PRECONCENTRATION OF PB(II), CD(II), CU(II) AND HG(II) WITH 2-MERCAPTO-5-PHENYLAMINO-1,3,4-THIADIAZOLE IMPREGNATED ON SILICA-GEL

Silica gel modified by the addition of 2-mercapto-5-phenylamino-1,3,4- thiadiazole (MPATD) was developed for the preconcentration of Pb(II), Cd(II), Cu(II) and Hg(II) al trace levels. A ''series'' experimental p rocedure permitted the determination of the optimal working conditions (time and pH) and an ''on-column'' experimental method permitted the determination of the quantity of MPATD retained on silica gel, the upt ake capacity, the most suitable eluent and the minimum volume of eluen t for which the maximum quantity of metal cations is recovered. The ma ximal retention capacity on the impregnated silica gel columns was obt ained at pH 7.5-8 and was 1500 mu g g(-1) for Pb(II) and about 1000 mu g g(-1) for Cd(II), Cu(II) and Hg(II). The effect of preconcentration is relevant; on passing 11 of solution containing 1 mu g ml(-1) of ca tion through a column containing 5 g of impregnated silicagel, after e lution with 30-50 ml of the appropriate eluent the cation concentratio n increased about 15-20-fold. The determination of cations by flame AA S was statistically evaluated and showed recoveries higher than 96% fo r Pb(II), 98.5% for Cd(II) and 97.95% for Cu(II) after elution with 4 M HNO3 and about 99.15% for Hg(II) after elution with thiourea.