BUFFER SOLUTIONS BASED ON GLYCINE

Abstract

The acid-base interaction in the Gly-NaOH-H2O and Gly-monoethanolamine (MEA) – H2O systems was studied by pH-metric method in the temperature range 293-313 K. The ionmolecular composition of the Gly-NaOH-H2O system was calculated, the dissociation concentration constants for the second stage of the Gly at the isoelectric point, and the temperature dependences of ΔG, ΔH and ΔS of the indicated process at the isoelectrical point (μ= 4.94 ∙ 10-3 M) in the 293-313 K region were determined. It is shown Gly in aqueous solutions to exist at the ratio CNaOH / QGly <0.5 mainly in the zwitterion form. The content of the NH2CH2COO- anion is directly proportional to the CNaOH/QGly ratio. According to the calculated data, the functional dependence ΔG = f (T) for Gly passes through a maximum at Textr. ≈292 K. The Gly dissociation process in the isoelectric point is endothermic in the temperature range 293 – 313 K. Enthalpy-entropy compensation is noted, for which the isothermodynamic temperature is 303 K, and the free term is 56.8 kJ/mol. 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 aqueous solutions of Gly allow to maintain acidity in the physiological pH range and temperature range 308 – 313 K. It is shown that the buffer capacity of the Gly-NaOH-H2O and Gly-MEA-H2O systems can be varied within the limits 1∙10-3 - 4∙10-2 М and 5∙10-4 - 5∙10-2 М, respectively, changing the ratio CNaOH/QGly (CNaOH/QMEA) and temperature. The obtained data on the buffer capacity of the Gly-NaOH-H2O and Gly-MEA-H2O systems can be used in chemical analysis, microbiological and biochemical studies, and the acidity data of the solutions studied can simulate for the chemisorption of acid gases (CO2 and SO2).

Keywords

• гліцин
• водні розчини
• термодинаміка дисоціації
• буферна ємність