Quantitative Analysis of Coal-tar Dye Mixture with Ordinary Spectrophotometer by Dual-wavelength Spectrophotometric Method

On the standpoint of dual-wavelength spectrophotometry, each component in 156 groups of two-components mixture consisting 11 kinds of food colors and of 2 kinds of similar colors was directly analyzed with ordinary spectrophotometer without chromatography. Measurement for calibration equations was made in the 0.02N ammonium acetate solution ranging in concentration of these dyes from 0 to 10μg/ml.The reference wavelength (λ1) and measurement wavelength (λ2) chosen were shown in Table 2, and difference absorptivity between λ1 and λ2 were also shown in Table 3. Mean standard deviation between amounts of added dye and those of found dye in monoazomonoazo mixture was 0.03μg/ml (analyte+interfering dye=5μg/ml). In the case of acid red interfered by another dye, 0.099μg/ml was obtained, but the total mean standard deviation was 0.067μg/ml for all mixture groups. Dye contents in commercial dye were quantitatively analyzed by this procedure.