Optimization of Methodology for Determination of Inorganic Chromium Species in Sewage Sludge Samples by HPLC-ICP-MS/MS

This study developed a methodology for extracting and speciating Cr^III and Cr^VI in sewage sludge by high performance liquid chromatography, inductively coupled plasma tandem mass spectrometry (HPLC-ICP-MS/MS). The optimal procedure was solid-liquid extraction in a water bath with stirring at 50 °C for 16 h and 50 mmol L⁻¹ ethylenediaminetetraacetic acid (EDTA) extraction phase at pH 9.5. In the validated method, the recovery in the fortification experiment was greater than 70% and the relative standard deviation was less than 7%. Speciation analyses showed that all Cr^VI was spontaneously reduced to Cr^III in the sludge sample. The limits of detection and quantification were 0.060 and 0.20 µg L⁻¹, respectively, and the analyses of Cr^III by means of ICP-MS/MS were linear from 0.20 to 50 µg L⁻¹. The extraction efficiency of Cr specie in this validated method improved from 4.09 to 53.3% compared to the EPA 1311 method. The methodology was successfully applied to quantify Cr^III in a sludge sample with a lower concentration than that established by European legislation 80568/4225/91.

Keywords:
sewage sludge; chromium; extraction; reduction; inorganic chromium species