Christopher M. Barshick

Analysis of soils by glow discharge mass spectrometry

The analysis of soils by conventional solution-based techniques, such as inductively coupled plasma and thermal ionization mass spectrometry, is complicated by the need for sample dissolution or the combination of a solids atomizer with an auxiliary ionization source. Since time is an important consideration in waste remediation, there exists a need for a method of rapidly analysing many soil samples with little sample preparation; glow discharge mass spectrometry (GDMS) has the potential to meet this need. Because GDMS is a bulk solids technique, sample preparation is simplified in comparison to other methods. It appears that, even with the most difficult samples (geological materials, such as soils and volcanic rock), all that is required is grinding, drying and mixing with a conducting host material prior to electrode formation. As a first test of GDMS for soil analysis, a National Institute of Standards and Technology (NIST) Standard Reference Material (SRM) was analysed by direct current GDMS. Fifty-one elements were quantified from a single cathode using ion beam ratios and ‘standard’ relative elemental sensitivity factors (RSF). Average errors for the suite of elements were less than a factor of 4 and 1.4 for uncorrected and corrected values, respectively. User-generated RSF values were applied to the analysis of several elements in NIST SRM 2704 Buffalo River Sediment. In the absence of isobaric interferences, accuracies ranging from 0.6 to 73% were observed, demonstrating the potential of the technique for the determination of many elements. The presence of entrained water and inhomogeneity resulting from cathode preparation is thought to affect matrix-to-matrix reproducibility. While further success depends on developing means of circumventing mass spectral interferences and addressing factors affecting plasma chemistry, the immediate goal of developing a screening method for priority metals in soils was met.

Direct Measurement of Uranium Isotopic Ratios in Soils by Glow Discharge Mass Spectrometry

Since the current methodology mandated by the environmental protection agency (EPA) for the determination of isotope ratios of priority metals in sediments, sludges, and soils is both time consuming and labor intensive, it would clearly be of great value in environmental surveys if there were a procedure capable of direct analysis of these materials with little or no sample preparation. A method that holds promise in this regard is glow discharge mass spectrometry (GDMS). GDMS has several characteristics that make it worthy of evaluation; essentially all elements are amenable to analysis, preliminary results indicate isotopic biases are small, and the determination of isotopic ratios at the sub-ppm level is a reasonable hope since detection limits are in the sub-ppb range. Furthermore, previous studies have indicated that GDMS is a fairly precise method for providing isotopic information with good precision; precisions better than 0.05% relative standard deviation (RSD) have been obtained.

Factors Influencing the Quantitative Determination of Trace Elements in Soils by Glow Discharge Mass Spectrometry

The influence of oxygen content, conducting host matrix, and soil composition on the quantitative determination of trace elements in soils by glow discharge mass spectrometry was examined. Oxygen content and conducting host matrix identity influenced relative sensitivity factors employed in the quantitative interpretation of the glow discharge mass spectra. Soil composition did not influence these relative sensitivity factors. Unknown soils taken from the field were analyzed with the use of a set of relative sensitivity factors obtained from standard soils with certified compositions. The quantitative results from glow discharge mass spectrometry of these unknowns compared favorably with quantitative results from inductively coupled plasma atomic emission spectrometry and laser ablation solid sampling inductively coupled plasma mass spectrometry.

Development of a technique for the analysis of inorganic mercury salts in soils by gas chromatography/mass spectrometry

Abstract A technique has been developed to analyze environmentally relevant samples for organic and inorganic mercury compounds. A solid phase microextraction (SPME) fiber was used as a sampling medium in both water and water/soil slurries. Quantification of inorganic mercury was accomplished through a chemical alkylation reaction designed to convert an inorganic mercury salt to an organomercury compound prior to GC/MS analysis; this was found to be the rate limiting step in the analysis. Two alkylating reagents were investigated: methylpentacyanocobaltate (III) (K3[Co(CN)5CH3]) and methylbis(dimethylglyoximato)pyridinecobalt (III) (CH3Co(dmgH)2Py). Methylbis(dimethylglyoximato)pyridinecobalt (III) was found to be superior for this application because it produced a single reaction product, methylmercury iodide, with an efficiency of ∼95%. Detection limits were ∼7 ppb in water and ∼2 ppm in soil. The poorer results in soil were due to an increase in background signal (∼10 times compared to water) and a reduction in analyte signal (as much as 100 times). This reduction in signal intensity is believed to be caused by complex soil chemistry. Manipulation of the solution chemistry [e.g. oxidation of mercury (0) → mercury (II)], before or during the alkylation step, may improve the detection limits and increase the number of elements amenable to analysis. Keywords: Gas chromatography/mass spectrometry; Inorganic analysis; Elemental; Mercury compounds; Chemical alkylation

Elemental and Organometallic Analyses of Soil Using Glow Discharge Mass Spectrometry and Gas Chromatography/Mass Spectrometry

Glow discharge mass spectrometry (GDMS) and gas chromatography/mass spectrometry (GC/MS) have been evaluated as techniques for total elemental assay in soil. GDMS analysis demonstrated accurate elemental quantification for lead and tin (approximately 20% error at the 10 ppm level). Limitations were encountered, however, when the element of interest was volatile, as in the case of mercury, or when the element was not an inorganic salt but a volatile organometallic compound. GC/MS was investigated as an alternative means of providing both organometallic compound analysis and elemental quantification. A solid-phase microextraction fiber was demonstrated to be an effective sampling medium for several organometallic compounds in both water and a water/soil slurry. Quantification of inorganic mercury species was facilitated by using an alkylating reagent (methylpentacyanocobaltate (III)) to produce an organomercurial that could be analyzed by GC/MS. Although the reaction proceeded as anticipated, several additional observations were made that may be exploited in future studies.

Analysis of solution residues by glow discharge mass spectrometry.

A technique for the analysis of microliter volumes of solution by glow discharge mass spectrometry (GDMS) has been successfully demonstrated. Cathode preparation involves mixing an aliquot of the sample solution with a pure conducting powder, followed by drying and pressing before conventional GDMS analysis. The analyte signal at the 100-ppm level was observed to be stable to better than 5% for the duration of the analysis (30–45 min). Internal and external reproducibilities were better than 5%, and the ion signal intensity was linear with concentration over at least four orders of magnitude. Quantification was demonstrated by means of user-defined relative sensitivity factors. Relative standard deviations were better than 15% for the elements investigated, with no preconcentration of the analyte.

Pulsed-Gas Glow Discharge for Ultrahigh Mass Resolution Measurements with Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

A new pulsed-gas glow discharge (GD) source has been developed for use with an external ion source Fourier transform ion cyclotron resonance (FTICR) mass spectrometer. With pulsed argon gas introduction into the GD source, the gas load and pressure in the mass analyzer region were greatly reduced; this resulted in improved mass resolution. Mass resolution of greater than 1 450 000 (fwhm) has been achieved for Cu(+) ions from a brass sample, the highest reported for any type of GD mass spectrometer. The pulsed-gas GD source promises analytical usefulness for ultrahigh resolution measurements in GD mass spectrometry.

Isotope ratio measurements using glow discharge mass spectrometry

Abstract Glow discharge mass spectrometry (GDMS) has been evaluated for its ability to measure isotope ratios in solids. Isotope ratios were measured for B, Cu, Sr, Ag, Sb, Re and Pb in concentrations ranging from 15 ppm to pure metal. External precision of better than 0.03% has been achieved for isotope ratios measured using pure solid elemental samples; typical precision is better than 0.1% for elements present in concentrations greater than 0.5 wt.%. For elements present in concentrations of 10–20 ppm, precision was about 1%. Isotopic bias was

Ultrahigh mass resolution glow discharge mass spectrometry : direct analysis of heavy isotope mixtures

Abstract A number of advantages can be realized in the coupling of glow discharge (GD) sources to Fourier transform ion cyclotron resonance (FTICR) mass spectrometers. Foremost among these is mass resolving power in the range of 1 part in 200 000–700 000, a considerable improvement over all currently available commercial instrumentation, which has a maximum resolution of 20000. At the higher resolving power, closely spaced isotopic pairs such as 238 U and 238 Pu, 198 Hg and 198 Pt, and 204 Pb and 204 Hg can be analyzed without the conventional time consuming chemical separation step that normally precedes an isotopic measurement.

An improved ion guide for external ion injection in glow discharge—fourier transform ion cyclotron resonance mass spectrometry.

To improve the existing ion transport optics of our glow discharge (GD)-Fourier transformion cyclotron resonance (FT-ICR) mass spectrometer, we simulated several ion trajectories between the GD source region and the ICR analyzer cell. These calculations suggested that a number of simple improvements, including the use of an ion flight tube and an electrically isolated conductance limit, would increase the efficiency of ion transfer through the fringing fields of the FT-ICR superconducting magnet and into the ICR analyzer cell. Ion beam intensity was monitored as a function of the distance between the GD source and the analyzer cell before and after implementing these improvements. A twentyfold improvement in the transport efficiency, as well as a fifteenfold enhancement in detected ET-ICR signals, was observed.