Speciation Determination of Chromium(VI) and Chromium(III) in Soil Samples after Cloud Point Extraction

Abstract

To measure the different activity of chromium(VI) and chromium(III) in soil samples, chromium(VI) and total chromium (CrVI + CrIII) was extracted by KCl extracting agent and alkali fusion, respectively. Cloud point extraction (CPE) for speciation determination of chromium with double-slotted quartz tube atom trap–flame atomic absorption spectrometry (STAT-FAAS) was developed. Preconcentration of chromium(VI) and total chromium in different pH solutions was achieved by CPE, with ammonium pyrrolidine dithiocarbamate (APDC) as the chelating agent and Triton X-114 as the cloud point extractant. The conditions of CPE and determination were studied. Under the optimal conditions, the enrichment factor was 50 for chromium from the initial 100-mL sample solution to the final 2-mL determined solution. Compared to the FAAS method, the sensitivity was improved seven-fold for chromium by the STAT-FAAS method. The limit of detection was 0.082 µg/L for chromium.

Keywords:

• Ammonium pyrrolidine dithiocarbamate
• cloud point extraction
• double-slotted tube atom trap–flame atomic absorption spectrometry
• soil
• speciation of chromium

Acknowledgments

This project is supported by the Natural Science Foundation of Jiangsu Province (BK2008121), the Natural Science Foundation of Jiangsu Education Committee (07KJB150112), the Preliminary Research of the National Natural Science Foundation of China (08XLY05), and the Natural Science Foundation of Xuzhou Normal University (07XLB10).

Notes

^a 0.10 mmol L⁻¹ EDTA solution added.

^a Content of Cr(III) calculated by subtracting Cr(VI) from total Cr.

^b Spiked in the sample just prior to extraction or digestion.