In this study, a new deep eutectic solvent (DES) consist of tetrabuthylammonium bromide (TBABr) and 1-octanol at 1:2 M ratio was prepared for the first time and characterized by Fourier transforminfrared spectroscopy (FTIR), proton nuclear magnetic resonance (H-1 NMR) and carbon nuclear magnetic resonance (C-13 NMR) techniques. The new DES was used as an extraction solvent in the ultrasound assisted liquid-liquid microextraction (UA-LLME) of Erythrosine (E127) in blood, urine, pharmaceutical tablet and syrup samples. Accurate and sensitive determination of erythrosine was accomplished with the combination use of DES-UA-LLME and UV-Vis spectrophotometric detection. Before applying UA-LLME, while protein precipitation was applied to blood samples, pharmaceutical tablets were homogenized and dissolved in methanol. The proposed DES-UA-LLME/UV-VIS procedure was applied directly to urine, syrup sample and supernatant of blood and tablet samples with high recoveries in range of 90% and 100%. Erythrosine in the aqueous sample phase was extracted into 200 mu L hydrophobic DES phase at pH 7.0. The effect of important analytical variables such as pH of sample solution, mol ratio of DES components, volume of DES, ultrasonic-based extraction time, sample volume and salt effect were optimized. The preconcentration factor (PF), limit of detection (LOD), intra-day and inter-day relative standard deviations (RSD, %) for the developed procedure were found as 40, 3.75 mu g.L-1, 2.6% and 4.6%, respectively. (C) 2020 Elsevier B.V. All rights reserved.