Analysis of illegal dyes in food by LC/TOF-MS

A sensitive and accurate methodology was developed for the analysis of seven illegal dyes (Sudan I, Sudan II, Sudan III, Sudan IV, Sudan Orange G, Sudan R and Para Red,) used as additives in food products, such as chilli powder and steak sauces. The analytical methodology consisted of solvent extraction with acetonitrile followed by liquid chromatography time-of-flight mass spectrometry detection. Accurate mass measurements were crucial in order to achieve a high degree of specificity for the target analytes in such complex samples. The dyes were effectively extracted from spice and sauce matrices achieving recoveries higher than 75%. Because of the excellent mass accuracy obtained for the target analytes (better than 2 ppm), no cleanup of the samples was required using this methodology, thus leading to a better precision and reproducibility of the results from the quantitative point of view. Calibration curves were linear and covered two orders of magnitude (from 0.01 to 1mg L-(1)) for all the compounds studied with the exception of Para Red. A detailed study of matrix effects is also included in this work, showing a clear improvement when dilution of the extracts was carried out. Method detection limits were in the low mg kg-(1) range, and the precision, calculated as the relative standard deviation, ranged from 5 to 15%. The methodology was successfully applied to market samples in a survey performed as part of a regional research programme organized by the Andalusian Health Service in Spain, and a positive confirmation for Sudan I was obtained in a chilli powder sample.