Aspirin--a national survey I: Semiautomated determination of aspirin in bulk and tablet formulations and salicyclic acid in tablet formulations.

A semiautomated assay to determine aspirin (acetylsalicylic acid) in aspirin tablets, powdered tablet composites, and pure drug substances is presented. The sample was dissolved in alcoholic buffer, diluted, and extracted with chloroform. The absorbance of the chloroform solution was read at 280 nm. Results obtained by the USP XIX and semiautomated methods are compared. The proposed method is accurate and precise, and common excipients do not interfere. Recoveries of 100% were obtained. A semiautomated assay for salicylic acid in aspirin tablets also is presented. The sample was dissolved in alcoholic buffer, ferric nitrate was added, and the absorbance of the resulting purple color was read at 532 nm. The method is suitable as a rapid screening procedure for testing the salicylic acid content of aspirin products. Results obtained by the USP XIX and semiautomated methods are compared, and the accuracy and precision of the proposed method are given. One hundred seventy tablet samples and 34 bulk drug substances were analyzed for aspirin and salicylic acid content. Approximately 5% of the tablet samples failed to meet the USP XIX limits for aspirin content, and 10% failed to meet the limits for salicylic acid.