As regulations are introduced that require the rice producers and suppliers around the world to make large numbers of analyses for compliance purposes, there will be a need for low-cost, rapid, reliable screening procedures for the determination of inorganic arsenic in rice. Recently the Feldmann group at Aberdeen University reported [1] a procedure based on the Arsenator test-kit, which is designed to determine inorganic arsenic in drinking water down to concentrations of 5 µg per L. It is difficult to extract arsenic compounds into dilute acid with anything less than a 10-to-1 ratio of extractant (vol in mL) to mass of rice (in g), so the method has a detection limit of about 50 µg per kg, which is useful in the context of current regulations in Europe and in the US (for infant rice cereal). As we are attempting to decrease the costs to a minimum, our approach has been to adapt the Hach EZ test kit, which is considerable less expensive than the Arsenator. The Hach EZ test is based on the generation of arsine by reaction of the inorganic species with powdered zinc in acid solution followed by the reaction of the arsine, purged from the solution by the co-evolution of hydrogen, with mercuric bromide on a paper support. The resulting depth of the yellow/brown color is compared with colors on a standard chart, either visually or with the help of analysis of a digital image, obtained by a cell-phone camera or flat-bed scanner. The Arsenator employs the same color-forming reaction but the arsine is generated by reaction with borohydride, added as a solid tablet. Our preliminary results indicate that the co-extracted matrix components interfere with the reaction at the surface of the zinc, and so in one approach we are investigating borohydride as the arsine generation reagent. Control of the kinetics of this reaction is crucial, and we have adopted several approaches: perforated gelatin capsules, a double teabags, and several sorts of polysaccharide gels. For this latter study, we have enlisted the help of students in chemistry classes in a local high school. In a second approach, we studying the reaction with zinc in presence of nickel and iron salts, which the approach implemented in the “Rapid” kits made by Industrial Test systems. Some versions of these kits use 500 mL of test solution (the EZ kit needs 50 mL) and have detection capabilities of below 1 µg per L in solution. 1. Bralatei, E; Lacan, S; Krupp, E; Feldmann, J. Anal. Chem. 2015, 87, 11271–11276.

Methods based on field test kits

255th National Meeting (2018)

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