Description
This method is applicable to the qualitative and quantitative determination of water-soluble synthetic colours in most food types. The applicability of the method to foods with a high fat content is however uncertain, since the collaborative study of the method gave unsatisfactory results for all colours in the fatty food (fish roe). The method is applicable for concentrations higher than 5 mg/L. Positive results must be confirmed by another method e.g. thin layer chromatography (e.g. NMKL 114). Solid samples are dissolved in hot water or alternatively the colours are extracted with methanol-ammonia solution. Fatty samples are defatted with petroleum ether. Some samples require prior splitting of the matrix with papain. Extracts/ solutions are purified on polyamide. Liquid samples may also be cleaned and concentrated directly on a sample preparation cartridge. The colours are separated by HPLC on a reversed –phase C18 column with an eluent containing an ion pairing reagent. The colours are determined at wavelengths of 480 and 546nm, respectively. All colours but one may be determined in one chromatographic run, quinoline yellow is detected at e.g. 416 nm.