Masaki Ohata

Studies on the speciation of inorganic and organic antimony compounds in airborne particulate matter by HPLC-ICP-MS

There is a considerably increasing concern about the speciation of antimony because anthropogenic emission has resulted in an increasing concentration of antimony in the environment. Apart from inorganic Sb species, methylated Sb species have been detected in a variety of environmental samples. However, little is known about the distribution of Sb species in airborne particulate matter (APM). The speciation of Sb species in APM was performed using both anion-exchange and size-exclusion HPLC-ICP-MS detection. A Japanese quality control sample for APM (AS-1, 92 μg g−1 Sb) and an APM sample collected in Tokyo (APM sample, 56 μg g−1 Sb) were investigated. In aqueous extracts of APM sample and AS-1, apart from the major Sb(V) species (ca. 80%), trimethylantimony species (TMSb) and several hydride active unknown Sb species were for the first time detected.

Speciation of selenium compounds with ion-pair reversed-phase liquid chromatography using inductively coupled plasma mass spectrometry as element-specific detection

For selenium speciation analysis, the hyphenation of chromatographic separation with element-specific detection has proved a useful technique. A powerful separation system, which is capable of resolving several biologically and environmentally important selenium compounds in a single column, is greatly needed. However, that has been difficult to achieve. In this paper eight selenium compounds, namely, selenite [Se(IV)], selenate [Se(VI)], selenocystine (SeCys), selenourea (SeUr), selenomethionine (SeMet), selenoethionine (SeEt), selenocystamine (SeCM) and trimethylselenonium ion (TMSe+), were separated by using mixed ion-pair reagents containing 2.5 mM sodium 1-butanesulfonate and 8 mM tetramethylammonium hydroxide as a mobile phase. The separation of these anionic, cationic and neutral organic selenium compounds on a LiChrosorb RP18 reversed-phase column took only 18 min at a flow-rate of 1.0 ml/min with isocratic elution, and baseline separation among the six organic Se compounds was achieved. Inductively coupled plasma mass spectrometry (ICP-MS) was employed as element-specific detection. A comparison of ICP-MS signal intensity obtained with a Barbington-type nebulizer and with an ultrasonic nebulizer (USN) was made. Different signal enhancement factors were observed for the various selenium compounds when a USN was used. The speciation technique was successfully applied to the study on chemical forms of selenium in a selenium nutritional supplement. Selenomethionine was found to be the predominant constituent of selenium in the supplement.

Spatial Characterization of Emission Intensities and Temperatures of a High Power Nitrogen Microwave-induced Plasma

The spatial characterization of a high power nitrogen microwave-induced plasma (N 2 -MIP), using an Okamoto cavity, was undertaken. The plasma operating conditions were fixed during all the experiments at a microwave frequency of 2.45 GHz, an incident power of 1.3 kW, a plasma gas flow rate of 11.0 l min -1 , a carrier gas flow rate of 1.0 l min -1 and a sample uptake rate of 1.6 ml min -1 . A Ca solution was used to measure the emission intensity distribution for both Ca atom and ion lines in the N 2 -MIP, and an Fe solution was used to determine the excitation temperature distribution of the N 2 -MIP, which was obtained by using a Boltzmann plot under the assumption of LTE. In addition, rotational temperature measurements were carried out using the N 2 + (0–0):B 2 Σ u + →X 2 Σ g + band. Because the H β line (486.13 nm) could not be excited in the N 2 -MIP, measurement of the electron number density was carried out by a method involving the Saha equation using both the emission intensity ratio (Ca II:Ca I) and the excitation temperature of the N 2 -MIP. The degree of ionization of various elements in the N 2 -MIP was also calculated. The spatial characteristics of the N 2 -MIP were compared with those of the Ar-ICP.

Reversed-phase liquid chromatography with mixed ion-pair reagents coupled with ICP-MS for the direct speciation analysis of selenium compounds in human urine

A sensitive and robust method for the determination of five inorganic and organic Se species in human urine by reversed-phase liquid chromatography with mixed ion-pair reagents coupled with inductively coupled plasma mass spectrometry (HPLC-ICP-MS) is described in this paper. A good separation for anionic, cationic and neutral Se species, namely selenate [Se(VI)], selenourea (SeUr), selenomethionine (SeMet), selenoethionine (SeEt), and trimethylselenonium ion (TMSe+), was achieved within 15 min on a LiChrosorb RP 18 reversed-phase column by using mixed ion-pair reagents of 2.5 mM sodium 1-butanesulfonate and 8 mM tetramethylammonium hydroxide, with isocratic elution at a flow rate of 1.0 mL min−1. The detection limits of the five Se species obtained by HPLC-ICP-MS ranged from 0.6 to 1.5 ng Se mL−1 using an injection volume of 20 µL. It is noteworthy that the urine sample can be directly injected into the analytical system without any pre-treatment, except a filtration with a 0.45 µm membrane filter, and that the determination of Se species was free from chloride-induced matrix interference. In addition, no serious deterioration in column performance or decrease in the sensitivity of ICP-MS was observed for the experimental period of three months. In Japanese urine samples, no detectable SeMet, SeUr, and SeEt could be found, even if the total Se concentration was higher than 100 ng Se mL−1. On the contrary, TMSe+ and two unknown Se species (U1 and U2) were detected in the urine. The major unknown, U1, was found in all of the measured urine samples, suggesting that it might be one of the important Se metabolites.

Evaluation of the detection capability of a high power nitrogen microwave-induced plasma for both atomic emission and mass spectrometry

In order to evaluate the detection capability of a high power N2-MIP (surface wave mode cavity) for AES and MS, a comparison of the detection limits between high power N2-MIP-AES and Ar-ICP-AES was conducted under almost the same plasma operating conditions and with the same measurement systems. Moreover, a comparison of the detection limits between high power N2-MIP-MS and Ar-ICP-MS was also carried out under optimum operating conditions for each instrument. The detection limits (3σ) were established as the detection capability for both plasma systems using a total of 55 wavelengths (atom and ion lines) for 21 elements for AES and a total of 38 m/z values for 22 elements for MS. The detection limits obtained for N2-MIP-AES (0.4–3000 ng ml–1) were from one to two orders of magnitude worse than those for Ar-ICP-AES. On the other hand, the detection limits for N2-MIP-MS (1–3600 pg ml–1) were almost the same or one order of magnitude worse than those for Ar-ICP-MS. The detection capability of a high power N2-MIP was evaluated both from results in this work and from those given previously.

Comparison of 795 nm and 265 nm femtosecond and 193 nm nanosecond laser ablation inductively coupled plasma mass spectrometry for the quantitative multi-element analysis of glass materials

The figures of merit of femto- and nanosecond laser ablation inductively coupled plasma mass spectrometry applying near infrared, middle ultraviolet, and far ultraviolet radiation at 795 nm, 265 nm, and 193 nm, respectively, for the quantitative multi-element analysis of glass materials were compared. Major, minor, and trace elements of four glass reference materials including NIST612, BCR-2G, GSE-1G, and BAM-S005A were quantified against NIST610 applying Ca or Si as an internal standard. Deviations between measured element concentrations and literature values were compared and it was demonstrated that all systems provide similar results when using Ca as an internal standard. By contrast, concentrations obtained by femtosecond laser ablation at 795 nm with Si as an internal standard showed deviations by up to 20% under the operating conditions chosen. Furthermore, Si-normalized fractionation indices calculated for nanosecond laser ablation at 193 nm as well as femtosecond laser ablation at 795 nm and 265 nm suggested these discrepancies to be, on the one hand, due to changes in the composition and/or particle size distribution of aerosols formed over the sampling time. On the other hand, Ca-normalized fractionation plots for femtosecond laser ablation at 795 nm turned out to be less informative with respect to quantification accuracy and, in addition, questioned their general significance. An adaptation of instrumental parameters was found to result in fractionation indices closer to unity signifying that both fluence and spot size are crucial parameters, controlling compositions and/or particle size distributions.

Aerosol entrainment and a large-capacity gas exchange device (Q-GED) for laser ablation inductively coupled plasma mass spectrometry in atmospheric pressure air

A new gas exchange device (Q-GED) that allows a carrier gas flow of 0.8 L min−1 atmospheric air to be exchanged with Ar combined with aerosol entrainment applied to the analysis of large or heterogeneous samples using Laser Ablation (LA) is reported. The exchange of air components with Ar in the Q-GED was tested using GC-TCD and ICPMS. In ICPMS, no change in oxide levels, or gas blanks, was observed, suggesting a complete exchange of air with Ar. Measured sensitivities were in the same range as sensitivities obtained using LA with an Ar atmosphere, however, the sensitivities were approximately 2-fold lower than those obtained when ablating in He. It was demonstrated that particle transport efficiencies can be enhanced when using quasi-closed cell approaches to control and influence the aerosol expansion volume. Therefore, a plume entrainment device was designed and optimized by computational fluid dynamics, produced using rapid prototype printing, and applied to LA-QGED-ICPMS. Quantitative multi-element analysis of various geological glass reference materials is reported using NIST SRM 612 as the external calibration standard, with relative differences to preferred values of less than 15%. No additional temporal signal dispersion was observed when comparing the new setup with closed cell approaches when using the same flow rates. As opposed to the former GED I-type, a higher spatial resolution can be obtained without destructive sample preparation for large-scale stalagmites. In a proof of concept, it was shown that the same concentration variations were detected for closed cell and GED-based approaches in large-scale stalagmites.

Accurate determination and certification of bromine in plastic by isotope dilution inductively coupled plasma mass spectrometry

The accurate analytical method of bromine (Br) in plastic was developed by an isotope dilution inductively coupled plasma mass spectrometry (ID-ICPMS). The figures of merit of microwave acid digestion procedures using polytetrafluoroethylene (PTFE) or quartz vessels were studied and the latter one was suitable for Br analysis since its material was free from Br contamination. The sample dilution procedures using Milli-Q water or ammonium (NH3) solution were also studied to remove memory effect for ICPMS measurement. Although severe memory effect was observed on Milli-Q water dilution, NH3 solution could remove it successfully. The accuracy of the ID-ICPMS was validated by a certified reference material (CRM) as well as the comparison with the analytical result obtained by an instrumental neutron activation analysis (INAA) as different analytical method. From these results, the ID-ICPMS developed in the present study could be evaluated as accurate analytical method of Br in plastic materials and it could apply to certification of Br in candidate plastic CRM with respect to such regulations related to RoHS (restriction of the use of hazardous substances in electrical and electronics equipment) directive.

Effect of adding oxygen gas to a high power nitrogen microwave-induced plasma for atomic emission spectrometry

Abstract In order to investigate the effect of adding oxygen gas (O 2 ) to a high power nitrogen microwave-induced plasma (N 2 -MIP: 2.45 GHz, surface wave mode) for atomic emission spectrometry, the signal intensities for atom and ion lines of Ca, V, Ti, Mg, and Cd were observed by adding O 2 gas into N 2 outer gas in a range from 0 to 20%. From the observation of the background spectrum in a wavelength range of 200–400 nm, it was found that NO band spectra were enhanced largely with an increase in the addition of O 2 gas. The excitation temperatures ( T ex ) observed decreased from 5500 to 4800 K with an increase in the percentage of adding O 2 gas from 0 to 20%. The relatively large signal enhancement was observed for all atom lines of Ca, V, Ti, Mg, and Cd when O 2 gas was added to N 2 outer gas. The emission signals for some of ion lines of Ca, V, Ti, and Mg also showed a signal enhancement when a small amount of O 2 gas was added. It was considered that the reason for the enhancement phenomena of the ion lines of these elements was attributed to the mechanism of the charge transfer reaction.

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.