HPLC Separation of Acetylsalicylic Acid and Its Related Compounds with Core-shell Type Reversed-phase Columns and Rapid Evaluation of Stability of Aspirin Tablets Suspension

This paper describes the separation and determination of acetylsalicylic acid (aspirin, AP) and its related compounds by HPLC employing various core-shell (CS) type reversed-phase columns. Among seven CS type columns, large retention was observed in a pentabromobenzyl (PBr) type column, on the other hand, cyanopropyl (CN) type column gave low retention. For the elution order of eleven compounds investigated, caffeine retained in a PBr column and a Biphenyl column compared with those in other columns, showing effective & pi;-& pi; interaction. Retention order of acetylsalicylic acid and its decomposed compound salicylic acid (o-SA) was reversed in a RP-Amide column, showing effective electrostatic interaction between the column and the analyte. From the investigation of each CS column selectivity, a Biphenyl column was selected for the fast assay of Aspirin tablets due to the largest resolution between AP and o-SA. Under the HPLC conditions of a mobile phase, acetonitrile 30 % and 0.05 mol L-1 phosphate buffer (pH 3.0), a Biphenyl column, and ethenzamide as an internal substance (IS), a fast determination of AP in tablets by an IS method was successfully achieved within 2.5 min. Stability of AP changed dosage form (suspension in water) and AP suspension mixed with other suspended medicine Magmitt (MgO) was evaluated by the method. After storage for 30 min at room temperature, around 20 % AP was decomposed to o-SA in the mixed suspension medicine, indicating the loss of AP effectiveness (platelet aggregation inhibitory activity).