Quantitative reflectance spot test for the determination of acetylsalicylic acid in pharmaceutical preparations

This paper describes a quantitative reflectance spot test procedure for the determination of acetylsalicylic acid (ASA) in pharmaceutical preparations. The method is based on the reaction of salicylic acid, obtained from the hydrolysis of ASA, with Fe(III) forming a deep blue-violet compound. Medicines containing ASA can be easily analyzed by the proposed method as it is not necessary to do any separation. The final mixture is placed on a sheet of filter paper, and the reflectance is directly measured. Nine commercial medicines containing acetylsalicylic acid were analyzed with the proposed method. The mean RSD was 0.9%. Results were compared with those obtained with the United States Pharmacopoeia recommended procedure (RSD 0.6%). The quantitative detection limit is 0.6 mg ASA in the working solution. For a degree of freedom nu = 4 (nu = n(1)+ n(2)-2) and a confidence coefficient alpha = 0.05 all the results agree under the tabulated t-Student test value (2.78).