Toshihiro Shirasaki

Elemental mass spectrometry using a nitrogen microwave-induced plasma as an ion source

Abstract A new mass spectrometry instrument for trace element analysis was developed that uses a 1.3 kW doughnut-shaped nitrogen high power microwave-induced plasma (MIP-MS). The fundamental analytical features of this doughnut-shaped plasma were studied. Background spectra for distilled water, nitric acid, hydrochloric acid and sulfuric acid, the acids being 1% ( v v ) aqueous solutions, were investigated. In the background spectrum for distilled water, there is no structured peak in the mass range from 49 to 90 amu where most analyte ions are distributed. As a result it is possible to determine K, Ca, Cr, Fe and Se at their major isotopes, which are interfered by polyatomic species in an argon inductively coupled plasma mass spectrometer (ICP-MS). The high power nitrogen MIP-MS exhibited single ppt to sub ppt detection limits for most elements under the multielement scanning condition. However, for the elements As and Se, which have high ionization potentials (> 9.8 eV), the detection limits exhibit high values that are one order of magnitude greater when compared with those of K, Ca and V (

Arsenic preconcentration viasolid phase extraction and speciation by HPLC-gradient hydride generation atomic absorption spectrometry

A novel method for arsenic speciation is developed by interfacing solid phase preconcentration-liquid chromatography (LC) separation-gradient hydride generation (GHG)-quartz flame atomic absorption spectrometry (QFAAS). A MnO2 mini-column is used to preconcentrate the arsenic species of As(III), As(V), MMA and DMA, during which process, As(III) is converted to As(V)viaoxidation by MnO2, while other species remain unchanged. The recovery of As(V) (i.e., the total amount of arsenate and arsenite in the original sample), MMA and DMA from the MnO2 mini-column is facilitated by tetramethylammonium hydroxide (TMAH). After LC separation with C30 columns, arsenic species in the eluate are subject to gradient hydride generation with detection by QFAAS. On the other hand, cellulose fibre selectively adsorbs the chelating complex between As(III) and ammonium pyrrolidine dithiocarbamate (APDC). After elution with HNO3, As(III) in the original sample is quantified by graphite furnace atomic absorption spectrometry (GFAAS), and the amount of As(V) is obtained by subtraction. A sample volume of 2.0 mL derives enrichment factors of 14.0–19.2 for the arsenic species. By injecting 20 μL of eluate into the LC system (the eluate of As(III)-PDC complex is injected into the GFAAS), detection limits of 0.019, 0.33, 0.39, 0.62 μg L−1 are obtained for As(III), As(V), MMA and DMA respectively. RSDs of less than 4.2% are achieved at the level of 2 μg L−1 for As(V), MMA, DMA and 1 μg L−1 for As(III). The procedure is evaluated by speciating arsenic in snow water and Hijiki samples.

Study on solvent-loading effect on inductively coupled plasma and microwave-induced plasma sources with a microliter nebulizer

Abstract To investigate the solvent-loading effect, a microliter nebulizer, called a sonic spray nebulizer (SSN), was used to introduce a sample solution at the microliter per minute level into an inductively coupled plasma (ICP) and into a nitrogen microwave-induced plasma (MIP). We compared the ICP to the MIP, and the SSN to a conventional concentric nebulizer (CCN). Our results confirm that a certain amount of water solvent is useful for analyte excitation in an Ar-ICP, since hydrogen released from the water enhances the energy transfer inside the plasma. However, we found the dominant water–solvent effect in the N2-MIP source was to consume MIP energy, rather than to promote the analyte excitation. Therefore, a means of solvent removal should be used with a N2-MIP. We also discuss other differences between the ICP and the MIP. With the SSN, several organic solvents were successfully introduced into the ICP without degrading the plasma stability.

Characteristics of liquid electrode plasma for atomic emission spectrometry

Liquid electrode plasma atomic emission spectrometry (LEP-AES) is a recently developed elemental analysis method that uses microplasma. LEP forms in a vapor bubble generated inside a narrow-center microchannel by using high-voltage DC pulse power. We studied the characteristics of LEP and atomic emission of lead (Pb), as an example element, which has not been described in detail. We estimated the plasma parameters and observed the expansion and shrinkage of a vapor bubble with discharge as well as the time course and spatial distribution of the atomic emission of Pb (405.78 nm). The applied voltage was 2.5 kV and the pulse width was less than 3 ms, which produced a current of about 100 mA. We found that the excitation temperature was about 8000 K and the electron density was about 1 × 1015 cm−3. We also found that two quite different emission phases occurred separately during the time course. The first emission phase corresponds to the first expansion and shrinking of the bubble around atmospheric pressure and the second emission phase corresponds to the re-expansion of the bubble and emission at reduced pressure with higher atomic and lower background emissions. Maximum atomic and background emissions were observed at the narrowed center of the microchannel, but there was an additional local maximum atomic emission region at the anode side bubble–liquid interface where the background emission was very low, which would be a better condition for sensitive measurement. The limit of detection determined in our experiment was 4.0 μg L−1 for Pb.

Atomic emission spectrometry in liquid electrode plasma using an hourglass microchannel

Liquid electrode plasma atomic emission spectrometry (LEP-AES) is a new elemental analysis method that uses microplasma. LEP forms in a vapor bubble generated inside a narrow-center microchannel by using high-voltage DC pulse power. In this study, we used a novel hourglass microchannel having a 3-dimensionally and axisymmetrically narrowed shape, which caused a bright emission roughly 200 times that of the flat microchannel used in our previous study. We observed the spatial distribution of atomic emission and determined the limit of detection (LoD) by utilizing the confirmed spatial distribution. We found that the spatial distribution of atomic emission for 41 elements in our experiments could be classified into three patterns in accordance with a maximum emission point: anode side, narrow-center, and cathode side. Atomic emission was measured at the maximum emission point and the calibration curve for each element was made to determine the LoD. The LoD of 25 tested elements in our experiment ranged from 1 μg L−1 for Li to 306 μg L−1 for V.

Study of the Roles of Chemical Modifiers in Determining Boron Using Graphite Furnace Atomic Absorption Spectrometry and Optimization of the Temperature Profile During Atomization

The measurement conditions for determining boron using graphite furnace-atomic absorption spectrometry (GF-AAS) were investigated. Differences in the boron absorbance profiles were found using three different commercially available GF-AAS instruments when the graphite atomizers in them were not tuned. The boron absorbances found with and without adjusting the graphite atomizers suggested that achieving an adequate absorbance for the determination of boron requires a sharp temperature profile that overshoots the target temperature during the atomization process. Chemical modifiers that could improve the boron absorbance without the need for using coating agents were tested. Calcium carbonate improved the boron absorbance but did not suppress variability in the peak height. Improvement of boron absorbance was comparatively less using iron nitrate or copper nitrate than using calcium carbonate, but variability in the peak height was clearly suppressed using iron nitrate or copper nitrate. The limit of detection was 0.0026 mg L(-1) when iron nitrate was used. It appears that iron nitrate is a useful new chemical modifier for the quick and simple determination of boron using GF-AAS.

Substoichiometric isotope dilution mass spectrometry as a new analytical method

A novel analytical method, the substoichiometric isotope dilution mass spectrometry (SIDMS) has been proposed. This method consists of the substoichiometric separation of the element in question and the subsequent intensity measurement of a stable isotope of the element with a mass spectrometer. In SIDMS, the correction of the mass discrimination of isotope measurement is not necessary and the use of expensive enriched stable isotopes may be avoided. The validity and the usefulness of SIDMS are demonstrated by the substoichiometric extraction of iron(III) with 4-isopropyltropolone and 3,5-dichlorophenol following microwave-induced plasma mass spectrometry.