Effect of water vapour pressure on moisture sorption and the stability of aspirin and ascorbic acid in tablet matrices

The high-performance liquid chromatographic method described enables the quantitation of the components and the main impurities of tablets containing aspirin, acetaminophen, and ascorbic acid. A C8 reverse-phase column was used; the mobile phase was methanol-0.2 M phosphate buffer (pH 3.5)-water (20:10:70). Results obtained for a brand of effervescent tablets, normally aged for 5 years and stressed at 37 degrees C, 50 degrees C, or in 79% relative humidity at room temperature, are reported. Salicylic acid was the main product of decomposition. Diacetyl-p-aminophenol was observed to be formed by transacetylation.