Optimization of chromatographic methods for the determination of fungicide residues in cucumbers. [Doctoral dissertation] | Optimizacija hromatografskih metoda i određivanje ostataka fungicida u plodovima krastavca. Doktorska disertacija

The paper deals with the optimization and validation of the method for the determination of azoxystrobin, metalaxyl and chlorothalonil in cucumbers, which implies establishing the optimal parameters for their chromatographic analysis and defining the basic parameters of the validation with the aim of obtaining the exact and veracious results. The determination of the detection limit (LOD), the quantification limit (LOQ), repeatability, precision and linearity of the detector response, for all the studied fungicides, were carried out by gas (GC) and liquid chromatography (HPLC). the cucumber samples treated with the compounds Quadris 25% SC in the amount of 0.75 and 1.0 l/h and Folio Gold in the amount of 3.0 l/h, with the water consumption of 600 l/h, were collected immediately after the drying of the deposit, two, four, seven and fourteen days on the fungicide application over two experimental years. The determination of the residues of azoxystrobin, metalaxyl and chlorothalonil in cucumbers by various chromatographic techniques produced very close results. The average values of the azoxystrobin residues at the application of 187.5 g a.s./ha (0.75 l/ha Quadris 25% SC) in 2006 were 2.0613, 1.0527 and 0.3287 mg/kg, after the drying of the deposit, 2 and 4 days on the application. The average values of the azoxystrobin residues in 2007 after the drying of the deposit, 2 and 4 days on the application were 2.0927, 1.109 and 0.316 mg/kg. By the application of 250 g a.s./ha (1.0 l/ha Quadris 25% SC), the residues were determined at 2.457, 1.2917 and 0.2472 mg/kg after the drying of the deposit, 2 and 4 days on the application in 2006 and by the same sampling order in 2007, the residues were 2.4327, 1.3531 and 0.4897 mg/kg. The average values of the residues of metalaxyl and chlorothalonil detected in cucumbers, treated by the compound Folio Gold in the amount of 3.0 l/h, i.e. 112.5 g metalaxyl/ha and 1500g chlorothalonil/ha in 2006 were 0.2590, 0.1365, 0.1292, 0.0915 and 0.0590 mg/kg, i.e. 0.3641, 0.2120, 0.1810, 0.1714 and 0.1064 mg/kg, after the drying of the deposit, 2 and 4, 7 (PHI) and 14 days on the application. The residues of metalaxyl and chlorothalonil in 2007 after the drying of deposit, 2, 4, 7 (PHI) and 14 days on the application were 0.3125, 0.1581, 0.1441, 0.1190 and 0.0765 mg/kg i.e., 0.3930, 0.2471, 0.2000, 0.1889 and 0.1234 mg/kg. Based on the obtained data on the content of azoxystrobin, metalaxyl and chlorothalonil in the treated cucumbers, it can be concluded that the PHI of 4 days is adequately regulated for azoxystrobin, but that the PHI of 7 days for metalaxyl an chlorothalonil can be reduced as the detected residues, shortly after the application do not exceed MDK for cucumbers. For the cucumbers of gherkin type the PHI should be even longer than 7 days taking into account that MRL for metalaxyl is 0.05 mg/kg (The Official gazette RS 25/2010).