Solid-phase extraction and spectroscopic determination of synthetic dyes Sunset Yellow (E110) and Ponceau 4R (E124) in foodstuffs using alumina modified with polyhexamethylene guanidine

Alumina, modified with polyhexamethylene guanidine (Al2O3–PHMG), was suggested for simultaneous preconcentration and determination of food dyes using diffuse reflectance spectroscopy. Adsorption of synthetic dyes the Sunset Yellow (E110) and Ponceau 4R (E124) was studied; Al2O3–PHMG adsorbent extracted dyes in a wide range of acidity at pH 1–8. Synthetic dyes were quantitatively extracted at pH 1-2 and 5-6. The best adsorption capacity was observed at pH 1–2 and was 95 and 85 μmol g-1 for Sunset Yellow and Ponceau 4R, respectively. The maxima of bands in the diffuse reflectance spectra were at 470 nm (Sunset Yellow) and 510 nm (Ponceau 4R). An increase in the concentration of dyes on the adsorbent surface led to an increase in the intensity of the band in the diffuse reflectance spectra; this was used for their adsorption-spectroscopic determination. Limit of detection, calculated by the 3s-criterion, was 5 µg L-1 for Sunset Yellow and 7 µg L-1 for Ponceau 4R. The analytical range of dye concentrations was 0.02–10.0 mg L-1 for Sunset Yellow and 0.02–11.0 mg L-1 for Ponceau 4R. The relative standard deviation did not exceed 0.09 (n=10). The proposed method was tested for determination of Sunset Yellow and Ponceau 4R in soft beverages and jelly.