Quantitative imaging of trace elements in solid samples by online isotope dilution laser ablation-inductively coupled plasma-mass spectrometry.

For quantitative visualization of trace elements, an online isotope dilution (ID) laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) method capable of accurately correcting the detection amount of targets is presented. Two aerosols from an ablated sample and a nebulized isotopically enriched spike solution were mixed online using a dual-port spray chamber. In this paper, transmission efficiency (TE) of each of the two gas streams to the ICP-MS detector is revealed, and the quantification values were corrected by including the ratio of TEs in the calculation of the online ID method. To verify the developed method, Fe and Sr as model elements in five certified reference materials (CRMs, glass: SRM 610, 612, 614, alloy: SS-356, -383) were quantified without the use of matrix-matched CRMs. The resultant values agreed with the certified values of CRMs in the range of 92.7-104.7% and 92.8-109.0% for Fe and Sr, respectively. The LODs (3σ) were 0.54 and 0.17 µg g-1 for Fe and Sr, respectively. In addition, the applicability of this method to quantitative imaging of unknown solid samples was demonstrated for actual biological hard tissues (a mouse incisor, human primary tooth, and fish otolith) using the result of shot-analysis. The results were consistent with the reported concentration range obtained by wet chemical analysis.

Analysis of groundwater flow line of the Goshiki-numa pond community using elevation-considered principal component analysis.

To reveal the dynamics of underground water flows, measuring many factors and chemical components are usually required. However, it is difficult for the human sense to find the right answers using the many chemo-data in different factors. Although principal component analysis is one of the useful means in a multivariate analysis (chemometrics) that can reduce the multivariable to only 2-D or 3-D and can successfully categorize quantitative multidata into several groups based on the similarity of water quality, underground water flows are difficult to elucidate owing to the lack of continuous information. This paper presents the dynamics of groundwater around the Goshiki-numa pond community (Goshiki-numa), National park of Japan, using multi-chemical component analysis and elevation-considered principal component analysis. Despite the difficulty of understanding the dynamics of groundwater flows of the pond community using limited factors thus far, an elevation-considered principal component analysis (e-PCA) presented herein has revealed the underground water flows around Goshiki-numa ponds by inputting 19 factors × 102 water (total 1,938 data) collected from 2011 to 2014 and 2016. This e-PCA proved to be an effective chemometrics technique for revealing underground water flows. It is believed to apply not only to analytical sciences but also to environmental sciences, civil engineering, and other fields dealing with multidata of water quality.

Direct Quantification of Attogram Levels of Strontium-90 in Microscale Biosamples Using Isotope Dilution-Thermal Ionization Mass Spectrometry Assisted by Quadrupole Energy Filtering.

Although thermal ionization mass spectrometry (TIMS) has been employed for the high-precision analysis of isotope ratios, direct quantification of artificial mono-nuclide in the environment is difficult by even using isotope dilution (ID) due to the coexistence of the great magnitude of natural stable nuclides or isobars. In traditional TIMS and ID-TIMS, a sufficient amount of stable Sr doped on a filament is required to realize a stable and adequate ion-beam intensity (i.e., thermally ionized beams). However, the background noise (BGN) at m/z 90, detected by an electron multiplier, disturbs 90Sr analysis at low concentration levels due to peak tailing of a significant 88Sr ion beam dependent on the 88Sr-doping amount. Here, TIMS assisted by quadruple energy filtering was successfully employed for the direct quantification of attogram levels of an artificial monoisotopic radionuclide strontium-90 (90Sr) in microscale biosamples. Direct quantification was achieved by integrating the ID quantification of natural Sr and simultaneous 90Sr/86Sr isotope ratio analysis. Additionally, the measurement amount calculated by the combination of the ID and intercalibration was corrected for the net result amount of 90Sr by subtracting dark noise and the detected amount derived from the survived 88Sr, which are equivalent with the BGN intensity at m/z 90. Background correction revealed that the detection limits were in the range of 6.15 × 10-2-3.90 × 10-1 ag (0.31-1.95 µBq), depending on the concentration of natural Sr in a 1 µL sample, and the quantification of 0.98 ag (5.0 µBq) of 90Sr in 0-300 mg/L of natural Sr was successful. This method could analyze small sample quantities (1 µL), and the quantitative results were verified against authorized radiometric analysis techniques. Furthermore, the amount of 90Sr in actual teeth was successfully quantified. This method will be a powerful tool for measuring 90Sr in the measurement of micro-samples, which are required to assess and understand the degree of internal radiation exposure.

Preparation of Highly Concentrated Uniform-Sized Silver Nanoparticles via Use of Thermoresponsive Zwitterionic Surfactants.

Despite the popular use of citrate for the reduction of silver ions, this process suffers from slow crystal growth and broad size distribution. The rapid and effective synthesis of highly concentrated and stable spherical silver nanoparticles (AgNPs) confined in the surfactant-rich phase of thermoresponsive 3-(alkyldimethylammonio)-propyl sulfate surfactants obtained after reaction with citrate ions at high temperature is described. The present approach using the zwitterionic surfactant offers an alternative rapid approach for production of AgNPs and an in situ phase separation step that serves to "extract" and concentrate the AgNPs in the surfactant-rich phase. Almost all (synthetic yield 99.9%, extraction efficiency 98.6%) of the synthesized AgNPs with a diameter of 21.0 ± 2.5 nm were incorporated into the phase-separated surfactant-rich phase at pH 11, and the capacity (maximum concentration) was 3.4 × 1013 particles/mL. The AgNPs were stable upon long-term storage (at least 3 months).

Mass-spectrometric determination of iodine-129 using O2-CO2 mixed-gas reaction in inductively coupled plasma tandem quadrupole mass spectrometry.

This paper presents a mass-spectrometric method for determining the radionuclide iodine-129 (129I) from the significant amount of interference in inductively coupled plasma tandem quadrupole mass spectrometry (ICP-MS/MS) using a dynamic reaction cell passing a mixture gas of O2 and CO2. Thus far, mass spectrometry analysis of trace amounts of 129I has been hampered by the presence of xenon-129 (129Xe) and the formation of polyatomic ions from excess amounts of stable isotope 127I. In this study, flowing a mixture gas of O2 and CO2 into the dynamic reaction cell (Q2) successfully removed both 129Xe interference and polyatomic interference (127IH2) in the analysis of 129I in ICP-MS/MS. The resulting ratio of (background noise of m/z 129)/127I was 4.6 × 10-10 ± 3.3 × 10-10, which enables the analysis of 10 mBq/L of 129I in the presence of 100 mg/L of stable 127I without chemical separation. The detection limit of this method was 0.73 mBq/L (= 0.11 ng/L) with an APEX-Q sample inlet desolvation device. For demonstration purposes, spike and recovery analysis of rainwater was performed, and good agreement between the spiked and recovered amounts was achieved.

Sensitivity enhancement in inductively coupled plasma mass spectrometry using nebulization methods via nitrogen mixed gas effect.

We demonstrate the sensitivity enhancement in inductively coupled plasma mass spectrometry (ICP-MS) by combining ultrasonic nebulization via the nitrogen mixed gas effect. We showed the effect of nitrogen gas concentration (0-5%) in the nebulizer gas on the signal sensitivity for 63 elements using commercially available (concentric and ultrasonic) nebulizers. In addition, the limit of detection (ng L-1) was calculated in each case. Finally, we compared the sensitivity (i.e., the slope of the calibration curve), background noise intensity, and three-dimensional intensity distribution in the plasma to elucidate the effects of the concurrent use of mixed gas plasmas and nebulization methods.

Online solid-phase extraction-inductively coupled plasma-quadrupole mass spectrometric quantification of 90Sr using 88Sr/86Sr isotope dilution method.

Due to the lack of a correlation with the natural Strontium (Sr) isotopes, it is difficult to apply the isotope dilution (ID) method to an artificial radioactive mononuclide Strontium-90 (90Sr), in inductively coupled plasma-quadrupole mass spectrometry (ICP-QMS). Meanwhile, online solid-phase extraction (SPE)-ICP-QMS (SPE-ICP-QMS) serves as an automatic sequential analytical technique for measuring the ultra-trace amounts of radionuclides; however, apparent assay values obtained using this method are often negatively affected by differences in the sample matrix composition between standard and actual samples. In this study, the pg L-1 level of 90Sr was successfully measured by combining online SPE-ICP-QMS and the ID method with 88Sr/86Sr ratios in one sample injection, without the radioactive standard. Although naturally occurring abundant isobaric 90Zr significantly influences 90Sr quantification during mass spectrometry, consecutive separations between automated SPE and dynamic reaction cell (DRC) oxidation enable 90Sr quantification, even in the presence of isobaric 90Zr (acceptable down to 5.7 × 10-9 of 90Sr/Zr in sample solution), using this method. Through this method, both radioactive 90Sr and naturally occurring Sr were simultaneously quantified using 88Sr-to-86Sr and 88Sr-to-90Sr ratios without radioactive 90Sr standard solutions. This simultaneous quantification of stable Sr and 90Sr was achieved within 15 min with good recovery rates. The limit of detection of 90Sr was 1.1 pg L-1 (equivalent to radioactivity 5.6 Bq L-1) for a 10 mL injection. Finally, water collected from an actual contaminated water storage tank at the Fukushima Daiichi Nuclear Power Plant (Fukushima, Japan) was analyzed using the proposed method, and the obtained results agreed well with those obtained using conventional analytical methods.

A part per trillion isotope ratio analysis of 90Sr/88Sr using energy-filtered thermal ionization mass spectrometry.

Strontium-90 is a major radioactive nuclide released by nuclear accidents and discharge waste. Input of such radioactive nuclide into earth surface environment causes potential threat of long-term internal exposure when taken up by organism. Rapid and precise measurement of 90Sr in variety of environmental sample is important to understand the distribution and dynamics of 90Sr in the local environment after the accident and to assess the effect of radioactive nuclide inputs on bodies. However, previous 90Sr measurement techniques have drawbacks such as long measurement times for radiometry and high detection limits for mass spectrometry. Here we present a technique to accurately measure a significantly small amount of 90Sr in natural environmental samples using an energy-filtered thermal ionization mass spectrometry. Our technique achieved a 90Sr detection limit of 0.23 ag, which corresponds to a 90Sr activity of 1.2 µBq. The detection limit was lowered by two orders of magnitude compared with the previous mass spectrometric 90Sr analyses. The ability of our technique will expand the applicability of mass spectrometric 90Sr survey not only to the rapid 90Sr survey upon nuclear accidents but also to study a long-term environmental diffusion of radioactive materials using size-limited environmental and biological samples.

Adsorption Behavior of Pu(IV), Am(III), Cm(III), and U(VI) on Desferrioxamine B-immobilized Micropolymer and Its Applications in the Separation of Pu(IV).

The adsorption properties of Pu(IV), Am(III), Cm(III), and U(VI) on desferrioxamine B-immobilized micropolymeric resin (DMPs) and adsorbed species were elucidated using thermodynamic constants and log ß values. This allowed the determination of adsorption characteristics (91, 95, 88, and 97% for Pu(IV), Am(III), Cm(III), and U(VI), respectively) and individual pH-independent adsorption properties. Pu(IV) could be separated from Am(III), Cm(III), and U(VI) at pH 2. The separation of Pu(IV) from Am(III), Cm(III), and U(VI) was achieved by controlling the pH of the solution using a single resin.

Online Solid-Phase Extraction-Inductively Coupled Plasma-Quadrupole Mass Spectrometry with Oxygen Dynamic Reaction for Quantification of Technetium-99.

Quantification of pg/L levels (i.e., 0.6 mBq/L) of radioactive technetium-99 (99Tc) was achieved within 15 min in the presence of isobaric and polyatomic interference sources such as ruthenium-99 (99Ru) and molybdenum hydride (98Mo1H) at 3-11 orders of magnitude higher concentrations. Online solid-phase extraction-inductively coupled plasma-quadrupole mass spectrometry (ICP-QMS) with oxygen (O2) dynamic reaction cell (online SPE-ICP-MS-DRC) was shown to be a thorough automatic analytical system, circumventing the need for human handling. At three stepwise separations (SPE-DRC-Q mass filters), we showed that interference materials allowed the coexistence of abundance ratios of 1.5 × 10-13 and 1.1 × 10-5 for 99Tc/Mo and 99Tc/Ru, respectively. A classical mathematical correction using the natural isotope ratio of 99Ru/102Ru was used to calculate the residues of 99Ru. Using this optimized system, a detection limit (DL; 3σ) of 99Tc was 9.3 pg/L (= 5.9 mBq/L) for a 50 mL injection and sequential measurements were undertaken at a cycle of 24 min/sample. For the measurement of a lower concentration of 99Tc, an AG1-X8 anion-exchange column was used to study 20 L of seawater. Its DL was approximately 1000 times greater than that of previous methods (70.0 fg/L). Thus, this method withstands coexistences of 5.8 × 10-18 and 3.5 × 10-9 for 99Tc/Mo and 99Tc/Ru, respectively. Spike and recovery tests were conducted for environmental samples; the resulting values showed good agreement with the spike applied.

Shape- and Size-Controlled Fabrication of Gold Nano-Urchins via Use of a Mixed Sodium Borohydride and Ascorbic Acid Reductant System.

Urchin-shaped gold nanoparticles (AuNUs) are anisotropic nanomaterials with unique chemical and physical properties of interest for a variety of applications. However, synthesizing AuNUs with controlled sizes and shapes remains challenging. We demonstrate that a combination of sodium borohydride (NaBH4) and ascorbic acid (AA) as reducing agents can produce an aqueous dispersion of AuNUs after just 9 min at room temperature (25 °C). The AuNUs were size- and shape-controlled using a molar ratio for NaBH4/AA/HAuCl4 = 1:1:1 at pH 3. The added aurate was almost entirely (98.8%) consumed in the formation of AuNUs. The resultant AuNU concentration was 1.1 × 1010 particles/mL. The diameters observed in transmission electron microscopy were 145.1 ± 37.4 nm. The AuNUs had an average of 12 spikes and an average volume of 3.7 × 105 nm3. The partition volume between the spikes and the core of particles was 3:2. The AuNUs had a pink color and exhibited an absorption wavelength maximum at 540 nm. It is assumed that the AuNUs originate from icosahedral seeds and urchin shapes emerge from connecting smaller-sized seeds and larger-sized core particles.

Determination of Characteristic vs Anomalous 135Cs/137Cs Isotopic Ratios in Radioactively Contaminated Environmental Samples.

A contamination with the ubiquitous radioactive fission product 137Cs cannot be assigned per se to its source. We used environmental samples with varying contamination levels from various parts of the world to establish their characteristic 135Cs/137Cs isotope ratios and thereby allow their distinction. The samples included biological materials from Chernobyl and Fukushima, historic ashed human lung tissue from the 1960s from Austria, and trinitite from the Trinity Test Site, USA. After chemical separation and gas reaction shifts inside a triple quadrupole ICP mass spectrometer, characteristic 135Cs/137Cs isotope signatures (all as per March 11, 2011) were obtained for Fukushima- (∼0.35) and Chernobyl-derived (∼0.50) contaminations, in agreement with the literature for these contamination sources. Both signatures clearly distinguish from the characteristic high ratio (1.9 ± 0.2) for nuclear-weapon-produced radiocesium found in human lung tissue. Trinitite samples exhibited an unexpected, anomalous pattern by displaying a low (<0.4) and nonuniform 135Cs/137Cs ratio. This exemplifies a 137Cs-rich fractionation of the plume in a nuclear explosion, where 137Cs is a predominant species in the fireball. The onset of 135Cs was delayed because of the longer half-life of its parent nuclide 135Xe, causing a spatial separation of gaseous 135Xe from condensed 137Cs, which is the reason for the atypical 135Cs/137Cs fractionation in the fallout at the test site.

Isotope Dilution-Total Evaporation-Thermal Ionization Mass Spectrometric Direct Determination of Radioactive Strontium-90 in Microdrop Samples.

Thermal ionization mass spectrometry (TIMS) was used to directly quantify an ultratrace of radioactive 90Sr in microliter droplet samples. No chemical separation was required in removing isobaric interferences on M = 90 such as 90Zr and organic molecules in the mass spectrum because the difference in evaporation and ionization (emission) temperature among organic molecules, Zr and Sr, allows us to control the emission manner and significantly suppress the isobaric interferences. Direct quantification was achieved by improving the intercalibration of Faraday cups and ion counting in an isotope dilution (ID) method. Furthermore, the use of a total evaporation method (TE) enhanced the detection efficiency by the complete collection of the 90Sr ion beam from the samples and minimized the complexity of the fractionation effect in the isotope ratio calculation. In this study, 1 fg of 90Sr (equal to activity of 5 millibecquerel (mBq)) in a very low-volume sample with 108 times greater isobaric interference from 90Zr was successfully measured using the proposed ID-TE-TIMS method. The limit of detection was 0.029 fg (equal to 0.15 mBq) without any preconcentration. To demonstrate the wide usability of this method, low-volume samples of tears, eyelashes, saliva, environmental standards, and water samples (i.e., seawater and ground water) were analyzed within 1 h. The relationship of the measured values between this ID-TE-TIMS method and a radiometric analysis was shown to have good linearity.

Rapid Micelle-Mediated Size-Controlled Fabrication of Calcium Sulfate Nanorods Using Silver Nanoparticles.

Calcium sulfate nanorods (CS-NRs) are valuable materials utilized in various applications, particularly in the medical field. In this work, the size-controlled synthesis of CS-NRs was carried out on the basis of the micelle-mediated phase separation phenomenon. A nonionic surfactant, Triton X-114, was employed for the thermoresponsive phase separation of a homogeneous solution to a surfactant-rich phase. Whereas each specific ion, Ca2+ and SO42-, was difficult to individually extract when present at concentrations less than their equilibrium concentration (solubility product constant, Ksp), the synthesized CS microrods (CS-µRs) were extracted into the surfactant-rich phase (enrichment factor = ca. 50). The presence of nitric acid increased the size of the materials up to 6707 ± 3488 nm on the long side and 87 ± 37 nm on the short side. The addition of silver nanoparticles (Ag-NPs) to the reaction mixture led to the formation of much smaller products, i.e., uniform CS-NRs whose sizes were in the range of 89 ± 15 nm (long side) and 25 ± 4 nm (short side). The size of the extracted Ag-NPs and CS-NRs decreased with an increase in added Ag-NP concentration until their microscopic observation became difficult. The factors (such as additive concentration, pH, temperature) affecting size control were evaluated.

Development of Online Dilution System for Quantification of 90Sr Using Automatic Solid-phase Extraction Inductively Coupled Plasma Mass Spectrometry.

In this paper, we propose an online dilution system for the rapid quantification of radioactive strontium-90 (90Sr) with inductively coupled plasma mass spectrometry coupled solid-phase extraction and O2 dynamic reaction (cascade ICP-MS). The proposed system automatically provides a higher dilution ratio, which is at most 3.3 ± 0.2-times the ratio obtained by the previous method, without increasing the analysis time (<15 min). A detection limit of 2.7 Bq/kg wet (0.54 pg/kg wet) was achieved. The recovery test results were consistent with two different spiked values.

Synthesis and evaluation of a diethylammonio-propylsulfate amphoteric ionic column for the high-performance liquid chromatography-mass spectrometric separation and detection of amino acids.

A diethylammonio-propylsulfate amphoteric ionic resin was synthesized and employed as the stationary phase for high-performance liquid chromatography-mass spectrometry (LC-MS) separation and detection of amino acids. The influence of experimental conditions such as mobile phase composition, column length and temperature upon the amino acid separations was evaluated. However, temperature, addition of water-miscible organic solvent to the mobile phase and mobile phase gradients were not effective at improving the separations. In contrast, the use of an unbuffered pure water mobile phase proved successful for the separation and detection of amino acids. The observed order of elution seems to parallel the isoelectric points of the respective amino acids and suggests that this diethylammonio-propylsulfate stationary phase column functions as an amphoteric ion-exchanger. Under optimized chromatographic conditions, the detection limits for the amino acids were in range of 0.07-0.44 pmol (pico-mole). The method was also successfully applied for the analysis of an actual commercial sample.

Nanoparticle induced formation of self-assembled zwitterionic surfactant microdomains which mimic microemulsions for the in situ fabrication and dispersion of silver nanoparticles.

The effective synthesis of highly concentrated and stable spherical silver nanoparticles (Ag-NPs) enclosed within microdomains formed by the Ag-NP induced self-assembly of zwitterionic surfactants is described. In this paper, the rapid and efficient synthesis of dispersed and stable Ag-NPs in zwitterionic surfactants, such as 3-(nonyldimethylammonio)- or 3-(decyldimethyl-ammonio)-propyl sulfate (C9- or C10-APSO4) that self-assemble in the presence of the Ag-NPs to form microdomains akin to microemulsions (ME) without the need of any organic solvent, co-surfactant or polymer is presented. Essentially all (>99.9%) of the synthesized Ag-NPs (TEM diameter 16.8 ± 4.3 nm) were incorporated and dispersed within the ME microdomains (213.5 ± 48.0 nm). A mechanism for formation of ME and its enclosing of the Ag-NPs in the ME is proposed.

Rapid Quantification of Radioactive Strontium-90 in Fresh Foods via Online Solid-Phase Extraction-Inductively Coupled Plasma-Dynamic Reaction Cell-Mass Spectrometry and Its Comparative Evaluation with Conventional Radiometry.

This paper describes a rapid quantification method for radioactive strontium (90Sr) in fresh foods (perishable foods) and has been comparatively evaluated with the common classical radiometric quantification method. Inductively coupled plasma-dynamic reaction cell-mass spectrometry with online solid-phase extraction (cascade-ICP-MS) rapidly determines 90Sr in a pure water-based sample. Despite its advantages, its application to fresh foods (perishable foods) has not yet been reported; however, the analytical potential of this method for fresh foods must be evaluated. In this study, 90Sr was determined in 12 fresh foods via improved cascade-ICP-MS (Icas-ICP-MS). Addition and recovery tests were demonstrated using real samples of grape, apple, peach, Japanese pear, rice, buckwheat, soybean, spinach, shiitake mushroom, grass, sea squirt, and flounder. With a decomposed solution of Japanese pear, the measurement value coincided with the amount of spiked 90Sr. The reproducibility of the measurements was represented by relative standard deviations of 14.2 and 5.0% for spiked amounts of 20 and 200 Bq/kg, respectively (n = 10), and the recovery rates were 93.7 ± 7.1%. In this case, the limit of detection (LOD) was 2.2 Bq/kg (=0.43 pg/kg). These results were compared with the data obtained using a common classical radiometric quantification method (nitrate precipitation-low background gas flow counter (LBC) method) in the same samples. Both the methods showed equivalent performances with regard to reproducibility, precision, and LODs but different analysis times. Icas-ICP-MS required ∼22 min for analysis, whereas the nitrate precipitation-LBC method required 20 days, confirming that Icas-ICP-MS is the suitable method for analyzing 90Sr in fresh foods.