A Study on the Reliability of UNI EN ISO 17075 Method for the Determination of the Cr(VI) Content in Leather

Abstract

The UNI EN ISO 17075 method for Cr(VI) detection in leather presents several drawbacks. One of these is the choice of an alkaline extraction pH, which produces severe false positive results. Summary: The hexavalent chromium content in 14 leather samples, resulted positive to the presence of Cr(VI) according to the UNI EN ISO 17075 method in two certified laboratories, was re-determined, using the official extracting method at pH 8 and a different phosphate extraction buffer at pH 4.4 containing 5% NaCl. The well-known transient nature of Cr6, that is the decrease of its amount in leather during time, required a re-activation by thermal treatment before analysis. The results show that the official method systematically gives false-positive values and that 10 of the 14 examined leather samples, when extracted with a buffer at pH 4.4, proved to have acceptable levels of Cr(VI). In addition we found that Solid Phase Extraction (SPE) cartridges, either normal or end-capped, absorb about 10% of chromate and this indicates that the calibration curves should be obtained after filtering each standard with the SPE employed.