Ľubomír Švorc

Flow-injection amperometric determination of glucose using a biosensor based on immobilization of glucose oxidase onto Au seeds decorated on core Fe3O4 nanoparticles

An amperometric biosensor based on chemisorption of glucose oxidase (GOx) on Au seeds decorated on magnetic core Fe3O4 nanoparticles (Fe3O4@Au) and their immobilization on screen-printed carbon electrode bulk-modified with manganese oxide (SPCE{MnO2}) was designed for the determination of glucose. The Fe3O4@Au/GOx modified SPCE{MnO2} was used in a flow-injection analysis (FIA) arrangement. The experimental conditions were investigated in amperometric mode with the following optimized parameters: flow rate 1.7 mL min(-1), applied potential +0.38 V, phosphate buffer solution (PBS; 0.1 mol L(-1), pH 7.0) as carrier and 3.89 unit mm(-2) enzyme glucose oxidase loading on the active surface of the SPCE. The designed biosensor in FIA arrangement yielded a linear dynamic range for glucose from 0.2 to 9.0 mmol L(-1) with a sensitivity of 2.52 µA mM(-1) cm(-2), a detection limit of 0.1 mmol L(-1) and a quantification limit of 0.3 mmol L(-1). Moreover, a good repeatability of 2.8% (number of measurements n=10) and a sufficient reproducibility of 4.0% (number of sensors n=3) were achieved. It was found that the studied system Fe3O4@Au facilitated not only a simpler enzyme immobilization but also provided wider linear range. The practical application of the proposed biosensor for FIA quantification of glucose was tested in glucose sirup samples, honeys and energy drinks with the results in good accordance with those obtained by an optical glucose meter and with the contents declared by the producers.

Voltammetric determination of penicillin V in pharmaceutical formulations and human urine using a boron-doped diamond electrode

Simple, sensitive and selective differential pulse voltammetric method for determination of penicillin V on a bare (unmodified) boron-doped diamond electrode has been developed. Penicillin V provided highly reproducible and well-defined irreversible oxidation peak at very positive potential of +1.6V (vs. Ag/AgCl). The optimum experimental conditions for oxidation of penicillin V were achieved in acetate buffer solution (pH 4.0). The modulation amplitude of 0.1V, modulation time of 0.05s and scan rate of 0.05Vs(-1) were selected as optimum instrumental parameters for differential pulse voltammetry. Linear response of peak current on the concentration in the range from 0.5 to 40μM with coefficient of determination of 0.999, good repeatability (RSD of 1.5%) and detection limit of 0.25μM were observed without any chemical modifications and electrochemical surface pretreatment. The effect of possible interferents such as stearic acid, glucose, urea, uric acid and ascorbic acid appeared to be negligible which evidently proved the good selectivity of method. The practical analytical utility of proposed method was demonstrated by determination of penicillin V in pharmaceutical formulations (tablets) and human urine samples with satisfactory recoveries (from 98 to 101% for tablets and 97 to 103% for human urine).

Increase of biogas production from pretreated hay and leaves using wood-rotting fungi

Wood-decaying mushrooms can be applied for the pretreatment of lignocellulosic substrates such as leaves, hay and straw. The use of wood-decaying fungus Auricularia auricula-judae for the decomposition of sweet chestnut (Castanea sativa) leaves and hay is discussed in the proposed paper. Such pretreated substrate was employed in the anaerobic processes for biogas production. Comparison of pretreated and non-pretreated substrate revealed that an increase of 15 % in the biogas production can be achieved using the pretreated substrate. Composition of organic compounds in the sludge during the anaerobic process was identified by HPLC. The obtained results show that the utilization of pretreated leaves and hay leads to a gradual increase of the concentration of formic, acetic, and volatile fatty acids as well as to the formation of some aldehydes, ketones, and alcohols.

Self-assembled sensor based on boron-doped diamond and its application in voltammetric analysis of picloram

A self-assembled sensor based on a boron-doped diamond was investigated as a sensitive tool for voltammetric analysis of a member of a pyridine herbicide family - picloram. A cyclic voltammetry and a differential pulse voltammetry were applied for investigation of the voltammetric behaviour and quantification of this herbicide. Picloram yielded one well-developed irreversible oxidation signal at a very positive potential about +1.5 V vs. Ag/AgCl/3 mol L−1 KCl electrode in an acidic medium and 1 mol L−1 H2SO4 was chosen as a suitable supporting electrolyte. Operating parameters of differential pulse voltammetry were optimized and the proposed voltammetric method provided a high repeatability (a relative standard deviation of 20 repeated measurements at a concentration level of picloram of 50 µmol L−1 equaled to 2.58%), a linear concentration range from 2.5 to 90.9 µmol L−1 and a low limit of detection (LD = 1.64 µmol L−1). Practical usefulness of the ‘environmentally-green’ electrochemical sensor was verified by an analysis of spiked water samples with satisfactory recoveries.

Sensitive electrochemical determination of yohimbine in primary bark of natural aphrodisiacs using boron-doped diamond electrode

For the first time, a simple and sensitive analytical method for the direct determination of yohimbine is presented using differential pulse voltammetry with a boron-doped diamond electrode. Two irreversible oxidation peaks, a distinct one at +0.80 and a second poorly-defined one at +1.65 V, were observed when cyclic voltammetry was carried out in Britton–Robinson buffer solution at pH 7 (vs. Ag/AgCl). With optimized differential pulse voltammetric parameters (pulse amplitude 100 mV, pulse time 25 ms, step potential 5 mV and scan rate 10 mV s−1), the current response of yohimbine at +0.80 V was linearly proportional to the concentration in the range from 0.25 to 90.9 μmol L−1 with a low detection limit of 0.13 μmol L−1 (0.046 mg L−1) and a good repeatability (relative standard deviation of 2.5% at 18.4 μmol L−1 for n = 6). The practical applicability of the developed method was demonstrated by the assessment of the total content of yohimbine in extracts of the primary bark of natural aphrodisiacs such as Pausinystalia yohimbe and Rauvolfia serpentina with recoveries in the range of 92–97%. The proposed electrochemical procedure represents an inexpensive and effective analytical alternative for the quality control analysis of products containing yohimbine and other biologically and structurally related alkaloids used as natural dietary supplements.

Simple and Rapid Quantification of Folic Acid in Pharmaceutical Tablets using a Cathodically Pretreated Highly Boron-doped Polycrystalline Diamond Electrode

ABSTRACT A simple, rapid, and sensitive electroanalytical method for the direct quantification of folic acid was developed using square-wave voltammetry with a cathodically pretreated highly boron-doped polycrystalline diamond electrode. The morphology and structure of this electrode were investigated by scanning electron microscopy and Raman spectroscopy. The electrochemical behavior of folic acid was studied by cyclic voltammetry and an irreversible oxidation peak was observed at +0.78 volt vs. Ag/AgCl in Britton-Robinson buffer at pH 5. Using optimized square-wave voltammetric parameter values, the response of folic acid was linear from 0.1 to 167 micromolar with a limit of detection of 30 nanomolar with good repeatability. The influence of some interfering compounds was also evaluated. The method was successfully applied to the quantification of folic acid in pharmaceutical tablets. Considering the importance of the analyte upon human health, the boron-doped diamond electrode may be employed as an effective alternative electroanalytical approach.

Electroanalytical application of a boron-doped diamond electrode for sensitive voltammetric determination of theophylline in pharmaceutical dosages and human urine

In this paper, a novel voltammetric method for the determination of 1,3-dimethylxanthine alkaloid theophylline is elaborated using differential pulse (DPV) and square-wave voltammetric (SWV) modes on a boron-doped diamond electrode. Direct oxidation of the analyte at very positive potentials was observed by cyclic voltammetry, as evidenced by the presence of a well-shaped irreversible peak at +1.63 V (vs. Ag/AgCl electrode) in 1 mol L−1 sulphuric acid. After optimization of experimental conditions, the current response of theophylline was proportionally linear from 2 to 380 μmol L−1 using both pulse techniques. The developed electroanalytical method yielded low detection limits of 0.91 and 1.45 μmol L−1 associated with good intra-day repeatability (relative standard deviation of 3.2 and 2.5%) using DPV and SWV, respectively. The influence of some possible interferents was also evaluated. The practical feasibility of the proposed methodology was tested in the analysis of pharmaceutical dosages and human urine samples and good recovery values were accomplished (93.2–102.5%). The results of analysis of pharmaceuticals were also in close agreement at a 95% confidence level with those obtained using the titration (reference) method. Taking these attributes into consideration, the proposed sensor may be employed as a simple and effective analytical tool in drug control analysis and analysis of biological samples as well as a useful alternative to previously utilized modified electrodes in this field.

The doping level of boron-doped diamond electrodes affects the voltammetric sensing of uric acid

In this work, the electrochemical oxidation and subsequent determination of uric acid was investigated using boron-doped diamond electrodes with various B/C ratios (0–2000 ppm). The cyclic voltammetric study showed one irreversible oxidation peak at +(1.1–1.25) V (vs. Ag/AgCl/3 M KCl) in the presence of Britton–Robinson buffer (pH 2.25) depending on the boron content. Employing differential pulse voltammetry using the 2000 ppm boron-doped diamond electrode the acquired analytical parameters were as follows: a limit of detection of 7.7 μM, a limit of quantification of 26 μM and intra-day repeatability (relative standard deviation of 2.9% for n = 15). After performing an interference study, the method was applied to the determination of uric acid in biological samples (human urine). The uric acid concentrations determined in the urine samples were compared with the reference values stated in the literature. The proposed methodology using boron-doped diamond electrodes could find applications in uric acid sensing within clinical, pharmaceutical and environmental analysis.

Toxicity reduction of 2-(5-nitrofuryl)acrylic acid following Fenton reaction treatment

Monitoring the enforcement of an EU-wide ban of nitrofuran antibiotics in the food production chain is a challenging task, given the nature of nitrofuran compounds. The original and modified Fenton reactions are advanced oxidation processes that can eliminate the toxicity of nitrofurans. 2-(5-Nitrofuryl)acrylic acid (I) was degraded as a model compound by the original Fenton reaction with ferrous sulphate, by Mohr’s salt at pH 3 and 7, and finally by advanced Fenton process (AFP) (Fe0/H2O2/H2SO4). In addition, the growth inhibition of Escherichia coli, a G− bacterium, was tested both before and after AFP treatment. The results showed that a small degradation efficiency of this treatment process led to the toxicity changes and that the toxicity of I after AFP treatment process decreased. It seems that the treatment of polluted water using the Fenton reaction and its modifications would be a suitable method for degradation of nitrofuran derivatives in polluted water.

Rapid electrochemical platform for nicotine sensing in cigarettes and chewing gums

Abstract A novel protocol for the simple and rapid determination of nicotine using square-wave voltammetry at boron-doped diamond electrode was developed. The effect of pH of supporting electrolyte, scan rate and square-wave voltammetric parameters was examined. Behavior study revealed that nicotine provided two irreversible oxidation peaks, the first one well-shaped at +1.14 V and the second one poorly-defined at +1.61 V vs. Ag/AgCl electrode in the presence of phosphate buffer (pH 9.0). Under optimal experimental conditions (modulation amplitude of 40 mV, frequency of 50 Hz and scan rate of 0.225 V · s-1), the current response of nicotine was proportionally linear in the concentration range from 9.9 × 10-6 to 1.7 × 10-4 mol · L-1 (R2 = 0.996) with the detection limit of 6.1 × 10-6 mol · L-1 (0.989 mg · L-1) and the relative standard deviation of 8.8 % (number of measurements n = 10, 5.7 × 10-5 mol · L-1 nicotine). The proposed procedure was applied to the quantification of nicotine in cigarettes and chewing gums with the determined values in good agreement with those declared by producer. In this respect, the developed protocol could represent an effective and rapid alternative to chemically modified electrodes in analysis of alkaloids.