Abstract

The separation and determination of Cr^VI and Cr^III were carried out by using a combination of ion-exchange resins and inductively coupled plasma mass spectrometry (ICP-MS). Once in solution the species were retained on Dowex 1-X8 and Dowex 50W-X8 resins, for Cr^VI and Cr^III, respectively. Following elution of the Cr^VI with HNO₃ and of the Cr^III with HCl, and after elimination of chloride ions, chromium contents were determined by ICP-MS. The sample dissolution and preparation method was developed using CrO₃ (Cr^VI) and Cr₂O₃ (Cr^III) mixtures. A general method was established, consisting in the leaching of the soluble chromium species (Cr^VI and any soluble Cr^III compound) with a NaOH–Na₂CO₃ solution, and in digesting the residue (insoluble Cr^III compounds and Cr metal) by fusion with NaHSO₄ and extracting the melt with HCl. The obtained solutions were submitted to the ion-exchange speciation processes. The scope of the method was investigated by analysing two electric arc furnace flue dust samples: MS-2 (carbon steel flue dust) and MS-3 (stainless-steel flue dust). The determination limits (10s), considering test samples of 10 mg, were 0.1 µg g⁻¹ for both Cr^VI and Cr^III. Validation of the proposed method was carried out by analysis of BCR CRM 544 and by standard additions of CRM 544 to CrO₃–Cr₂O₃ mixtures; recoveries of both chromium species (Cr^VI and Cr^III) close to 100%, with precision values better than 3%, were achieved. External calibration and isotope dilution (ID) were applied for ICP-MS measurements; the latter system (ID) was developed for application to Cr measurements in steelmaking solid wastes, to overcome any possible interference from the complex sample matrix.