Illegal Dyes in Food and Spices – A 2006 LGC LC-UV/Visible Method Reviewed and Updated for 19 Dyes

Intermittent findings of illegal dyes in foods continue to be a feature of international trade. Herein the validation of a 2006 LC-UV/Visible method for a limited number of such dyes in chilli powder has been reviewed and a new multi-dye general screening method is proposed. Both methods apply 90:10 acetonitrile:acetone extraction at 40C and reverse phase gradient elution liquid chromatography (LC) with UV/Visible detection. No clean-up, other than filtration, and no concentration stage is required. Of the 23 dyes investigated for the new screening method in chilli powder, canned chicken in a curry sauce, fennel, palm oil, paprika and turmeric, 19 are adequately dealt with by the new method. Recovery, linearity and within-day precision data are reported and although limits of detection (LOD) were not extensively investigated they appear to be consistent with previous LOD data. The dyes covered by the proposed general screening method are Orange II, Sudan I–IV, Sudan Black B, Sudan Red 7B, Sudan Red G, Methanil yellow, Dimethyl yellow, Auramine O, Bixin, Fast Garnett GBC, Rhodamine B, Oil Orange SS, Orange G, Sudan Orange G, Naphthol Yellow, Acid Red 73, Toluidine Red, Sudan Red B, and Para Red. Poor sensitivity was exhibited for Orange G, Naphthol Yellow, Congo Red and Acid Red 73. Turmeric proved to be a very challenging matrix for which the proposed general screening method in its present format is not applicable. While the remaining dyes are adequately resolved by the general screening method some display close retention times. For these, the small number of problematic dyes and when confirmation is required, mass spectrometric detection is recommended.