Separation and Preconcentration of Platinum Group Metals and Gold on Modified Silica and XAD Sorbents in the Presence of Cationic Surfactants for Their Determination by ICP-AES

Abstract

Various modified silica sorbents and unmodified silica were tested for the separation and preconcentration of 10-200 ng cm-3 from 50-1 000 cm3 sample volume of platinum group metals (PGMs), Pt(IV, II), Pd(II), Ir(IV), Rh(III), Os(VI), Ru(IV) and Au(III) in the form of ion associates of their chloro and bromo complexes with cationic surfactants. [1-(Ethoxycarbonyl)pentadecyl]trimethylammonium bromide (Septonex®), benzyl(dodecyl)dimethylammonium bromide (Sterinol®), trimethyl(tetradecyl)ammonium bromide or hexadecyl(trimethyl)ammonium chloride and 0.1 M HCl or 0.1 M HBr are suitable for the purpose. 100% recovery for Pd(II), Pt(IV) and Au(III) was obtained with octadecyl silicas Separon™ SGX C18, Separon™ SGX RPS and Phenyl™ silica in the presence of 0.006 M Septonex® or 0.003 M Sterinol®. The retained PGMs and Au(III) were eluted with acetonitrile and determined by inductively coupled plasma atomic emission spectrometry (ICP-AES) after evaporation of organic solvent in the presence of 0.1 M HCl. The enrichment factor on Separon™ SGX RPS reaches 100. A 1 000 : 1 excess of Cl-, NO3-, SO42-, Na+, K+, Ca2+, Mg2+, Fe3+ or Al3+ does not interfere with the preconcentration of PGMs and Au(III) on this sorbent. With the silica-based anion exchanger Separon™ SGX AX, the 100% recovery is observed for Ir(IV), Pd(II), Pt(IV) when the elution is performed with 5 M HCl or 5 M HNO3. Macroporous sorbents Amberlite™ XAD2 and Amberlite™ XAD4 are suitable for the retention of Au(III), Pd(II) and Pt(IV) from 0.1 M HCl and 0.006 M Septonex®. 100% recovery is achieved using acetonitrile as eluent but there is no preference of these sorbents to modified silica. In this way, the recovery of 0.1-0.2 μg cm-3 Au(III), Pd(II), Pt(IV) was also successfully tested with spiked matrices of soil extracts, power station dust samples and natural waters.