Chemiluminescence analysis of captopril: comparison between luminol and rhodamine B-sensitized cerium(IV) methods

Two chemiluminescence methods for the determination of captopril are compared in the present paper. The first method is based on the reaction of captopril with the luminol-hydrogen peroxide-copper(II) system, the copper(II) ion acting as a key species in the light-emitting process. The catalytic activity of copper(II) decreases due to complex formation with the sulphhydrylic captopril analyte. Application of this indirect method allows captopril determinations in the 8.0-1.0 microM range as starting concentrations. Similarly, captopril was capable of generating chemiluminescence from acid cerium(IV) solutions, a reaction that could be analytically exploited by the inclusion of the rhodamine B fluorophore yielding a sensitized-type of chemiluminescence emission that allowed quantitation of captopril concentrations in the 0.1-6.0 microM range with a detection limit of 0.037 microM (original concentration). For both types of reaction the experimental conditions were optimized and a direct application was carried out on a commercial drug formulation.