Aqueous Biphasic Systems Based on Tetrabutylammonium Bromide for Extraction and Determination of Azorubine, Allura Red, Sunset Yellow, Tartrazine and Fast Green in Food Samples

Aqueous biphasic systems (ABSs) based on tetrabutylammonium bromide (TBABr) and potassium thiocyanate or citrate (K₃Cit) were proposed as "green" tools for liquid-liquid microextraction of Azorubine, Allura Red, Sunset Yellow, Tartrazine and Fast Green followed by spectrophotometric determination. The dye extraction into the water-saturated tetrabutylammonium thiocyanate phase, which separates from water when mixing aqueous solutions of TBABr and KSCN, depends on the hydrophobicity of dyes. Only Azorubine is extracted quantitatively at HCl concentration ≥ 0.05 mol L^-1, with an equimolar TBABr/KSCN ratio and total concentration of 0.4 mol L^-1 in less than 1 min. To estimate the hydrophobicity and identify factors affecting the distribution of dyes in ABSs, the experimental 1-octanol-water distribution coefficients of the dyes were determined. In contrast, all the dyes studied are quantitatively extracted into the TBABr-K₃Cit-H₂O ABS regardless of their hydrophobicity. The effects of pH, concentration of phase-forming components, extraction/centrifugation time and other factors were investigated for both ABSs. The linearity ranges and detection limits were 0.05-2.60 mg L^-1 and 0.006-0.02 mg L^-1, respectively. The proposed procedures were applied for the determination of dyes in food samples.