Direct Current Glow Discharge Mass Research Articles

The use of a secondary cathode to analyse solid non-conducting samples with direct current glow discharge mass spectrometry: potential and restrictions.

A direct current glow discharge mass spectrometer has been used to analyse solid non-conducting samples: glass, polycarbonate, marble, aluminium oxide and Teflon. This is made possible by the use of a so-called secondary cathode. The methodology of this concept is investigated and analytical figures of merit are presented.

Improvement of analyte to interferent line intensity ratio in direct current glow discharge mass spectrometry

Elemental analysis by quadrupole mass spectrometry with direct current powered glow discharge ion source has been improved for flat Cu samples. The line ratio of analyte to Ar-related interferents can be enhanced for several orders of magnitude when ion source geometry, ion extraction system and operating parameters are optimised quasi-simultaneously. Such an extreme improvement may partially be explained by different ion energy distributions depending on their origin: matrix and analytes, working gas, residual gases. Probably it is due to a synergistic effect of several processes needing further investigation.

Glow Discharge Mass Spectrometric Analysis of Atmospheric Particulate Matter

A direct current (dc) glow discharge mass spectrometer has been used to analyze atmospheric particulate matter. The sample preparation used is simple and time-saving. The air is sucked by a pump through a single-orifice impactor stage, in which the aerosols are impacted on a metal support, forming a central spot. This metal plate is directly used as a cathode in a dc glow discharge mass spectrometer. Evaluation of the sample loading and of the discharge parameters allowed us to optimize the signal intensity and to minimize its decrease, the latter being a consequence of its consumption by continuous sputtering in the discharge. The available aerosol analysis time could be prolonged to more than 3 h, a time span necessary to perform a multielement analysis using a magnetic sector instrument and long integration times. A NIST reference aerosol was measured to evaluate the quantitative analysis potential. The internal reproducibility was better than 10% RSD, and the limits of detection were estimated to be in the low ppm or sub ppm region. Even without the use of any standards or correction factors, glow discharge mass spectrometry could offer good semiquantitative results, based only on the use of an internal standard.

Optimization of secondary cathode thickness for direct current glow discharge mass spectrometric analysis of glass

Direct current glow discharge mass spectrometry can be used for the analysis of solid non-conducting samples by application of the secondary cathode technique. In the work reported, the thickness of this secondary cathode, a conducting diaphragm placed in front of the sample, was evaluated. Variation of the secondary cathode thickness results in a variation of the electrode configuration and of the discharge voltage required for stable atomization of the non-conductor. Both parameters were evaluated separately using conducting samples. Thickness and voltage were found to have an opposite effect on the sample signal intensity obtained and on the crater shape created. Generally, it could be concluded that, for the determination of elements at low concentrations in glass plates, a thin secondary cathode is preferable, but that the use of a thick secondary cathode results in a flatter crater profile, which is important for depth profiling.

Direct Current Glow Discharge Mass Spectrometric Analysis of Macor Ceramic Using a Secondary Cathode

A direct current glow discharge mass spectrometer has been used for the analysis of Macor, a nonconducting glass ceramic. To overcome the problem of the conductivity barrier, a tantalum secondary cathode was placed in front of the flat Macor sample. Although the sample characteristics of Macor (the electrical conductivity and the surface roughness) are very comparable to those of glass, the optimum discharge conditions for Macor analysis were found to be significantly different from those previously reported for glass. Nevertheless, successful measurements of Macor could be performed, revealing limits of detection in the sub-ppm range.

Use of a direct current glow discharge mass spectrometer for the chemical characterization of samples of nuclear concern

Direct current GDMS has been applied to conducting and non-conducting nuclear samples, namely, different types of nuclear fuels, cladding materials and nuclear-waste glasses. For the non-conducting oxide-based nuclear samples the relative sensitivity factors (RSFs), applied for quantitative analysis, are affected by the oxygen content in the matrix. For these samples the effect of ‘getter metals,’ such as tantalum and titanium as binder material, has been investigated and the results compared with those obtained using silver as the host matrix. Moreover, when tantalum was used as a secondary cathode, it was found to behave as a getter of oxygen. For the quantitative analysis of nuclear-waste glasses the use of matrix specific RSFs was necessary. Comparisons with RSFs obtained from other workers are made. Metallic alloys were analysed using several analytical techniques. The GDMS results obtained applying RSFs from the major metallic element uranium were in agreement with those from independent techniques, such as titration, thermal ionization MS and ICP-MS.

An innovative sample preparation procedure for trace and ultra-trace analysis on non-conducting powders by direct current glow discharge mass spectrometry

A novel preparation procedure has been developed in order to obtain stable, pin-shaped samples for the elemental analysis of non-conducting powders by direct current glow discharge mass spectrometry (dc GDMS): up to now, this technique has been mainly used for the characterization of metals and semiconductors. This work deals with a particular analytical application of the infiltration process, which is frequently employed for producing metal-matrix composites (MMC) for structural applications. The preparation procedure has been tested on germanium dioxide GeO 2, an inorganic compound available as high-purity powder. However, the method is, in principle, of general applicability: considering the quality of the results obtained so far, it might be particularly suitable for the detection of traces in powdered, non-conducting materials such as ceramics, bio-inorganics, soils, sediments and for the quantitation of major and minor elements in cases where limited amounts of samples are available (e.g. archaeological findings). The reproducibility of the preparation process is satisfactory: repeated observations by reflected light microscopy (RLM) prove that the oxide grains are homogeneously distributed within a well bounded region of the metallic host matrix. The use of composite pin-shaped samples leads to a rapid stabilization of the plasma discharge, with the consequence that the analytical results are generally superior to those obtained on similar samples prepared by more conventional procedures. In particular, from the ratio of the signals due to Ge + and GeO +, it can be seen that a large predominance of the former species is quickly established in the plasma, with a correspondingly fast achievement of high detection sensitivities.

Relative sensitivity factors in direct current glow discharge mass spectrometry using Kr and Xe gas ? Estimation of the role of Penning ionization

Relative sensitivity factors (RSF) (Fe=1) were determined for steel, aluminium and copper standard samples by direct current glow discharge mass spectrometry using Kr and Xe as discharge gas. In general, the RSF values in Kr and Xe were higher than in Ar; however for S and P in Kr gas and P, As and Se in Xe gas they were considerably lower. This decrease is related to the relative importance of the Penning ionization process in overall ionization of the sputtered species. The results showed the percentage of Penning ionization to account for 75.6–82.0% for Se, As and P and 64.2% for S.

Comparison between direct current and radiofrequency glow discharge mass spectrometry for the analysis of oxide-based samples

Glow discharge mass spectrometry (GDMS) using either a direct current (dc) or a radiofrequency (rf) discharge has been evaluated. For conducting samples, comparable results are obtained, as indicated by the uniformity in relative sensitivity factors (RSFs). For the analysis of rare earth oxide materials, the RSFs for dc GDMS are far less affected by changes in discharge pressure and sample to exit-orifice distance than those obtained for rf GDMS. Despite the higher variability of RSFs for rf GDMS, very stable and reproducible plasma conditions are obtained when working at a fixed pressure and distance. The latter is indicated by the internal (within-sample) and external (sample-to-sample) reproducibility of less than 5 and 15%, respectively.