Pre-treatment of drugs
For the analysis of each speciality five tablets were taken, carefully ground up, combined and homogenised. Then an amount sufficient for the preparation of 20 ml of solution, 5 × 10−2 M, of active principle, i.e. acetylsalicylic acid, to perform measurements using the biosensor method or the cyclic voltammetric method, or the fluorimetric method, was weighed out, or else the amount necessary to prepare 100 ml of solution, 1 × 10−3 M, employed to perform the measurements by the differential pulse voltammetric method.
The weighed quantity of each drug speciality was dissolved in the proper buffer, depending on the method used and then homogenised (at 10 000 rpm for 5 min). The homogenate was then analysed directly using both the biosensor and the DPV voltammetric method, or else was centrifuged (at 3000 rpm for 15 min) and the supernatant analysed directly in the case of the fluorimetric and cyclic voltammetric methods.
In the case of measurements carried out using the biosensor based method but on the same quantities by weight of each sample, 150 mg of each drug, carefully ground up and homogenised as described above, were weighed, dissolved in 20 ml of the buffer solution and then analysed directly.