Related Experiment Video
Updated: Jun 28, 2026

Evaluation of Drug Sorption to PVC- and Non-PVC-based Tubes in Administration Sets Using a Pump
Published on: March 11, 2017
Acid-base equilibria of diazepam and prazepam in montmorillonite suspensions
1Department of Pharmaceutical Analytical Chemistry, University of Assiut, Assiut, Egypt.
Abstract:
The distribution of ionic species of diazepam and prazepam in aqueous and aqueous montmorillonite clay suspensions at several pH conditions (pH 1-12) was monitored spectrophotometrically. Measurements were performed at 284 and 365 nm for diazepam and 285 and 361 nm for prazepam. The interaction between the negative clay surface and protonated species of the drugs studied relative to the unchanged species is responsible for the apparent displacement of pK(a) values from 3.3 and 2.7 to 4.4 and 3.9 for diazepam and prazepam respectively. Changes in the partial molar free energy of the ionic species of both drugs (DeltaG(i)) as a result of interactions with montmorillonite suspensions was -1.47 and -1.72 for diazepam and prazepam respectively. The effect of an additional ionic solute i.e. sodium chloride was also studied. The recovered amounts of both drugs from five different concentrations of veegum at pH 2, 5 and 10 indicates the effect of drug-clay interactions in drug analysis.
Related Concept Videos
Leveling Effect and Non-Aqueous Acid-Base Solutions
The Leveling Effect of a Solvent
A generic acid (HA) reacts with the generic base (B-) to yield the corresponding conjugate base (A-) and conjugate acid (HB):
Weak Base Solutions
Solvating Effects
Acid and Bases: Ka, pKa, and Relative Strengths
Basicity of Heterocyclic Aromatic Amines
Basicity of Aliphatic Amines
To measure the basicity of amines, two conventions are generally used. The first defines Kb as the basicity constant for the deprotonation reaction of water by the amine, as presented in Figure 1. Conventionally, lower Kb indicates higher...

