INDIRECT VOLTAMMETRIC DETERMINATION OF LANTHANIDES IN THE PRESENCE OFMORDANT-RED-19

Complexes of lanthanide with Mordant Red 19 (MR19) are shown to be ads orbed and can be electrochemically reduced at mercury electrodes at a more negative potential than where MR19 is reduced. Based on these pro perties, an analytical application for the determination of lanthanide s is demonstrated by linear sweep voltammetry (LSV) and by highly sens itive adsorptive stripping voltammetry (AdSV). By applying AdSV, the d etection limit of several lanthanides is about 5.0 x 10(-10) M with an accumulation time of 5 min and the linear response range is from 5.0 x 10(-8) M to 1.0 x 10(-6) M. A typical relative standard deviation is found to be 5.2% at the 5.0 x 10(-8) M level. The results from LSV sh ow that the difference in peak potentials (Delta E-p) between complex and MR19 increases when the atomic number of lanthanide ion is increas ed. Because the smallest Delta E-p due to the presence of La3+ is stil l large enough to distinguish the complex peak from dye peak, it is po ssible to recognize all members of lanthanide ions selectively with MR 19, regardless of whether they are light or heavy ones. It is also pos sible to perform simultaneous analysis for some mixtures. In addition, the range of lanthanide concentration, for which quantitative analysi s is valid, becomes wider as a result of using LSV as well as AdSV.