High-speed separation of arsenic compounds using narrow-bore high-performance liquid chromatography on-line with inductively coupled plasma mass spectrometry

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Abstract
The growing importance of arsenic speciation analysis has led to the development of a wide range of high-performance liquid chromatographic based hyphenated techniques. During the present study a method was developed for the high-speed separation of several biologically and environmentally important arsenic compounds. The method is based on the use of an octadecyldimethylsilyl reversed-phase narrow-bore HPLC column. Separation of anionic arsenic species [arsenite (Aite), dimethylarsinic acid (DMAA), monomethylarsonic acid (MMAA), and arsenate (Aate)] can be achieved using a mobile phase containing 5 mM tetrabutylammonium hydroxide as the ion-pairing reagent, at pH 6.0, in less than 2 min, when employing a flow rate of 0.7 ml min−1. Adding 4-hydroxyphenylarsonic acid as the internal standard prolongs the total separation time by 30 s. On-line coupling with inductively coupled plasma mass spectrometry affords high sensitivity, as well as low limits of detection (low ppb or pg of arsenic). The influence of mobile phase pH and ion-pairing reagent concentration on the separation efficiency was studied. A loss of resolution occurs with increasing ion-pairing reagent concentration; the optimum pH is between 6.0 and 6.2. The ion-pair reversed-phase narrow-bore HPLC-ICP-MS method was subsequently applied to the speciation of arsenic in wine and kelp samples. Aite at trace levels was found to be the only arsenic species present in several wines. Average spike recoveries for Aite, Aate, MMAA and DMAA were 95 ± 3, 94 ± 5, 98 ± 1 and 92 ± 1%, respectively, for all wines examined. The method was also used for the speciation of four arsenosugars and DMAA in a kelp powder extract.

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