The performance of hydroxypropyl methylcellulose (HPMC) capsules is closely related to parameters such as its degree of substitution, viscosity, and purity. Therefore, standardized testing methods are necessary to ensure that its quality meets application requirements. The testing process covers multiple key indicators, involving chemical analysis, physical property testing, and instrumental testing techniques, applicable to scenarios such as production quality control, R&D optimization, end-application verification, and import/export trade.
Key testing indicators for HPMC include degree of substitution (methoxy and hydroxypropoxy content), viscosity, moisture content (loss on drying), ash content (residue on ignition), pH value (acidity/alkalinity), gelation temperature, and water-insoluble matter.
Degree of substitution is typically determined using gas chromatography (GC) or nuclear magnetic resonance (NMR). Viscosity is measured using a rotational viscometer (e.g., Brookfield type). Moisture content is measured using the Karl Fischer method. Ash content is measured using a high-temperature ignition method (e.g., muffle furnace). pH value is measured using a precision pH meter. Gel temperature can be measured visually or spectrophotometrically. The HPMC content in the formulation can be determined using the diphenylamine colorimetric method (spectrophotometry).
