A fluorometric photo-induced four-way calibration method for the determination of multiclass pesticides in citrus products

CULZONI, MARÍA J.; ANTONIO, MARINA; ALCARAZ, MIRTA R.; FALCONE, RUBÉN D.

Roma

Congreso; XVIII Chemometrics in Analytical Chemistry; 2022

Pesticide usage has become an indispensable practice in agriculture production as it positively impacts crop yields and food quality worldwide by reducing diseases and controlling plagues. However, the side effects of their extensive use can be detrimental to the environment and human health, and cause long-term negative effects due to their high stability and bioaccumulation [1]. Hence, stringent regulations have been implemented by different agencies and governments by establishing the maximum residue levels of pesticides (MRLs), which are the residue levels not likely to be exceeded in a specific food or commodity [2,3] when pesticides are applied by their directions for use. In this work, a four-way multivariate calibration method is presented for the simultaneous determination of 5 pesticides - thiabendazole (TBZ), carbendazim (CBZ), pirimiphos-methyl (PMM), imidacloprid (IMD), and clothianidin (CLT) - in citrus products. Third-order data were acquired by registering the photo-induced fluorescence of the analytes as excitation-emission fluorescence matrix (EEM) at different times of UV irradiation. The use of organized media (micelles) was implemented to enhance the fluorescent signal of the compounds. First, in an attempt to obtain the optimal experimental conditions that yield the best performance of the method, a central composite design was implemented to evaluate the effect of the pH and the surfactant Hexadecyltrimethylammonium chloride (HTAC) on the intensity and the reaction velocity of each analyte. HTAC and phosphate buffer were chosen as reagents accordingly to preliminary studies. All the experiments were performed by using the same concentration of each analyte, and the acquired third-order data were subjected to PARAFAC resolution. The optimal experimental conditions were finally set as pH 11.5 and 0.032 mol/L HTAC. The total UV-irradiation time was completed at 6 minutes. The calibration sample sets were built in 5 concentration levels in triplicate for each analyte individually, except for TBZ and CBZ since it has been demonstrated that TBZ presents an inner-filter effect on CBZ [3]. TBZ/CBZ binary samples were prepared by following a random design. Besides, 16 validation samples containing the 5 analyzed compounds were prepared by following a random design at concentration levels different from those used for calibration. Lemon juice samples were pretreated by using a QUECHERS-based methodology. Next, the quadrilinearity of the corresponding 4-way data arrays comprising calibration/validation samples was evaluated by applying 4-way PARAFAC. For CLT, non-quadrilinearity type 1 was observed due to a lack of reproducibility in the photo-induced reaction mode; thus, U-PLS/RTL and APARAFAC were evaluated, being the former the one which retrieved the best results. In the case of IMD, the implemented chemometric models were not capable of providing satisfactory results shedding light on a possible lack of quadrilinearity due to an unexpected inner-filter phenomenon. For TBZ and CBZ, U-PLS/RTL was implemented as it has been proved that this model can cope with a non-quadrilinearity type 2 given by inner-filter effects.Except for IMD, all models accomplished satisfactory results in the predictive analysis of the validation samples, with mean recoveries (R ̅%) ranging between 98.6 and 102.9%. In all cases, the lack of significant differences between R ̅% values and 100% was demonstrated through a hypothesis test. Moreover, the relative error prediction (REP%) values were below 9.1% demonstrating the good predictive performance of the developed method.Finally, these results suggest that second- and third-order advantages promote a high likelihood of success in the resolution of samples of high complexity such as citrus products.