Saraiva et al. 2021 — Cr(III) and Cr(VI) speciation in bread and breakfast cereals using SS-ID HPLC-ICP-MS
This study developed and validated a highly sensitive method for simultaneous Cr(III) and Cr(VI) speciation in bread and breakfast cereals using species-specific isotope dilution (SS-ID) combined with HPLC-ICP-MS. The method is significant because it addresses a long-standing controversy about the presence of Cr(VI) in foods: using SS-ID, which corrects for species interconversion during sample preparation, the authors found no detectable Cr(VI) in any of the bread or breakfast cereal samples tested. All chromium was present as Cr(III). This is methodologically important because older studies that reported Cr(VI) in foods likely suffered from artefactual Cr(III)-to-Cr(VI) oxidation during alkaline extraction, a systematic error that SS-ID catches and corrects.
Key numbers
Cr(III) concentrations in bread samples: 5.2 to 176 µg/kg Cr(III) concentrations in breakfast cereals: 23.8 to 350 µg/kg Cr(VI) in all samples: not detected (below LOQ of 0.047 µg/kg)
Quantification limits:
- Cr(III): LOQ = 0.014 µg/kg
- Cr(VI): LOQ = 0.047 µg/kg These are exceptionally low LOQs, achieved through the isotope dilution correction; several orders of magnitude lower than conventional ETAAS methods.
Method validation metrics:
- Bias: 0.31 to 0.49% (excellent)
- CVr (repeatability): 1.3–4.4% for Cr(III); 0.6–7.9% for Cr(VI)
- CVR (intermediate reproducibility): 1.3–4.4% for Cr(III); 2.0–8.9% for Cr(VI)
Total Cr by ICP-MS: Results were comparable to the SS-ID Cr(III) values, confirming that essentially all Cr in these matrices is Cr(III) and that total-Cr analysis is an acceptable proxy in grain-based products when validated methods are used.
Methodological finding on Cr(VI) absence: EFSA has stated that Cr exists in food exclusively as Cr(III) because of the reducing feature of food matrices. This study provides strong analytical confirmation using the most selective available method, supporting that prior Cr(VI) detections in food were likely analytical artefacts from Cr(III) oxidation during alkaline extraction procedures without isotope dilution correction.
Methods (brief)
SS-ID HPLC-ICP-MS at Anses (France) and DTU National Food Institute (Denmark). Species extraction: sequential EDTA complexation of genuine Cr(III) followed by 1,5-diphenylcarbazone (DPCO) complexation of Cr(III) reduced from Cr(VI). Anion exchange HPLC separation in <3 min. Validated over 5 days, 3 series in duplicate. This is currently the state-of-the-art method for food Cr speciation.
Implications
Certification: This is a landmark methodological reference for Cr speciation in grain-based foods. The finding that Cr(VI) is absent in bread and cereals, supported by SS-ID correction, has direct implications for how HMT&C should interpret total-Cr findings in grain products: total Cr in grain matrices is essentially all Cr(III), not Cr(VI). For the HMT&C analyte vocabulary (which lists Cr-VI separately), this means the relevant concern in bread/cereal matrices is whether any Cr-VI is present at all — and the best current evidence says it is not, at least in grain products with high organic matter that drives reduction. Testing claims for Cr-VI in these matrices should therefore be interpreted with awareness of method artefact risk.
Courses: Core reference for the Cr speciation module. The SS-ID approach and the controversy around Cr(VI) in food are essential topics for any audience evaluating Cr-VI testing claims.
App: For grain-based ingredients, the app can treat total Cr as Cr(III) when source data does not specify speciation, consistent with this evidence. Cr-VI risk in grain products should default to “not detected” in the absence of SS-ID speciation evidence to the contrary.
Wiki pages updated on ingest
- chromium
- chromium-hexavalent
- bread
- arsenic-speciation (analogy to Cr speciation method principles)
- chromium-speciation