Enhanced chemiluminescence of carminic acid-permanganate by CdS quantum dots and its application for sensitive quenchometric flow injection assays of cloxacillin

A novel chemiluminescence (CL) system is introduced based on the oxidation of carminic acid by KMnO₄ in acidic conditions. CdS quantum dots (QDs) were synthesized using a facile hydrothermal method which efficiently enhanced the intensity of the CL system. A possible mechanism for the proposed system is presented using the kinetic curves, CL spectra, photoluminescence (PL), and ultraviolet-visible (UV-Vis) analysis. The emission intensity of the KMnO₄-carminic acid-CdS QDs system was quenched in the presence of a trace level of cloxacillin. Based on this quenching effect, a novel and sensitive flow injection CL method was developed for determining cloxacillin concentrations. At optimal experimental conditions, the decreased CL intensity had a good linear relation with the cloxacillin concentration in the range of 0.008 to 22.0 mg L^-1. The detection limit (3σ) was 5.8 μg L^-1. The precision of the method was calculated by analyzing samples containing 4.0 mg L^-1 of cloxacillin (n=11), and the relative standard deviations (RSD%) were 2.08%. The feasibility of the method is also demonstrated for determining cloxacillin concentrations in environmental water samples and a pharmaceutical formulation.