Single-sided membrane introduction mass spectrometry for on-line determination of semi-volatile organic compounds in air.

Construction, optimization, and testing of a novel single-sided configuration for a semi-permeable [poly(dimethylsiloxane); PDMS] membrane introduction system for mass spectrometry is described. On-line detection of semi-volatile organic compounds of environmental interest is shown, including lindane (a pesticide), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) (an explosive), butylated hydroxytoluene (BHT) (an antioxidant), 1,2-dichlorobenzene, dimethylmethyl phosphonate (DMMP) (a chemical warfare agent simulant) and naphthalene. The technique has limits of detection in the sub-ppb range. with rise times of 4 to 7 s and fall times of 12 to 36 s and a response that is linear over 4 orders of magnitude (from 0.1 ppb to 1000 ppb for DMMP). The cycle time, from crude air sampling to acquisition of results, is approximately 1 min. No sample preparation is necessary.     

A universal temperature controlled membrane interface for the analysis of volatile and semi-volatile organic compounds

A universal temperature controlled membrane interface (TCMI) has been constructed for hollow-fibre membranes. The membrane temperature is controllable in the range -70 to 250 degrees C using an electric heater and a flow of cooled nitrogen or helium gas. Volatile and semi-volatile organic compounds may be detected either by continuous diffusion across the membrane or by in-membrane pre-concentration followed by thermal desorption into the detector. The TCMI interface is demonstrated in combination with mass spectrometry and GC-MS, for the determination of VOCs and SVOCs in aqueous and air samples and for the on-line monitoring of a bioreactor.     

Selective and sensitive detection of organic contaminants in water samples by on-line trace enrichment–gas chromatography–mass spectrometry

Liquid chromatographic (LC) type trace enrichment is coupled online with capillary gas chromatography (GC) with mass spectrometric (MS) detection for the analysis of aqueous samples. A volume of 1–10 ml of an aqueous sample is preconcentrated on a trace-enrichment column packed with a polymeric stationary phase. After cleanup with HPLC-grade water the precolumn is dried with nitrogen and subsequently desorbed with ethyl acetate. A fraction of 60 μl is introduced on-line into a diphenyltetramethyldisilazane-deactivated retention gap under partially concurrent solvent evaporation conditions and using an early solvent vapor exit. The analytes are separated and detected by means of GC–MS. The potential of the LC–GC–MS system for monitoring organic pollutants in river and drinking water is studied. Target analysis is carried out with atrazine and simazine as model compounds; the detection limits achieved under full-scan and multiple ion detection conditions are 30 pg and 5 pg, respectively. Identification of unknown compounds (non-target analysis), is demonstrated using a river water sample spiked with 168 pollutants varying in polarity and volatility.     

On-line flow injection analysis of volatile organic compounds in seawater by membrane introduction mass spectrometry

The combination of flow injection analysis with membrane introduction mass spectrometry for analysis of volatile organic compounds (VOCs) in seawater is examined and is compared to measurements made in water. Membrane introduction mass spectrometry is performed using a benchtop ion trap mass spectrometer, and characterization of various aspects of the flow injection and ion trap combination for the analysis of volatile organic compounds (including anthropogenic halocarbons) in seawater is carried out. The analyte responses are shown to be linear over several orders of magnitude (e.g. for methylene chloride), independent of seawater pH (e.g. for chlorobenzene) and independent of matrix effects for the VOCs studied. A comparison of the performance of a microporous (Teflon) membrane with that of an amorphous silicone membrane is made, and the former is shown to provide lower detection limits which are in the parts-per-trillion range (300 ppt for chlorobenzene, 190 ppt for trans-1,2-dichloroethene). The microporous membrane provides faster response times by a factor of four to five for relatively more polar compounds, such as chlorobenzene. An analysis of a seven-component mixture demonstrates the ability of this on-line combination to allow multicomponent analysis of mixtures of some complexity.     

Novel applications of highly sensitive liquid chromatography/mass spectrometry/mass spectrometry for the direct detection of ultra-trace levels of contaminants in water

Recent advances in the sensitivity of liquid chromatography/mass spectrometry (LC/MS) instrument technology provide the basis for the direct detection, i.e. without sample pre-concentration, of organic contaminants in water in the ng/L range. Novel applications for the analysis of atrazine and some of its desalkylated and hydroxylated degradation products, the pharmaceutical compounds diclofenac and carbamazepine, sulfonylurea herbicides, and iodinated X-ray contrast media have been developed. For each analyte a specific tandem mass spectrometric (MS/MS) transition has been selected and the corresponding mass spectrometric parameters optimised. All analytes could be analysed within three specific analytical runs including different high-performance liquid chromatography (HPLC) conditions. Detection limits were determined to be better than 10 ng/L for the direct analysis of the compounds in water except for X-ray contrast media, for which detection limits were found to be up to one order of magnitude higher. The methods have been successfully utilised for the analysis of natural waters. Matrix effects frequently occurring in LC/MS have shown to be low to moderate in the case of X-ray contrast media. This work demonstrates that for the analysis of a large number of water contaminants, the sample pre-concentration step could possibly be omitted.     

Proton transfer reaction mass spectrometry for the sensitive and rapid real-time detection of solid high explosives in air and water

Relying on recent developments in proton transfer reaction mass spectrometry (PTR-MS), we demonstrate here the capability of detecting solid explosives in air and in water in real time. Two different proton transfer reaction mass spectrometers have been used in this study. One is the PTR-TOF 8000, which has an enhanced mass resolution (m/Δm up to 8,000) and high sensitivity (~50 cps/ppbv). The second is the high-sensitivity PTR-MS, which has an improved limit of detection of about several hundreds of parts per quadrillion by volume and is coupled with a direct aqueous injection device. These instruments have been successfully used to identify and monitor the solid explosive 2,4,6-trinitrotoluene (TNT) by analysing on the one hand the headspace above small quantities of samples at room temperature and from trace quantities not visible to the naked eye placed on surfaces (also demonstrating the usefulness of a simple pre-concentration and thermal desorption technique) and by analysing on the other hand trace compounds in water down to a level of about 100 pptw. The ability to identify even minute amounts of threat compounds, such as explosives, particularly within a complex chemical environment, is vital to the fight against crime and terrorism and is of paramount importance for the appraisal of the fate and harmful effects of TNT at marine ammunition dumping sites and the detection of buried antipersonnel and antitank landmines.

External interface for trap-and-release membrane introduction mass spectrometry applied to the detection of inorganic chloramines and chlorobenzenes in water.

Construction and evaluation of an external configuration trap-and-release membrane introduction system for mass spectrometry is described. This novel interface allows independent control of the temperature of the membrane and eliminates the dependence of membrane heating efficiency on its position in the ion source. The external trap-and-release MIMS configuration is successfully applied to detection of inorganic chloramines and chlorobenzenes. The method is shown to give temporal resolution of volatile vs. semi-volatile compounds, which increases its sensitivity for semi-volatiles in the presence of volatiles and provides an additional selectivity parameter. Further selectivity is provided by tandem mass spectrometry.     

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.     

Determination of ochratoxin A at parts-per-trillion levels in cereal products by immunoaffinity column cleanup and high-performance liquid chromatography/mass spectrometry

Ochratoxin A (OTA) is a toxic and potentially carcinogenic fungal toxin found in a variety of food commodities. A new sensitive method has been developed to quantify OTA in cereal products by reversed-phase liquid chromatography (LC) with mass spectrometric (MS) detection. Ochratoxin B was used as the internal standard. OTA was extracted from cereal products with acetonitrile-water, and the extract was diluted with a buffer; the diluted extract was cleaned up on an immunoaffinity column before LC/MS analysis. Two multiple-reaction monitoring transitions were used, one for quantification of OTA and one for confirmation of identity. The method was shown to be highly sensitive, with a low decision limit (CCalpha) of 0.012 microg/kg and a detection capability (CCbeta) of 0.021 microg/kg. Within-laboratory repeatability coefficient of variation values were 7.1, 3.7, and 3.1%, and the corresponding recoveries were 104, 106, and 103% for rice samples fortified with OTA at 0.05, 0.10, and 0.15 microg/kg, respectively. Method validation was performed according to the criteria of European Commission Decision 2002/657/EC. All criteria as presented in the Commission Decision were fulfilled. This method is the first fully validated method using immunoaffinity chromatography for cleanup and MS for detection in the analysis of cereals for OTA. The method was also successfully applied to cereal-derived products. The analytical results for determination of the OTA content of cereal products commercially available in Hong Kong are also reported.     

Determination of atrazine, deethylatrazine and simazine in water at parts-per-trillion levels using solid-phase extraction and gas chromatography/ion trap mass spectrometry

Methods for trace analysis of atrazine and simazine in water have been developed by using stable-isotope dilution with detection by gas chromatography/mass spectrometry. D(5)-Atrazine was used as the internal standard for the determination of atrazine and deethylatrazine, while (13)C(3)-simazine was used for simazine analysis. Water samples were fortified with known amounts of the internal standards and submitted to solid-phase extraction with a C(18) bonded-silica cartridge. A gas chromatograph coupled with an ion-trap mass spectrometer was used to analyze the water sample extracts. Method detection limits were 38 parts-per-trillion (ppt) for atrazine and deethylatrazine and 75 ppt for simazine. The accuracy of the method, represented by relative analytical errors, was less than 15%, and the method precision was less than 5% (relative standard deviation, n = 9). The method was successfully applied to analyze surface water samples collected from a reservoir and a river at ppt levels.     

Development of proton-transfer ion trap-mass spectrometry: on-line detection and identification of volatile organic compounds in air

We present a newly developed instrument that uses proton-transfer ion trap-mass spectrometry (PIT-MS) for on-line trace gas analysis of volatile organic compounds (VOCs). The instrument is based on the principle of proton-transfer reaction-mass spectrometry (PTR-MS): VOCs are ionized using PTRs and detected with a mass spectrometer. As opposed to a quadrupole mass filter in a PTR-MS, the PIT-MS instrument uses an IT-MS, which has the following advantages: (1) the ability to acquire a full mass spectrum in the same time as one mass with a quadrupole and (2) extended analytical capabilities of identifying VOCs by performing collision-induced dissociation (CID) and ion molecule reactions in the IT. The instrument described has, at its current status, limits of detection between 0.05 and 0.5 pbbv for 1-min measurements for all tested VOCs. The PIT-MS was tested in an ambient air measurement in the urban area of Boulder, Colorado, and intercompared with PTR-MS. For all measured compounds the degree of correlation between the two measurements was high (r ² > 0.85), except for acetonitrile (CH₃CN), which was close to the limit of detection of the PIT-MS instrument. The two measurements agreed within less than 25%, which was within the combined measurement uncertainties. Automated CID measurements on m/z 59 during the intercomparison were used to determine the contributions of acetone and propanal to the measured signal; both are detected at m/z 59 and thus are indistinguishable in PTR-MS. It was determined that m/z 59 was mainly composed of acetone. An influence of propanal was detected only during a high pollution event. The advantages and future developments of PIT-MS are discussed.     

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.     

A rapid and sensitive analysis of diphenylarsinic acid in water by gas chromatography/mass spectrometry.

A rapid and sensitive analytical method using pentafluorothiophenol (PFTP) derivatization was applied to detect diphenylarsinic acid (DPAA) in water. In this study, the optimum derivatization conditions, such as acid concentration, reaction time and reaction temperature, were investigated to develop a suitable procedure for DPAA determination. After extracting the derivatives into benzene, the determination was carried out by gas chromatography/mass spectrometry (GC/MS) with selected ion monitoring (SIM). The detection limit of the method was 9.4 microg/l, and the overall recoveries obtained from real environmental samples were 88.9 - 104.7% and coefficient variations were 5.1 - 13.9%.     

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).     

Passive sampling for volatile organic compounds (VOCs) in air at environmentally relevant concentration levels

A sensitive and reliable method is described for the determination of aromatic and chlorinated hydrocarbons (benzene, toluene, o-, m-, p-xylene, trichloromethane, trichloroethane, trichloroethene and tetrachloroethene) in indoor and outdoor air at environmental concentration levels. The procedure can be easily extended to other VOCs. Using passive samplers the VOCs have been adsorbed onto charcoal during a four-week sampling period and subsequently desorbed with carbon disulfide. After injection with a cold split-splitless multi-injector the VOCs have been separated by capillary gas chromatography. Quantification has been achieved using an electron capture detector (ECD) and a flame ionization detector (FID) switched in series. A limit of about 1 g/m³ for aromatic hydrocarbons and of about 0.01 g/m³ for chlorinated hydrocarbons has been obtained. The procedure has been successfully applied in the framework of a field study to measure indoor and outdoor air concentrations in Essen and Borken, two differently polluted areas of Northrhine-Westphalia.     

Sorbent-based sampling methods for volatile and semi-volatile organic compounds in air. Part 2. Sorbent selection and other aspects of optimizing air monitoring methods

Sorbent tubes/traps are widely used in combination with gas chromatographic (GC) analytical methods to monitor the vapour-phase fraction of organic compounds in air. Applications range from atmospheric research and ambient air monitoring (indoor and outdoor) to occupational hygiene (personal exposure assessment) and measuring chemical emission levels. Part 1 of this paper reviewed the main sorbent-based air sampling strategies including active (pumped) tube monitoring, diffusive (passive) sampling onto sorbent tubes/cartridges plus sorbent trapping/focusing of whole air samples that are either collected in containers (such as canisters or bags) or monitored online. Options for subsequent extraction and transfer to GC(MS) analysis were also summarised and the trend to thermal desorption (TD)-based methods and away from solvent extraction was explained. As a result of this trend, demand for TD-compatible sorbents (alternatives to traditional charcoal) is growing. Part 2 of this paper therefore continues with a summary of TD-compatible sorbents, their respective advantages and limitations and considerations for sorbent selection. Other analytical considerations for optimizing sorbent-based air monitoring methods are also discussed together with recent technical developments and sampling accessories which have extended the application range of sorbent trapping technology generally.     

The use of solid-phase microextraction in conjunction with a benchtop quadrupole mass spectrometer for the analysis of volatile organic compounds in human blood at the low parts-per-trillion level

The analysis of volatile organic compounds (VOCs) in whole human blood at the low parts-per-trillion level has until recently required the use of a high-resolution mass spectrometer to obtain the specificity and detection limits required for epidemiological studies of VOC exposure in the general public. Because of the expense and expertise required to operate and maintain a high-resolution instrument, the applicability of this method has been limited. These limitations are overcome in a new method using automated headspace solid-phase microextraction (SPME) in conjunction with a gas chromatograph and a benchtop quadrupole mass spectrometer. A combination of SPME and multiple single-ion monitoring minimizes the interferences and chemical noise associated with whole blood samples. This method permits the analysis of 10 VOCs in human blood while simplifying the sample preparation and reducing the possible exposure of the analyst to blood aerosols. Twelve samples can be run successively in a fully automated mode, thus eliminating the need for operator attention. Detection limits are below 50 ppt (pg/mL) for a majority of the VOCs tested with a 5-mL sample.     

A new gas chromatography/mass spectrometry method for the simultaneous analysis of target and non-target organic contaminants in waters

In this study we developed a GC–MS method for the analysis of priority pollutants, personal care products (PCPs) and other emerging contaminants in waters using large volume injection with backflushing. Analyses are performed in the SIM/scan mode, so that in addition to the targeted organic contaminants, this method allows the simultaneous screening of non-target compounds. The scan data are analysed using Deconvolution Reporting Software (DRS) which screens the results for 934 organic contaminants. Deconvolution helps identify contaminants that are buried in the chromatogram by co-extracted materials and significantly reduces chromatographic resolution requirements, allowing shorter analysis times. All compounds have locked retention times and we can continually update and extend the mass spectral library including new compounds. Linearity and limits of detection in SIM and full-scan mode were studied. Method detection limits (MDLs) in effluent wastewater ranged in most of the cases from 1 to 36 ng/L in SIM mode and from 4 to 66 ng/L in full-scan mode; while in river water from 0.4 to 14 and 2–29 ng/L in SIM and full-scan mode, respectively. We obtained a linearity of the calibration curves over two orders of magnitude. The method has been applied to the screening of a large number of organic contaminants – not only to a subset of targets – in urban wastewaters from different wastewater treatment plants and also in river waters. Most of the target compounds were detected at concentration levels ranging from 11 to 8697 ng/L and from 7 to 1861 ng/L in effluent wastewater and river waters, respectively. Additionally, a group of 12 new compounds were automatically identified using the AMDIS and NIST libraries. Other compounds, such as the 4-amino musk xylene, a synthetic fragrance metabolite, which was not included in the databases, but has been manually searched in the full-scan chromatograms.     

Pressure-assisted electrokinetic injection for on-line enrichment in capillary electrophoresis-mass spectrometry: a sensitive method for measurement of ten haloacetic acids in drinking water

Haloacetic acids (HAAs) are by-products of the chlorination of drinking water containing natural organic matter and bromide. A simple and sensitive method has been developed for determination of ten HAAs in drinking water. The pressure-assisted electrokinetic injection (PAEKI), an on-line enrichment technique, was employed to introduce the sample into a capillary electrophoresis (CE)–electrospray ionization–tandem mass spectrometry system (ESI-MS/MS). HAAs were monitored in selected reaction monitoring mode. With 3 min of PAEKI time, the ten major HAAs (HAA10) in drinking water were enriched up to 20,000-fold into the capillary without compromising resolution. A simple solid phase clean-up method has been developed to eliminate the influence of ionic matrices from drinking water on PAEKI. Under conditions optimized for mass spectrometry, PAEKI and capillary electrophoresis, detection limits defined as three times ratio of signal to noise have been achieved in a range of 0.013–0.12 μg L⁻¹ for ten HAAs in water sample. The overall recoveries for all ten HAAs in drinking water samples were between 76 and 125%. Six HAAs including monochloro- (MCAA), dichloro- (DCAA), trichloro- (TCAA), monobromo- (MBAA), bromochloro- (BCAA), and bromodichloroacetic acids (BDCAA) were found in tap water samples collected.     

A rapid and sensitive liquid chromatography/tandem mass spectrometry method for determination of docetaxel in human plasma

A novel, rapid and sensitive isocratic liquid chromatography/tandem mass spectrometry (LC/MS/MS) method was developed for quantification of docetaxel in human plasma with paclitaxel as internal standard. The high sensitivity and specificity of MS/MS detection enabled the use of a small volume of plasma (0.05 mL) and a simple liquid-liquid extraction procedure. Furthermore, a very short run-time (3 min) fulfilled the need for monitoring plasma levels of docetaxel from large-scale clinical studies. The calibration curve for docetaxel was linear over the range 5-1000 ng/mL with coefficients of correlation >0.999 using only 0.05 mL plasma. The intra- and inter-day precisions (CV) of analysis were <7%, and accuracy ranged from 96 to 110%. The applicability of the method was demonstrated in a pharmacokinetic study of a 1-h infusion of docetaxel with dosages of 75 mg/m(2). Possible conjugated metabolites of docetaxel were not detected in patients' samples.