Identification of arsenobetaine and a tetramethylarsonium salt in the clam Meretrix lusoria

Abstract
Chemical forms of arsenic were examined in six tissues (gill, mid‐gut gland, siphon, foot, mantle and adductor muscle) of the clam Meretrix lusoria. The gill was found to contain higher levels of arsenic than the other tissues. Regardless of the nature of the tissues, the presence of arsenobetaine was established by HPLC0ICP; it was a minor arsenic compound in gill but a major one in the other tissues. The major arsenic compound in gill, which was more cationic than arsenobetaine, was obtained in a relatively pure state by ion‐exchange chromatography, gel filtration and HPLC. It was positive to the Dragendorff reagent and iodine vapor but negative to ninhydrin reagent. Its 1HNMR spectrum exhibited only one signal at δ 1.7 (singlet) and its FAB mass spectrum gave a base peak at m/e 135 [(CH3)4As+] and two significant peaks at m/e 120 [(CH3)3As] and 106 [(CH3)2AsH]. These results suggested that the major arsenic compound in gill exists as a tetramethylarsonium salt (CH3)4As+ · X. The tetramethylarsonium salt was also found as a minor component in the tissues other than the gill.

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