A kinetic spectrophotometric method for determining residues of insecticide diflubenzuron 1(4-chlorphenyl)-3-(2,6-diflubenzoyl)urea (DFB) has been developed and validated. Kinetic method was based on the inhibitory effect of DFB on the oxidation reaction of sulfanilic acid (SA) by hydrogen peroxide in the presence of Co 2+ ions in a phosphate buffer, which was monitored at 370 nm. DFB can be measured in the concentration interval 0.102 – 3.40 μg mL -1 and 3.40 – 23.80 μg mL -1 . The detection and quantification limits of the method were calculated according to the 3σ criteria and found to be 0.077 μg mL -1 and 0.254 μg Ml -1 , respectively. The relative standard deviations for five replicate determinations of 0.102, 1.70 and 3.40 μg mL -1 DFB were 2.08, 1.22 and 1.21 %, respectively, for the first concentration interval, and the recovery percentage values were from 94.12 to 97.35 %. HPLC method was used as a parallel method to verify results of the kinetic method. The kinetic method was successfully applied to determine diflubenzuron concentrations in spiked water and baby food samples after solid phase extraction of the samples. The F and t values at 95% confidence level are lower than the theoretical ones, confirming agreement of the developed and the HPLC method.

The mongraph presents the development and validation of kinetic methods for analysis of quantitative determination of the content of pesticides on the basis of their inhibitory influence in the chosen indicatory reactions. Spectrophotometry procedure allowed observing the speed of chemical reactions at wave length of maximum absorption of the obtained transitory complex metal ion-pesticide-substrate. Detecting the effect of pesticides on the speed of chosen indicatory reactions, allowed presuming the possible mechanism of their effect by building triple complex due to bonding of the metal ion to free electrons of donor atoms in the pesticide molecule. The mongraph explains the inhibitory effect of pesticides expressed by decrease of catalytic activity of the catalyst, due to the fact that depending on both the stability of the formed triple complex and strength of the bond between the donor pesticide atom and metal ion, much more energy is needed for such complex to decompose, which leads to decrease of the speed of indicatory reaction. During the elaboration of kinetic methods, we observed the effect of reaction parameters on the speed o indicatory reactions, the aim of which was to choose the optimal experimental conditions for determination of pesticides. In a part of the mathod elaboration, we tested the effect of pH values in reacction environment, the concentration of indicatory substances and the catalyst on the speed of chosen indicatory reactions. We constructed the calibration curves for determining the pesticides and tested the accuracy and precision of the proposed kinetic methods. We also tested the effect of interference on the speed of inhibitory reactions. The work also icluded defining limits for detection and limits for determination of the tested pesticides. The elaborated kinetic methods were applied for determining pesticides in food and water samples. The food and water samples required a complex preparation due to the presence of numerous substances that had an effect on determining the pesticides by applying these methods. The present distracting substances in the samples were removed by applying extraction methods, which at the same time increased the selectivity of kinetic methods. Validation of the proposed kinetic methods was performed by comparing the obtained results with the results obtained by the reerent HPLC method.