Discovery and structural elucidation of the illegal azo dye Basic Red 46 in sumac spice

Abstract

An unknown red dye was discovered in a sumac spice sample during routine analysis for Sudan dyes. LC-DAD and LC-MS/MS did not reveal the identity of the red substance. Nevertheless, using LC-high-resolution MS and isotope ratio comparisons the structure was identified as Basic Red 46. The identity of the dye was further confirmed by comparison with a commercial hair-staining product and two textile dye formulations containing Basic Red 46. Analogous to the Sudan dyes, Basic Red 46 is an azo dye. However, some of the sample clean-up methodology utilised for the analysis of Sudan dyes in food prevents its successful detection. In contrast to the Sudan dyes, Basic Red 46 is a cation. Its cationic properties make it bind strongly to gel permeation columns and silica solid-phase extraction cartridges and prevent elution with standard eluents. This is the first report of Basic Red 46 in food. The structure elucidation of this compound as well as the disadvantages of analytical methods focusing on a narrow group of targeted analytes are discussed.

Keywords:

• food adulteration
• azo dye
• Sudan red
• Basic Red 46
• structure elucidation
• high resolution mass spectrometry

Acknowledgements

The authors thank Peter Arnegger, from the Official Food Control Authority of the Canton Thurgau (Kantonales Laboratorium Thurgau), for his support with the LC-MS/MS system. The companies Erba AG (Zurich, Switzerland) and Textilcolor (Sevelen, Switzerland) are acknowledged for their free samples of Basic Red 46.