Radiofrequency Glow Discharge Mass Spectrometry Research Articles

Signal Enhancement with Stacked Magnets for High-Resolution Radio Frequency Glow Discharge Mass Spectrometry.

A method for signal enhancement utilizing stacked magnets was introduced into high-resolution radio frequency glow discharge-mass spectrometry (rf-GD-MS) for significantly improved analysis of inorganic materials. Compared to the block magnet, the stacked magnets method was able to achieve 50-59% signal enhancement for typical elements in Y2O3, BSO, and BTN samples. The results indicated that signal was enhanced as the increase of discharge pressure from 1.3 to 8.0 mPa, the increase of rf-power from 10 to 50 W with a frequency of 13.56 MHz, the decrease of sample thickness, and the increase of number of stacked magnets. The possible mechanism for the signal enhancement was further probed using the software "Mechanical APDL (ANSYS) 14.0". It was found that the distinct oscillated magnetic field distribution from the stacked magnets was responsible for signal enhancement, which could extend the movement trajectories of electrons and increase the collisions between the electrons and neutral particles to increase the ionization efficiency. Two NIST samples were used for the validation of the method, and the results suggested that relative errors were within 13% and detection limit for six transverse stacked magnets could reach as low as 0.0082 μg g-1. Additionally, the stability of the method was also studied. RSD within 15% of the elements in three nonconducting samples could be obtained during the sputtering process. Together, the results showed that the signal enhancement method with stacked magnets could offer great promises in providing a sensitive, stable, and facile solution for analyzing the nonconducting materials.

Effect of H2/Ar mixtures on the analysis of conducting and insulating materials by radiofrequency glow discharge mass spectrometry

The effect of the addition of hydrogen to a radiofrequency–argon glow discharge coupled to a time of flight mass spectrometer has been studied. Pressure and forward power conditions in the discharge were kept constant. The hydrogen concentrations added to the argon plasma gas were 0.5%, 1% and 10% v/v and two types of homogeneous samples were investigated: a conducting material (nickel-base) and two glasses. A decrease of the dc-bias voltage with increasing H2 concentration was observed at every forward power assayed. For the nickel material, the analytical signals turned out to be higher in 10% H2/Ar and 1% H2/Ar discharges than in pure Ar, while for 0.5% H2/Ar the increases were just obtained at the lowest power assayed. Concerning the glass samples, signal increases were obtained at the powers assayed for most analytical signals using 0.5% H2/Ar instead of pure Ar.

Trace and ultratrace analysis of gallium arsenide by different mass spectrometric techniques

The capability of different solid-state mass spectrometric methods [spark source mass spectrometry (SSMS), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), radiofrequency glow discharge mass spectrometry (rf GDMS) and secondary ion mass spectrometry (SIMS)] in comparison with inductively coupled plasma mass spectrometry (ICP-MS) was investigated by the trace analysis of GaAs. For trace analysis using solid-state mass spectrometry, a semiconducting laboratory GaAs standard (using high-purity GaAs) doped with Zn, B, Si, Ge, Sn, Sb, P, S, Se and Te (in the µg g–1 concentration range) was prepared by the liquid encapsulation vertical Bridgeman technique. A selected piece of the synthetic laboratory GaAs standard was investigated directly by SIMS, SSMS, rf GDMS and LA-ICP-MS. For the quantification of SIMS measurements single element ion-implanted GaAs certified reference standards were used. After dissolution of the GaAs sample in high-purity HNO3–H2O2, the concentrations of the doped elements were measured by ICP-MS and inductively coupled plasma atomic emission spectrometry (ICP-AES). By using the results of SIMS, ICP-MS and ICP-AES for the selected piece of the synthetic laboratory GaAs standard, relative sensitivity coefficients (RSCs) of the elements in SSMS, rf GDMS and LA-ICP-MS were determined. The experimentally determined RSCs were used for correcting measured concentrations in an unknown GaAs sample.In order to reduce matrix effects in ICP-MS, a procedure for complete GaAs matrix separation in a chlorine–argon stream at 280 °C was evaluated. The recoveries of 24 elements after the chlorination of GaAs were determined to be nearly 100% (except for Sn and Ta). Ultratrace analysis of semiconducting GaAs after matrix separation was carried out by double-focusing sector field ICP-MS. The detection limits of ultratrace elements in GaAs after matrix separation (in the low ng g–1 concentration range) were better by about one order of magnitude compared with measurements without matrix separation and were comparable to those obtained by solid-state mass spectrometry.

Cryogenically cooled sample holder for polymer sample analysis by radiofrequency glow discharge mass spectrometry

A cryogenically cooled sample holder has been constructed for use in the analysis of polymeric materials by radio frequency glow discharge mass spectrometry (rf-GDMS). Passage of liquid nitrogen through the body of a brass sample backing plate cools the sample down to temperatures of approximately −170°C. The cryo-cooled sample holder is readily adaptable to existing direct insertion probe assemblies commonly used in GDMS instrumentation. The benefits of low temperature cooling are illustrated in terms of the ability to analyze thermally sensitive polymers without evidence of degradation, greater temporal stability of the ion signal, and the reduction of proton transfer reactions to polymer fragment species (due to the presence of residual water vapor). Implementation of the cryo-cooled sample holder opens up many possibilities for the direct analysis of solid polymers by rf-GDMS.

Investigations on cluster and molecular ion formation by plasma mass spectrometry

The formation of molecular and cluster ions of different inorganic materials in plasma mass spectrometry – spark source mass spectrometry (SSMS), radiofrequency glow discharge mass spectrometry (rf GDMS), laser ionization mass spectrometry (LIMS), inductively coupled plasma mass spectrometry (ICP-MS) and laser ablation ICP-MS (LA-ICP-MS) – was investigated and compared. Similar abundance distributions of cluster ions were observed for a graphite sample, for boron nitride/ graphite and for metal oxide/graphite mixtures using different plasma mass spectrometric methods. A correlation of intensities of metal argide ions in ICP-MS with their bond dissociation energies was used to estimate unknown dissociation energies of molecular ionic species. For the elements of the 2nd or 3rd period in the periodic table, the intensities of most argon molecular ions (ArX+) measured by ICP-MS rise with increasing atomic number in a similar manner to the theoretically calculated bond dissociation energies of argon molecular ions.

Application of RF GDMS for trace element analysis of nonconducting La 0.65 Sr 0.3 MnO 3 ceramic layers

Radio-frequency glow discharge mass spectrometry (RF GDMS) has been applied to the determination of trace elements in ceramic perovskite layers (La0.65Sr0.3MnO3) using synthetic standards. For the preparation of these standards high-purity powder of the basic material (La0.65Sr0.3MnO3) was doped with trace elements in concentrations from 20 to 500 μg/g and the mixture was pressed to compact samples. The resulting calibration curves and the calculated relative sensitivity factors (RSF) differed only from 0.4 to 2 for different elements. For nearly all elements the standard deviations in the determination of trace elements in La0.65Sr0.3MnO3 were better than 15% and detection limits (using the 3σ-criterion) were below 10 μg/g. Changes of the discharge parameters (RF power, pressure of the discharge gas (Ar) in the RF glow discharge) have no significant influence on the sensitivity to elements.

Analysis of semiconducting materials by high-resolution radiofrequency glow discharge mass spectrometry

The analytical capabilities of a high-resolution mass spectrometer in combination with a 13.56 MHz glow discharge ion source for the analysis of semiconducting materials (silicon carbide and gallium arsenide) were studied. It was shown that single positively charged ions of sample material have about 10 eV higher average energy than the ions of the discharge and residual gas. Therefore effective energy separation of the ions of analyte from the ions of the discharge and residual gas was achieved by adjusting the ion transfer optics (breadth and position of energy slit), which improves the analytical capabilities of the developed method. Some analytical applications are presented to illustrate the performance of r.f. GDMS for the bulk analysis of semiconducting materials. The results of the trace element analysis of gallium arsenide and silicon carbide samples are compared with data of independent methods (LIMS, ICP..AES, SIMS).

Mass spectrometric analysis of ceramic components for solid oxide fuel cells

For the determination of trace impurities in ceramic components of solid oxide fuel cells (SOFCs), some mass spectrometric methods have been applied such as spark source mass spectrometry (SSMS), laser ionization mass spectrometry (LIMS), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and inductively coupled plasma mass spectrometry (ICP-MS). Due to a lack of suitable standard reference materials for quantifying of analytical results on La x Sr y MnO3 cathode material a matrix-matched synthetic standard-high purity initial compounds doped with trace elements-was prepared in order to determine the relative sensitivity coefficients in SSMS and LA-ICP-MS. Radiofrequency glow discharge mass spectrometry (rf-GDMS) was developed for trace analysis and depth profiling of thick non-conducting layers. Surface analytical techniques, such as secondary ion mass spectrometry (SIMS) and sputtered neutral mass spectrometry (SNMS), were used to determine the element distribution on surfaces (homogeneity) and the surface contaminants of SOFC ceramic layers.

Trace and surface analysis of ceramic layers of solid oxide fuel cells by mass spectrometry.

For the trace analysis of impurities in thick ceramic layers of a solid oxide fuel cell (SOFC) sensitive solid-state mass spectrometric methods, such as laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and radiofrequency glow discharge mass spectrometry (rf-GDMS) have been developed and used. In order to quantify the analytical results of LA-ICP-MS, the relative sensitivity coefficients of elements in a La(0.6)Sr(0.35)MnO(3) matrix have been determined using synthetic standards. Secondary ion mass spectrometry (SIMS) - as a surface analytical method - has been used to characterize the element distribution and diffusion profiles of matrix elements on the interface of a perovskite/Y-stabilized ZrO(2) layer. The application of different mass spectrometric methods for process control in the preparation of ceramic layers for the SOFC is described.

Radiofrequency glow discharge mass spectrometry for gas chromatographic detection: a new departure for elemental speciation studies

An rf glow discharge source operating at 30 W power and about 0.6 mbar pressure was utilized as a detector for tetraalkyltins separated by gas chromatography. These were the optimized power and pressure values. Detection levels of about 1 pg were comparable to some of the lowest reported literature values, even with a non-vented chromatographic experiment. NIST SRM 2715 Lead in Reference Fuel was used to test the analytical capabilities of the technique with good results. In an exciting new departure for elemental speciation studies, structural information can be obtained by scanning the mass spectrum at each chromatographic peak. Fragment information was also available from the SRM.

Analysis of ceramic layers for solid oxide fuel cells by laser ablation inductively coupled plasma mass spectroscopy

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was used for the direct analysis of ceramic layers [La0.65Sr0.3MnO3 and yttria-stabilized ZrO2(YSZ)] forming parts of solid oxide fuel cells. For the quantitative determination of trace element concentrations calibration was performed with matrix-matched synthetic laboratory standards, prepared specially for these ceramic materials. With a few exceptions the regression coefficients of the calibration curves were better than 0.995 (n= 15). The detection limits for most elements are in the range 0.1–2 µg g–1 in La0.65Sr0.3MnO3 and YSZ. Investigations on ceramics, doped with trace elements with concentrations of some 100 µg g–1, showed lower concentrations of the elements than were added, owing to the sintering process at temperatures of 1400 °C. In non-doped YSZ layers different elements were determined at concentrations from sub-µg g–1 to hundreds of µg g–1. The results were found to be in good agreement with those obtained by other methods (ICP-MS and radiofrequency glow discharge mass spectrometry).

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.