Using QuEChERS sample preparation technique followed by ICP-Ms method to determination Cr(III) and Cr(VI) in seawater

Abstract

Currently, Cr(III) and Cr(VI) are analyzed directly in trace level using anion-exchange liquid chromatography inductively coupled plasma mass spectrometry (LC – ICP – MS), which is well-known as an expensive and complicated method. Therefore, determination of Cr(VI) and Cr(III) by spectrometer or combine with ICP (or AAS) is seemly prefer to choose in almost laboratories although this method presents a higher limit of detection (LOD) and is influenced by salt ions in seawater. In this study, after forming reddish-violet complex by adding diphenylcarbazide (DPC) to seawater samples, a QuEChERS extraction technique was applied to separate Cr from high salt level matrix and transfer the Cr(VI)-DPC structure to the acetonitrile phase. In case of determination of total Cr, the Cr(III) in samples had to convert to Cr(VI) by oxidate with KMnO4 before adding DPC. Then, a digestion process with HNO3 – H2O2 mixture was implemented before analyzing Cr(VI) by ICP-MS. The Cr(III) is calculated indirectly based on total Cr and Cr(VI) results. This method had a linear concentration range of Cr(VI) from 0.02 to 50 µg/L with a detection limit of 0.015µg/L, the relative standard deviations under 3,03%, and the recovery was 92-108 % for seawater. According to the outcome of parallel experiment with common method, which used spectrometer and did not apply QuEChERS extraction step, the ICP-MS method presented a better result with smaller LOD, RSD, and recovery range.