Abstract
A flow-injection (FI) fluorimetric method for the determination of dimethylarsinic acid (DMAA) is proposed. The assay is based on the reaction of the herbicide with peroxydisulphate in UV light to produce arsenate, which reacts with molybdate and thiamine to form thiochrome. The thiochrome is fluorimetrically monitored at 440nm with excitation at 375nm. The calibration graph is linear in the range 0.14–14μgml−1 with an accuracy of 0.5%. The limit of detection is 0.014μgml−1 and the sample throughput is 60 samples per hour.The proposed method can be used for the determination of DMAA in the presence of inorganic arsenic and for the speciation of arsenic compounds making use of a strong cation exchange resin.DMAA can be pre-concentrated on a cation exchange resin in the H+-form. In this way, it can be determined over the range 5.6–560ngml−1 with a detection limit of 0.6ngml−1.The usefulness of the method is demonstrated by determining DMAA residues in irrigation waters and vegetables.
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