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 μM 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 μM range with a detection limit of 0.037 μM (original concentration). For both types of reaction the experimental conditions were optimized and a direct application was carried out on a commercial drug formulation.