Spectrophotometric Determination of Arsenic in Steels by FIA Using Filter-Tube Concentration Method

Abstract

The flow-injection analysis of arsenic in steels using a Teflon (PTFE) filter tube concentration method was investigated. Arsenic coprecipitated with beryllium hydroxide at pH 10, which was collected with a filter tube for 5 min. The precipitate was eluted with 1 M nitric acid at 0.6 ml/min, and the eluate was reacted with ammonium molybdate; the molybdoarsenate complex was reduced with ascorbic acid. The obtained molybdenum blue complex was determined by spectrophotometry at 840 nm. In the presence of phosphorus, which shows the same behavior as arsenic, the absorbance A₂ was proportional to the sum of the concentration of arsenate and phosphate. The absorbance A₁, which was obtained by reducing the arsenate to arsenite with thiosulfate, corresponded to the concentration of phosphate alone. Then, the arsenate concentration was given as A₂ − A₁. The calibration curve for arsenic was linear over the range of 0 to 100 ppb. The limits of detection and determination for arsenic were 0.7 and 2 ppb, respectively. The relative standard deviation for 20 ppb As was 1.3% (n = 8). The iron as a matrix did not interfere with the determination of As up to a million-fold to arsenic amount. The determination results for arsenic in available steel certified reference materials, which did not include phosphorus, showed good agreements with the certified values.