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Determination of chromium species in tanned leather samples


Chrome tanning using trivalent chromium salts as tanning agents is the most widespread tanning technique accounting for over 80% of global leather production. While Cr(III) is not considered as toxic it can be unintentionally oxidized into hexavalent chromium, a known mutagenic and carcinogenic. The European Union regulates Cr(VI) content to 3 mg/kg in leather products coming into direct contact with skin.

The International Organization for Standardization (ISO) has issued two standard methods for the selective extraction of Cr(VI) from  tanned leather using a phosphate buffer buffer: K2HPO4 ·3H2O at pH 8.0. The analysis of the extract is performned either by colorimetry (ISO 17075-1) or ion chromatography (ISO 17075-2). Both methods rely on the complexation of Cr(VI) with 1,5-diphenylcarbazide (DPC) for UV–Vis detection and offer a limit of quantification (LOQ) of 3 mg/kg for Cr(VI). Actually a method with a quantification limit of 3 mg/kg cannot be recommended to control an upper limit of 3 mg/kg. Even further, recent studies have revealed that Cr(III) may provoke allergic skin reactions, calling for the determination of both species. Such speciation analysis using mostly liquid chromatography coupled with inductively coupled plasma-mass spectrometry (LC-ICP-MS) has been described for foodstuffs, environmental and pharmaceutical samples or cosmetic products but not for leather samples.  

The new study:
A group of scientists working at the Normandie University (UNIROUEN) aimed at the development of a speciation method for the determination of Cr(III) and Cr(VI) in leather samples. Both species should be determined in the same analytical run, limiting the possibility for interconversions during extraction and analysis. Also the method should be able to differentiate both species even in a great excess of Cr(III), as normally found in leather samples. In order to achieve these objectives, different conditions were tested for the analysis through IC-ICP-MS, including two different columns, different mobile phases and different pH of the samples.    

Cr(III) was extracted from leather samples (200 mg) with 4 ml of 50 mmol/L EDTA (adjusted to pH 10 with NH4OH) at 100°C in a microwave digestion system.  On the other hand, Cr(VI) was extracted from leather samples with K2HPO4 ·3H2O at pH 8.0 for 3 h under magnetic stirring, as described in ISO 17075 protocol. Both extracts were analyzed with the same IC-ICP-MS setup under the same analytical conditions. In order to monitor possible interconversions, isotopic chromium speciation standards were used as samples and followed the whole extraction protocols. The results of this study confirmed that the optimized method preserves chromium speciation during extraction and analysis.

Figure 1: Schematic presentation of the chromium speciation analysis for leather samples

The optimization of the IC separation resulted in the selection of an AS7 ion-exchange column, and 75 mmol/L NH4NO3 adjusted to pH 3 with nitric acid as the eluent. Optimized ICP-MS detection was achieved with a dwell time of 0.05 s.   The method was validated with respect to linearity, LOD, LOQ and interday precision. Limit of detection and limit of quantification for Cr(III) were found to be 0.016 and 0.054 μg/L (0.3 and 1.1 μg/kg), respectively, and for Cr(VI) 0.13 and 0.43 μg/L (7 and 22 μg/kg), respectively. Finally, the method was applied to real colored leather samples from the luxury industry, allowing the determination of both species, even when there is a huge difference of concentration between Cr(III) and Cr(VI).

The original publication

Mónica Gisel Arellano-Sánchez, Juliette Vievard, Lamia Moufarrej, Christine Devouge-Boyer, Marie Hubert-Roux, Carlos Afonso, Mélanie Mignot, Separation, speciation and quantification of both chromium (VI) and chromium (III) in tanned leather samples: a comparative study and validation of analytical methods, Collagen and Leather, 5 2023) 18. DOI: 10.1186/s42825-023-00125-7

Used Instrumentation:

Thermo Scientific - iCAP RQ ICP-MS

Related Studies:

S.J. Davis, W.R. Wise, S. Recchia, A. Spinazze, M. Masi, The Evaluation of the Detection of Cr(VI) in Leather, Analytica, 3/1 (2022) 1-13. DOI: 10.3390/analytica3010001

M.G. Arellano-Sánchez, C. Devouge-Boyer, M. Hubert-Roux, C. Afonso, M. Mignot, Chromium determination in leather and other matrices: a review. Crit Rev Anal Chem., 52 (2021) 1–20. DOI: 10.1080/10408347.2021.1890545

M.G. Arellano-Sánchez, C. Devouge-Boyer, M. Hubert-Roux, C. Afonso, M. Mignot, Quantitative extraction of chromium VI and III from tanned leather: a comparative study of pretreatment methods. J Leather Sci Eng., 3 (2021) 30. DOI: 10.1186/s42825-021-00071-2.

Y.S. Hedberg. Chromium and leather: a review on the chemistry of relevance for allergic contact dermatitis to chromium. J Leather Sci Eng., 2 (2020) 20. DOI: 10.1186/s42825-020-00027-y

M. Fontaine, Y. Clement, N. Blanc, C. Demesmay, Hexavalent chromium release from leather over time natural ageing vs accelerated ageing according to a multivariate approach. J Hazard Mater. , 368 (2019) 811–8. DOI: 10.1016/j.jhazmat.2018.12.112

Y.S. Hedberg, B. Erfani, M. Matura, C. Lidén, Chromium(III) release from
chromium-tanned leather elicits allergic contact dermatitis: a use test study.
Contact Derm., 78 (2018) 307–14. DOI: 10.1111/cod.12946.

International organization for standardization. ISO 17075-1:2017 [IULTCS/
IUC 18–1] Leather—Chemical determination of chromium(VI) content in
leather—Part 1: Colorimetric method
[Internet]. 2017.

International organization for standardization. ISO 17075-2:2017 [IULTCS/
IUC 18-2] Leather—Chemical determination of chromium(VI) content in
leather—Part 2: Chromatographic method
[Internet]. 2017.

L.I. Dias da Silva, F.V. Marinho Pontes, M. Castro Carneiro, M.I. Couto Monteiro,  M. Dominguez de Almeida, A. Alcover Neto, Evaluation of the chromium bioavailability in tanned leather shavings using the SM&T sequential extractions scheme. Chem Speciat Bioavailab. 23 (2011) 183–7. DOI: 10.3184/095422911X13027118597382

I. Rezić, M. Zeiner, Determination of extractable chromium from leather.
Monatsh Chem., 140 (2009) 325–8. DOI: 10.1007/s00706-008-0026-1

Bahri Basaran, Mete Ulas, Behzat Oral Bitlisli, Ahmet Aslan, Distribution of Cr (III) and Cr (VI) in chrome tanned leather, Indian J. Chem. Technol., 15 (2008) 511-514. available from NISCAIR

J. Scancar, T. Osterman, N. Bukovec, R. Milacic, Critical Appraisal of Analytical Procedures for the Determination of Cr(VI) in Dyed Leather by 1,5 Diphenylcarbazide Spectrophotometry after Sample Dilution or Color Removal, J. Am. Leather Chem. Assoc., 102 (2007) 85-92. available from Journals@UC

P. Pastore, G. Favaro, A. Ballardin, D. Danieletto, Evidence of Cr(VI) formation during analysis of leather. Talanta, 63 (2004) 941–7. DOI: 10.1016/j.talanta.2004.01.010.

Christiane Hauber, Formation, Prevention & Determination of Cr(VI) in Leather, UNIDO Report US/RAS/92/120, September 2000, available from UNIDO

R. Milacic, J. Scancar, M. Urbanc, Is spectrophgotometry a reliable technique for determination of Cr(VI) in leather samples ?, J. Soc. Leather Technol. Chem., 82 (1998) 91-94.

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last time modified: June 13, 2023


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