Spectrophotometric resolution of ternary mixtures of Tartrazine, Patent Blue V and Indigo Carmine in commercial products

Four spectrophotometric methods are described and applied to resolve ternary mixtures of the food dyes Tartrazine (E-102), Patent Blue V (E-131) and Indigo Carmine (E-132). The simultaneous determination of these three dyes was firstly accomplished by two derivative methods using the "first derivative" and the "ratio spectrum-zero crossing derivative", which were satisfactorily used to determine synthetic mixtures of these colorants in different ratios and in three commercial products. Direct absorption spectra of compounds were used to optimize the spectral data set to perform the calibration by partial least squares-1 and principal component regression algorithms. Both calibration models were evaluated by internal validation (prediction of dyes concentration in its own designed training set of calibration), by cross-validation (obtaining statistical parameters that show the efficiency for a calibration fit model) and by external validation over synthetic and commercial mixtures. The four described procedures do not require any separation step. Repeatability and reproducibility studies were achieved over two series of nine standards for each dye showing no significant differences at 95% confidence level in the four spectrophotometric methods. A comparison of the two derivative and the two multivariate calibration results obtained in commercial products was performed resulting in a good agreement of the values obtained. (C) 1999 Elsevier Science B.V. All rights reserved.