High productivities and economic benefits in modern agriculture have been accomplished only by the use of pesticides. The introduction of these compounds in the food chain can be considered a risk for human health due to their toxicity. So, pesticides residues and their degradation products resulted by hydrolytic, photochemical and microbial processes in soil and cereals must be monitored and controlled. The aim of this research was to develop rapid and sensitive HPLC-DAD methods for residues detection of several pesticides, imidacloprid, amidosulfuron, bromoxynil and deltamethrin, from soil and some crops, maize, wheat and rape seeds, cultivated in Banat County-Moravita Zone. In order to perform the pesticides extraction, the samples were subjected to an ultrasonic technique, at 59 kHz and 30°C, during 30-45 min., using acetonitrile and acetonitrile-water mixture as solvents. Acetonitrile alone proved to be more appropriate for this purpose. The HPLC analyses were conducted on HPLC-DAD apparatus, Dionex Ultimate 3000 (Dionex Corp., USA), equipped with quaternary pump LPG 3400A, thermostat of columns TCC-3000 and a C-18 Acclaim® 120 Silica-reversed-phase (4.6x150 mm, 5 µm) column, using different compositions of acetonitrile-water as mobile phase. The presented HPLC - Dionex system proved to be very suitable for determination of pesticides residues in soil and crops.

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Previous studies have shown that pyrazine-2,3-dicarboxylic acid (PDCA) can be obtained through quinoxaline (Q) oxidation with electrochemically regenerated KMnO 4 using Pt, Ni, stainless steel, Cu, brass and bronze electrodes. This corresponds to a smaller oxidant consumption as compared to the chemical oxidation reaction, a smaller energy consumption, an increase in the PDCA manufacturing efficiency and a significantly smaller impact on the environment due to secondary products removal (both from Q oxidation as well as from KMnO 4 production). This paper presents the analysis methods used for the quantitative determination of PDCA obtained through Q oxidation (such as conductometric titration, UV-VIS and IR spectrophotometry) as well as those used for monitoring Mn 7+ and Mn 6+ concentrations (UV-VIS spectrophotometry and the visual method). The right conditions for applying these methods were established in order to properly evaluate the electrochemical process.

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