Determination of ¹³5Cs and ¹³5Cs/¹³7Cs atomic ratio in environmental samples by combining ammonium molybdophosphate (AMP)-selective Cs adsorption and ion-exchange chromatographic separation to triple-quadrupole inductively coupled plasma-mass spectrometry.

Since the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident in 2011, the activity ratio of (134)Cs/(137)Cs has been widely used as a tracer for contamination source identification. However, because of the short half-life of (134)Cs (2.06 y), this tracer will become unavailable in the near future. This article presents an analytical method for the determination of the long-lived (135)Cs (t(2/1) = 2 × 10(6) y) and the atomic ratio of (135)Cs/(137)Cs, as a promising geochemical tracer, in environmental samples. The analytical method involves ammonium molybdophosphate (AMP)-selective adsorption of Cs and subsequent two-stage ion-exchange chromatographic separation, followed by detection of isolated radiocesium isotopes via triple-quadrupole inductively coupled plasma-mass spectrometry (ICP-MS/MS). The AMP-selective adsorption of Cs and the chromatographic separation system showed high decontamination factors (10(4)-10(5)) for interfering elements, such as Ba, Mo, Sb, and Sn. Using ICP-MS/MS, only selected ions enter the collision/reaction cell to react with N2O, reducing the isobaric interferences ((135)Ba(+) and (137)Ba(+)) and polyatomic interferences ((95) Mo(40)Ar(+), (97) Mo(40)Ar(+), (119)Sn(16)O(+), and (121)Sb(16)O(+)) produced by sample matrix ions. The high abundance sensitivity (10(-9) for the (135)Cs/(133)Cs ratio) provided by ICP-MS/MS allowed reliable analysis of (135)Cs and (137)Cs isotopes with the lowest detection limits ever reported by mass counting methods (0.01 pg mL(-1) and 0.006 pg mL(-1), respectively). The developed analytical method was successfully applied to the determination of (135)Cs and (137)Cs isotopes in environmental samples (soil, litter, and lichen) collected after the FDNPP accident for contamination source identification.

Toxic and nontoxic components of botulinum neurotoxin complex are evolved from a common ancestral zinc protein.

Zinc atoms play an essential role in a number of enzymes. Botulinum neurotoxin (BoNT), the most potent toxin known in nature, is a zinc-dependent endopeptidase. Here we identify the nontoxic nonhemagglutinin (NTNHA), one of the BoNT-complex constituents, as a zinc-binding protein, along with BoNT. A protein structure classification database search indicated that BoNT and NTNHA share a similar domain architecture, comprising a zinc-dependent metalloproteinase-like, BoNT coiled-coil motif and concanavalin A-like domains. Inductively coupled plasma-mass spectrometry analysis demonstrated that every single NTNHA molecule contains a single zinc atom. This is the first demonstration of a zinc atom in this protein, as far as we know. However, the NTNHA molecule does not possess any known zinc-coordinating motif, whereas all BoNT serotypes possess the classical HEXXH motif. Homology modeling of the NTNHA structure implied that a consensus K-C-L-I-K-X(35)-D sequence common among all NTNHA serotype molecules appears to coordinate a single zinc atom. These findings lead us to propose that NTNHA and BoNT may have evolved distinct functional specializations following their branching out from a common ancestral zinc protein.

Determination of Rubidium by ID-ICP-QMS/QMS with Fluoromethane as the Reaction Cell Gas to Separate Spectral Interference from Strontium.

A determination of rubidium (Rb) was carried out by isotope dilution (ID) using an inductively coupled plasma tandem quadrupole mass spectrometer (ICP-QMS/QMS) with an octupole reaction-cell (ORC). Spectral interference of 87Sr with the measurement of 87Rb was effectively removed by using fluoromethane (CH3F) as the reaction cell gas at the optimum flow rate. In comparison to the measurement obtained with a mathematical correction, good precision for the analysis of the Rb isotope could be obtained independent of the concentration of Sr without any chemical separation in advance. The usefulness of the present approach was confirmed by an analysis of Rb in multiple certified reference materials (CRMs) for food and environmental analysis, for which the results agreed with their certified values in the range of expanded uncertainty.

Applications and Uncertainty Estimation of Single Level Standard Addition Method ICP-MS for Elemental Analysis in Various Matrix.

The standard addition method (SAM) based on gravimetric sample preparation was investigated as an approach for the removal or cancelling of matrix effects in measurements by inductively coupled plasma mass spectrometry (ICP-MS). Deduction of the equations and experimental confirmation of the method are both given in the present work. After measuring both spiked and non-spiked samples by ICP-MS, the concentration of an element could be calculated based on the signal intensity ratio to an internal standard. A practical example was provided for the measurement of Fe in a certified reference material (CRM), i.e. NMIJ CRM 7512-a (milk powder). The validity of the method had been confirmed by the results of international comparisons with various kinds of matrix, including bioethanol, human serum, biodiesel fuel, drinking water, infant formula milk power, and seafood. The suggested method had been applied to measurements of multiple elements in three CRMs, including tap water, milk powder, and tea leave powder, respectively.

Experimental Confirmation of SrF(CH3F)0-4+ and SrF(H2O)(CH3F)0-3+ Cluster Ions Generated in the Reaction-cell of ICP-QMS/QMS.

Multiple unknown high-order cluster ions were observed as the results of ion-molecule reactions between strontium ions and fluoromethane molecules in the reaction-cell of an inductively coupled plasma tandem quadrupole mass spectrometer (ICP-QMS/QMS). In order to elucidate the structures of these unknown cluster ions, isotope-enriched fluoromethane (CD3F) was used as the reaction-cell gas compared to natural fluoromethane (CH3F). As results, SrF(CH3F)0-4+ and SrF(H2O)(CH3F)0-3+ cluster ions were experimentally confirmed in the present work, while SrF(H2O)(CH3F)0-3+ cluster ions in the reaction-cell of ICP-QMS/QMS were observed and confirmed for the first time in the world.

Analysis of Fluorine in Drinking Water by ICP-QMS/QMS with an Octupole Reaction Cell.

The analysis of fluorine was carried out by measuring BaF+ ions with an inductively coupled plasma tandem quadrupole mass spectrometer (ICP-QMS/QMS). After optimization, a radio frequency power of 1300 W was found to benefit for the production of BaF+ ions while suppressing the production of BaOH3+ ions. After optimization of the reaction cell gas, it was found that the best performance for measuring BaF+ could be achieved at a flow rate of O2 in the range from 0.65 to 0.75 mL min-1. The signal intensity of BaF+ depended linearly on the concentration of Ba when it was not higher than 100 mg kg-1. The co-existence of metallic cations, such as Na in the sample, might suppress the generation of BaF+ ions in the plasma, while anions might not cause such a kind of interferences. The background equivalent concentration (BEC) and the lower detection limit (LDL) of fluorine were 0.4 and 0.06 mg kg-1, respectively, by adjusting the samples to a 10 mg kg-1 Ba matrix. The concentration of fluorine in a certified reference material (ERM-CA015a) was determined with the present method, for which the observed value was (1.36 ± 0.05)mg kg-1, which agreed with the certified value (1.3 ± 0.1)mg kg-1, where both values were shown as (mean value ± expanded uncertainty) with a coverage factor of (k = 2) for calculating the expanded uncertainty giving a level of confidence of approximately 95%. The present method was applied to the analysis of a tap water sample collected in the laboratory, for which the results of recovery tests gave a recovery around 100% with good reproducibility.