Acid-base equilibria in γ-butyrolactone studied by use of pH-ISFETs

摘要

pH-ISFETs were used in the study of" acid- base equilibria in γ-butyrolactone (GBL). After the spectrophotometric determination of the pK_a value of 3,5-dichloropicric acid, the pK_a values and homo-conjugation constants of various acids (including the conjugate acids of bases) were determined potentiometrically using a Ta_2O_5-type pH-ISFET. The values of pK_a in GBL were in a linear relation with those in propylene carbonate (PC) and 1.0 units smaller on average. The difference in pK_a between GBLand PC was mainly attributable to the difference in proton solvation. The autoprotolysis constant of GBL, roughly estimated by a rapid titration with a Si_3N_4-ISFET, was about 30 on the pA_(SH) scale. A comparative study was made of the response speedsof the Ta_2O_5- and Si_3N_4-type pH-ISFETs and a conventional pH-glass electrode. The result was Si_3N_4-ISFET > Ta_2O_5-ISFET > glass electrode. Because GBL is not stable against acids and bases, the use of pH-ISFETs was much more convenient than the use of the conventional-glass electrode.