Simultaneous Determination of 1-Naphthylacetic Acid and Thiabendazole in Strawberry Tree Berries and Citrus Fruits by Fluorescence Spectrometry

An accurate, sensitive spectrofluorimetric method was developed to determine 1-naphthylacetic acid and thiabendazole simultaneously in fruits in a simple, expeditious manner. Broadband overlap between the conventional spectra of the two compounds was resolved by using first-derivative constant-wavelength synchronous fluorescence spectrometry. The proposed method is based on the intrinsic fluorescence of the two agrochemicals in ethanol. The sensitivity and selectivity of the determination were optimized by examining the influence of various factors on the fluorescence intensity. Based on the results, analyses were performed in 30% (v/v) ethanol–water mixtures at a pH 4.7 adjusted with sodium citrate buffer. Using the derivative signals at 304 and 286 nm for 1-naphthylacetic acid and thiabendazole, respectively, provided linear calibration graphs over the range 10–100 and 30–120 ng mL−1, and limits of detection of 1.99 and 0.17 ng mL−1, respectively. The analytical figures of merit of the proposed method were calculated in the light of the error propagation theory. The sensitivity, repeatability, reproducibility and limits of detection obtained are acceptable for determining the two agrochemicals in strawberry tree berries and citrus fruits without the need for a time-consuming prior separation. The proposed method is simple, reliable and cost-efficient, which makes it an attractive choice for fast selective screening purposes.