Application of isodiphenylthiourea immobilized silica gel to flow injection on-line microcolumn preconcentration and separation coupled with flame atomic absorption spectrometry for interference-free determination of trace silver, gold, palladium and platinum in geological and metallurgical samples

A simple and highly selective flow injection on-line preconcentration and separation-flame atomic absorption spectrometric method was developed for the routine analysis of trace amounts of silver, gold, palladium and platinum in geological and metallurgical samples. The selective preconcentration of the noble metals was achieved in a wide range of sample acidities (0.5-3.0 M HNO3 or HCl for Ag, Au and Pd) on a microcolumn packed with an isodiphenylthiourea immobilized silica gel (DPTSG). The noble metals retained on the microcolumn were effectively eluted with thiourea solution. With the use of a 0.85 mL microcolumn (about 0.14 g of DPTSG) the present system tolerated up to 25.0 mg mL(-1) of common base metal ions and 100.0 mg mL(-1) of anion when 0.040 mug mL(-1) of Ag-I, 0.200 mug mL(-1) of Au-III, 0.200 mug mL(-1) of Pd (II) and 1.00 mug mL(-1) of Pt-IV were preconcentrated for 60 s with a sample flow rate of 5.0 mL min(-1). The limits of detection were 0.33 ng mL(-1) for Ag-I, 3.2 ng mL(-1) for Au-III, 4.7 ng mL(-1) for Pd-II and 69 ng mL(-1) for Pt-IV, respectively, with the relative standard deviation being not more than 3.0%. The analytical results obtained by the proposed method for geological and metallurgical samples were in good agreement with the certified values.