A gradient anion exchange chromatographic method for the speciation of arsenic in lobster tissue extracts

A gradient anion exchange chromatographic technique was developed for the separation of arsenobetaine (AsB), arsenocholine (AsC), arsenite (AsIII), arsenate (AsV), monomethylarsonic acid (MMAA) and dimethylarsinic acid (DMAA) in one chromatographic run. This technique used low residue ammonium carbonate buffer and the inductively coupled plasma-mass spectrometry (ICP-MS) chromatograms showed little baseline drift. Gradient elution improved peak shape and peak separation. The separation was completed in approximately 27 min with low detection limits (0.017–0.029 μg As kg−1). Baseline resolution of all the arsenic species evaluated was achieved when the concentration of AsC was less than approximately 12.5 μg As kg−1. This technique was successfully applied to different extracts of a standard reference material, TORT-2, and lobster tissue. AsB was found to be the major arsenic species present. AsC, DMAA, MMAA and AsV were also found, although MMAA was not detected in all of the TORT-2 extracts. Two unknown peaks found may be due to the presence of arsenosugars or other arsenic species. Discrepancy between extraction recoveries previously determined using flow injection–ICP-MS and the high-performance liquid chromatography–ICP-MS was observed in some cases. The differences may be due to the extraction technique and/or conditions at which the extractions were performed.