Collect. Czech. Chem. Commun. 2000, 65, 1865-1874

Separation and Preconcentration of Cr(VI) as Ion Associate Using Solid Phase Extraction

Vítězslav Otruba, Jan Pivnička and Viktor Kanický*

Laboratory of Plasma Sources for Chemical Analysis, Faculty of Science, Masaryk University Brno, Kotlářská 2, CZ-611 37 Brno, Czech Republic


A method of separation and preconcentration of Cr(VI) was developed based on sorption on modified silica gel (C18) of an ion associate of Cr(VI) anion with a quaternary base. The study was performed with the following quaternary onium salts: [1-(ethoxycarbonyl)- pentadecyl]trimethylammonium bromide, 1-hexadecylpyridinium chloride, benzyl(dodecyl)- dimethylammonium bromide, butyl(triphenyl)phosphonium bromide and tetraphenylarsonium chloride. Benzyl(dodecyl)dimethylammonium bromide was found the optimum ion-pairing reagent. Sample containing Cr(III) and Cr(VI) in the presence of 0.005 mol/l of benzyl(dodecyl)dimethylammonium bromide was pumped with a peristaltic pump through the column containing the sorbent. The optimum pH range 4-5 was maintained with 0.05 mol/l phosphate buffer. Elution was accomplished using 95 vol.% ethanol and the recovery of Cr(VI) was (96 ± 6)% in the concentration range 0.005-1 mg/l of Cr(VI); even in a tenfold excess of Cr(III) the recovery of Cr(VI) was 99.8% with the relative standard deviation of repeatability about 2.4% Cr in the eluate was determined by emission flame spectrometry (Cr I 425.435 nm) in an air-acetylene or N2O-acetylene flame with the limits of detection 10 or 2 ng/ml, respectively. Hence, with a typical preconcentration factor of 200, the limits of detection in natural aqueous samples were 50 and 10 pg/ml, respectively. Calibrations were linear at least up to 10 mg/l.

Keywords: Chromium; Chromates; Ion associates; Surfactants; Solid phase extraction; Flame emission spectrometry; Silica gel C18; Sorption; Quaternary ammonium salts.

References: 31 live references.