A group of scientists from France have compared, optimized and validated methods for the determination of chromium (III) and chromium (VI) species in tanned leather samples. The final method was applied to real samples, allowing the determination of both species, even when there is a huge difference of concentration between Cr(III) and Cr(VI).
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 new study:
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.
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.
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
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
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
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last time modified: June 13, 2023