Hideyuki Sakamoto

Arsenic speciation with gradient hydride generation interfacing liquid chromatography and atomic absorption spectrometry

Arsenic speciation was performed based on liquid chromatographic separation followed by gradient hydride generation (GHG) and quartz atomizer atomic absorption spectrometric detection. The arsenic species, i.e., arsenate (As(V)), arsenite (As(III)), monomethylarsonic acid (MMA), dimethylarsinic acid (DMA) and trimethylarsine oxide (TMAO), were separated on C30-5 columns, and the concept of gradient hydride generation facilitates high conversion efficiency of the arsenic species into corresponding hydrides. The use of 2% L-cysteine in the GHG process gives rise to further improvements on the hydride generation efficiency of 13% to 32% for the arsenic species. The hydrides were separated in a unique design of gas–liquid separator, which not only ensures a complete separation but minimizes the dispersion of hydrides when delivering into the atomizer, resulting in a maximum of 13-fold improvement on the sensitivity of As(V) compared to previous studies. A separation process was finished within 800 s by injecting 100 µL sample solution, achieving detection limits of 0.9, 1.4, 1.4, 1.6, 1.5 µg/L, respectively, for As(V), As(III), MMA, DMA and TMAO. Precisions of less than 3% and 6% RSD were obtained for the five arsenic species at 100 µg/L and 20 µg/L, respectively. Three arsenic species, i.e., As(V), DMA and TMAO, were identified in Hijiki samples by this procedure.

Arsenic preconcentration viasolid phase extraction and speciation by HPLC-gradient hydride generation atomic absorption spectrometry

A novel method for arsenic speciation is developed by interfacing solid phase preconcentration-liquid chromatography (LC) separation-gradient hydride generation (GHG)-quartz flame atomic absorption spectrometry (QFAAS). A MnO2 mini-column is used to preconcentrate the arsenic species of As(III), As(V), MMA and DMA, during which process, As(III) is converted to As(V)viaoxidation by MnO2, while other species remain unchanged. The recovery of As(V) (i.e., the total amount of arsenate and arsenite in the original sample), MMA and DMA from the MnO2 mini-column is facilitated by tetramethylammonium hydroxide (TMAH). After LC separation with C30 columns, arsenic species in the eluate are subject to gradient hydride generation with detection by QFAAS. On the other hand, cellulose fibre selectively adsorbs the chelating complex between As(III) and ammonium pyrrolidine dithiocarbamate (APDC). After elution with HNO3, As(III) in the original sample is quantified by graphite furnace atomic absorption spectrometry (GFAAS), and the amount of As(V) is obtained by subtraction. A sample volume of 2.0 mL derives enrichment factors of 14.0–19.2 for the arsenic species. By injecting 20 μL of eluate into the LC system (the eluate of As(III)-PDC complex is injected into the GFAAS), detection limits of 0.019, 0.33, 0.39, 0.62 μg L−1 are obtained for As(III), As(V), MMA and DMA respectively. RSDs of less than 4.2% are achieved at the level of 2 μg L−1 for As(V), MMA, DMA and 1 μg L−1 for As(III). The procedure is evaluated by speciating arsenic in snow water and Hijiki samples.