Ignacio Naranjo Rodríguez

Use of a carbon paste modified electrode for the determination of 2-nitrophenol in a flow system by differential pulse voltammetry

The electrochemical reduction of 2-nitrophenol at a bentonite-modified carbon paste electrode by rapid scan differential pulse voltammetry in a flow system is studied, and a method for the direct voltammetric determination in sea water is proposed. A formic acid/sodium formate buffer solution of pH 4 was used as carrier. The potential range and the scan rate were selected according to the response of the analyte. 2-Nitrophenol showed a reduction potential within the cathodic range for the carbon electrode; a well-defined single peak was obtained. It is not necessary to remove the paste from the electrode after each new injection because the surface activity of the electrode remained constant at least during the time of a single complete analysis. A linear relationship between peak height and concentration was obtained in the range 0.05–5 mg l−1 with a detection limit of 0.02 mg l−1 and a relative standard deviation of 3.6%. Several chloro- and nitrophenols were tested to assess their influence on 2-nitrophenol signals.

Use of a bentonite-modified carbon paste electrode for the determination of some phenols in a flow system by differential-pulse voltammetry

The electrochemical behaviour of some phenols (methyl-, chloro- and nitrophenols) included in the US Environmental Protection Agency List of Priority Pollutants at a bentonite-modified carbon paste electrode in a flow system was studied. A fixed proportion of artificial sea-water was used in the sample solution so that the applicability of the methodology to marine environments could be tested. Amounts of bentonite from 5 to 10% were used. For methyl- and nitrophenols, a good stability of the electrode surface activity was observed after a series of repeated injections, with relative standard deviations between 0.40 and 2.98% (n = 16). Recovery studies were carried out on real sea-water samples spiked with 0.5 or 2.5 mg l - 1 of the pollutants; recoveries from 95.4 to 101.1% were obtained.

Voltammetric determination of 2-nitrophenol at a bentonite-modified carbon paste electrode

A bentonite-modified carbon paste electrode has been applied to the determination of 2-nitrophenol by differential pulse voltammmetry. The electrochemical reduction of 2-nitrophenol at −0.8 V is carried out in an artificial sea water-formic acid/sodium formate medium at pH 4. The peak height was found to be dependent on the pH over the range 2–11; the presence of a secondary process was observed in the pH range 8–11. The peak potential showed a dependence on pH, with two linear regions with different slopes. A linear relationship between peak intensity and concentration was obtained in the range 0.07–10 mgl−1, with a detection limit of 0.03 mg 1−1 and a coefficient of variation of 1.3% at 5 mg 1−1. The effects of organic and inorganic species on the 2-nitrophenol determination were studied with a view to testing the resolution of the voltammetric technique. The proposed method has been applied to sea water samples with good results.

Polarographic study of acrolein and its determination by flow injection with amperometric detection at a mercury electrode.

Abstract A study of the electrochemical behavior of acrolein at a dropping mercury electrode using different polarographic techniques is described. Theoretical studies of the reversibility of the wave of acrolein were carried out using two different polarographic techniques: direct current tast and differential pulse. Differential pulse polarography may be used to determine acrolein concentration in a Britton-Robinson buffer solution of pH 10 in the ranges 2 × 10−710−8 and 5 × 10−8–10−4 mol dm−3 and a coefficient of variation of 1.7% for a concentration of 10−5mol dm−3. A flow injection method with amperometric detection at a potential of −1.4V using a mercury electrode is also described. Before each injection, any drop hanging from the tip of the capillary needs to be dislodged and a new electrode drop dispensed; three different drop sizes were tested. A linear relationship between peak intensity and acrolein concentration was obtained in the range 10−5-10−7 mol dm−3, with a detection limit of 9.8 × 10−8 mol dm− 3 and a coefficient of variation of 2.9% for a 2 × 10−7 mol dm−3 concentration. Several organic and inorganic species were tested in order to ascertain whether they interfered with the signal for acrolein. The proposed methods were applied to the determination of acrolein in seawater samples.