The presence of pesticide residues in agricultural products raises serious environmental and health concerns. The development of simple, sensitive and selective analytical methodologies is crucial to monitor the use of these substances. Early fluorometric assays investigated the possibility of quantifying some strobilurins (important fungicide class) using photoderivatization as a tool for the fluorimetric determination. Photoderivatization was applied to induce the formation of products with a more rigid molecular structure, thus with higher fluorescent quantum efficiency with less residue generation. Better results were obtained for kresoxim-methyl (KRESO) with gain of 2820% after UV exposure and trifloxystrobin (TRIF) with gain of 791%. The flexibility and sensitivity of spectral techniques arise from the fact that waveforms can be used to select different classes of chromophores. In this sense, fluorescence is a promising tool capable of detecting small differences between similar substances or materials. Presenting more selectivity than the emission and fluorescence excitation techniques, the synchronized scanning fluorescence (where both excitation and emission monochromators are scanned simultaneously) discriminates against small differences by means of the specific Δl of the analyte to be determined. In this work, it was associated synchronized scanning fluorescence as instrumental tool for the selective determination of these fungicides in the presence of possible interferents (in this case, triazoles presents in commercial formulations). Solutions of KRESO (30.0 µg mL^-1) and TRIF (40.0 µg mL^-1), using acetonitrile/ultrapure water (50/50% v/v for KRESO and 70/30% for TRIF), were prepared separately and combined with triazoles (tebuconazole, TEB or cyproconazole, CIP). Afterwards, the solutions were exposed to UV radiation for 15s (reactor of own manufacture - LEEA PUC-Rio). The measurements were made by spectrofluorimetry Perkin Elmer LS45 at Δλ = 64 nm (λ_exc/em = 373/437 nm) and Δλ = 36 nm (λ_exc/em = 338/374 nm) for KRESO and TRIF, respectively. In Table 1 are presented the sample compositions and the ratio between the fluorescent signal intensities of the mixture (analyte + interferent) by analyte solution. The analytical response of these substances in function of the measured signal presented promising results (LOD 9.7 ng mL^-1 and CV_(n=5) < 5% for KRESO and LOD 58.0 ng mL^-1 and CV_(n=5) < 3% for TRIF). As according to European (EU 2016/486) and the Brazilian (SINITOX/ICICT/FIOCRUZ, 2015) legislations, the LODs are below the required specifications. Based on these results, the synchronized scanning fluorescence can be considerate a simple and selective tool for the determination of KRESO and TRIF. Applicability in complex samples are still in progress.

Table 1: Sample compositions and ratio between the fluorescent signal intensities of the mixture (I_{analyte + interferent}) by analyte solution (I_analyte).