Speciation of Cr(III) and Cr(VI) in geological and water samples by ytterbium(III) hydroxide coprecipitation system and atomic absorption spectrometry.

A novel coprecipitation method with ytterbium(III) hydroxide has been established for speciation of Cr(III) and Cr(VI) in geological and water samples. At pH 10, while Cr(III) was quantitatively recovered, Cr(VI) was recovered under 10% levels. Total chromium was determined reducing of Cr(VI) to Cr(III) in acidic media with KI reagent. The concentration of Cr(VI) was calculated by the concentration difference between the total chromium and Cr(III). For the quantitative recovery of Cr(III), parameters such as pH, amount of ytterbium, centrifugation time and speed, matrix effect, KI amount, and sample volume were investigated. The preconcentration factor was 30. The limit of detection was obtained as 1.1 μg/L for Cr(III). The accuracy was checked by analyte addition and analyses of standard reference materials (TMDA-54.4 Certified Reference Water, NIST 2710 Montana Soil). Method has been successfully applied to the chromium speciation for industrial waste water of leather factories located in Bor-Nigde, and also for mine and soil samples.