High-performance liquid chromatography-inductively coupled plasma mass spectrometry based method for the determination of organic arsenic feed additives and speciation of anionic arsenics in animal feed.

A novel method has been developed to detect two organic arsenic animal feed additives including roxarsone and p-arsanilic acid, as well as other arsenic species such as arsenite, dimethylarsinic acid, monomethylarsonic acid, arsenate, and 4-hydroxyphenylarsonic acid, by using high-performance liquid chromatography coupled to an inductively coupled plasma mass spectrometer (HPLC-ICP-MS). The influence of the type and concentrations of ion-pairing reagents on the separation efficiency of the different arsenic compounds was examined. The effects of the mobile phase pH on the retention of arsenic species on the chromatography column were studied. When a gradient elution procedure was used, the best separation of the seven arsenic species could be achieved in <20 min with a mobile phase consisting of 8% methanol and 92% aqueous tetrabutylammonium hydroxide (4 mM, pH 6.25) followed by 92% trifluoroacetic acid aqueous solution (0.1%, pH 2.0). Liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) was used as an assistant tool to screen arsenobetain (AsB) in the feed samples by monitoring the reaction at m/z 179-->120. The extractions of arsenic compounds from formula feed samples were studied, and results showed that the extraction with methanol/water (1:1) mixture yielded the most efficient percent compound recovery and the fastest extraction time for all arsenic species. Under optimum conditions, the limits of detection were <1.7 microg of As kg(-1), and the recoveries of all seven arsenic species were >78.5% with the relative standard deviation of <10%. The ion-pair reversed phase HPLC-ICP-MS method was then successfully applied to the speciation of arsenic in feedstuff and formula feed samples.