A. Guiberteau

Indirect voltammetric determination of carbaryl and carbofuran using partial least squares calibration

Abstract A differential pulse voltammetric method is proposed for the determination of the carbamate pesticides carbaryl and carbofuran, based on the anodic peaks observed following their alkaline hydrolysis (formation of phenol derivatives). Linear relationships between the oxidation peaks and concentration were obtained in the ranges 5 × 10 −7 to 10 −4 M for carbaryl and 5 × 10 −7 to 5 × 10 −5 M for carbofuran, the relative standard deviations being 1.62 and 1.86%, respectively. The method was applied to the determination of these compounds in formulations. Different chemometric methods (PLS-1, PLS-2 and CLS) were examined for the resolution of the overlapped peaks of both compounds and their determination in mixtures. The best results were obtained with the PLS-1 method, which was applied to determine both compounds in river water samples.

Study and determination of the pesticide Imidacloprid by square wave adsorptive stripping voltammetry

An electroanalytical method has been developed for the detection and determination of the pesticide 1-(6-chloro-3-pyridylmethyl)-N-nitroimidazolidin-2ylidineamine (Imidacloprid) by square wave adsorptive stripping voltammetry on a hanging mercury drop electrode (HMDE) in aqueous solution with Britton-Robinson buffer as supporting electrolyte. The best adsorption conditions were found to be pH 7.2, an accumulation potential of -1050 mV (HMDE vs. Ag/AgCl-KCl 3M) and an accumulation time of 50 s. Effects of square wave frequency, step potential and pulse amplitude were examined for the optimization of instrumental conditions. Calibration curve is linear in the range 2 x 10(-8)-5 x 10(-7) M with a detection limit of 1.6 x 10(-8) M (Clayton et al. method). The method is applied to the direct determination of the pesticide in river water samples. For a concentration of 4.1 x 10(-8) M a recovery value of 104+/-3% is obtained. In order to determine lower concentrations, previous preconcentration and cleaning steps (liquid-liquid extraction into CH(2)Cl(2) and solid-phase extraction with Sep-Pak C(18) cartridges) are carried out. The recovery values obtained in spiked river water are 89+/-4% for 2 x 10(-8) M and 90+/-6% for 8 x 10(-9) M.

Comparison of chemometric methods : Derivative ratio spectra and multivariate methods (CLS, PCR and PLS) for the resolution of ternary mixtures of the pesticides carbofuran carbaryl and phenamifos after their extraction into chloroform

The resolution of a ternary mixture of the pesticides carbofuran, carbaryl and fenamiphos in heterogeneous media (after extraction into CHCl 3 ) by the application of different chemometric methods such as derivative ratio spectra (DD), classical least squares (CLS), principal components regression (PCR) and partial least squares (PLS) was performed. CLS, PCR and PLS were applied with the absorption spectra or with their transformations (logarithm or first or second derivative). Also, different data preprocessing algorithms were examined. Second-derivative spectra were used for DD. A comparison of the results obtained in the analysis of these compounds by the different methods was made by using analysis of variance (ANOVA). These methods were successfully applied to the analysis of spiked river water samples.

Resolution by polarographic techniques of the ternary mixture of captan, captafol and folpet by using PLS calibration and artificial neuronal networks.

The simultaneous polarographic determination of the ternary mixture of captan-captafol and folpet is studied. The polarographic signals of these compounds in their mixture show a high overlapping. For this reason different chemometric methods such as PLS, PCR and artificial neuronal network (ANN) have been utilized for the simultaneous determination of these compounds in mixtures. The calibration model is built from solutions containing river water of known pesticide concentrations and the signals obtained by Sampled DC and DPP (differential pulse polarography) have been used. The analysis of both synthetic and real samples (river water) has been carried out by PLS with satisfactory results in most cases. It is possible to determine 0.25 ppm of each pesticide in river water samples after a preconcentration step by extraction into diethyl ether. ANN has also been applied to improve the results obtained by the PLS tool when the sampled DC current is recorded or when liquid-solid extraction with C18 cartridges is performed.

Use of Neural Networks and Diode-Array Detection to Develop an Isocratic HPLC Method for the Analysis of Nitrophenol Pesticides and Related Compounds

SummaryWe have used an artificial neural network to optimize the composition of the mobile phase for an isocratic HPLC method for the analysis of nitrophenol pesticides and related compounds, on the basic of different response functions, and have compared the results with those obtained by application of response-surface methodology. These studies resulted in the selection the mobile phase 10:30:15:45 methanol-acetonitrile-tetrahydrofuran-buffer solution (0.1m acetic acid and 0.1m sodium perchlorate); the flow-rate was 1 mL min−1. Under these conditions a chromatogram showing twelve well-resolved peaks was obtained in 14 min. Although the peaks corresponding to ethylparathion and medinoterb acetate overlapped severely, it was possible, by use, of a diode-array spectrophotometer for detection, and by combining the absorbance measured at different wavelengths as the signal, to separate the peaks corresponding to one or other of the compounds. Calibration plots were constructed for the concentration range 2–10 ppm. Detection limits, calculated by the method of Clayton et al., were approximately 0.32–0.69 ppm. The method has been applied to the analysis of these compounds in fortified river water samples, after previous preliminary preconcentration by solid-liquid extraction on a C18 cartridge.

Rapid and Sensitive Determinations of Carbaryl, Carbofuran and Fenobucarb by Liquid Chromatography with Electrochemical Detection

A rapid and sensitive procedure is described for the determination of the N-methylcarbamates pesticides, carbaryl, carbofuran and fenobucarb, by liquid chromatography. The pesticides are previously hydrolyzed, in a separate step, to their phenolic derivatives, which, after the separation in a high speed column in a time lower than 2.5 min, are detected in a high sensitivity amperometric cell at a potential of +0.6 V. The method presents detection limits around 0.7 ppb and has been satisfactorily applied to the analysis of these compounds in spiked river water samples.

Rapid determination of α-endosulfan and β-endosulfan in formulations and potatoes by high performance liquid chromatography

Abstract A new and rapid method is described to determine α- and β-endosulfan in formulations and potatoes by reversed phase high performance liquid chromatography. A mobile phase water:acetonitrile (35:65) was found to be the optimum to carry out the analytical separation and photometric detection at 210 nm was selected to perform the determination of the mixture of stereoisomers.

SPECTROPHOTOMETRIC DETERMINATION OF THE FUNGICIDE CAPTAN

A spectrophotometric method for the determination of the fungicide captan has been developed based on its reaction with thiosemicarbazide. The absorbance was measured at 315 nm. The effects of the proportion of water, thiosemicarbazide concentration, pH and temperature on this reaction was studied to select the best chemical conditions. The calibration graph was obtained between 1.2 and 30 ppm and the detection limit is 0.5 ppm. The RSD (n=10) was 1.34%. Possible interference of various pesticides was examined. The method was applied to the determination of captan in agrochemical formulations. Results agree well with the labelled values and also with results that were obtained by a polarographic method.