SIMULTANEOUS DETERMINATION OF ACETYLSALICYLIC-ACID AND CAFFEINE IN PHARMACEUTICALS BY FLOW-INJECTION WITH FOURIER-TRANSFORM INFRARED DETECTION

A fast quality control methodology has been developed for the simultaneous determination of acetylsalicylic acid (ASA) and caffeine in pharmaceuticals by flow injection-Fourier Transform Infrared Spectrometry. The method is based on the solubilization of ASA and caffeine in CH2Cl2 and the use of a flow system to introduce samples and standards in the spectrometer. Two solutions, containing 90 and 110% of the reported concentration of the two active principles in the sample, were employed in order to control the extreme tolerance levels accepted by the International Pharmacopeia for the composition of formulations. A 300 mul volume of each solution was injected in turn, into a carrier stream of the sample, and their absorbances were measured at wavenumbers of 1770 and 1661/cm for ASA and caffeine, respectively. The absorbance values obtained for the carrier, at the same wavenumbers, were interpolated between those obtained for the standards. This rapid methodology provides a simultaneous quantitative evaluation of the concentration of ASA and caffeine in pharmaceuticals. The method permits us to carry out 53 injections/hr and provides a sensitivity of 0.231 absorbance units/mg ml/mm for ASA and 1.065 for caffeine. Accurate results were obtained for the analysis of different samples containing one or both compounds in the presence of excipients which are insoluble in CH2Cl2 and also in the presence of other active principles, such as acetaminophen or ergotamine tartrate.