DETERMINATION OF ARSENIC IN IRON, COPPER AND NICKEL BY METAL FURNACE AAS AFTER COPRECIPITATION WITH MANGANESE-DIOXIDE

Metal furnace AAS has been used to determine arsenic (As) in iron, copper and nickel. The proposed analytical procedure is as follows: sample (0.1 approximately 2.0 g) was dissolved in 20 approximately 30 ml of HNO3 (1+1). The pH except for the case of Fe samples was adjusted to pH 1.0 approximately 2.0 with aqueous ammonia. Arsenic (As) was coprecipitated with manganese dioxide by adding KMnO4 and Mn2+. If more than 50-mu-g of Sn was contained in Cu or Ni, 0.2 g of Fe had to be added in order to coprecipitate As from HNO3 solution, because Sn(OH)4 was formed in the solution (pH 1.0 approximately 2.0) and it interfere with dissolving the precipitate. The precipitate was dissolved in a mixture of HNO3-H2O2 to which 5 mg of Ca was added and the solution diluted to 50 ml with water. Twenty microliters of this solution was injected into a tungsten boat, and dried at 180-degrees-C, for 30 s, ashed at 1500-degrees-C for 20 s by ramp mode, and then atomized at 2300-degrees-C for 2 s. The absorbance of As was interfered with the matrices of sample solutions, but addition of 100-mu-g/ml alkaline-earth metals (Ca, Mg and Ba) proved to eliminate these interferences. The same calibration curve prepared with standard solutions could be used for any samples. Fairly accurate results were obtained by this method for NIST, BAS and BAM standards.