Determination of arsenic in iron and steel by differential pulse anodic stripping voltammetry at a rotating gold-film electrode

A simple, rapid and reproducible method is described for the direct determination of arsenic at the mu g/g level in iron and steel based on differential pulse anodic stripping voltammetry without any separation of iron matrix. Electroinactive arsenic(V) was chemically reduced to arsenic(III) by potassium iodide prior to the stripping voltammetric determination, The interference of iron(III) was eliminated by reducing it with potassium iodide to iron(II). The generated iodine was reduced with L(+)-ascorbic acid. Arsenic(III) was electrodeposited from a 3 ml aliquot of the acid solution (0.3M HCl-0.1M HNO3-0.15M KI-0.1M L(+)-ascorbic acid pH=ca. 0.1) containing 3 mg of a sample on a rotating gold-film electrode (gold plated on glassy carbon) at -0.5 V v's. SCE for 180 s, The deposit was then anodically stripped at a scan rate of 40 mV/s to + 0.2 V vs. SCE. The calibration graph (peak height vs. concentration curve) prepared with standard arsenic solutions was linear in the range from 10 ng/ml to at least 40 ng/ml of arsenic and passed through the origin (correlation coefficient >0.998); with a sensitivity of ca. 0.2 mu A/(ngAs/ml). Antimony(III), bismuth(III) and copper(ll) interfered with the arsenic determination severely. The proposed method has been successfully applied to the determination of 50.4 and 448.8 mu g/g of arsenic in iron and steel, with relative standard deviations of less than 2.4% (n=5), without any troublesome preconcentration steps using harmful chemicals, For a deposition time of 180 s,about 80% of arsenic(III) was accumulated and the detection limit (3 sigma was 1.0 mu g/g. The time required for an analysis was within 40 min.