Preconcentration and Separation of Gold on Modified Silica Gel

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Abstract
Selective preconcentration of gold in the form of ion associates of Au(III) chloro complex or Au(I) cyano complex with quaternary bases was studied using modified silica gel. Solutions containing gold in the presence of the complexing anion and a quaternary base were pumped through a Separon™ SGX C18 column. After elution with 96 vol.% ethanol, the eluate was evaporated in the presence a complexing agent (chloride or cyanide). The resulting aqueous solutions were analyzed with inductively coupled plasma atomic emission spectrometry. The influence of concentration of onium salts, chlorides, nitrates, and the influence of the sample volume on the sorption were studied. The sorption flow rate and the elution volume were optimized, and the separation from a geological sample matrix was verified. The best recovery (100%) of preconcentration of Au(III) chloro complex was obtained with [1-(ethoxycarbonyl)pentadecyl]trimethylammonium bromide and 1-hexadecylpyridinium chloride at concentrations of 0.006 and 0.004 mol dm-3, respectively. The sorption flow rate of a sample may vary in the range 0.4-7 cm3 min-1, the elution volume was between 5 and 6 cm3. The recovery decreased with increasing sample volume above 250 cm3 and was diminished by 10% in the presence of nitrates above 0.4 mol dm-3. Major accompanying elements Fe and Mn, which considerably interfere at the Au I 242.795 nm line, were quantitatively separated from gold. A Czech certified reference material 1001 Mokrsko was analyzed using the developed preconcentration technique and inductively coupled plasma atomic emission spectrometry, inductively coupled plasma mass spectrometry, and atomic absorption spectrometry. Sorption of ion associates of Au(I) cyano complex was also efficient.

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