ARSENOBETAINE AND OTHER ARSENIC COMPOUNDS IN THE CH-COUNCIL-OF-CANADA-CERTIFIED-REFERENCE-MATERIALS DORM-1 AND DORM-2

A silica-based cation-exchange column was used to determine the arseni c compounds in the National Research Council of Canada (NRCC) CRMs DOR M 1 and DORM 2 (Dogfish Muscle), With a 20 mM aqueous pyridine mobile phase at pH 3.0, the concentration of arsenobetaine was only 10.7 mg k g(-1) As in the extract of DORM 1, When the same extract was chromatog raphed on an anion-exchange column, 15.9 +/- 0.3 mg kg(-1) As (arsenob etaine) were found. The calibration for arsenobetaine was linear from 0.5 mu g dm(-1) As to 10 mg dm(-3) As, When the extracts were diluted with water the cation-exchange results approached the anion-exchange r esults. The multi-element capabilities of ICP-MS allowed the simultane ous monitoring of arsenic and alkali metals, Sodium and potassium were found to co-elute with arsenobetaine. When aqueous solutions of arsen obetaine with 250 mg dm(-3) Na were chromatographed, the signal obtain ed for arsenobetaine was only 60% of the signal without sodium in the solution, When the pH of the 20 mM aqueous pyridine mobile phase was l owered, the alkali metals were separated from arsenobetaine and the re sults obtained from cation-exchange chromatography were not significan tly different from the anion-exchange results, Because DORM 1 is no lo nger available, the arsenic compounds in DORM 2 were determined, No si gnificant difference was found for the concentration of arsenobetaine (15.6 +/- 0.7 mg kg(-1) As for DORM 1; 16.0 +/- 0.7 mg kg(-1) As for D ORM 2). The concentrations of the minor arsenic compounds (dimethylars inic acid, arsenocholine, the tetramethylarsonium cation and an unknow n arsenic compound) in DORM 2 were only half the concentrations in DOR M 1.