efsa-opinion-chromium-food-drinking-water
efsa-opinion-chromium-food-drinking-water
efsa-opinion-chromium-food-drinking-water
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3.2.2.2. Chromium speciation analysis<br />
Chromium in <strong>food</strong> and <strong>drinking</strong> <strong>water</strong><br />
The methods of analysis for <strong>chromium</strong> species have been reviewed by several authors, mainly in <strong>water</strong><br />
or environmental matrices (Swietlik, 1998; Sarzanini, 1999; Camara et al., 2000; Kotaś and Stasicka,<br />
2000; Yalcin and Apak, 2004; Unceta et al., 2010; Amouroux et al., 2011; Namiesnik and Rabajczyk,<br />
2012; Rakhunde et al., 2012; Water Research Foundation, 2012) and rarely in <strong>food</strong> (Gomez and<br />
Callao, 2006). Analytical techniques generally used for Cr speciation can be separated into two<br />
groups. The first group so-called ‘off line methods’ brings together methods that can determine Cr(VI)<br />
or Cr(III) after a pretreatment of the sample and the second group so-called ‘on line methods’<br />
corresponds to on-line hyphenated techniques allowing the determination of both species<br />
simultaneously. When applied to solid samples, these methods require a previous extraction step.<br />
Chromium speciation analysis in <strong>food</strong> is influenced by the nature of the matrix and by the analytical<br />
method used. Consequently, the main difficulty is to preserve the initial distribution of <strong>chromium</strong><br />
species in the sample because of losses and/or cross-species transformations that may occur (Novotnik<br />
et al., 2013). Extraction is one of the most critical steps, because two conflicting issues need to be<br />
addressed: obtaining high extraction efficiency and minimising losses (Unceta et al., 2010). Once in<br />
solution, pH, exposure to light, the type of storage container and high storage temperatures may affect<br />
the stability of <strong>chromium</strong> species (EN 13804:2013). Only a few methods were optimised for the<br />
speciation of <strong>chromium</strong> in some <strong>food</strong>stuffs.<br />
A fluorimetric detection of Cr(VI) combined with flow injection analysis (FIA), has been developed<br />
for analysis of tomato juice samples (Paleologos et al., 1998). Cr(VI) (LOD: 50 µg/L) and total<br />
<strong>chromium</strong> is measured and Cr(III) (LOD: 20 µg/L) is determined by difference.<br />
A speciation method for <strong>chromium</strong> in cow’s milk by solid-phase extraction/dynamic reaction cell<br />
inductively coupled to plasma mass spectrometry (SPE/DRC-ICP-MS) was developed by Ambushe et<br />
al. (2009). Pre-concentration and separation procedures of Cr(VI) were adapted from the work of<br />
Lameiras et al. (1998). Ion-exchange columns were used to separate Cr(VI) from Cr(III). The LODs<br />
were 0.091 and 0.085 µg/L for total Cr and Cr(VI), respectively against 0.20 (total Cr) and 0.15 µg/L<br />
(Cr(VI)) by electrothermal atomic absorption spectrometry (ETAAS) (Lameiras et al., 1998). The<br />
method of Lameiras et al. (1998) was also adapted for the selective determination of Cr(VI) in<br />
powdered milk infant formulas with a LOD of 1.8 µg/L in reconstituted milk samples by ETAAS<br />
(Soares et al., 2000).<br />
A selective alkaline extraction (with 0.01 M NaOH) of Cr(VI) and quantification by GFAAS was<br />
developed to analyse bread samples (Soares et al., 2010). LOQs were 4.95 and 5.60 μg/kg for total<br />
<strong>chromium</strong> and Cr(VI), respectively. Another selective alkaline extraction of Cr(VI) with 0.1 M<br />
Na 2 CO 3 and quantification of this species (LOQ of 70 μg/kg) by GFAAS was developed to analyse tea<br />
samples (Mandiwana et al., 2011). Cr(VI) represents up to 10 % of the average total <strong>chromium</strong> in<br />
bread and and 3-21 % of <strong>water</strong> soluble Cr(VI) in tea samples.<br />
The recent developments in speciated isotope-dilution mass spectrometry (SIDMS; i.e. spiking the<br />
samples with isotopically enriched species) with hyphenated ICP-MS techniques has dramatically<br />
improved the quality and accuracy of the data on speciation analysis. The use of isotopically enriched<br />
Cr species (i.e. spikes) as tracers overcame the traditional problems related to non-quantitative<br />
recoveries and the formation of <strong>chromium</strong> artefacts that can occur during the extraction and<br />
derivatisation steps (Amouroux et al., 2011; Novotnik et al., 2012a,b). Using this technique and high<br />
performance liquid chromatography coupled to ICP-MS detection (SID-HPLC-ICP-MS) to follow<br />
Cr(VI) and Cr(III) species interconversions during the extraction procedures (LOQs of about 0.1 µg/L<br />
for both species), Novotnik et al. (2013) repeated the experiments of Soares et al. (2010) and<br />
Mandiwana et al. (2011) mentioned above. In contrast to their results, no Cr(VI) was found in these<br />
samples and it was experimentally proven that added 53 Cr(III) was not oxidised in tea infusions and<br />
extracts of bread samples, while almost all added 50 Cr(VI) was reduced in tea infusions due to the<br />
presence of antioxidants. In conclusion, these results emphasized the significance of the use of<br />
adequate analytical methodologies in the evaluation of Cr(VI) contents in <strong>food</strong>stuffs and other<br />
biological and environmental matrices and that results on Cr speciation that are not supported by<br />
EFSA Journal 2014;12(3):3595 28