The influence of hydrochloric, chloric, sulfuric and sulfurous acids (HCl, HClO4, H2SO4 and SO2×H2O, respectively) on protolytic equilibria in the system monoethanolamine (MEA) – tropeolin OOO (TrOOO) – water (CMEA = 0.1 M; pH = 1.0 ÷ 9.5) was studied by pH-metric, spectrophotometric and colorimetric methods. The acid-base behavior of the HOCH2CH2NH2 – TrOOO – H2O system was investigated at CTrOOO = 1,12 ×10-4 М, CMEA = 1,0×10-4  ÷ 1,0 М (pH = 8,25 ÷ 12,05), T = 293 K. TrOOO in this system exists in two tautomeric forms due to acid-base dissociation of the 4-OH group and associates formed by H-bonding with MEA molecules. There is a direct ratio between the pH values ​​of solutions and the total color difference (ΔE76), in contrast to the specific color difference (SCD). The difference in the behavior of the H2SO4 – HOCH2CH2NH2 – TrOOO – H2O system from the systems with HCl and HClO4 is due to the fact that the interaction of the first acid with MEA (8,0 £ pH) forms an ionic associate [HOCH2СH2NH3]2(SO4), which is more stable than ionic pairs [[HOCH2СH2NH3](HSO4), [HOCH2СH2NH3](ClO4), [HOCH2СH2NH3]Cl и [HOCH2СH2NH3](O3S-C­10H6-N=N-C6H4-SO3)[H3NCH2СH2OH]. Acid-base dissociation constants in systems significantly depend on the structure and physicochemical parameters of the mineral acid. In the electronic absorption spectra of the SO2 – MEA – TrOOO – H2O system (pH £ 7,5), there is a pronounced isobestic point at 415 nm, due to the dynamic equilibrium between ion-molecular forms. The coincidence of the maxima on the curves ΔE76 = f(pH) and SCD = f(pH) for the indicated system, in contrast to others studied in this work, was stated. The difference between the spectrophotometric and colorimetric behavior of the SO2 – MEA – TrOOO – H2O system from behavior of the systems with HCl, HClO4, and H2SO4 systems is due to the sulfur(IV)oxyanions with an azo indicator redox interaction.

The acid-base interaction in the aminoethanesulfonic acid (taurine, Tau) – potassium aminoethanesulfonate – water system was studied by pH-, redox- and conductometric methods in the temperature range 293–313 K. The ion-molecular composition of NH2CH2CH2SO3H –NH2CH2CH2SO3K – H2O system was calculated. It is shown aminoethanesulfonic acid in aqueous solutions to exist at the ratio CKOH/QTau < 0.5 mainly in the zwitterion form similar to systems with glycine, aminomethanesulfonic acid and its N‑alkylated derivatives. The content of the aminoethanesulfonate anion is directly proportional to the CKOH/QGly ratio. The studied system ionic strength and acid-base dissociation constant for the second stage of the aminoethanesulfonic acid concentration and temperature dependences were determined. The ionic strength values at the isoelectric point (mi.p.)are directly proportional to С0Tau and practically do not depend on the temperature within the error for the same series С0Tau and С0KOH .The pH limits of the buffer action are determined and the buffer capacity of these systems is estimated. It has been established that effective buffer zones of Tau aqueous solutions can to maintain acidity in the higher then physiological pH range at temperature range 293–313 K. The buffer capacity of NH2CH2CH2SO3H – NH2CH2CH2SO3K – H2O system exceeds the analogous values of YNHCH2SO3H – YNHCH2SO3K – H2O (Y = H, CH3, CH2CH2OH, C(CH3)3 and C2H5C6H5) systems. The obtained data on the buffer capacity of the aminoethanesulfonic acid – potassium aminoethanesulfonate – water system can be used in chemical analysis, microbiological and biochemical studies, and the acidity data of the solutions studied can simulate the chemisorption of acid gases (carbon and sulfur dioxides).