The following commercial chemicals were used: ortho phosphoric acid (p.a., or TraceSELECT Ultra) from Fluka (Buchs, Switzerland); pyridine from Merck (Merck, Darmstadt, Germany); and hydrogen peroxide 30 % (p.a.), aqueous ammonia 25 % (suprapure), 65 % nitric acid (p.a.), and formic acid (p.a.) from Roth (Carl Roth, Karlsruhe, Germany). Chemicals were used without further purification except for the nitric acid which was distilled in a quartz sub-boiling distillation unit. Water used throughout was from a Milli-Q Academic water purification system (Millipore GmbH, Vienna, Austria) with a specific resistivity of 18.2 MΩ*cm.
Individual standard solutions (1000 ± 3 μg L−1 in 2 % nitric acid) for total element determinations of As, Cd, Mo, Pb, Sb, Se, U, W, and Zn (in the urine samples) and Ge, In, and Lu (internal standards) were obtained from CPI International (Santa Rosa, CA, US). For arsenic speciation, stock solutions containing 1000 mg As L−1 of each of the following species were prepared in water: arsenite (As(III) and arsenate (As(V)) prepared from NaAsO2 and Na2HAsO4.7 H2O, respectively, purchased from Merck (Darmstadt, Germany); dimethylarsinate (DMA) prepared from sodium dimethylarsinate purchased from Fluka (Buchs, Switzerland); methylarsonate (MA) prepared in-house from sodium arsenite and methyl iodide (Meyer reaction); and arsenobetaine (AB), as the bromide salt, prepared in-house following the method of Cannon et al.11 The purity of the synthesized standards (MA and AB) was established by NMR and HPLC/mass spectrometry. Other arsenic standards (trimethylarsine oxide, arsenocholine, tetramethylarsonium ion, oxo and thio-dimethylarsinylethanol and oxo- and thio-dimethylarsinylacetic acid) were prepared as previously reported;12 ,13 (link) these standards were used to check the identity of minor peaks which occasionally appeared in the chromatograms.
The certified reference materials for total element measurements were NIST 1643e, trace elements in water (National Institute of Standards & Technology, Gaithersburg, Maryland, US) certified for As, Cd, Mo, Pb, Sb, Se, & Zn; and NIES No. 18, human urine (National Institute for Environmental Studies, Tsukuba, Japan) certified for As, Se & Zn. In addition, Seronorm™ control urine (Sero AS, Billingstad, Norway) and an in-house urine sample served as non-certified reference materials. The certified reference material for determining arsenic species was NIES No 18, human urine, certified for AB and DMA. Our in-house reference urine was used as a control for iAs, MA, DMA, and AB.
Individual standard solutions (1000 ± 3 μg L−1 in 2 % nitric acid) for total element determinations of As, Cd, Mo, Pb, Sb, Se, U, W, and Zn (in the urine samples) and Ge, In, and Lu (internal standards) were obtained from CPI International (Santa Rosa, CA, US). For arsenic speciation, stock solutions containing 1000 mg As L−1 of each of the following species were prepared in water: arsenite (As(III) and arsenate (As(V)) prepared from NaAsO2 and Na2HAsO4.7 H2O, respectively, purchased from Merck (Darmstadt, Germany); dimethylarsinate (DMA) prepared from sodium dimethylarsinate purchased from Fluka (Buchs, Switzerland); methylarsonate (MA) prepared in-house from sodium arsenite and methyl iodide (Meyer reaction); and arsenobetaine (AB), as the bromide salt, prepared in-house following the method of Cannon et al.11 The purity of the synthesized standards (MA and AB) was established by NMR and HPLC/mass spectrometry. Other arsenic standards (trimethylarsine oxide, arsenocholine, tetramethylarsonium ion, oxo and thio-dimethylarsinylethanol and oxo- and thio-dimethylarsinylacetic acid) were prepared as previously reported;12 ,13 (link) these standards were used to check the identity of minor peaks which occasionally appeared in the chromatograms.
The certified reference materials for total element measurements were NIST 1643e, trace elements in water (National Institute of Standards & Technology, Gaithersburg, Maryland, US) certified for As, Cd, Mo, Pb, Sb, Se, & Zn; and NIES No. 18, human urine (National Institute for Environmental Studies, Tsukuba, Japan) certified for As, Se & Zn. In addition, Seronorm™ control urine (Sero AS, Billingstad, Norway) and an in-house urine sample served as non-certified reference materials. The certified reference material for determining arsenic species was NIES No 18, human urine, certified for AB and DMA. Our in-house reference urine was used as a control for iAs, MA, DMA, and AB.
