Electrospray mass spectrometry method to prevent the reduction of hexavalent to pentavalent chromium.

RATIONALE: Electrospray mass spectrometry (ESI-MS) is one of the most effective methods for assessing the state of metals in solution. For ions with a redox potential close to ~0.55 V, such as Cr6+ , reduction of the metal in solution occurs in the ESI-MS system. In our studies, it was observed that [HCrO4 ]- undergoes reduction, resulting in the formation of [CrO3 ]- . The precise mechanism remains ambiguous. The reduction of hexavalent chromium to pentavalent chromium is supported by Frost diagrams, reinforcing our confidence in the validity of the ESI-MS measurement method. The reduction mechanism in ESI-MS was clarified, and a system was devised to eliminate electron donation during the reduction of Cr6+ in solution. METHODS: To determine the state of Cr6+ by ESI-MS, CrO3 in solid form was dissolved in ultrapure water to prepare a solution of 500 × 10-6  mol/L (µM) concentration. The pH was adjusted to 4.0, 5.3, 6.3, 8.2 and 9.1 and subsequently measured. CrO3 solutions with various concentrations of 10, 100 and 500 µM were prepared and adjusted to a pH of ~7 using tetramethylammonium hydroxide to measure Cr6+ under different conditions. RESULTS: Cr6+ in solution was soluble and existed as an oxoacid with a negative charge independent of pH. Cr6+ was stable over a wide pH range at various concentrations. The ESI-MS method determined the negative ion [HCrO4 ]- as the stable ion, but [CrO3 ]- was also present as a byproduct. Therefore, we were interested in the presence of other species, such as [CrO3 ]- , which could have formed owing to the reduction of Cr6+ . CONCLUSIONS: In ESI-MS system, it undergoes reduction to form [CrO3 ]- . The high flow rate of ultrapure water in pump insulated the acceptance of electrons by Cr6+ preventing its reduction. Further in-depth ESI-MS studies could explain the complex formation and behavior of Cr6+ in aqueous solution.

Mercury concentrations in the tissues of blue shark (Prionace glauca) from Sagami Bay and cephalopods from East China Sea.

The toxicity of mercury (Hg), is generally known, and around 90% of Hg exist as methylmercury (CH3Hg+) in marine organism. Mercury concentrates in sharks and whales, which are at the top of the food chain as predators to cephalopods. The concentrations of Hg in liver and muscle of blue shark, caught in Sagami Bay, and in digestive gland and mantles of Todarodes pacificus, Sepia madokai, and Uroteuthis edulis caught in East China Sea were measured and analyzed. The Hg concentrations in the sharks, squids, and cuttlefishes determined in this study were almost same as those in the other sea regions. In addition, the Hg concentration in the blue shark was higher in the muscle than in the liver. In S. madokai and U. edulis, Hg accumulated in the digestive gland but not in the mantle. Although the Hg concentration in the digestive gland of T. pacificus is lower than those of S. madkai and U edulis, Hg concentration in the mantle is critically higher. More than 90% of Hg is present as CH3Hg+ in muscle of blue shark and mantle of T. pacificus. This feature is explained due to amino acids with the thiol groups and chain genes in the muscle of blue shark as well as in the mantle of T. pacificus. Myosin in the mantle of T. pacificus and blue shark enhances the stability of CH3Hg+. The amount of Hg in the digestive gland of T. pacificus could be too large to store; thus, Hg is released to the mantle, whereas the nutrients in the digestive gland of T. pacificus are supplied to other tissues. It is considered that the muscle fiber of T. pacificus is strong; therefore, large amounts of myosin levels may be present in T. pacificus than in S. madokai and U. edulis.

Modified ion exchange separation for tungsten isotopic measurements from kimberlite samples using multi-collector inductively coupled plasma mass spectrometry.

Tungsten isotope composition of a sample of deep-seated rock can record the influence of core-mantle interaction of the parent magma. Samples of kimberlite, which is known as a carrier of diamond, from the deep mantle might exhibit effects of core-mantle interaction. Although tungsten isotope anomaly was reported for kimberlites from South Africa, a subsequent investigation did not verify the anomaly. The magnesium-rich and calcium-rich chemical composition of kimberlite might engender difficulty during chemical separation of tungsten for isotope analyses. This paper presents a simple, one-step anion exchange technique for precise and accurate determination of tungsten isotopes in kimberlites using multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). Large quantities of Ca and Mg in kimberlite samples were precipitated and removed with aqueous H(2)SO(4). Highly pure fractions of tungsten for isotopic measurements were obtained following an anion exchange chromatographic procedure involving mixed acids. That procedure enabled efficient removal of high field strength elements (HFSE), such as Hf, Zr and Ti, which are small ions that carry strong charges and develop intense electrostatic fields. The tungsten yields were 85%-95%. Advantages of this system include less time and less use of reagents. Precise and accurate isotopic measurements are possible using fractions of tungsten that are obtained using this method. The accuracy and precision of these measurements were confirmed using various silicate standard rock samples, JB-2, JB-3 and AGV-1.

Speciation of dissolved silicates in natural waters containing alkaline and alkaline-earth ions. A case study--waters from arid lands (North West China).

The concentration of silica in water samples from the desert area of Xinjiang, N. W. China, has been measured by colorimetry with ammonium molybdate. The observed pattern of dependence of the concentration of silica on the concentration of sodium ion (Na(+)) in the water samples is consistent with the pattern obtained by experiments on in-vitro dissolution of silica gel in sodium chloride (NaCl) solution. This indicates that the dissolution of silica in the hydrologic system in this area depends on the concentration of Na(+). Calcium ion (Ca(2+)), which is known to play an important role on the dissolution of silica on the basis of in-vitro experiments, was observed to take little part in the dissolution of silica in actual natural water samples. This implies that the Ca(2+) is bound to the hydrogen carbonate anion or that the Ca(2+) content of natural water containing salts is very low, owing to precipitation. In these samples silicate-Na(+) was identified as the dissolution species of silica; it was also ascertained that Ca(2+) did not form complexes with silicate species. These observations resulted from direct identification of dissolved chemical species by use of FAB-MS (fast atom bombardment mass spectrometry). The research indicates that in water samples in this critically arid region the concentration of "dissolved" silica is basically determined by the concentration of Na(+), indicative of pure inorganic conditions in the desert area of Xinjiang, N.W. China.