Isolation of salicylsalicylic acid, acetylsalicylsalicylic acid, and acetylsalicylic anhydride from aspirin tablets by extraction and high-pressure liquid chromatography.

Aspirin and four salicylate impurities of aspirin (salicylic acid, acetylsalicylsalicylic acid, acetylsalicylic anhydride, and salicylsalicylic acid) were resolved by silica gell TLC and by high-pressure liquid chromatography (HPLC) on a reversed-phase C18 column. Care was necessary in the choice of a column because of similar column failed to resolve these five compounds. Salicylsalicylic acid was isolated from aspirin tablets by extraction followed by reversed-phase C18 HPLC. The structure of this compound was confirmed by comparison with an authentic sample of salicylsalicylic acid by HPLC, TLC, IR and UV spectrophotometry, and mass spectrometry. Two other compounds, acetylsalicylic anhydride and acetylsalicylsalicylic acid, which had been previously identified by chromatography as impurities in aspirin, were isolated and further characterized.