PREPARATION OF THE VARIABLE-VALENCY THALIDASINE(TD) PVC MEMBRANE SELECTIVE ELECTRODE AND ITS APPLICATION IN THE pKa DETERMINATION OF THALIDASINE

The construction and performance characteristics of a new variable-valency TD-PVC selective electrode was described. It is based on the TPB. TD ion-pair complex, which was used as electro-active material. The electrode membrane was composed of the complex, PVC and DBP in the ratio of 1:8:8 (w/w/w). The electrode showed Nernstian response from 10^-3 to 10^-5 mol/L in NaCl—HC1 (I=0.05) solution over pH range of 5.0 to 6.0 with a slope of 58.2 mV/pC. The detection limit was found to be 2.5×10^-5 mol/L. The electrode response was quite fast and stable, and the slopes of calibration curves were quite reproducible.It was observed that the E-pC relation can not be simply described by Nernstian equation over wide pH range. The slopes of electrode response and electrode potentials varied in concordance with pH value of the solution. By using the S-pH relation, the Ka₁ was found to be (2.5±0.2)×10^-4. (25℃, I=0.05). Accordingly, Ka₂ was found to be (8.1±0.9)×10^-8(25℃, I=0.05) by using E-pH relation.