Ammonium carbonate

All materials used were of analytical grade or better unless otherwise stated. MilliQ (18 MΩ cm) water was used throughout. A 1000 mgL⁻¹ As stock solution (as H₃AsO₄) was purchased from Peak Performance (CPI International, USA) as were Te (1000 mgL⁻¹) and In (1000 mgL⁻¹) standards for use as internal standards, for calibration of arsenic species. Dimethylarsinic acid disodium salt (100%) supplied by Argus-Chemicals (Italy) was dissolved in MilliQ water and diluted as required. Disodium methyl arsonate hexahydrate (99.5%) was supplied by Chem-Service (USA); disodium hydrogen arsenate heptahydrate (As^V), sodium arsenite (As^III) and ammonium carbonate were purchased from BDH (UK). Chemicals used for extractions were purchased from Sigma-Aldrich: MeOH (> 99.9%), DCM (> 99.8%), hexane (> 97%). Hydrogen peroxide (puriss p.a., > 30%) was also purchased from Sigma-Aldrich. Two nitric acids were used: trace select (> 69%) was purchased from Fluka (UK) and puriss p.a. (> 65%) was purchased from Sigma-Aldrich; the puriss p.a. acid was used throughout unless otherwise stated.

Morphine, Morphine-d3, 6-MAM, 6-monoacetylMorphine-d3 (6-MAM-d3), codeine, codeine-d3, and 6-AC were purchased from Lipomed (Arlesheim, Switzerland). Methanol (HPLC grade), acetonitrile (HPLC grade), ammonium carbonate, formic acid, and ammonium hydroxide were obtained from BDH (Poole, UK). Ammonium formate was obtained from Sigma-Aldrich (Steinheim, Germany). Clean Screen^® solid phase extraction (SPE) cartridges (CSDAU203) were obtained from United Chemical Technologies (Bristol, PA, USA).

All chemicals used were of analytical grade or better and Milli-Q water from a Millipore water dispensing system (Millipore, France) was used throughout unless otherwise stated. Hydrogen peroxide (H₂O₂) (for trace analysis, ≥30%) and nitric acid (HNO₃) (ROTIPURAN Supra, 69%) were supplied by Supelco (Sigma-Aldrich, France) and Carl Roth (Germany) respectively. Ammonium carbonate was obtained from BDH (UK) and methanol (HPLC grade) was purchased from Honeywell (USA). Arsenate standards used for external calibration of the iAs analysis were prepared from a stock solution of disodium hydrogen arsenate heptahydrate (98.5%) supplied by Argus Chemicals (Italy) dissolved in Milli-Q water. DMA and MMA standards used for spiking experiments were prepared from dimethylarsinic acid disodium salt (100%) supplied by Argus Chemicals (Italy) and disodium methyl arsonate hexahydrate (99.5%) purchased from Chem-Service (USA), respectively. Standards for total As analysis were prepared from 1000 mg L⁻¹ As standards supplied by LabKings (Netherlands). Indium and germanium internal standards were prepared from 1000 mg L⁻¹ stock solutions purchased from Peak Performance (CPI International, USA).