Simultaneous determination of amaranth and ponceau 4r isomers in their mixtures by constant center and ratio H-point standard addition methods

The amaranth and ponceau 4r isomers of azo dyes are generally added for coloring food products not only to make them visually aesthetic but also to reinstate the original appearance lost during the production process. However, many countries in the world have banned the use of most azo dyes in food, and their usage is highly regulated by domestic and export food supplies. The regulatory authorities and food analysts adopt highly sensitive and selsctive analytical methods for monitoring as well as assuring the quality and safety of food products [1].In this work, two sensitive and accurate spectrophotometric methods are described for determination of the amaranth and ponceau 4r isomers in their mixtures by the constant center coupled with spectrum subtraction method (CC-SS) [2-3] and the ratio H-point standard addition method (RHPSAM) [4]. No separation step is required for these novel methods. The wavelength pair 457.8 and 571 nm was employed to obtain the highest accuracy. The results of applying this method showed that amaranth and ponceau 4r could be determined simultaneously with concentration ratios from 5:1 up to 1:5 in the mixed samples, and the linear dynamic ranges were found to be 2-20 μg mL-1 for both analytes. In the CC-SS method, the wavelength pair 456.8 and 550.2 nm was used. The linear concentration range for the amaranth and ponceau 4r isomers in this method were found to be 2-20 and 1-30 μg mL-1, respectively. Both proposed methods (CC-SS and RHPSAM) were also successfully applied to the determination of amaranth and ponceau 4r in water samples.