Measurement of Surface pH of Pharmaceutical Solids: A Critical Evaluation of Indicator Dye-Sorption Method and its Comparison With Slurry pH Method

Role of Salt and Excipient Properties on Disproportionation in the Solid-State

“…Since all seven basic excipients produced some levels of free base in the benzocaine mesylate/excipient blends, these results should provide insight into the effect of excipient basicity and other factors on the extent of conversion. Although a poor surrogate for the exact microenvironmental pH conditions at a solid surface (25)(26)(27)(28)(29), particularly for the less soluble/hygroscopic excipients, solution/suspension pH values for the excipients are listed in Table II. Also listed in Table II are literature values of surface pH and corresponding pH of 10% wt/vol.…”

Microenvironmental pH Control and Mixed Polymer Approaches to Optimise Drug Delivery with Hydrophilic Matrix Tablets

“…However, it has been reported that the diffuse reflectance UV spectroscopy approach using solution state calibration curves of the indicator dye may not be applicable to the determination of microenvironmental pH where the dye is in an adsorbed state on a surface. Determining the pH of a concentrated slurry with a glass electrode and a pH meter may still therefore provide a judicious approach to determining microenvironmental pH, as it is a simple and reliable approach and the extent of the reliability of the dye method may be dependent on the compound studied and the indicator dye chosen [27].…”

Controlled Release Systems Containing Solid Dispersions: Strategies and Mechanisms

“…A modified dissolution apparatus and constant-surface area discs, which have been incorporated with a micro-pH probe to measure the pH at the surface of the dissolving compact (177), have been used. Other approaches include pH measurement of a slurry (178); the indicator dyesorption method in the measurement of solid surface pH (179); electron paramagnetic resonance imaging (EPRI), which was originally used to evaluate pH M inside pHcontrolled matrix tablets containing pH-sensitive spin labels (180); quantification of spatial distribution pH M by confocal laser scanning microscopy (CLSM) (181); and direct pH M determination, which was developed by Siepe et al (176) and is easily applicable to a dry solid and has been applied in recent studies (32,33). Additionally, for polymers with properties like HPMC, by determining the cloud points, it is possible to predict if a matrix could show burst release in a given electrolyte solution.…”