Comparison of Three Photochemical-Fluorimetric Methods for Determination of Chloroquine

Abstract

Chloroquine [7-chloro-4-(4-diethylamino-1-methylbutylamino)quinoline] is both fluorescent and photochemically unstable. The primary photoproduct was also found to be both photoactive and fluorescent. Three fluorimetric methods for measurement of original chloroquine concentration were evaluated: (1) digital integration of the fluorescence decay signal from chloroquine (380 nm); (2) digital integration of the fluorescence increase due to the photoproduct (480 nm); (3) analog recording of product fluorescence as a function of exposure time. The digital methods gave better precision (0.6%) and limit of detection (0.1 ppb) by one and two orders of magnitude, respectively. Sensitivity using integration of native chloroquine fluorescence was better by an order of magnitude than that for integration of photoproduct signal and is therefore the method of choice. The analog method was much less sensitive than either digital procedure. The photochemical conversion of chloroquine to intermediate (fluorescent) and final (nonfluorescent) products was studied. Oxygen increases the photochemical quantum yields and decreases fluorescence quantum yields, but satisfactory analytical data are obtained with air-saturated solutions. Speed of analysis and limits of detection exceed previously reported methods.