Ratio spectra derivative spectrophotometry for the determination of furosemide and spironolactone in a capsule formulation.

The determination of furosemide and spironolactone in a capsule formulation has been investigated using techniques such as Vierordt's method and derivative spectroscopy dA/d lambda and d2A/d lambda2 applying the zero-crossing technique following reported methods. In our hands, using standard mixtures, these methods gave unreliable results. We have therefore investigated the use of ratio spectra derivative spectrophotometry for this determination. The technique of ratio spectra derivative spectrophotometry was developed in 1990, and has recently been used for a number of analyses of co-formulated products. The method was applied to the analysis of standard mixtures of the two drugs and the combined contents of 20 capsules resulting in values (mean +/- standard deviation) of 102.1 +/- 1.9% and 101.4 +/- 4.0% of the stated content for furosemide and spironolactone, respectively. Similarly, the analysis of individual capsules resulted in values of 101.5 +/- 1.6% and 102.2 +/- 1.4% of the stated content for furosemide and spironolactone, respectively.