Comparison of enzymatic extraction procedures for use with directly coupled high performance liquid chromatography-inductively coupled plasma mass spectrometry for the speciation of arsenic in baby foods

A method has been developed for the speciation of arsenic in a variety of baby foods using directly coupled high performance liquid chromatography (HPLC) and inductively coupled plasma mass spectrometry (ICP-MS). Ion exchange HPLC separation using gradient elution and sodium sulphate as the mobile phase resulted in good resolution and a fast separation of the following species: arsenobetaine, monomethylarsonic acid, dimethylarsinic acid and arsenate. The arsenicals were extracted by two enzymatic digestion procedures, based on the action of trypsin or pancreatin. The results from the enzyme digested samples were compared with those obtained for total arsenic by microwave-oven digestion. The reliability of the procedure was also checked by analysing the total reducible arsenic species by hydride generation-AAS and by analysing two certified reference materials. The enzymatic digestion procedures were also evaluated on pure standards to ensure that no species alteration occurred during the extraction process. Trypsin was found to work well although the pancreatin extraction had a deleterious effect on the chromatography, with the dimethylarsinic acid peak co-eluting with the arsenobetaine. Pancreatin was therefore concluded to be unsuitable for the speciation process, although the total amount of arsenic extracted was comparable to the trypsin extraction. Values for the total arsenic content in the baby foods were found to range between 0.25 and 4.7 mug g(-1). Arsenobetaine was the only arsenic species detected in most samples, but an unidentified species was detected in one sample. (C) 2001 Elsevier Science B.V. All rights reserved.