Critical appraisal of analytical procedures for the determination of Cr(VI) in dyed leathers by 1,5 diphenylcarbazide spectrophotometry afeter sample dilution or color removal

Colored chemical species in leather extracts may contribute to the measurement signal in spectrophotometric determination of Cr(VI), resulting in false positive Cr(VI) concentrations. In the present work the efficiency of sample dilution, or color removal by the use of RP C18 columns and columns filled with florisil, to reduce color interferences prior to spectrophotometric determinations of Cr(VI) in dyed leathers were evaluated. Limits of detections were 2.5 mg kg' Cr(VI) when samples were diluted (1:5) and 0.5 mg kg -1 Cr(VI) after color removal by RP C18 or florisil. In all procedures applied repeatability and reproducibility of measurements were better than ± 5 %. The accuracy of the 1,5 diphenylcarbazide spectrophotometric determination of Cr(VI) was tested by analysis of the certified reference material CRM 544, Cr(VI) in lyophilized solution. By spiking leather extracts it was experimentally proven that the use of decolorizing agents did not change Cr(VI) speciation. The experimental data also indicated that in some of the leather extracts analyzed colored species caused severe positive interference effects that could not be reduced by dilution or the use of RP C18. Florisil was found to be an efficient decolorizing agent and enabled accurate and reliable determination of Cr(VI) in dyed leathers by 1,5 diphenylcarbazide spectrophotometry.