Forensically Robust Determination of the Illegal Dye Dimethyl Yellow in a Refractory Curcuma Oleoresin–Surfactant Matrix—a Case Study

The presence of illegal dyes such as the Sudan reds in spices is a well-recognised problem, and numerous methods of analysis have been described for their determination. However, some spice-derived matrices present particular problems. Oleoresins, complex extracts of spices containing phenolic natural pigments and terpene-like lipids, are used in the formulation of oriental sauces, pickles and processed spiced meals and hence likely to penetrate far into the food chain. Described herein is a case in which a false positive finding of one of the less commonly used illegal dyes in an oleoresin had the potential to trigger a costly food recall. Rapid resolution of the false positive by liquid chromatography–tandem mass spectrometry (LC-MS/MS) came at the cost of subsequent decontamination of the instrument, incurring significant downtime. The analytical difficulties posed by the presence of a surfactant to improve oleoresin dispersive properties with other foods are discussed. We conclude that as LC-UV methods cannot deal with the possible matrix interferences, they must not be used for the analyses of illegal dyes in spice oleoresins. A combination of gel permeation chromatography with liquid–liquid and solid-phase cleanup is described that enables facile deployment of LC-MS/MS to an oleoresin–surfactant matrix for the forensically robust determination of dimethyl yellow at concentrations below the current “action limit” for illegal dyes of 500 μg kg−1.