New automatic fluorescence monitoring system for insecticides in surface and groundwater. Applications to pyrethroids in the Niayes agricultural area of Senegal

Abstract

In this paper, we present the design of a new automatic fluorescence monitoring system (AUTOFLUO) for real-time control of pesticide contamination in natural waters. This system was used to analyse two fluorescent pyrethroid insecticides, phenothrin (PHE) and permethrin (PER), currently used in the Niayes agricultural district in Senegal. The results were then compared with those obtained using the classical fluorescence method (FLUO). The analytical parameters (λex, λem, and pH) were optimised. Phenothrin exhibits maximum excitation and emission wavelengths of 221 and 321 nm, respectively, whereas permethrin has these values at 210 and 297 nm. The optimum pH value was determined to be 7 for PHE and 8 for PER. The linearity of both the calibration and standard addition curves was validated through variance analysis. A Student's t-test demonstrated that the intercept values of the calibration curves were not significantly different from zero (p > 5 %). The limit of detection (LOD) ranges from 0.02 to 5.16 ng mL⁻¹, while the limit of quantification ranges from 0.07 to 17.18 ng mL⁻¹. Comparing these LOD values with those reported in the literature demonstrates the high sensitivity of the AUTOFLUO method. Both insecticides were analysed in spiked natural waters using the standard addition procedure. Satisfactory recovery rates were obtained by the FLUO (88.9 % to 97.6 %) and the AUTOFLUO (95.7 % to 102.8 %) methods. The low intraday and interday relative standard deviations (< 2 % and < 4 % respectively) attest to the repeatability and reproducibility of the measurements. The satisfactory tolerance limits of the interfering species validate the method's selectivity. These results demonstrate that the AUTOFLUO system is suitable for reliably monitoring pesticides in natural waters.