The Evaluation of the Detection of Cr(VI) in Leather

The topic of hexavalent chromium (Cr(VI)) in leather has been debated throughout the whole supply chain for years. However, its significance has recently increased due to proposed changes in European legislation concerned with skin-sensitising substances suggesting that acceptable Cr(VI) concentrations in leather goods should be lowered from 3 mg kg−1 to 1 mg kg−1. The proposition of a stricter limit and current analytical difficulties created the need for a review of current standard test methods. The research presented in this paper investigates both the colorimetric (Part 1) and chromatographic (Part 2) methods under BS EN ISO 17075. The focus of the study was to identify possible sources of interference leading to large statistical variance in results and to define the limit of quantification with respect to the proposed new compliance limit. This study into the colorimetric method has shown that the presence of Cr(III), dyes, and proteins can be significant interferences, becoming critical at low Cr(VI) concentrations. Dilution factors worsen the problem of detecting low concentrations: a reliable quantitative detection of 0.01 mg kg−1 and 0.003 mg kg−1 Cr(VI) in solution are required at the 3 mg kg−1 and 1 mg kg−1 compliance limits in leather, respectively. BS EN ISO 17075 part 1 was shown to be incapable of reliably resolving to 3 mg kg−1 or below in leather. Part 2 shows a marked improvement in detection limits and reliability; however, data suggest that 1 mg kg−1 Cr(VI) is not reliably detectable in leather. Suggested improvements to the established test methods and a possible alternative are discussed.