Liquid waveguide spectrophotometric measurements of arsenate and particulate arsenic, as well as phosphate and particulate phosphorus, in seawater

• Published in: Journal of oceanography 2017-08, Vol.73 (4), p.439-447
• Main Authors: Hashihama, Fuminori, Suwa, Shuhei, Kanda, Jota
• Format: Article
• Language: English
• Subjects: Analogs; Arsenates; Arsenic; Chemical analysis; Chemical vapor synthesis; Coefficient of variation; Coefficients; Contamination; Detection; Detection limits; Digestion; Earth and Environmental Science; Earth Sciences; Field tests; Flow system; Freezing; Freshwater & Marine Ecology; Glass fibers; Heating; Molybdate; Molybdenum; Oceanography; Original Article; Oxidation; Phosphates; Phosphorus; Pollution; Polytetrafluoroethylene; Preservation; Reaction time; Sample preservation; Seawater; Spectrophotometry; Water analysis
• ISSN: 0916-8370; 1573-868X
• DOI: 10.1007/s10872-017-0412-6

Sensitive methods for the determination of arsenate and particulate arsenic (PAs), as well as phosphate and particulate phosphorus (PP), in seawater are described. The method for arsenate and phosphate was established by applying automated liquid waveguide spectrophotometry. Because the reaction time for the formation of the arsenate-molybdate complex is longer than that for the phosphate-molybdate complex, a long Teflon tube submerged in a heating bath was installed in the conventional phosphate flow system. The arsenate was quantified as the difference between absorbances of molybdenum blue dyes with (only phosphate) and without (phosphate + arsenate) arsenate reduction treatment. Contamination was observed in the reagent for arsenate reduction and must be corrected. Linear dynamic ranges up to 1000 nM were confirmed for arsenate and phosphate. The detection limits for arsenate and phosphate were 5 and 4 nM, respectively. Freezing was a reliable sample preservation technique for both arsenate and phosphate. The method for PAs and PP was established by combining conventional persulfate oxidation of PP and the automated liquid waveguide spectrophotometry of arsenate and phosphate. The digestion efficiencies of organic As analogs were >93%. Contamination in the glass fiber filter was negligible. Field tests confirmed that the coefficients of variation (CVs) of 10–19 nM arsenate and 4–151 nM phosphate were 7–20 and 1–25%, respectively, while the CVs of 0.9 nM PAs and 10.2 nM PP were 11 and 4%, respectively.