Trace Level Arsenic Quantification through Methyl Red Bromination

Abstract

A simple protocol has been developed for the quantification of trace level arsenic through methyl red bromination. The proposed method is based on the oxidation of arsenic(III) to arsenic(V) by the bromine and the residual bromine’s reaction with methyl red to form colorless bromo methyl red. As the concentration of arsenic increases, the bleaching of the dye decreases due to bromine consumption. Measuring the intensity of the unreacted methyl red at 515 nm forms the basis of arsenic quantification. The molar absorptivity of this method has been found to be 2.25 × 103 L/mol/cm. The method obeys Beer’s law in the concentration range 0 - 0.25 μg/mL. The Sandell sensitivity and the limit of detection (LOD) were found to be 0.03 μg/mL/cm2 and 0.03 μg/mL respectively. The relative standard deviation has been found to be 0.35% at 1.0 μg/mL. The reaction conditions have been optimized and the interference due to various common cations and anions were studied. The proposed method has been successfully applied to the determination of trace level arsenic in various environmental samples like water, soil and vegetable samples.