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A simple hydrodynamic chronoamperometric method based on the application of an unmodified carbon paste electrode (CPE) and bulk-modified with different contents of MnO2 was investigated for the determination of H2O2. The optimized method involving the CPE with 5% of MnO2 was applied for the determination of the H2O2 consumption in samples of groundwater from the Central Banat region (Province of Vojvodina, Serbia) treated by the Fenton (Fe(2+) and H2O2) and Fenton-like (Fe(3+) and H2O2) reagents to remove natural organic matter at different initial concentrations of iron species, and of their ratios to the initial concentration of H2O2. Under optimized conditions, with a working potential of 0.40V vs. the saturated calomel electrode and a phosphate buffer solution (pH 7.5) as supporting electrolyte, the method enabled the quantitation of H2O2 in the concentration interval from 1.4 to 65 μg mL(-1) with a relative standard deviation of less than 10%. The results obtained for the H2O2 consumption are in good agreement with those obtained by parallel measurements related to the efficiency of organic matter removal., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Abstract: The present work describes the preparation of a simple, sensitive, and reliable H2O2 sensor made from carbon paste surface modified with a composite of platinum nanoparticles (< 5 nm) on graphitized carbon (Pt-C, 10% Pt on Vulcan XC72) by simply drop-coating. The unmodified carbon paste electrode (CPE) and the modified one (Pt-C/CPE) were characterized by scanning electron microscopy in combination with energy-dispersive X-ray spectrometry and by cyclic voltammetry. The Pt-C/CPE showed remarkable electrocatalytic properties toward the electrochemical redox reaction of H2O2 compared to CPE in phosphate (0.1 mol dm−3; pH 7.50) and acetate (0.1 mol dm−3; pH 4.50) buffer supporting electrolytes. Amperometry of H2O2 in the concentration range from 0.15 to 1.45 µg cm−3 with the Pt-C/CPE showed acceptable linearity, while the obtained values of LOQs were 0.06 µg cm−3 (pH 7.50, working potential 0.20 V, stirred solution) and 0.10 µg cm−3 (pH 4.50, working potential 0.50 V). The proposed analytical methods were applied to the determination of the H2O2 content in commercially available personal care products: disinfection (pH 7.50) and contact lens cleaning (pH 4.50) solutions. In both cases, obtained amperometric results are in good agreement with those measured by the traditional spectrophotometric method and with H2O2 concentration declared by producers. The Pt-C/CPE was also tested for monitoring of the H2O2 residual concentration in contact lens solution during its neutralization/decomposition process by solid Pt catalyst. At 6 h of neutralization treatment, 24.68 μg cm−3 of the H2O2 was determined which is below allowed H2O2 concentration concerning the limit of eye irritation.Graphical abstract: [ABSTRACT FROM AUTHOR]

In this comparative study a traditional paraffin oil and graphite powder based carbon paste electrode (CPE) was surface modified with multiwalled carbon nanotubes (MWCNTs) and with composites of MnO 2 -MWCNT or Pt-MWCNT by drop coating method to prepare simply, sensitive and reliable voltammetric sensors either for the determination of H 2 O 2 or after additional modification of the appropriate sensor surfaces with glucose oxidase (GOx) for the determination of glucose via H 2 O 2 in selected samples. The scanning electron microscopic characterization in combination with energy dispersive X-ray spectrometry of the composite materials confirmed that the mediators, MnO 2 and Pt particles, are randomly distributed on the surface of the MWCNTs, and represent nearly 5% (m: m) of the composites expressed as Pt and Mn. Cyclic voltammetric (CV) investigations were performed in acetate (pH 4.50), phosphate (pH 7.50) and borate (pH 9.18) buffers to characterize the basic electrochemical behaviors and to select the working potentials suitable for hydrodynamic chronoamperometric (HA) determination of H 2 O 2 under different circumstances. The CV responses showed that in slightly alkaline media all investigated electrodes, i.e., CPEs unmodified and modified with plain MWCNTs and MWCNTs based composites are in principle applicable, but with different efficiency at different potentials, with favorable reduction and acceptable oxidation of H 2 O 2 at the Pt-MWCNT/CPE and predominately oxidation at the MnO 2 -MWCNT/CPE. The reproducibility of the responses with the MnO 2 -MWCNT/CPE is poor, but can be improved by electrochemical conditioning. The latter one performed well in alkaline supporting electrolyte (pH 9.18), while in the case of the Pt-MWCNT/CPE the signals are much better established in slightly acidic medium (pH 4.50). The analytical methods were optimized, mainly with the Pt-MWCNT/CPE as the preferential electrode, in terms of pH and working potential for the HA determination of H 2 O 2 in spiked milk samples including the development of an appropriate sample treatment procedure. This electrode was also used for the design of a very simple and reliable first generation oxidase biosensor for determination of glucose content in human infusion via its enzymatic reaction product H 2 O 2 . [ABSTRACT FROM AUTHOR]

In this work, the applicability of screen printed carbon electrode bulk modified with MnO 2 as a mediator was investigated for hydrodynamic chronoamperometric determination of the H 2 O 2 content during the Fenton (Fe 2 + , H 2 O 2 ) and the catalytic, visible light-assisted, photo-Fenton (Fe 2 + , H 2 O 2, hν) based removal of the worldwide used neonicotinoid insecticide acetamiprid which has a pyridine ring and a cyano-imine group in its basic skeleton. For the optimisation of the analytical method cyclic voltammetric, differential pulse voltammetric and hydrodynamic chronoamperometric experiments were performed in model solutions containing the phosphate buffer supporting electrolyte pH 7.5, H 2 O 2 , and/or Fe 2 + and acetamiprid. Under optimized conditions at the working potential of 0.40 V vs. saturated calomel electrode in the slightly alkaline supporting electrolyte, electrocatalytic hydrodynamic chronoamperometric determination of H 2 O 2 showed a linear dynamic range from 0.01–1.24 mM, and the relative standard deviation did not exceed 4.2%. In the investigated samples (after appropriate pH adjustment, filtering, and storage of the deep-frozen sample with defrosting immediately before the measurements) the H 2 O 2 contents were determined from the hydrodynamic chronoamperometric curves by the standard addition method. Parallel HPLC-DAD measurements were performed to monitor the concentration/removal of acetamiprid. In the case of the photo-Fenton process (initial concentrations: 0.31; 2.0 and 3.0 mM of acetamiprid, Fe 2 + and H 2 O 2 , respectively) after 10 min of irradiation H 2 O 2 was consumed, while during the Fenton process acetamiprid was removed after 20 min of treatment and around 10% of the initial concentration of the H 2 O 2 remained still unused. [ABSTRACT FROM AUTHOR]