Fast and direct screening of polyaromatic hydrocarbon (PAH)-contaminated sand using a miniaturized membrane inlet mass spectrometer (mini-MIMS)

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 degrees 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 (approximately 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 (<10 kg) on-site mass spectrometry system for PAH screening at contaminated sites.     

Utilization of a multimembrane inlet and a cyclic sudden sampling introduction mode in membrane inlet mass spectrometry

Sudden sampling introduction into a membrane inlet mass spectrometer (MIMS) considerably improves the selectivity of the membrane inlet and is therefore applicable even for compounds with low permeabilities through a silicone membrane. In this study the basics of cyclic non-steady-state sudden increase sample injection were studied using a three-membrane inlet and a portable sector double-focusing mass spectrometer. The operational parameters of the inlet system providing the most efficient enrichment of volatile organic compounds (VOCs) in air were defined. Simulation of the diffusion process following sudden sample introduction into the three-membrane inlet was also carried out. Experimental testing of the three-membrane inlet system with the cyclic sudden sample injection mode for benzene, toluene, styrene, and xylene in air was performed. The simulation and the experimental results demonstrated that, when this mode is used, the VOCs/nitrogen relative enrichment factor of samples introduced into the mass spectrometer equipped with a three-membrane inlet is increased by a factor of approximately 10(5) compared with a direct introduction method. This effect may be used to decrease detection limits of compounds obtained with mass spectrometry to decrease matrix flow through the inlet at the same detection limits.     

Trace level analysis of volatile and semi-volatile organic compounds in water using a membrane/jet separator interfaced to an ion trap mass spectrometer

An ion trap mass spectrometer, equipped with a membrane/jet separator interface, is used for the direct detection of volatile and semi-volatile organic compounds in aqueous solutions. Aqueous sample is passed through a capillary membrane, the outside surface of which is continuously purged by helium. The permeate is pneumatically transported to the mass spectrometer via a jet separator which acts as an additional enrichment device. The performance and response characteristics of non-porous silicone and microporous polytetrafluoroethylene (PTFE) membranes are studied. The microporous membrane allows sufficient water to pass for it to be used as a reagent gas for chemical ionization. Both types of membranes provide detection limits in the parts per trillion (pptr) to parts per billion (ppb) range with a linear dynamic range of 3 orders of magnitude for some volatile organic compounds. Results show that there is no detectable matrix effect on response in the selected cases examined. The use of microporous membranes to analyze more polar compounds, such as 5-hydroxymethyl furfuraldehyde and lactic acid, is also demonstrated. The effects of other experimental parameters, such as membrane temperature and length, on sensitivity are also investigated.     

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.     

Preparation and properties of surface modified ceramic membranes. Part II. Gas and liquid permeabilities of 5 nm alumina membranes modified by a monolayer of bound polydimethylsiloxane (PDMS) silicone oil

A new way to prepare hydrophobic membranes is reported. Polydimethylsiloxane oil (and any other silicone oil molecules) was grafted onto a porous alumina membrane (or any hydroxylated ceramic or glass) by heating, to 180°C, producing a covalently grafted monolayer of silicone oil, chemically and thermally stable, unaffected by organic solvents but susceptible to alkali attack (as is the silicone oil itself). The membrane is totally impermeable to pure water, and organic solvents may be extracted from water mixtures by pervaporation. Very high permeation fluxes were obtained, suggesting possible use of these silicone/ceramic membranes in extraction of volatile organic compounds (VOCs). This simple modification can be applied to macroporous membranes increasing hydrophobicity without pore blocking.     

Determination of ammonia, ethanol and acetic acid in solution using membrane introduction mass spectrometry

Methods have been developed to allow applications of membrane introduction mass spectrometry (MIMS) to monitor solution phase components of fermentation broths using electron ionization. The solutions are transported by flow injection analysis (FIA) through a direct insertion membrane probe, fitted with a silicone membrane in the sheet configuration. Analytes of interest pass through the membrane and are ionized by electron implant ionization. The compounds monitored are ammonia, acetic acid, and ethanol, with ammonia being detected as the monochloramine derivative which is generated at pH 10 upon addition of hypochlorite. Quantitation is achieved using external standard solutions. The dynamic range for the quantification of ammonia is 2-8000 ppm, and for ethanol and acetic acid 10-1000 ppm. This method provides rapid detection of analytes of interest, on-line monitoring capabilities, and the advantage of electron ionization. The introduction of samples into the mass spectrometer is achieved readily and automatically, the response time is a few seconds, and there are no memory effects.     

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.     

Application of membrane inlet mass spectrometry for online and in situ analysis of methane in aquatic environments

A method is presented for the online measurement of methane in aquatic environments by application of membrane inlet mass spectrometry (MIMS). For this purpose, the underwater mass spectrometer Inspectr200-200 was applied. A simple and reliable volumetric calibration technique, based on the mixing of two end member concentrations, was used for the analysis of CH₄ by MIMS. To minimize interferences caused by the high water vapor content, permeating through the membrane inlet system into the vacuum section of the mass spectrometer, a cool-trap was designed. With the application of the cool-trap, the detection limit was lowered from 100 to 16 nmol/L CH₄. This allows for measurements of methane concentrations in surface and bottom waters of coastal areas and lakes. Furthermore, in case of membrane rupture, the cool-trap acts as a security system, avoiding total damage of the mass spectrometer by flushing it with water. The Inspectr200-200 was applied for studies of methane and carbon dioxide concentrations in coastal areas of the Baltic Sea and Lake Constance. The low detection limit and fast response time of the MIMS allowed a detailed investigation of methane concentrations in the vicinity of gas seepages.     

Performance of an ion trap mass spectrometer modified to accept a direct insertion membrane probe in analysis of low level pollutants in water

Modifications to a Finnigan ITS40 ion trap mass spectrometer are described which allow its use with a direct insertion probe. Details are given of the fabrication of a membrane probe for such an instrument. The membrane probe, which includes facilities for heating the fluid, employs a tubular membrane which is located just outside the electrode structure of the ion trap. Direct analysis of organic compounds in aqueous solution is demonstrated using a silicone membrane, with compounds such as benzene, chlorobenzene and dichloroethene being studied below the 1 ppb level. The effects of operating parameters including probe temperature, ion trap temperature, solution flow rate, mass spectrometer scan speed, and instrument tune procedures are explored in detail. Optimum performance characteristics are identified and trace level detection of eight organic compounds in the parts per trillion range is demonstrated. In seven of the eight cases studied, detection limits are below the EPA practical limit of quantitation levels. It is shown that the most sensitive mode of operation is when steady state passage of the analyte across the membrane is achieved, however, the time required for this is long in the case of some samples, and a dynamic flow injection analysis procedure is then favored. Use of the modified inlet system for solid sample introduction via a standard solids probe is also demonstrated.     

等离子体聚合法制备膜蒸馏用疏水微孔复合膜

本文以八氟环丁烷为单体,采用等离子体聚合法将亲水性硝酸纤维素微孔膜改性,制得疏水硝酸纤维素微孔复合膜。所得疏水微孔复合膜可用于膜蒸馏,并具有优良的膜蒸馏性能,其通量达到反渗透水平。利用扫描电镜、X-射线显微分析和XPS等分析手段研究了聚合条件对所得复合膜结构性能的影响.     

Fouling and protein adsorption effect of low-temperature plasma treatment of membrane surfaces

Adsorption of proteins and the effect of the chemical nature of membrane surfaces on protein adsorption were investigated using¹⁴C-tagged albumin and several microporous membranes (polyvinilydene fluoride, PVDF; nylon; polypropylene, PP; and polycarbonate, PC). The membrane surfaces were modified by exposing them to low-temperature plasma of several different monomers (n-butane, oxygen, nitrogen alone or as mixtures) in a radiofrequency plasma reactor. Transients in the permeability of albumin solutions through the membranes and changes in flux of distilled water through the membranes before and after adsorption of albumin were used to investigate the role of protein adsorption on membrane fouling. The results show that the extent of adsorption of albumin on hydrophobic membranes was considerably more than that on hydrophilic membranes. The hydrophilic membranes were susceptible to electrostatic interactions and less prone to fouling. A pore-blocking model was successfully used to correlate the loss of water flux through pores of defined geometry     

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.     

快速测量挥发性有机物的膜进样-飞行时间质谱仪的设计和应用

研制了一种膜进样-微型飞行时间质谱仪, 该仪器使用双层50 μm硅橡胶膜作为大气压下直接进样的接口. 实验结果表明, 随着样品流速的提高, 膜富集效率信号强度呈线性提高. 双膜中间具有真空差分系统, 富集得到的样品被迅速抽走, 进样系统中样品无记忆效应. 样品在膜中的响应时间为100 s, 而打开差分系统后仅需10 s信号即下降为平稳状态. 与毛细管直接进样相比, 双层膜的富集作用显著, 在相同的实验条件下使用膜进样技术测定10×10-6 (体积分数)苯、甲苯和对二甲苯的信号强度分别提高了280, 370和600倍. 膜进样系统与真空紫外光软电离方式联用, 对于苯的检出限已经达到了25×10-9 (体积分数), 线性范围为3个数量级. 由于采用了软电离方法, 无碎片离子产生, 所以能够根据分子量进行快速定性分析. 将该仪器应用于香烟主烟气中可挥发性有机物的在线分析, 得到50多种可挥发性的有机物. 实验结果表明, 膜进样-飞行时间质谱将在在线分析(特别是环境监测)方面具有广泛的应用空间.     

Membrane-moderated stripping process for removing VOCs from water in a composite hollow fiber module

The “stripmeation” process for removing volatile organic compounds (VOCs) from water has been introduced and studied. An aqueous solution of the VOC is passed through the bores of hydrophobic microporous polypropylene hollow fibers having a plasma polymerized silicone coating on the fiber outside diameter; a vacuum is maintained on the shell side of the fiber. The VOC is stripped into the gas-filled pores of the hydrophobic substrate, permeates through the nonporous silicone skin and is recovered by condensation of the shell-side permeate stream. Removal of trichloroethylene (TCE) present in a concentration range 200–1040 ppm has been studied at 25°C. Process performance has been obtained over a range of flow rates. The observed TCE permeation and removal behavior has been modeled using a resistances-in-series approach; the two important resistances are the tube-side aqueous boundary layer resistance and the vapor permeation resistance of TCE through the silicone coating. Employing the known Graetz solution for the tube-side flow and the measured vapor permeation resistance of TCE, values of the overall TCE mass-transfer coefficient have been obtained. These values compare well with the experimental values. The conventional pervaporation process where the liquid feed solution is in contact with the nonporous silicone membrane has also been studied by passing the feed on the shell side. The tube-side feed-based operation performs much better than the shell-side based operation.     

Environmental applications of membrane introduction mass spectrometry

The purpose of this review is to highlight the versatility of membrane introduction mass spectrometry (MIMS) in environmental applications, summarize the measurements of environmental volatile organic compounds (VOCs) accomplished using MIMS, present developments in the detection of semi-volatile organic compounds (SVOCs) and forecast possible future directions of MIMS in environmental applications.     

Removal of aromatic compounds in the aqueous solution via micellar enhanced ultrafiltration: Part 1. Behavior of nonionic surfactants

The effects of nonionic surfactants having different hydrophilicity and membranes having different hydrophobicity and molecular weight cut-off on the performance of micellar-enhanced ultrafiltration (MEUF) process were examined. A homologous series of polyethyleneglycol (PEG) alkylether having different numbers of methylene groups and ethylene oxide groups was used for nonionic surfactants. Polysulfone membranes and cellulose acetate membranes having different molecular cut-off were used for hydrophobic membranes and hydrophilic membranes, respectively. The concentration of surfactant added to pure water was fixed at the value of 100 times of critical micelle concentration (CMC). The flux through polysulfone membranes decreased remarkably due to adsorption mainly caused by hydrophobic interactions between surfactant and membrane material. The decline of solution flux for cellulose acetate membranes was not as serious as that for polysulfone membranes because of hydrophilic properties of cellulose acetate membranes. The surfactant rejections for the cellulose acetate membranes increased with decreasing membrane pore size and with increasing the hydrophobicity of surfactant. On the other hand the surfactant rejections for polysulfone membranes showed totally different rejection trends with those for cellulose acetate membranes. The surfactant rejections for the polysulfone membranes depend on the strength of hydrophobic interactions between surfactant and membrane material and molecular weight of surfactants.     

On-line monitoring of biotechnological processes by gas chromatographic-mass spectrometric analysis of fermentation suspensions

An on-line monitoring system has been developed for the control of a biorreactor for the anaerobic pretreatment of an industrial waste water. The monitoring system is based on a process mass spectrometer with a temperature controlled membrane inlet. The membrane introduction mass spectrometer (MIMS) is coupled with a resistively heated metal gas chromatography capillary column, which serves as a transfer line between the bioreactor and the MIMS. Sampling and injection is performed by means of a pneumatically driven membrane probe, which enables monitoring of soluted and gaseous substances in the fermentation broth. The system can also be coupled to other processes.     

Direct detection of polyaromatic hydrocarbons, estrogenic compounds and pesticides in water using desorption chemical ionisation membrane inlet mass spectrometry

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.     

Enzyme immunoelectrode for insulin incorporating a membrane partially treated with water vapour plasma

An enzyme immunoelectrode for the amperometric determination of serum insulin is described. The device consists of an immunoreactive membrane combined with a hydrogen peroxide electrode. The surface of a microporous hydrophobic polypropylene membrane is modified by water vapour plasma treatment to make it partially hydrophilic. Subsequent treatment with octamethylenediamine and glutaraldehyde enables the surface of this membrane to interact with various proteins. Anchoring of the antibody to Protein A immobilized on the membrane was effective for immunoreactivity.