous solutions, including a phthalate monoester carboxylate that is not readily detected by conventional MIMS. This new interface demonstrates the potential for extending the range and versatility of MIMS.     

Flow-Based Methods with Chemiluminescence Detection for Food and Environmental Analysis: A Review

This paper presents an overview of flow-based methods in food and environmental analysis using chemiluminescence (CL) detection covering the period from 2005 to the present. The review discussses both automated flow methods of analysis [such as flow-injection analysis (FIA), sequential-injection analysis (SIA) and their variants] and separation techniques [liquid chromatography (LC) and capillary electrophoresis (CE) coupled to CL detection]. The most widely used CL reactions are presented together with representative applications in food and environmental analysis (determination of naturally occurring compounds, contaminants, additives as well as determination of inorganic and organic compounds).     

Stir-bar sorptive extraction: A view on method optimisation,novel applications,limitations and potential solutions

Introduced in 1999 as a novel solventless sample preparation method, stir-bar sorptive extraction (SBSE) has become a popular analytical technique for the pre-concentration of organic compounds into a polydimethylsiloxane (PDMS)-coated stir-bar. In the last 10 years, hundreds of applications in the environmental, food and biomedical fields can be found in the literature. However, only PDMS-coated stir-bars are commercially available, which reduces the applicability of SBSE to the extraction of the non-polar compounds due to the poor extractability of more polar analytes. In this review, a view on method optimisation, limitations, potential solutions such as in-house coatings and derivatisation and novel applications in multi-residue analysis and passive sampling are revised.     

Environmental and pharmaceutical analysis of dithiocarbamates

The current review aims at a comprehensive survey of analytical methods for the determination of dithiocarbamates (DTCs) in environmental and pharmaceutical samples. Besides parent compounds, analytical approaches for various metabolites and degradation products of DTCs are considered. Special emphasis is given to analyte stability as DTCs are considerably reactive interacting with various organic and inorganic compounds; in addition, depending on the chemical nature of the substance, DTCs are prone to oxidation and hydrolysis under alkaline and acidic conditions, respectively. The review mainly focuses on chromatography but also covers applications in electrophoresis, spectrophotometry, and biosensing.     

Microwave-assisted extraction: Application to the determination of emerging pollutants in solid samples

Flame retardants, surfactants, pharmaceutical and personal care products, among other compounds, have been the object of numerous environmental studies. In this chapter, the application of microwave-assisted extraction (MAE) in the development of analytical methods for several groups of organic compounds with growing concern as emerging pollutants has been considered. Compared to other extraction techniques, optimization of MAE experimental conditions is rather easy owing to the low number of influential parameters (i.e. matrix moisture, nature of the solvent, time, power, and temperature in closed vessels). The great reduction in the extraction time and solvent consumption, as well as the possibility of performing multiple extractions, increasing the sample throughput, can also be highlighted among MAE advantages. In summary, the study of several applications of MAE to environmental problems demonstrates that this technique constitutes a good alternative for the determination of organic compounds in environmental samples. It can be used as a rapid screening tool, and also to obtain detailed information on the sources, behaviour and fate of emerging pollutants in environmental matrices.     

General applications of fused silica capillary column (FSCC) chromatography to the analysis of non-priority pollutant organics in environmental samples

Further applications of fused silica capillary columns (FSCC) to the analysis of environmental samples are presented. The chromatographic behavior (RT, RRT) of organic compounds of environmental significance not listed as Consent Decree Priority Pollutants is investigated on an SE-54 FSCC. Retention indices (RRT) and mass spectral response factors (RF) are presented for a total of 28 compounds including a number of chloro- and nitro-substituted anilines, alkylpyridines, and alkylquinoline derivatives. The direct application of the FSCC/MS interface to the analysis of these compounds in actual environmental samples is presented, including vent emissions from a fungicide manufacturing process, and contaminated soil and water samples from two metropolitan Boston construction sites.