Synthesis of silica gel immobilized thiourea and its application to the on-line preconcentration and separation of silver, gold and palladium

A new silica gel based chelating sorbent with thiourea as a functional group was used for the flow injection (FI) on-line preconcentration and separation of trace levels of silver, gold and palladium. Its sorption characteristics were evaluated by FI-FAAS. The selected metal ions were adsorbed on a column packed with thiourea modified silica gel (TuSG) with a sampling flow rate of 5.0 ml min(-1), eluted with 5% thiourea with a flow rate of 2.5 ml min(-1) and determined by FAAS. Common co-existing ions did not interfere with the preconcentration and determination. The detection limits, defined as three times of the standard deviation of the blank (3 sigma), of Ag, Au and Pd are 1.3, 14 and 21 ng ml(-1), respectively, with a 1 min sample loading time. The RSD is not more than 3.0% for 0.040 mu g ml(-1) of Ag, 0.20 mu g ml(-1) of Au and 0.30 mu g ml(-1) of Pd. With 40 min of the sample loading time, 1.0 ng ml(-1) of Ag, 5.0 ng ml(-1) of Au and 7.5 ng ml(-1) of Pd were successfully preconcentrated. The total dynamic capacity of TuSG was 24.5, 50.9 and 30.3 mg g(-1) for Ag, Au and Pd, respectively. The sorbent exhibited excellent stability. Its sorption properties did not change after 1000 cycles of use. The selected metals in a secondary nickel alloy, an anode slime, an electrolytic solution and three national certified ore samples were determined satisfactorily using the proposed method.