A simple 2-directional high-performance thin-layer chromatographic method for the simultaneous determination of curcumin, metanil yellow, and sudan dyes in turmeric, chili, and curry powders.

A method using simple extraction and 2-directional high-performance thin-layer chromatography (HPTLC) was developed for the simultaneous determination of curcumin, metanil yellow, and sudan dyes in turmeric, chili, and various mixed curry powder formulations. The method offers resolution (Rf) of turmeric pigments, namely, curcumin (0.77), demethoxycurcumin (0.69), bis(demethoxy)curcumin (0.61), and the synthetic dye metanil yellow (0.05) by the first-directional mobile phase, chloroform-methanol (9 + 1, v/v). The resolution (Rf) of sudan I (0.30) and sudan IV (0.23) was achieved by the second-directional mobile phase, toluene-hexane-acetic acid (50 + 50 + 1, v/v/v). Natural pigments of both turmeric and chili showed no interference in the detection and quantification of synthetic colors. The limit of detection and limit of quantification values for curcumin, metanil yellow, sudan I, and sudan IV were 17.39, 42.90, 15.45, and 7.01 and 52.71,130.0, 46.80, and 21.24 ng/spot, respectively. Analysis of a few market samples showed the presence of metanil yellow (1.5-4.6 mg/g), sudan I (4.8-12.1 mg/g), and sudan IV (0.9-2.0 mg/g) in loose turmeric and chili samples, whereas the curcumin content in turmeric and mixed curry powder samples ranged from 6.5 to 36.4 and from 0.3 to 1.9 mg/g, respectively. The method is relatively simple, offers reasonable sensitivity, and can be used to screen a large number of samples.