The Varian ICP-MS was used for all arsenic measurements. ICP-MS setup was fully controlled by Varians ICP-MS Expert software, which provides one-step instrument setup, optimization and method development. Prior to connecting the ICP-MS to LC, it was tuned to high sensitivity mode automatically by using the auto optimization routine included in the software. The ICP-MS nebulizer was then connected to the LC column using a 20 cm length of PEEK tubing (0.010 I.D.). See Tables 1-3 for the ICP-MS and LC conditions used.
Reagents and samples
Deionized water (18 MΩ cm, Millipore MilliQ, Billerica, MA, USA) was used for all solution preparations (calibration solutions and mobile phase).
Arsenic pentoxide and arsenic trioxide were obtained from SPEX CertiPrep (Metuchen, NJ USA). Arsenobetaine (AsB, C5H11AsO2) was obtained from Sigma Aldrich (Castle Hill, NSW Australia). Cacodylic acid (dimethylarsenic acid, DMA) and monosodium acid methane arsonate (MMA) were purchased from Chem Service (West Chester, PA USA). All calibration solutions were prepared daily.
Mobile phase LC
Ammonium carbonate (Merck, Kilsyth, Victoria, Australia) and either Suprapur ammonia solution obtained from Merck (Kilsyth, Victoria, Australia) or AR Select Plus nitric acid, (Mallinckrodt Baker, Phillipsburg, NJ, USA) were used for pH adjustments of the mobile phase. The mobile phase was prepared daily.
Standard Reference Material 1640, Trace Elements in Natural Water was obtained from the National Institute of Standards and Technology (Gaothersburg, MD, USA). Trace Metals in Fish (HPS CRM-TMF Lot #123921), Trace Metals in Drinking Water (HPS