Analytical scenarios for Cr(III) and Cr(VI) determination in extracts of leather: Assessing Cr leaching under simulated use conditions.

Safety control of leather products is currently based solely on the extractable Cr(VI) content, though leached Cr(III) also poses a risk, as it may be potentially oxidized to Cr(VI). This study proposes three analytical sample preparation scenarios for group speciation of Cr eluted under conditions mimicking realistic usage of leather (NaCl, HNO3, lactic acid, NH3(aq)), using UV-Vis spectrophotometry with 1,5-diphenylcarbazide (DPC) as the detection technique. The 1st scenario determines Cr(VI), and total content of Cr after oxidation with KMnO4, using sodium azide to remove the excess oxidant. The 2nd scenario utilizes cation-exchange sorbent (SCX) for Cr(VI) isolation in lactic acid and NH3(aq) extracts and depletion of sample matrix, which allows for determination of Cr(VI) traces. The 3rd scenario employs SCX extraction supported with photolysis for colored extracts, where 20 min of UV irradiation with small addition of 30% H2O2 replaces KMnO4 oxidation. Changing the oxidation conditions simplifies the procedure, reduces reagent use, and improves the precision of the speciation analysis. The procedure of speciation determination supported by SCX and/or photolytic matrix simplification allows detection of significantly lower Cr contents (both forms), and enhances the "green" profile of the method.