Ion Chromatography with Post Column Derivatization for the Determination of Hexavalent chromium in Dyed Leather. Influence of the Preparation Method and of the Sampling Location

Abstract

Since 2015, a European restriction limits the hexavalent chromiumcontent to not more than 3 mg/kg in leather products (UE-301-2014, 25 March 2014, §47, annex XVII of REACh). Owing tospectrophotometric interferences encountered with the establishedEuropean standard EN ISO 17075:2007 when colored leathershave to be analyzed, this article proposes the analysis of hexavalentchromium using ion chromatography with post-columnderivatization and spectrophotometric detection. In order to avoidany pre-treatment of the crude extract an on-line solid phaseextraction step is introduced by inserting a high capacity reversedphase guard column. The efficiency of the on-line purification isdemonstrated (quantitative removal of the dye present in theextract) and allows the direct analysis of crude extracts in lessthan 6 minutes. The overall chromatographic method is validatedfollowing procedures described by the French standard NF T90-210. The measurement error (bias) was determined at 7.2% at thepresupposed limit of quantification 5 ?g/L (corresponding to ahexavalent chromium content of 0.25 mg/kg in leather) and at themedium concentration level and at 4.0% for the high-levelconcentration, with relative standard deviations of 5.1%, 2.9% and2.4% respectively. The recovery yields measured with spikedleathers range from 92 to 96% depending on the hexavalentcontent. The reliability of the method is also demonstratedthrough two inter-laboratories test involving several Europeanlaboratories. The crucial influence of the sample preparation isalso assessed in this work. It is demonstrated that the hexavalentchromium content of leathers is systematically underestimatedwhen the extraction is applied to leathers cut in small pieces andnot ground. In parallel, additional tests on leather samplinglocation show that the shoulder zone is not representative of therest of the skin in terms of hexavalent chromium content since ithas a higher hexavalent chromium content than all other samplingzones.