Volatile species of arsenic(iii) with fluoride for gaseous sample introduction into the inductively coupled plasma

Abstract

The volatilization of As and its introduction into an inductively coupled plasma (ICP) spectrometer are described. The method is based on the formation of gaseous arsenic trifluoride, generated by the reaction of As^III with fluoride in sulfuric acid medium. The volatile compound is obtained in a discontinuous or batch mode after injecting 200 µl of As sample and 120 µl of 3% m/v sodium fluoride solution into 500 µl of concentrated sulfuric acid. The gaseous arsenic trifluoride is fed directly to the ICP torch by a flow (750 ml min^–1) of Ar carrier gas. When the As emission intensity at 193.696 nm is measured versus concentration a linear calibration graph is obtained between 10 and 500 µg ml^–1 of As^III; the absolute detection limit is 20 ng working with a solution volume of 200 µl. The relative standard deviation for ten measurements of 50 µg ml^–1 of As^III is 5.38%. Interferences due to alkali, alkaline earth, metallic and metalloid elements were studied; anions were also considered. It was observed that interferences from most of the species studied are relatively small. However, the interferences due to alkaline earth elements and Pb are larger than those caused by other species probably owing to sulfate precipitation. Only nitrate produces severe interference. The method was applied to the determination of As in a liquid insecticide sample and the results were compared with those obtained using a standard method.