Speciation analysis of Cr(III) and Cr(VI) in bread and breakfast cereals using species-specific isotope dilution and HPLC-ICP-MS

This study reports the development and validation of a analytical approach for simultaneous Cr(III) and Cr(VI) speciation analysis in bread and breakfast cereals using species specific isotope dilution (SS-ID) and highperformance liquid chromatography (HPLC) coupled to inductively coupled plasma-mass spectrometry (ICPMS). The species were extracted by sequential complexation of genuine Cr(III) with ethylenediaminetetraacetic acid (EDTA) and subsequently of Cr(III) originating from reduction of Cr(VI) with 1,5-diphenylcarbazone (DPCO) in the same analytical run. Efficient HPLC separation of Cr(III)-EDTA and Cr(III)-DPCO complexes was carried out by anion exchange HPLC in less than 3 min. The method was validated by means of the accuracy profile approach by carrying out 3 measurement series in duplicate on 5 different days over a timespan of one month. The quantification limits were 0.014 mu g kg-1 for Cr(III) and 0.047 mu g kg-1 for Cr(VI), respectively. The measurement bias ranged from 0.31 to 0.49 %, whereas the coefficient of variation in terms of repeatability (CVr) varied from 1.3-4.4 % for Cr(III) and from 0.6-7.9% for Cr(VI). Similarly, the coefficient of variation in terms of intermediate reproducibility (CVR) ranged from 1.3-4.4% for Cr(III) and from 2.0-8.9% for Cr(VI), respectively. The method was successfully applied to the analysis of a selection of bread and breakfast cereals samples. Cr(VI) was not detected in any of these samples while Cr(III) levels ranged between 5.2 and 176 mu g kg- 1 for bread samples and between 23.8 and 350 mu g kg-1 for breakfast cereals. These results were comparable with the levels of total Cr analysed in the same samples by ICP-MS. The method developed in this study on the basis of SS-ID and sequential species complexation is a powerful analytical tool for accurate and precise quantification of Cr(III) and Cr(VI) at trace levels and allows for correction of any species interconversion during sample preparation.

Automated summary

This study developed and validated an analytical approach for simultaneous Cr(III) and Cr(VI) speciation analysis in bread and breakfast cereals using SS-ID and HPLC-ICPMS. The method efficiently extracted and separated the Cr(III) and Cr(VI) species, with validation showing accurate quantification and precision. The results demonstrated the method's ability to accurately analyze trace levels of Cr(III) and Cr(VI in food samples.