Determination of chromium in iron and steel by adsorptive stripping voltammetry with diphenylcarbazide

A sensitive and selective method is described for the determination of chro mium at the low ppm level in iron and steel by differential pulse adsorptiv e cathodic stripping voltammetry with diphenylcarbazide as complexing agent . The complex of chromium(VI) with diphenylcarbazide, Cr(III)-diphenylcarba zone, was adsorbed on a graphite electrode for 5 min with open circuit in a nitric-sulfuric acids mixture solution containing phosphoric acid (pH=ca. 0.6), and subsequently was stripped in another solution (the acid mixture s olution in the absence of iron(III) and phosphoric acid) in the potential r ange 0.3 to -0.1 V vs. SCE at a scan rate of 50 mV/s. Most of the foreign m etals did not interfere by application of the non-electrolytic accumulation step. The calibration curve was linear over a concentration range 9.6 x 10 (-8) to 1.3 x 10(-6) M, Of chromium (correlation coefficient >0.999) and pa ssed through the origin. The detection limit (3 sigma) was 2.7 x 10(-8) M [ 1.43 ngCr(VI)/ml) for an accumulation time of 5 min. The determination of 8 to 500 massppm of chromium in iron and steel was achieved with good precis ion and accuracy within 1 h by the proposed method without any separation o f the matrix. The simple method developed can be also applied to the determ ination of chromium in obsolete steel scrap.