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 grou p was used for the flow injection (FI) on-line preconcentration and separat ion of trace levels of silver, gold and palladium. Its sorption characteris tics 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 load ing time. The RSD is not more than 3.0% for 0.040 mu g ml(-1) of Ag, 0.20 m u g ml(-1) of Au and 0.30 mu g ml(-1) of Pd. With 40 min of the sample load ing 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 2 4.5, 50.9 and 30.3 mg g(-1) for Ag, Au and Pd, respectively. The sorbent ex hibited excellent stability. Its sorption properties did not change after 1 000 cycles of use. The selected metals in a secondary nickel alloy, an anod e slime, an electrolytic solution and three national certified ore samples were determined satisfactorily using the proposed method.