ONLINE 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

A method has been developed for the on-line LC separation of Cr-III on a reversed-phase C-18 column in the presence of potassium hydrogen ph thalate, which is a recently introduced reagent for chromatography, It is much more selective for Cr-III in contrast to many other complex-f orming agents discussed in the literature, so that in its presence vir tually no ions are sorbed onto the C-18 column except for Cr-III. Henc e almost no interferences due to the matrix are found during the detec tion 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 mu l of sample solution the detect ion limits (3 sigma) were found to be 0.024 and 0.075 mg 1(-1) for tbe separation of Cr-III and Cr-VI with FAAS detection and the period nee ded for separation was under 60 s, For the preconcentration of the Cr- III content of a 5 ml sample solution, the detection limit (3 sigma) w as 0.73 ng ml(-1), the accuracy of the measurement was 3.8% RSD for th e preconcentration of 20 ng ml(-1) of Cr-III. The sensitivity of the m ethod enabled the determination of the Cr-III and Cr-VI content of sur face waters and various samples of natural origin at concentrations be low ng ml(-1) to be made. After reduction of Cr-VI to Cr-III with asco rbic acid and its preconcentration, the total Cr content of various sa mples could be determined.