Determination of total and soluble chromium(VI) in compost by ion chromatography–inductively coupled plasma mass spectrometry

Abstract

Ion chromatography coupled to inductively coupled plasma quadrupole mass spectrometry (IC-ICP-MS) was used for the specific determination of Cr(VI) in compost samples. Potential interferences from humic substances, carbon and chlorine species were avoided by chromatographic separation. Solution detection limits below 150 ng L−1 were obtained for injection volumes of 100 µL. Total Cr(VI) was determined by the previous alkaline digestion of the sample, following the method EPA3060A. Recoveries of pre- and post-digestion spikes (2.5 µg and 50 µg L−1 of Cr(VI) as potassium chromate, respectively) were better than 90%, indicating that the combined method can provide accurate results in spite of the high content of organic matter. Detection limits of 6 ng g−1 were obtained for the total Cr(VI) determination, the repeatability was better than 2% (at 30 µg L−1), and the reproducibility between extractions was around 6%. Soluble Cr(VI) was determined by the leaching of compost samples with water (liquid-to-solid ratio 10 : 1). A total Cr(VI) content of 1.2 µg g−1 was obtained for a compost from urban solid residues, whereas the soluble Cr(VI) in the pH range 4–10 was below the detection limit of the leaching method (1 ng g−1).