RESEARCH BACKGROUND: The objective of this paper is to introduce an instrumentally simple analytical tool for determination of cocoa solid content in chocolates. This electroanalytical method is based on amperometric oxidation of all present antioxidants in chocolates at boron-doped diamond electrode (BDDE) that is integrated in a flow injection analysis (FIA) wall-jet electrode system. EXPERIMENTAL APPROACH: As part of optimisation, thirteen commonly occurring antioxidants were investigated using cyclic voltammetry at the BDDE in 0.1 mol/L phosphate buffer with different methanol (MeOH) content. Working parameters, such as MeOH volume fraction, flow rate and detection potential, were optimised. Principally, the height of the oxidation peak (current response) representing the oxidation of the sum of antioxidants (total antioxidant content; TAC) was expressed as Trolox equivalents. RESULTS AND CONCLUSIONS: For analytical purpose, a linear range from 5 to 100 mg/L described by regression equation and characterised by high correlation coefficient R2=0.9994 was achieved. Obtained high positive correlation between the determined values of Trolox equivalent antioxidant capacity (TEAC) and cocoa mass fractions characterised by correlation coefficient of 0.9187 for eight randomly selected samples (one white, two milk, and five dark chocolates) confirmed that cocoa solids represent the main source of antioxidants (reducing agents). NOVELTY AND SCIENTIFIC CONTRIBUTION: The research demonstrates that TEAC values could be considered as an additional marker of cocoa content in the chocolate analysis to the commonly used theobromine (authenticity of food products). The developed FIA could therefore serve as simple analytical tool in the food quality control.
- Klíčová slova
- Trolox equivalent antioxidant capacity, amperometry, boron-doped diamond electrode, cocoa mass fraction in chocolate, flow injection analysis,
- Publikační typ
- časopisecké články MeSH
In this article, some new approaches to characterize the carbon paste mixtures and the respective carbon paste electrodes (CPEs) are presented, discussed, and critically evaluated. Particular attention has been paid to the changes of the ohmic resistance, relative to the dependence on composition of the CPE, the materials used, the time, and the position of storage. Four types of carbon pastes were examined, and for the interpretation of experimental data, a new simple model of "close-packing of spheres" has been applied. This model resembles the percolation theory for solid matter. In our case, however, it is possible to explain not only the "bent" or "broken" shape of the dependence of the electrode resistance upon the binder:carbon ratio and the corresponding electrochemical current response, but also differences caused by various material used and three various effects observed during the electrode aging. Furthermore, the report presents the significance of practical utilization of the recently introduced carbon paste index (denoted as chi(CPE)), which is a qualitative hitherto unused factor based on the evaluation of cyclic voltammograms for standard redox systems (e.g., [Fe(CN)(6)](3-/4-)) and specifying the electrochemical properties of a CPE. Some problems connected with homogeneity and stability of carbon pastes, their handling, storage, or eventual aging effects are also discussed.
- MeSH
- elektrická impedance MeSH
- elektrochemie * MeSH
- elektrody * MeSH
- uhlík chemie MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- uhlík MeSH
Hydrogen peroxide and nicotinamide adenine dinucleotide (NADH) may be determined amperometrically using screen-printed electrodes chemically modified with iron(III) hexacyanoosmate(II) (Osmium purple) in flow injection analysis (FIA). The determination is based on the exploitation of catalytic currents resulting from the oxidation/reduction of the modifier. The performance of the sensor was characterized and optimized by controlling several operational parameters (applied potential, pH and flow rate of the phosphate buffer). Comparison has been made with analogous complexes of ruthenium (Ruthenium purple) and iron (Prussian blue). Taking into account the sensitivity and stability of corresponding sensors, the best results were obtained with the use of Osmium purple. The sensor exhibited a linear increase of the amperometric signal with the concentration of hydrogen peroxide in the range of 0.1-100 mg L(-1) with a detection limit (evaluated as 3sigma) of 0.024 mg L(-1) with a R.S.D. 1.5% for 10 mg L(-1) H2O2 under optimized flow rate of 0.4 mL min(-1) in 0.1M phosphate buffer carrier (pH 6) and a working potential of +0.15 V versus Ag/AgCl. Afterwards, a biological recognition element--either glucose oxidase or ethanol dehydrogenase--was incorporated to achieve a sensor facilitating the determination of glucose or ethanol, respectively. The glucose sensor gave linearity between current and concentration in the range from 1 to 250 mg L(-1) with a R.S.D. 2.4% for 100 mg L(-1) glucose, detection limit 0.02 mg L(-1) (3sigma) and retained its original activity after 3 weeks when stored at 6 degrees C. Optimal parameters in the determination of ethanol were selected as: applied potential +0.45 V versus Ag/AgCl, flow rate 0.2 mL min(-1) in 0.1 M phosphate buffer carrier (pH 7). Different structural designs of the ethanol sensor were tested and linearity obtained was up to 1000 mg L(-1) with a maximum R.S.D. of 5.1%. Applications in food analysis were also examined.
- MeSH
- alkoholdehydrogenasa analýza MeSH
- alkoholické nápoje analýza MeSH
- analýza potravin metody MeSH
- biosenzitivní techniky metody MeSH
- elektrochemie metody MeSH
- enzymy imobilizované MeSH
- ethanol analýza MeSH
- ferrokyanidy chemie MeSH
- glukosa analýza MeSH
- glukosaoxidasa analýza MeSH
- katalýza MeSH
- NAD chemie MeSH
- oxid osmičelý chemie MeSH
- peroxid vodíku chemie MeSH
- sloučeniny ruthenia chemie MeSH
- železité sloučeniny chemie MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- srovnávací studie MeSH
- Názvy látek
- alkoholdehydrogenasa MeSH
- enzymy imobilizované MeSH
- ethanol MeSH
- ferric ferrocyanide MeSH Prohlížeč
- ferrokyanidy MeSH
- glukosa MeSH
- glukosaoxidasa MeSH
- iron hexacyanoosmate MeSH Prohlížeč
- NAD MeSH
- oxid osmičelý MeSH
- peroxid vodíku MeSH
- sloučeniny ruthenia MeSH
- železité sloučeniny MeSH
A new stripping method for the determination of arsenic in water samples with a gold film-plated carbon paste electrode has been developed for the use in constant current stripping analysis (CCSA). In the novelized procedure, differentiation between As(III) and chemically pre-reduced As(V), the effect of Cu(II) on the response of arsenic, and the stability of sample solutions were studied in detail. Compared to the voltammetric approach, the method utilizing CCSA offers a more rapid procedure with improved analytical characteristics such as reproducibility, selectivity over the Cu(II) ions, or lower detection limit (3 ppb for As(III) and 0.5 ppb for As(V), respectively). The possibilities of the optimized method are demonstrated by determinations of As(III), As(V), and total arsenic in samples of polluted river water.
- Publikační typ
- časopisecké články MeSH
