DYE COMPARISON BY INSTRUMENTAL COLORIMETRY

Dyes are important raw materials for the food, cosmetics and pharmaceutical industries. The FDA (U.S. Food and Drug Administration) classifies dyes as FD&C (Food, Drugs & Cosmetics) for ingestables, and D&C for use in drugs and cosmetics. Considering that precise and practical methods for pigment analysis and checking are still a demand of the industry, this work aims to compare dyes in different concentrations by color evaluation using spectrophotometry and image analysis. Two FD&C dyes (Tartrazine Yellow CI19140, Brilliant Blue FCF CI42090) and one D&C (Red 4 CI14700) were solubilized (0.04; 0.1; 0.4; 0.7 and 1.0 gL-1) in hydroalcoholic medium (50:50) and further analyzed in Konica Minolta CM5 spectrophotometer and in Verivide Digieye image analysis system, both in CIE2000 color space. The colorimetric data collected for the three dyes, in 5 dilutions and analyzed by two methods were plotted in 2D graph for visualization of the distribution in the parameters L*, a* and b*. Curves related to pigment concentration and Lab parameter were also constructed. The spectrophotometer and Digieye color analyzes presented R2 ≥ 0.97 of regression adjustment calculated in relation to the observed data. A significantly positive correlation was also found between the two methods (R ≥ 0.98). A comparison on spectrograms of the same pigment at different concentrations (0.04 at 1.0 g.L-1) was also developed for the spectrophotometric method. By calculating the relation between absorbation vs scatering of the spectrogram it was possible to differentiate the intensity of the pigments, functioning as a checking system (% color strength). The instrumental evaluation was able to measure color in dyes. Being an opportunity for control of raw materials, formulations and shelf-life of products.