Sensitive assay for picogram levels of Sudan I in chilli foodstuffs by flow injection chemiluminescence.

The determination of Sudan I in contaminated hot chilli products by luminol–myoglobin chemiluminescence was proposed. It was found that the Sudan dyes (Sudan I, II, III and IV) could bind to myoglobin and remarkably enhance the chemiluminescence signal from luminol–myoglobin system, and the increment of chemiluminescence intensity was proportional to the concentration of Sudan I, II, III and IV in the range of 0.1–300 pg mL−1, 5.0–1000 pg mL−1, 10.0–1000 pg mL−1 and 1.0–300 pg mL−1, respectively. At the flow rate of 2.0 mL min−1, a typical analytical procedure for Sudan dyes including sampling and washing was finished within 0.5 min with the relative standard deviation less than 3.0%. The present CL method was successfully applied to the determination of Sudan I in contaminated soy sauces and agreed well with HPLC data. The possible mechanism of the CL reaction was given.