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 CrIII 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 CrIII 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 CrIII. Hence almost no interferences due to the matrix are found during the detection of CrIII. The CrIII 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 CrIII and CrVI with FAAS detection and the period needed for separation was under 60 s. For the preconcentration of the CrIII 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 CrIII. The sensitivity of the method enabled the determination of the CrIII and CrVI content of surface waters and various samples of natural origin at concentrations below ng ml–1 to be made. After reduction of CrVI to CrIII with ascorbic acid and its preconcentration, the total Cr content of various samples could be determined.