Abstract

Hexavalent chromium (Cr6+) causes dermatitis and cancer, and is often quantified from chrometanned leather. Analysis for Cr6+ is generally carried out after extraction into 0.1 M potassium phosphate buffer (P-buffer pH8.0) according to the method of ISO 17075. However, since the pH value of chrometanned leather and sweat due to wear are on the acidic side, the above method for Cr6+ should be validated using acidic extracts. In the present study, acidic extracts from chrome-tanned leather were analyzed for Cr6+ comparing the results with those using alkaline extracts.

A sample of commercial chrome-tanned leather was used to investigate the influence of pH on the extractability of Cr6+. Chromium was extracted from the leather with P-buffer (pH3.0-11.0), acidic artificial perspiration (pH5.5) or 0.2% sodium sulfate (pH5.5). The contents of total chromium (Cr) and Cr6+ in each extract were respectively measured by inductive coupled plasma atomic emission spectroscopy and colorimetry with diphenylcarbazide. Less Cr was extracted in the range of pH5.5- 8.0, whereas more Cr was extracted in the more acidic and alkaline regions. By contrast, the amount of Cr6+ extracted increased moderately with increasing pH. When the P-buffer extract (pH8.0) was adjusted to pH3.0-11.0, the amount of Cr6+ increased with increasing pH, suggesting occurrence of a reversible conversion between Cr6+ and Cr3+. The extraction with P-buffer (pH8.0) may thus provide a falsely high value due to this conversion. P-buffer (pH5.5) showed a significantly higher extraction of Cr6+ than tests with artificial perspiration (pH5.5) and 0.2% sodium sulfate (pH5.5). The residue remaining after each extraction was re-extracted with a fresh aliquot of the appropriate extractant. The amount of Cr6+ in the second extract with P-buffer (pH5.5) exhibited a low extractability (about 9% of the amount of the first), whereas artificial perspiration (pH5.5), 0.2% sodium sulfate (pH5.5), and P-buffer (pH 8.0) showed a high extractability (about 41-67% of the amount of the first). It is thus concluded that extracting with P-buffer (pH5.5) is most efficient of the tested extractants for analyzing Cr6+ from chrome-tanned leather.