On-line chromatographic separation and determination of chromium(III) and chromium(VI) with preconcentration of the chromium(III) using potassium hydrogen phthalate, in various samples by flame atomic absorption spectrometry

Abstract

A method has been developed for the on-line LC separation of Cr^III on a reversed-phase C₁₈ column in the presence of potassium hydrogen phthalate, which is a recently introduced reagent for chromatography. It is much more selective for Cr^III in contrast to many other complex-forming agents discussed in the literature, so that in its presence virtually no ions are sorbed onto the C₁₈ column except for Cr^III. Hence almost no interferences due to the matrix are found during the detection of Cr^III. The Cr^III sorbed onto the column was eluted into the flame of an atomic absorption spectrometer using a mixture of methanol and water [80–20(%(v/v))]. With 100 µl of sample solution the detection limits (3σ) were found to be 0.024 and 0.075 mg l^–1 for the separation of Cr^III and Cr^VI with FAAS detection and the period needed for separation was under 60 s. For the preconcentration of the Cr^III content of a 5 ml sample solution, the detection limit (3σ) was 0.73 ng ml^–1, the accuracy of the measurement was 3.8% RSD for the preconcentration of 20 ng ml^–1 of Cr^III. The sensitivity of the method enabled the determination of the Cr^III and Cr^VI content of surface waters and various samples of natural origin at concentrations below ng ml^–1 to be made. After reduction of Cr^VI to Cr^III with ascorbic acid and its preconcentration, the total Cr content of various samples could be determined.