Rapid Analysis of the Food Colors in Foodstuffs Using Polyamide

A rapid and simple analysis procedure involving a batch system using polyamide (nylon-6 powder) was devised for the detection of food colors. The food colors were extracted from food with a mixture of 1% ammonia water and ethanol (4:6). The extract was filtered, and the filtrate was diluted two or three times with water. The colors in the solution were absorbed on a small amount of polyamide (10-30mg) in acid (pH 4-5). After filtration and rinsing with hot water, the polyamide was suspended and eluted with a small quantity (about 100μl) of a mixture of 28% ammonia water and ethanol (4:6). After five min, the supernatant was used for paper chromatography and thin layer chromatography on a silica gel plate or a polyamide sheet. The solvent systems for the chromatographies were as follows: paper chromatography, butanol-ethanol-1% ammonia water (6:2:3); silica gell thin layer chromatography, ethyl acetate-ethanol-28% ammonia water (3.3:1:1) or (4.5:1:0.7); polyamide thin layer chromatography, methanol-ethanol-isoamyl alcohol-28% ammonia water (15:10:5:3). The systems containing ammonia as described above were required for separation of the food colors. Compared with the wool dyeing method, the presented method did not require evaporation of alcohol, heating for adsorption or elution of the food colors or concentration of the eluate. It is rapid, simple and precise for the detection of the food colors in various colored foods.