The 1-butyl-3-methylimidazolium tetrafluoroborate, [bmim]BF4, is an ionic liquid when pure. The acid base properties of aqueous solutions of [bmim]BF4 were examined by potentiometric titration. Then, protonation constants of glycine in binary mixtures of water and [bmim]BF4 were determined, from potentiometric titration data obtained at T = 298.2 K and various ionic strengths of sodium chloride (0.25 <= I <= 1.00 mol . dm(-3)). The ionic strength dependence of the equilibrium constants of glycine was fitted to an extended Debye-Huckel equation to derive ionic strength dependence parameters. Comparison with literature data showed that, even at high concentrations, [bmim]BF4 is similar to the electrolyte [(C2H5)(4)NI], in that it does not interact significantly with other solutes. Solvatochromic parameters in the binary mixtures of water and [bmim]BF4 have been calculated by using Redlich-Kister equation. Kamlet-Abboud-Taft (KAT) solvatochromic equation allows us to determine the values of calculated protonation constants in different media. (C) 2013 Elsevier Ltd. All rights reserved.