Study of micelle and metal complexation-mediated fluorescence enhancements of raloxifene hydrochloride. Application to pharmaceutical analysis

Abstract

The fluorescence behavior of the selective estrogen receptor modulator raloxifene hydrochloride (RXF) was investigated for the first time. The weak fluorescence of RXF was greatly enhanced by 2.2 folds in borate buffer (pH8.0)/sodium dodecyl sulfate (SDS) solution. As well, complex formation with Al3+ in borate buffer (pH8.5) gave rise to 1.9 folds enhancement in RXF fluorescence. Based on these outcomes, two simple and sensitive fluorimetric methods were established for the quantification of RXF in tablets. The intensity of RXF-SDS fluorescence was optimum at 583nm after excitation at 290nm (Method-I) and that of RXF-Al3+ complex was optimum at 594nm after excitation at 296nm (Method-II). Different fluorescence parameters such as quantum yield and fluorophore brightness were calculated and compared with those of the drug itself. The molar ratio of RXF-Al3+ complex was calculated and a reaction pathway was deduced. Linearity was attained from 0.1 to 1.5 and from 0.1 to 2.0μg/mL with lower detection limits of 0.01 and 0.02μg/mL for Methods-I and -II, respectively. Application of the two methods to quantify RXF in tablets was successfully done with mean recoveries of 98.19±1.01% and 98.64±1.49%, respectively. The results obtained by the proposed methods and the official USP method agreed well.