Spectrophotometric determination of single synthetic food colour in soft drinks using ion-pair formation and extraction

Summary A simple spectrophotometric method has been developed for the determination of water‐soluble synthetic food colours in soft drinks involving ion‐pair formation with octadecyltrimethyl ammonium bromide at pH 5.6 and extraction of the ion‐pair into n‐butanol. The proposed method has been applied to determine amaranth, carmoisine, Green S, Orange G, Patent blue V, Ponceau 4R, Sunset yellow and tartrazine singly in soft drinks. The optimum experimental conditions for the method were reported. The percent‐age extraction for all the colours except Green S under the optimum conditions ranged from 98 to 100. The precision of the proposed method was in the range 1–2.4% at the level of 8.0 μg ml−1 for the food colours.