Improving pulsed radiofrequency glow discharge for time-of-flight mass spectrometry simultaneous elemental and molecular analysis.

The performance of radiofrequency (rf) millisecond pulsed glow discharge (PGD) coupled to a fast orthogonal time-of-flight mass spectrometer (TOFMS) for chemical characterization and quantification of organic volatile compounds was investigated by using two different GD chamber designs. The designs investigated had substantial differences in the way that the volatile organic compound is introduced into the GD and the distance between the cathode and the sampling cone of the mass spectrometer. Bromochloromethane was selected as the model analyte because of the practical interest of determining trihalomethanes at low concentrations, and also because of both its low boiling point (to avoid problems associated with condensations in the interface) and the fact that it has two different heteroatoms, making the fragmentation patterns easier to follow. Pulse shapes of element, fragment, and molecular parent ions obtained by using the two GD chambers under investigation were critically compared. Results revealed the critical effect of the GD chamber geometry in obtaining the three types of chemical information, temporally discriminated. The spectra of the gaseous samples and of a polymer containing TBBPA (solid sample) were also compared. Detection limits for bromochloromethane in the order of low ng L(-1), and the required high tolerance of the plasmas to the introduction of organic vapours, were achieved using one of the proposed GD designs. The capability of the designed system for the analysis of other volatile compounds, for example dimethyl disulfide and dimethyl selenide, was also successfully evaluated, making use of the analytical potential of the information obtained from the different pulse time regions.

Elemental ratio determinations and compound-independent calibration using microsecond pulsed glow discharge time-of-flight mass spectrometry.

A new prototype based on a microsecond pulsed glow discharge ion source coupled to a time-of-flight mass spectrometer was recently designed, constructed and analytically evaluated in our laboratory for simultaneous collection of elemental and molecular information, and as a gas-chromatographic detector of compounds of environmental concern. To investigate further the analytical capabilities of such a new setup, its capability for the determination of element ratios in volatile organic halogenated compounds has been explored. Moreover, compound-independent calibration has been carried out with the prototype as well. The results demonstrated that the intensity ratios (analyte to internal standard) were linear with the corresponding ratio of concentrations. Both for chlorine and bromine (measured in the prepeak) and for BrC (measured in the plateau) the slope was 1 and the intercept was 0. Moreover, detection limits were improved by more than 1 order of magnitude as compared with using external calibration. The applicability of the proposed approach has been demonstrated for the straightforward determination of chloroform in drinking and river waters.

Plasma-based mass spectrometry for simultaneous acquisition of elemental and molecular information.

Chemical speciation studies are commonly accomplished by resorting to hyphenated analytical techniques, consisting of a powerful chromatographic separation technique coupled to a highly sensitive elemental spectrometric detector. However, in addition to this element-selective information, complementary molecular spectrometric tools are often required for a complete identification of macromolecules. Therefore, there is an increased research effort focused towards the development of integrated instruments to carry out the complete chemical speciation within a sample using a single instrument. An outline of recent developments in plasma-based mass spectrometric instrumentation for such comprehensive chemical speciation studies is here presented and their pros and cons detailed. In this context, the use of complementary techniques operating in parallel after splitting to a single chromatographic separation (dual sources) providing simultaneously elemental and molecular information is critically reviewed. Also, instrumental developments involving the use of stationary plasma sources operated in non-traditional modes (e.g. low pressure and low power) are also discussed. Moreover, the capabilities of tunable plasma-based ionization sources (allowing different ionization processes and, so, quasi-simultaneously providing elemental and molecular information with a single instrument) as a relatively simple and cheap approach are revised.

Gas chromatography coupled to tunable pulsed glow discharge time-of-flight mass spectrometry for environmental analysis.

A tuneable microsecond pulsed direct current glow discharge (GD)-time-of-flight mass spectrometer MS(TOF) developed in our laboratory was coupled to a gas chromatograph (GC) to obtain sequential collection of the mass spectra, at different temporal regimes occurring in the GD pulses, during elution of the analytes. The capabilities of this set-up were explored using a mixture of volatile organic compounds of environmental concern: BrClCH, Cl(3)CH, Cl(4)C, BrCl(2)CH, Br(2)ClCH, Br(3)CH. The experimental parameters of the GC-pulsed GD-MS(TOF) prototype were optimized in order to separate appropriately and analyze the six selected organic compounds, and two GC carrier gases, helium and nitrogen, were evaluated. Mass spectra for all analytes were obtained in the prepeak, plateau and afterpeak temporal regimes of the pulsed GD. Results showed that helium offered the best elemental sensitivity, while nitrogen provided higher signal intensities for fragments and molecular peaks. The analytical performance characteristics were also worked out for each analyte. Absolute detection limits obtained were in the order of ng. In a second step, headspace solid phase microextraction (HS SPME), as sample preparation and preconcentration technique, was evaluated for the quantification of the compounds under study, in order to achieve the required analytical sensitivity for trihalomethanes European Union (EU) environmental legislation. The analytical figures of merit obtained using the proposed methodology showed rather good detection limits (between 2 and 13 microg L(-1) depending on the analyte). In fact, the developed methodology met the EU legislation requirements (the maximum level permitted in tap water for the "total trihalomethanes" is set at 100 microg L(-1)). Real analysis of drinking water and river water were successfully carried out. To our knowledge this is the first application of GC-pulsed GD-MS(TOF) for the analysis of real samples. Its ability to provide elemental, fragments and molecular information of the organic compounds is demonstrated.

Tuneable microsecond-pulsed glow discharge design for the simultaneous acquisition of elemental and molecular chemical information using a time-of-flight mass spectrometer.

A microsecond-pulsed direct current glow discharge (GD) was interfaced and synchronized to a time-of-flight mass spectrometer MS(TOF) for time-gated generation and detection of elemental, structural, and molecular ions. In this way, sequential collection of the mass spectra at different temporal regimes occurring during the GD pulse cycle is allowed. The capabilities of this setup were explored using bromochloromethane as model analyte. A simple GD chamber, developed in our laboratory and characterized by a low plasma volume minimizing dilution of the sample but showing great robustness to the entrance of organic compounds in the microsecond-pulsed plasma, has been used. An exhaustive analytical characterization of the GD-MS(TOF) prototype has been performed. Calibration curves for bromochloromethane observed at the different time regimes of the GD pulse cycle (that is, for elemental, fragment, and molecular ions from the analyte) showed very good linearity for the measurement of the different involved ions, with precisions in the range of 7-13% (relative standard deviation). Actual detection limits obtained for bromochloromethane were in the range of 1-3 microg/L for elements monitoring in the GD pulse "prepeak", in the range of 11-13 microg/L when monitoring analyte fragments in the plateau, and about 238 microg/L when measuring the molecular peak in the afterpeak regime.

Bromine determination in polymers by inductively coupled plasma-mass spectrometry and its potential for fast first screening of brominated flame retardants in polymers and paintings.

The impact of brominated flame retardants (BFRs) on the environment and their potential risk in animal and human health is a present concern. Therefore, existing legislation in the European Union demands that polymers with BFRs are identified and eliminated from the recycling process due to their potential health hazard. In this work, a flow-injection (FI) system coupled to inductively coupled plasma-mass spectrometry (ICP-MS) was optimized for the detection of traces of bromine in polymers, plastic paints and enamels containing BFRs. Sample preparation requires a microwave-assisted digestion in order to transfer bromine in polymeric samples to solution. After appropriate optimization of the digestion procedure and the ICP-MS detection, a detection limit (DL) of 4.2 mg kg(-1) was obtained for synthesized polyurethane standards containing known concentrations of bromine. The precision of the proposed method, evaluated as the R.S.D. of signals obtained for three replicates of polymeric standard BFRs at the normative EU level, was as low as 3.6%. This simple developed methodology was characterized for the screening of bromine in polymeric matrices. The proposed system provides rapid binary yes/no overall responses, being appropriate for the screening of bromine above a pre-set concentration threshold. The unreliability region (UR), given by the probability of false positives and false negatives (set at 5% in both cases), was in the range between 442 and 678 mg kg(-1) of bromine (at a cut-off level of 0.1% in BFRs by weight of homogeneous material fixed by the EU normative). Finally, the applicability of the proposed screening system was tested for the reliable control of bromine in different commercial samples including flame-retardant paints and enamels.

Quantification of bromine in flame-retardant coatings by radiofrequency glow discharge-optical emission spectrometry.

There is an increasing concern regarding the toxicity and environmental distribution and impact of brominated organic compounds employed as flame retardants. Thus, present interest in searching for new analytical techniques and methods allowing a rapid, simple and reliable detection of those compounds in materials and wastes potentially containing such flame retardants is not surprising. The feasibility of using radiofrequency glow discharge plasma spectrometry coupled with optical emission spectrometry (rf-GD-OES) as a rapid and simple tool to directly analyse bromine-containing flame-retardant polymeric layers is investigated here. Polymeric layers for calibration were made by mixing appropriate amounts of tetrabromobisphenol A, bisphenol A, phloroglucinol and diphenylmethane-4,4'-diisocyanate in tetrahydrofuran. The corresponding blanks (polymers without tetrabromobisphenol A) were also prepared. Detection of bromine was investigated both in the visible (at 470.48 nm) and in the near-infrared (at 827.24 nm) regions, using a charge-coupled device for detection. Discharge parameters affecting the emission intensity of bromine were first optimized (in argon and helium as possible plasma gases) and the analytical performance characteristics were then evaluated. The best detection limit (0.044% Br) was achieved measuring Br I 827.24 nm in a He discharge, using a forward power of 70 W and a pressure of 45 Torr. The linearity range extended up to 27% Br. Finally, the applicability of the rf-GD-OES method proposed to the quantitative analysis of bromine in solid materials coated with flame-retardant commercial paints was successfully demonstrated.