Spectrofluorimetric determination of phenylephrine in the presence of a large excess of paracetamol

Two independent spectrofluorometric methods were developed for the determination of phenylephrine (PHE) in pharmaceutical tablets containing a large excess of paracetamol (PAR) (between 30:1 and 100:1 in weight). One of them involves standard addition of phenylephrine (in the range 0-2.00 mg l(-1) in excess with respect to the content of the unknown sample) to a slightly acid aqueous solution (HCl) of the tablet components. The limits of determination and quantification were found to be 0.08 and 0.27 mg l(-1), respectively. A surface response optimisation approach, using a blocked cube star design was carried out to optimise the variables which have an influence on the fluorescence emission of the analyte. The optimal conditions obtained were excitation wavelength, 277 nm and concentration of paracetamol, 72 mg l(-1). As an alternative method, the multivariate partial least-squares (PLS) calibration of fluorescence excitation spectra was carried out. In this case the range of application is 0.80-2.00 mg l(-1) of phenylephrine. Both techniques were satisfactorily applied to several pharmaceutical tablets. The results provided by both methods are not statistically different. (C) 2000 Elsevier Science B.V. All rights reserved.