Spectrophotometric Determination of Chromium in Urban Soil with Alizarin Red or Fast Green FCF as Reactant

In HCl medium, fast green FCF was oxidized by Cr(Ⅵ) resulting a color-fading reaction and leading to decrease of absorbance at its absorption peak of 628 nm, while alizarin red was oxidized by Cr(Ⅵ) to give a color reaction leading to increase of absorbance at the absorption peak of 520 nm. Linear relationships between the magnitude of decrease in absorbance (of the color-fading reaction) or the magnitude of increase in absorbance (of the color reaction) and the mass concentration of Cr(Ⅵ) were found in the ranges of 0.2 to 4.0 mg·L^-1 and 0.5 to 14 mg·L^-1 with values of detection limits (3s/k) of 0.014, 0.051 mg·L^-1 respectively. Based on these facts, the 2 methods described above were applied to the determination of Cr(Ⅵ) in urban soil samples separately, giving results in consistency with those found by ICP-AES.