Determination of banned adulterants in turmeric and chilli powders using ultra-high-performance liquid chromatography

Abstract

Sudan I and metanil yellow are azo dyes, illegally used to impart bright red and yellow color to foods respectively. It is assumed that these appearances are due to adulteration. Regulations must be able to detect the substances in a cost-effective, efficient, and sensitive manner. A simple and precise ultra-high-performance liquid chromatography with photodiode array detector based analytical method is developed for detection and quantification of metanil yellow and Sudan 1 from turmeric and chili powders. The method necessitated no sample clean up from matrix components and the separation of the analytes was performed on a reversed-phase C18 column with an optimized solvent system consisting of 0.6305 g of ammonium formate + 100 µL of formic acid in HPLC grade water-methanol: acetonitrile (70:30 V/V) for metanil yellow at 413 nm and 0.2% formic acid in water-acetonitrile (30:70, V/V) for curcumin at 425 nm. Depending on the metanil yellow and Sudan I dye involved, LOD and LOQ were in the range of 0.05–0.12 μg/Kg and 0.3–0.5 μg/Kg in the turmeric and red chili powders respectively. The recovery, repeatability and reproducibility varied from 80.6 to 112.60% from 0.3 to 0.83%, and less than 20% RSD. Linearity obtained for metanil yellow and Sudan I was all r2 > 0.9999 and in the range of 0.5–1.0 mg/L and 0.05–5 mg/L respectively. The proposed method was applied to determine the concentration of curcumin and metanil yellow in 11 market samples, 24 rhizome powder samples and Sudan1 from 9 chili powder samples. This method has the potential to be used for illegal Sudan dyes and metanil yellow in turmeric and red chili powders due to its reliable, rapid and excellent precision.