Determination of food dyes in soft drinks containing natural pigments by liquid chromatography with minimal clean-up

The essential aim of this work was the optimisation and characterisation of a method for the determination of five synthetic food colours added to soft drinks with natural colours by liquid chromatography with minimal clean-up. The method is simple, rapid, inexpensive and broadly applicable to soft drinks. The results show that tartrazine (E-102), quinoline yellow (E-104), yellow orange (E-110), azo rubine (E-122) and ponceau (E-124) can be determined at low levels simultaneously. The method was evaluated by constructing calibration lines, measurement of recovery and precision, and the limits of quantification and detection. It involves direct injection of a beverage solution (homogenized and degassed) for reversed-phase HPLC analysis with visible detection at a single wavelength. Synthetic colours determination in soft drinks was not affected by the presence of other natural colours contained in drinks with fruit juice and flavour extracts. The results obtained with the samples confirm that the proposed method works well and is useful for serious control or screening of the addition of synthetic colours in soft drinks; the method is therefore recommended for use by the quality control departments of soft drink producers using synthetic food colours.