Spectrophotometric determination of iron with Xylenol Orange

Abstract

When a mixture of iron(III) and Xylenol Orange (XO), in a 0.1M hydrochloric medium, was heated in the presence of the other cations such as copper(II), only iron(III) was reduced to iron(II) with XO and a red iron(III)-XO complex was faded. By the addition of hydrogen peroxide to this solution, the iron(III)-XO complex was formed again. From the difference of the absorbance of the both solutions, iron was determined. The procedure is as follows: To the sample solution in a test tube, add 1.0 ml of 2.5 M hydrochloric acid and 5.0 ml of 0.2% XO solution. Dilute to 25 ml with water. After heat for 25 min in a boiling water bath and cool to room temperature. Transfer an aliquot of the solution into a cell to use as a reference solution. To the remainder of the solution in the test tube, add 0.1 ml of 30% hydrogen peroxide, and measure the absorbance of this solution at 535 nm against the reference solution. The slope of the calibration curves obtained was decreased in the presence of copper and large amounts of nickel and zinc. In this case, therefore, the amount of iron was obtained by the standard addition method. The other cations did not interfere, but titanium interfered seriously. The precision for the determination of (0.121.2) ppm of iron was found to be (0.68)% as the relative error and (0.78)% as the coefficient of variation.