Quantitative extraction of chromium VI and III from tanned leather: a comparative study of pretreatment methods

Mónica Gisel Arellano-Sánchez,Christine Devouge-Boyer,Carlos Afonso,Marie Hubert-Roux,Mélanie Mignot

doi:10.1186/s42825-021-00071-2

Abstract

In this study, seven pretreatment methods for chromium speciation in tanned leather were evaluated: acidic mineralization, ethylenediaminetetraacetic acid (EDTA) extraction, diethylenetriaminepentaacetic acid (DTPA) extraction, alkaline extraction (NH4OH), ammonium nitrate extraction (NH4NO3), water extraction, and phosphate buffer extraction. Acidic mineralization permitted the decomposition of the organic matter and ensured the complete digestion of leathers, giving access to the total content of chromium in each sample using inductively coupled plasma-atomic emission spectrometry (ICP-AES). From all the extractant media tested, EDTA proved to be the most efficient, allowing the extraction of Cr(VI) and Cr(III) as a Cr(III)-EDTA complex, quantitatively. Method validation is presented for EDTA extraction and direct mineralization. For the EDTA extraction, method detection limit (MDL) and method quantification limit (MQL) for total Cr in leather were 3.4 ppb and 11.2 ppb (µg of total Cr per L of extraction solution), respectively. Due to the lack of leather certified reference materials (CRMs) for Cr(VI), accuracy was evaluated by spiking leather samples with a Cr(VI) solution. The spike recovery of EDTA microwave assisted extraction ranged from 91.0 to 108.6%. Interday precision was also evaluated and all variation coefficients were below 5%, for both mineralization and EDTA extraction. This article provides an efficient procedure to extract quantitatively chromium from leather, while maintaining the speciation, which can be further followed by ion chromatography-inductively coupled plasma-mass spectrometry (IC-ICP-MS).

Highlights

Leather industry occupies a very important role in the development of global economy
The results suggested that repeated exposure to Cr-tanned leather with predominantly Cr(III) release is sufficient to elicit allergic contact dermatitis in Crallergic individuals
Samples used for these experiments had gone through different manufacturing processes, and were available in limited quantity, the content of chromium may vary from one sample to another

Summary

Introduction

Leather industry occupies a very important role in the development of global economy. Leather is used every day and everywhere in a variety of articles such as footwear, furniture, book covers, gloves, handbags, etc. In order to transform raw hide into leather, a process called tanning is required [1]. The electronic structure of chromium allows it to form coordination complexes, which makes it a remarkable tanning agent (i.e. Cr-collagen complexes via carboxylate functions). Chrome-tanning reaction is fast (6 h instead of 3 weeks, compared with vegetable tanning), confers high hydrothermal stability, hardly alters the structure of collagen, makes collagen more hydrophobic (water-resistant), and allows the retention of colorants since Cr(III) can act as a dye fixing agent [3].

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