Extractive spectrophotometric determination of chromium(III) in steels using 4-(2-pyridylazo)resorcinol and xylometazoline hydrochloride

Abstract

Chromium(III) forms a 1 : 3 orange-red anionic complex with 4-(2-pyridylazo)resorcinol (PAR) when heated in an acetate buffer medium (pH 4.0–5.5) on a water-bath, and this complex can be extracted quantitatively with the xylometazolonium (XMH) cation into chloroform. This ion association system exhibits a maximum absorbance at 530 nm, with a molar absorptivity of 4.8 × 10⁴ l mol^–1 cm^–1 and obeys Beer's law in the range 0–1.0 µg ml^–1 of chromium(III). Job's method of continuous variations revealed that the composition of the extracting species is 1 : 3 : 1 for Cr(III)-PAR-XMH. EDTA, when added after the formation of the complex between Cr(III) and PAR, can effectively mask the interference from Ca(II)(1000 µg), Ba(II)(1000 µg), Sr(II)(1000 µg), Tl(II)(1000 µg), Cd(II)(1000 µg), Mg(II)(500 µg), Hg(II)(500 µg), Al(III)(500 µg), Bi(III)(400 µg), V(V)(200 µg), Mn(II)(200 µg), Mo(VI)(200 µg), Cu(II)(150 µg) and W(VI)(150 µg) without any interference in the determination of chromium. This makes the method highly selective.