[Determination of Sudan Red dyes in hot chili products by humic acid-bonded silica solid-phase extraction coupled with high performance liquid chromatography].

Humic acid-bonded silica was prepared and used as solid-phase extraction material for the pretreatment of Sudan Red dyes in hot chili products, which was followed by high performance liquid chromatographic determination. This sorbent exhibits an excellent adsorption capacity for Sudan Red dyes. A sample was first extracted with n-hexane. Then the extract was cleaned up by humic acid-bonded silica cartridge and eluted with ethanol/dichloromethane (3:7, v/v). Some interferences in hot chili products such as natural pigments and oil were removed by washing step. Good linearities were achieved in the range from 0.05 to 5 mg/L for four Sudan dyes, with linear coefficient r2 values above 0.999. The limits of detection (LOD) in chili powder and chili oil were from 19.8 to 28.8 ng/g and 7.9 to 11.5 ng/g, respectively. Excellent method reproducibility was found by intra- and inter-day precisions (the relative standard deviations less than 9.1% and 8.8%, respectively). Recoveries for them in the real samples were between 82.6% and 94.0%. The proposed method is proved to be simple, rapid, and sensitive in the regular analysis of Sudan Red I, II, III and IV in foods.