Development of New Procedures for the Detection and Separation of Salicylic Acid and Acetylsalicylic Acid Using Thin-Layer Chromatography with Densitometry

Salicylic acid and its derivatives, such as acetylsalicylic acid, are commonly used non-steroidal anti-inflammatory agents. In the present work, different sorbents as the stationary phases and also various manners of detection using well known and new visualizing reagents have been tested for the separation and detection of the two compounds by adsorption and also partition thin-layer chromatography (TLC) with densitometry. Densitometric and spectrodensitometric analysis was used to evaluate the detectability of the examined compounds using the newly developed TLC procedures. Of all the applied manners of detection, the most universal to distinguish acetylsalicylic acid from salicylic acid in normal- as well as in reversed-phase TLC system is the use of methanolic solution of FeCl3 and CoCl2. The densitograms obtained under these conditions show symmetric and also by adsorption well separated TLC peaks of both compounds. The shape of all absorption bands of acetylsalicylic acid (ASA) and 2-hydroxybenzoic acid (SA) recorded using a scanning densitometer in the range of 200–700 nm is regular. In the case of adsorption TLC performed on chromatographic plates precoated with silica gel 60 F254 and silica gel 60, a very effective spray reagent was also Janus blue. The satisfactory results of detection on silica gel 60 plates assure the use of 1% NaOH as spray reagent followed by heating at 90°C for 60 min. The results performed in the present work confirm the utility of TLC in combination with densitometry in the qualitative screening and identification of SA and ASA. The most efficient manners of detection described in this work can be helpful in the quality control of acetylsalicylic acid, e.g., in monitoring the synthesis reaction of acetylsalicylic acid from salicylic acid as well as in the quality control of ASA in commercially available products.