Factorial design optimization of experimental variables in preconcentration of carbamates pesticides in water samples using solid phase extraction and liquid chromatography-electrospray-mass spectrometry determination.

An experimental design was applied for the optimization of extraction process of carbamates pesticides from surface water samples. Solid phase extraction (SPE) of carbamates compounds and their determination by liquid chromatography coupled to electrospray mass spectrometry detector were considered. A two level full factorial design 2(k) was used for selecting the variables which affected the extraction procedure. Eluent and sample volumes were statistically the most significant parameters. These significant variables were optimized using Doehlert matrix. The developed SPE method included 200mg of C-18 sorbent, 143.5 mL of water sample and 5.5 mL of acetonitrile in the elution step. For validation of the technique, accuracy, precision, detection and quantification limits, linearity, sensibility and selectivity were evaluated. Extraction recovery percentages of all the carbamates were above 90% with relative standard deviations (R.S.D.) in the range of 3-11%. The extraction method was selective and the detection and quantification limits were between 0.1 and 0.5 µg L(-1), and 1 and 3 µg L(-1), respectively.

Trace lead analysis based on carbon-screen-printed-electrodes modified via 4-carboxy-phenyl diazonium salt electroreduction.

This paper describes the use of 4-carboxyphenyl-grafted screen-printed carbon electrodes (4-CP-SPEs) for trace lead analysis. These novel and simple use of electrodes were easily prepared by the electrochemical reduction of the corresponding diazonium salt. Pb detection was then performed by a three-steps method in order to avoid oxygen interference: (i) immersion of the grafted screen-printed electrode (SPE) in the sample and adsorption of Pb(II), (ii) reduction of adsorbed Pb(II) by chronoamperometry (CA), and (iii) oxidation of Pb by Anodic Square Wave Voltammetry (SWV). The reoxidation response was exploited for lead detection and quantification. In order to optimize the analytical responses, the influence of the adsorption medium pH and the adsorption time were investigated. Moreover, an interference study was carried out with Cu(II), Hg(II), Al(III), Mn(II), Zn(II), Cd(II) and no major interference can be expected to quantify Pb(II). The described method provided a limit of detection and a limit of quantification of 1.2 × 10(-9)M and 4.1 × 10(-9)M, respectively. These performances indicate that the 4-CP-SPE could be considered as an efficient tool for environmental analysis.

Application of Doehlert matrix to determine the optimal conditions of electrochemical treatment of tannery effluents.

The oxidation of organic and inorganic pollutants present in tannery effluents has been realised by electrochemical way. The influence of the electrochemical reactor parameters was carried out by the use of Doehlert matrix. The obtained results have shown that the current intensity and the electrolysis time were the main influent parameters on the removal ratio of chemical oxygen demand (COD), total organic carbon (TOC), electrochemical oxidation of trivalent chromium and sulphite ions.

Degradation of Acid Orange 7 by electrochemically generated (*)OH radicals in acidic aqueous medium using a boron-doped diamond or platinum anode: a mechanistic study.

A comparative study of the degradation of Acid Orange 7 (AO 7) aqueous solutions in acidic medium of pH 3.0 by electro-Fenton process using Pt or boron-doped diamond (BDD) anode was reported. The oxidative degradation of AO 7 by electrochemically generated hydroxyl radicals follows a pseudo-first order kinetic with a similar rate constant with BDD or Pt anode. The absolute rate constant of the AO 7 hydroxylation reaction was determined as (1.10+/-0.04)x10(10)M(-1)s(-1) by using the competition kinetic method. The comparative study of TOC measurements during electro-Fenton treatment showed a higher mineralization rate with BDD than Pt anode at the first hours of electrolysis because of the higher oxidizing power of this anode. The electro-Fenton degradation of AO 7 was followed by monitoring the formation and evolution of aromatic intermediates which are oxidized to aliphatic carboxylic acids before mineralization (transformation to CO(2) and inorganic ions, i.e. sulphate, nitrate and ammonium). The follow-up of the solution toxicity evolution shows the formation of intermediates more toxic than AO 7 and the connection between toxicity and aromaticity. A mineralization reaction pathway of AO 7 by electro-Fenton degradation involving all the intermediates identified was proposed.