Spectrophotometric determination of Allura Red (R40) in soft drink powders using the universal calibration matrix for partial least squares multivariate method

The Kool-Aid powders (Kraft General Foods) contain one or two of the following dyes: Allura Red (FD and C Red-40, R40), Sunset Yellow (FD and C Yellow-6, Y6) Tartrazine (FD and C Yellow-5, Y5), Erythrosine B (FD and C Red-3, R3), Amaranth (FD and C Red-2, R2) and Brilliant Blue FCF (FD and C Blue 1, B1), depending on the taste of the drink. In this work the ''universal'' calibration matrix is proposed for the determination of R40 in soft drink powders by partial least squares method using spectrophotometric data. The training set of samples consists of 23 solutions: three of them contain only R40 at different concentrations and the rest of them are the binary mixtures of R40 with one of the following dyes: R3, R2, Y5 or Y6; all at the concentrations varying in the range 2-22 mg l(-1) (exception: R3 2-12 mg l(-1)). The good analytical performance of R40 calibration was obtained (R(2)=0.9993, RMSD=0.2125, REP=2.20%) and this calibration matrix was applied to the analysis of the real samples containing only one dye (R40) and to the samples containing also other dyes, commonly used as the color additives in drink powders. The results obtained were compared with the results of the official spectrophotometric method and with the results of PLS algorithm for different binary dye calibration matrices. A good statistical agreement was obtained in each case, which confirms that some interferences occurring in spectrophotometric determinations can be eliminated using PLS algorithm and including some possibly interfering compounds in calibration samples.