Persistence and dissipation behavior of dicamba and bentazon herbicides in water under laboratory conditions

The characteristics of water used in a spray mix influence the effectiveness of pesticides. It is important to know the pH of water used with a pesticide and the susceptibility of the pesticide to hydrolysis. In order to investigate the persistence, dissipation and degradation kinetics of bentazone and dicamba, laboratory study was conducted in deionized water (pH 7.0) at 2542°C (T1) and 442°C (T2). Herbicides were dissolved at rate of 0.05 mg/ml. Concentration of analytes was monitoried 0 (1h), 2, 4, 7, 10, 14, 18, 24 and 28 days after treatment and analysing as triplicate samples. Samples were analyzed by high pressure liquid chromatography (HPLC/DAD). The chromatographic separation was carried out with Zorbax Eclipse XDB-C,, (50 mm x 4.6 mm x 1.8 pm) analytical column, using reverse phase column with gradient conditions of mobile phase consist of water (with 0.05% H PO,) and acetonitrile. In T1 the dissipation were 1.3, 5.1, 7.5, 7.9, 8.1, 15.3, 24.1, 26.9% for dicamba and 11.5, 33.3, 44.6, 46.9,48.8, 49.6, 50.1, 51.8% for bentazone in 2, 4, 7, 10, 14, 18, 24, and 28 days. Corresponding dissipation in T2 experiment were 2.0, 2.7, 3.9, 5.0, 6.1, 6.9, 6.8, 8.0% for dicamba and 7.7, 15.2, 26.7; 29.4, 30.3, 30.6, 31.4, 31.9% for bentazone, respectively. The dissipation data in water showed the DT, and DT,, values 57.3 and 114.9 days ae for dicamba and 17.1 and 125.9 days for bentazone herbicide. Several simulation models were used to evaluate the experimental data, such as Exponential and Mittag-Leffler function. The dissipation of analized eo . herbicides residues over the time in water were described by the MittagLeffler function, with the best-fit model for dicamba and bentazone [1]. The dissipation of dicamba and bentazone residues on 25+2°C and 442°C es over the time in deinoized water were described by function a*Eo, (-bt). ag Coefficients a, b, a, 8 were obtained from the experimental data by using be fitting procedure. We got for dicamba and bentazone herbicides on a 25+2°C coefficients a=0.8, R=3.71,a=159.11,b=12.79 and a=2.17, B=4.56, Es a=1387.45, b=1.96 for 442 °C a=0.8, B=4.11, a=82.53, b=7.0 and a=0.99, rs G=3.15, a=205.81, b=0.117, respectively. The hydrolysis study indicated that the dicamba and bentazone pesticides hydrolysed faster at 25+2°C. These findings can be useful in the prediction of the dissipation behavior of this pesticides in the spray tank immediately before application. The dissipation rates of dicamba and bentazone pesticides depended on the temperature and pH of water to be used

Solid-phase extraction followed by high-performance liquid chromatography with diode array detection for screening of dicamba herbicide in water

Chlorinated acids are selective agricultural herbicides which are widely employed in agriculture and gardening for control the growth of different unwanted vegetable species in crops. Because of high water solubility and toxicological risk of some acid herbicides and their metabolic products, monitoring of their concentration in surface and groundwater is very important task. The acidic herbicides are manufactured in formulation as free acids, as their alkaline salts or as esters. The unionized free acids vary in water solubility (Table 1), but the acidic herbicides most frequently exist in ionized form at environmental pH values. Acidic herbicides formulated as salts are water soluble, while those formulations prepared as esters are less water soluble. In the environment, acidic herbicides formulated as esters have short hydrolysis half-life time (24-48 h) and therefore they are generally present as ionized acids. For most analytes, especially for the acidic herbicides, solid phase extraction (SPE) is the choice of sample treatment, which is followed by appropriate chromatographic separation and sensitive determination of target components. For the acidic herbicides, combination of physico-chemical parameters influences their extraction from aqueous solution. Ionogenicity (pKa) and hydrophobicity (logkow) are especially important in determining the approach of SPE for efficient sample clean-up for further chromatographic analysis of chlorophenoxy acid herbicide in water samples

Potentiometric application of boron- and phosphorus-doped glassy carbon electrodes

Acomparative study was carried out of the potentiometric application of boronand phosphorus-doped and undoped glassy carbon samples prepared at the same heat treatment temperature (HTT 1000°C). The electrochemical activities of the obtained electrode materials were investigated on the example of argentometric titrations. It was found that the electrochemical behaviour of the doped glassy carbon samples are very similar to a Sigri (undoped) glassy carbon sample (HTT 2400°C). The experiments showed that the potentiometric response depends on the polarization mode, the nature of the sample, the pretreatment of the electrode surface, and the nature of the supporting electrolyte. The amounts of iodide, bromide, and of chloridewere determined to be 1.27 mg, 0.80 mg and 0.54 mg, respectively, with a maximum relative standard deviation of less than 1.1%. The obtained results are in good agreement with the results of comparative potentiometric titrations using a silver indicator electrode. The titrationmethod was applied to the indirect determination of pyridoxine hydrochloride, i.e., vitamin B6