Naoko Nonose

Determination of metal impurities in sulfamic acid by isotope dilution electrothermal vaporization inductively coupled plasma mass spectrometry

Metal impurities present at sub-ng g–1–ng g–1 levels in high-purity sulfamic acid reagents were determined by isotope dilution inductively coupled plasma mass spectrometry (ID-ICP-MS) with sample introduction by electrothermal vaporization (ETV). Matrix constituents causing suppression and enhancement of analyte signals were removed from the sample introduction system at the pyrolysis stage before ETV-ICP-MS measurement. As the ETV device, both tungsten and graphite furnaces were employed. In graphite furnace ETV-ICP-MS, it was necessary to use a chemical modifier in order to enhance the signal sensitivity and to obtain a linear calibration graph. In tungsten furnace ETV-ICP-MS, a linear relationship between the analyte mass and the signal was achieved without the use of a modifier but the stability of the isotope ratio measurement was slightly poorer than that in graphite furnace ETV-ICP-MS. The relative standard deviations obtained by ETV-ICP-MS using both furnaces were 6–30%. The analytical results for two types of sulfamic acid reagent obtained by tungsten furnace ETV-ICP-MS agreed with those obtained by graphite furnace ETV-ICP-MS.

Removal of isobaric interferences in isotope dilution analysis of vanadium in silicon nitride fine ceramics powder by DRC-ICP-MS

The National Metrology Institute of Japan (NMIJ) is developing certified reference materials (CRMs) of non-oxide fine ceramics such as silicon carbide and silicon nitride, and isotope-dilution mass spectrometry (IDMS) has been used as one of the key analytical methods for the determination of trace metals in CRMs. IDMS essentially requires two isotopes free from spectral interference; however, it is quite difficult to find such isotopes, especially in the determination of first transition metals. Therefore, specific measurement techniques are necessary to exclude the effect of the spectral interference. Spectral interferences due to the matrix and/or solvent can be removed by ICP-SFMS under a medium resolution. However, it is impossible to remove isobaric interference even with ICP-SFMS. Particularly in the isotope-dilution (ID) analysis of V in fine ceramics using ICP-MS, isobaric interference causes severe problem because the mass spectra for one of the two V isotopes overlaps with that for 50Ti and 50Cr. The authors proposed a new selective method for determination of V in the presence of Ti and Cr using DRC-ICP-MS with a CH3F + NH3 mixed reaction gas. We found formation efficiencies of [MF2(NH3)4]+ (M = V, Cr, Ti) significantly differed with elements, and the optimum condition for selective formation of [VF2(NH3)4]+ was found by controlling the gas-flow rates of CH3F and NH3. The IDMS analytical result of V in fine ceramics with this improved system agreed well with that obtained by a matrix matching calibration method within the expanded uncertainty. In conclusion the reduction of isobaric interference in DRC-ICP-MS expands the application fields of IDMS.

Comparison of 265 nm Femtosecond and 213 nm Nanosecond Laser Ablation Inductively Coupled Plasma Mass Spectrometry for Pb Isotope Ratio Measurements

The analytical performance of 265 nm femtosecond laser ablation (fs-LA) and 213 nm nanosecond laser ablation (ns-LA) systems coupled with multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS) for Pb isotope ratio measurements of solder were compared. Although the time-resolved signals of Pb measured by fs-LA-MC-ICPMS showed smoother signals compared to those obtained by ns-LA-MC-ICPMS, similar precisions on Pb isotope ratio measurements were obtained between them, even though their operating conditions were slightly different. The mass bias correction of the Pb isotope ratio measurement was carried out by a comparison method using a Pb standard solution prepared from NIST SRM 981 Pb metal isotopic standard, which was introduced into the ICP by a desolvation nebulizer (DSN) via a dual-sample introduction system, and it was successfully demonstrated for Pb isotope ratio measurements for either NIST 981 metal isotopic standard or solder by fs-LA-MC-ICPMS since the analytical results agreed well with the certified value as well as the determined value within their standard deviations obtained and the expanded uncertainty of the certified or determined value. The Pb isotope ratios of solder obtained by ns-LA-MC-ICPMS also showed agreement with respect to the determined value within their standard deviations and expanded uncertainty. From these results, it was evaluated that the mass bias correction applied in the present study was useful and both LA-MC-ICPMS could show similar analytical performance for the Pb isotope ratio microanalysis of metallic samples such as solder.

Studies on Isotope Ratio Measurement of Cl by Inductively Coupled Plasma Triple-quad Mass Spectrometry

Fundamental studies on isotope ratio measurement of Cl were carried out using inductively coupled plasma triple-quad mass spectrometry (ICP-MS/MS) and the analytical performance obtained was compared to that obtained by ICP sector field mass spectrometer (ICP-SFMS). Though the polyatomic ion interferences of 16O18O1H and 36Ar1H with respect to 35Cl and 37Cl, respectively, made a negative effect on the accuracy and the precision for isotope ratio measurements of Cl, the ICP-SFMS could eliminate these interferences by medium mass resolution mode (m/Δm = 4000) and achieved the isotope ratio measurements with 0.2 - 0.5% of relative standard deviation (RSD) at the concentrations of Cl from 1 to 10 mg kg-1. In the case of ICP-MS/MS, both the single-MS mode without collision reaction gas and the MS/MS mode with collision reaction gases such as oxygen (O2) and hydrogen (H2) were examined and compared their analytical sensitivities as well as the precisions of isotope ratio measurement of Cl. The precisions of Cl isotope ratio measurements were 3 - 14% of RSD at the concentrations of Cl from 5 to 100 mg kg-1, when single-MS mode was carried out, even though the similar isotope ratios of 35Cl/37Cl could be obtained. In the case of O2 gas for MS/MS mode with mass-shift method, precisions of 0.3 - 2% of RSD were obtained at the concentration range of 1 - 100 mg kg-1. In the case of H2 gas, similar sensitivities as those obtained by ICP-SFMS and the precisions of 0.2 - 0.5% of RSD at the concentration range of 1 - 10 mg kg-1 were obtained. From these results, it was evaluated that the ICP-MS/MS in MS/MS mode with collision reaction gas could be used for Cl isotope ratio measurements for such studies as stable isotope tracers, isotope abundance measurements in nuclear chemistry and accurate determinations by isotope dilution mass spectrometry.

Determination of Ultra-trace Metal Impurities in High-purity Cadmium Using Inductively Coupled Plasma Mass Spectrometry after Matrix Separation with Anion Exchange Resin

The analytical method for ultra-trace metal impurities at μg kg-1 level in high-purity Cd was examined by inductively coupled plasma mass spectrometry (ICP-MS) combined with matrix separation by Bio-Rad AG MP-1M anion exchange resin. After the separation of Cd, the metal impurities such as Li, In, Cr, Mn, Fe, Co, Ni, Cu, Ga, Sr, Ba and Pb were measured by an ICP-quadrupole mass spectrometer (ICP-QMS) and ICP-sector field mass spectrometer (ICP-SFMS). From the comparison of measured results, it was evaluated that the analytical sensitivity by ICP-SFMS was 10 times higher than ICP-QMS. In addition, ICP-SFMS could obtain determined values of Li and Fe that could not be determined by ICP-QMS. These results suggest the ICP-SFMS combined with matrix separation by anion exchange resin could be utilized for the determination of ultra-trace metal impurities in high-purity materials for the assessment of the purity of the materials.

Precise determination of dissolved silica in seawater by ion-exclusion chromatography isotope dilution inductively coupled plasma mass spectrometry

Ion exclusion chromatograph (IEC) isotope dilution (ID) inductively coupled plasma mass spectrometry (ICP-MS) (IEC-ID-ICP-MS) was developed for measurement of dissolved silica in seawater, which was applied to production of certified reference materials (CRMs) of three concentration levels of nutrients (high, medium and low levels). IEC-ICP-MS has been employed to separate dissolved silica from seawater matrix. In the present study, in order to solve substantial problems due to spectral interference in ICP-MS and to improve the accuracy of IEC-ICP-MS beyond standard addition or conventional calibration methods, ID method was coupled with ICP-sector field mass spectrometry (operated under medium resolution,i.e., m/Δm=4000). In addition, effects of various operating parameters in ICP-MS on a silicon background level were also investigated to obtain lower background equivalent concentration (BEC). As a result, 3 ng g(-1) of the BEC and 0.5 % of relative standard uncertainties were achieved in the analyses of dissolved silica in seawater samples at concentration levels from 4.0 mg kg (-1) to 0.8 mg kg(-1) as silicon. The developed method was successfully validated by analyses of an artificial seawater containing a known amount of silicate and the seawater certified reference material MOOS-2 produced by the National Research Council Canada.

Determination of ultra-trace sulfur in high-purity metals by isotope dilution inductively coupled plasma sector field mass spectrometry combined with chemical separation procedure

The analytical method of ultra-trace sulfur (S) in high-purity metal by isotope dilution inductively coupled plasma mass spectrometry (ID-ICP-MS) combined with chemical separation procedure was developed in the present study. In order to determine the ultra-trace S in high-purity metal, a chemical separation with alumina column was carried out before ICP-MS measurement. This method enabled to prevent the polyatomic ion interference arising from the metal matrix and the signal suppression derived from the space charge effect in ICP-MS. In order to achieve high sensitive analysis, an ICP-sector field mass spectrometer (ICP-SFMS) was used. The isolation of polyatomic ion interference with respect to S was also carried out in medium-resolution mode. In addition, measurement conditions including detector dead time, which affects the precision and accuracy of the isotope dilution method, and washout conditions that were employed to reduce memory effects were optimized. The developed method was validated by the determination of S in a high-purity iron reference material (JSS-001-4). The analytical result obtained by the developed method (1.86 mg kg-1 ± 0.12 mg kg-1 (k = 2)) was in good agreement with the certified value (1.90 mg kg-1 ± 0.42 mg kg-1). The method was also applied to the determination of S in high-purity zinc, revealing a content of 0.08 mg kg-1 ± 0.08 mg kg-1 (k = 2). Since the developed method enabled the determination of ultra-trace S at μg kg-1 level in the high-purity zinc, it is expected to be useful for high sensitive and accurate determination of ultra-trace S in high-purity metals.

Quantitative Analysis of Major and Minor Elements in Lead-free Solder Chip by LA-ICP-MS

A method was established for the quantitative analysis of the elements (Cu, Ag, Pb, and Sn) in solder samples by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), with Sn-based matrix matched standard solutions for defining the calibration curves. It was found that chloride-ion presented in commercially available Sn standard solution resulted in a precipitation of AgCl and caused the deterioration of the linearity of the calibration curve for Ag. Therefore, a laboratory-made chloride-free Sn solution was used to prepare Sn matrix matched standard solutions so as to ensure the stability of the elements including Ag. For the quantitative analysis of solder samples by LA-ICP-MS, the operating conditions of the LA instruments were set to obtain a fluence of over 12 J cm-2. This is mainly because of larger LA-induced elemental fractionations using a fluence of <10 J cm-2. The results for Ag, Cu, Pb, and Sn in a certified reference material (NMIJ CRM 8203-a) were close to, or in agreement with, the certified values, indicating that the present method was valid for the quantitative analysis of the elements in solder samples. In comparison to the certified values, relatively larger uncertainties were obtained for the analytical results by LA-ICP-MS, which could be attributed to the dependence on the homogeneity of the sample because the sample aliquots used for analysis were much smaller than those required for the traditional analytical procedures (i.e., sample quantity ratio of ca. 1:13000). Further improvement of the uncertainty might be obtained by using a larger sample quantity for the analysis by LA-ICP-MS so as to improve the representativeness of the sample.

Final report of the key comparison CCQM-K88: Determination of lead in lead-free solder containing silver and copper

The CCQM-K88 key comparison was organized by the Inorganic Analysis Working Group of CCQM to test the abilities of the national metrology institutes to measure the mass fraction of lead in lead-free solder containing silver and copper. National Metrology Institute of Japan (NMIJ), National Institute of Metrology of China (NIM) and Korea Research Institute of Standards and Science (KRISS) acted as the coordinating laboratories. The participants used different measurement methods, though most of them used inductively coupled plasma optical emission spectrometry (ICP-OES) or isotope-dilution inductively coupled plasma mass spectrometry (ID-ICP-MS). Accounting for relative expanded uncertainty, comparability of measurement results was successfully demonstrated by the participating NMIs for the measurement of the mass fraction of lead in lead-free solder at the level of 200 mg/kg. It is expected that metals at mass fractions greater than approximately 100 mg/kg in lead-free solder containing silver and copper can be determined by each participant using the same technique(s) employed for this key comparison to achieve similar uncertainties mentioned in the present report. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).