J. Vicente

Voltammetric determination of methyl parathion, ortho, meta and para nitrophenol with a carbon paste electrode modified with C18

SummaryThe determination of methyl-parathion (MPT), ortho (ONP), meta (MNP) and para nitrophenol (PNP) has been studied by differential pulse voltammetry with a carbon-paste electrode modified with 50% (w/w) of C18. A study of the influence of the pH in the preconcentration cell and the measurement cell was carried out for an electrode with 50% modifier and an accumulation time of 5 min. The voltammograms were recorded with a sweep rate of 40 mV s−1 and a pulse amplitude of 50 mV. With the optimum conditions of pH for both of the steps, various other variables were studied. The variables for each compound were optimized and the possibility of application to the determination of a mixture of the four compounds was investigated. The determination limits found for all the compounds are: 2 ng ml−1 for ONP, 5 ng ml−1 for MNP, 4.3 ng ml−1 for PNP and 7.9 ng ml−1 for MPT. The method was applied to samples of a small lake which gathers rain water and water filtered from land on which cereals are grown.

Voltammetric determination of linuron at a carbon-paste electrode modified with sepiolite

The determination of linuron by differential pulse voltammetry with a carbon-paste electrode modified with 20% w/w sepiolite has been studied. The linuron is preconcentrated under open-circuit conditions at pH 2.0. With 0.01M potassium nitrate at pH 1.7 in the measurement cell, a sweep rate of 30 mV/sec and a pulse amplitude of 100 mV, an oxidation wave with a peak potential of 1.2 V is obtained. Under these conditions, determination limits of 75 ng/ml have been obtained, with a relative error of +2.8% and a relative standard deviation of 8.0%. The method has been applied to the direct determination of linuron in river water with no previous separation of the pesticide. Determination in sea-water is not possible, as chloride interferes at high concentration.

Determination of tetramethrin (neo-pynamin) by differential pulse voltammetry with a carbon paste electrode modified with sepiolite

SummaryA method is described for the determination of tetramethrin (neo-pynamin) by differential pulse voltammetry with a carbon paste electrode modified with 10% (w/w) sepiolite. Preconcentration was carried out under open circuit conditions in 0.01 mol/l acetic acid/potassium acetate medium at pH 5.3 over 10 min, recording the voltammogram in 0.01 mol/l of KH2PO4/K3PO4 at pH 12. This led to the appearance of a peak at −1.32 V against SCE at 40 mVs−1 and a pulse amplitude of 100 mV. Under these conditions determination limits of 45 ng ml−1 were achieved. The method was applied to the determination of tetramethrin in soil and water samples.

Determination of clonazepam by flow injection analysis

Clonazepam was determined by flow injection analysis using voltammetric (glassy carbon electrode) and spectrophotometric detectors. The sample solution (200 µl of 6.3–31.5 µg ml–1 and 250 µl of 0.6–31.5 µg ml–1 for voltammetric and spectrophotometric detection, respectively), was injected into the carrier stream, which was 0.1 M phosphate buffer solution (pH 7.0) containing 10%V/V of methanol. Sampling rates of 120 per hour were achieved, with high reproducibility of measurements (relative standard deviations below 1.1%). The systems were applied to the determination of clonazepam in pharmaceutical formulations and human urine.

Serum ferritin as prognostic marker in classical Hodgkin lymphoma treated with ABVD-based therapy

Ferritin levels might correlate with disease activity in classical Hodgkin lymphoma (cHL). We analyzed the prognostic significance of the ferritin value at diagnosis in 173 cHL patients treated with ABVD between 2003 and 2013. The 5-year overall survival (OS) and progression-free survival (PFS) probabilities were 80% and 64%, respectively. Patients with ferritin ≥ 350 μg/l [high ferritin group (HF), n = 62] were more likely to have advanced stage disease, B-symptoms and higher International Prognostic Score (IPS) compared with patients with ferritin < 350 μg/l [low ferritin group (LF), n = 111]. The complete remission (CR) rate and 5-year PFS and OS probabilities were lower in HF vs. LF patients (69% vs. 89%, p = 0.025; 40% vs. 78%, p < 0.001; 61% vs. 90%, p = 0.001; respectively). Multivariate analysis revealed that advanced stage (p = 0.001) and ferritin levels ≥ 350 μg/l (p = 0.002) were independent predictors for PFS. In conclusion, the ferritin level at diagnosis is a useful prognostic marker for cHL.

Isomeric Transformation Of 4-Aminobiphenyl by U.V. Radiation and its Influence on the Determination by Flow Injection Analysis with Amperometric and Spectrophotometric Detection.

Abstract Two flow-injection methods for the determination of 4-aminobiphenyl by amperometry (glassy carbon electrode) and spectrophotometry are proposed. A sample volume of 200 or 400 μl containing an analyte concentration of 0.1–1.0 μg ml−1 or 0.8–24.0 μg ml−1 for amperometric or spectrophotometric detection, respectively, is injected into a carrier stream containing 0.04 or 0.02 M Britton-Robinson buffer at pH 10.0 or 8.0, respectively. The throughput thus achieved is 200 (amperometry) and 240 samples/h (spectrophotometry) and the relative standard deviation less than 2.5% and 4.2% respectively. Both methods were applied to the determination of 4-aminobiphenyl in commercially available, legally permitted food colouring additive.

Electrochemical analysis of the alanine phenylthiohydantoin derivative by cathodic stripping voltammetry

A square-wave cathodic stripping voltammetry method for alanine determination as its phenylthiohydantoin (PTH-alanine) derivative is developed. To this end, all the chemical and instrumental variables affecting the determination of PTH-alanine are optimized. From studies of the mechanisms governing the electrochemical response of PTH-alanine, it was concluded that it is an electrochemically irreversible system with a diffusive-adsorptive reduction phenomenon. Under optimal conditions, the variation of analytical signal (I(p)) with PTH-alanine concentration is linear in the 2.4x10(-8)-4.8x10(-7) M range, with a LOD of 1.2x10(-8) M and a LOQ of 4.2x10(-8) M, a RSD (%) less than 11%, and a E(r) (%) less than 10%. The optimized method was applied to the determination of PTH-alanine obtained from a synthetic protein after Edman reaction and the results were corroborated by high-performance liquid chromatography with UV detection.

Determination of 2-amino-5-nitrothiazole by square-wave cathodic stripping voltammetry

An electrochemical method has been developed for the detection and determination of 2-amino-5-nitrothiazole (2,5-ANT) by adsorption square-wave voltammetric stripping. The best sensitivity/resolution ratio was obtained by adsorption at pH 8.0 using a phosphate buffer, an accumulation potential of −10 mV (vs. Ag/AgCl 3 mol/l) and an accumulation time of 15 s. Under these conditions, the proposed method provides a linear electrode response over the 2,5-ANT concentration range 5–300 ng ml−1, and a detection and determination limit of 4 and 7.5 ng ml−1, respectively. The method was applied to the determination of 2,5-ANT in bacon.