Zorica Stojanović

Rosmarinus Officinalis Leaves as a Natural Source of Bioactive Compounds

In an extensive search for bioactive compounds from plant sources, the composition of different extracts of rosemary leaves collected from different geographical zones of Serbia was studied. The qualitative and quantitative characterization of 20 rosemary (Rosmarinus officinalis) samples, obtained by microwave-assisted extraction (MAE), was determined by high performance liquid chromatography coupled to electrospray quadrupole-time of flight mass spectrometry (HPLC–ESI-QTOF-MS). The high mass accuracy and true isotopic pattern in both MS and MS/MS spectra provided by the QTOF-MS analyzer enabled the characterization of a wide range of phenolic compounds in the extracts, including flavonoids, phenolic diterpenes and abietan-type triterpenoids, among others. According to the data compiled, rosemary samples from Sokobanja presented the highest levels in flavonoids and other compounds such as carnosol, rosmaridiphenol, rosmadial, rosmarinic acid, and carnosic acid. On the other hand, higher contents in triterpenes were found in the extracts of rosemary from Gložan (Vojvodina).

Selenium determination in biscuits and pasta: development of chronopotentiometric stripping determination by using a sulphide as an internal standard.

Being common in chromatographic techniques internal standard method is rarely applied in electrochemical stripping determinations. One of the reasons for such rare use of this elegant quantification method is because optimal conditions of accumulation at the electrode for individual compounds producing a reproducible signal may vary significantly. These criteria are much stricter when selenium is in question due to very complex mechanism of its accumulation at mercury electrodes which implies simultaneous cathodic mercury dissolution and chemical reaction. Elements that are in the analytical step stripped cathodically from mercury electrodes are rare, further limiting the application of the internal standard method when electrochemical selenium determination is in question. In this work the possibility of using sulphide for selenium quantification by chronopotentiometric stripping analysis was investigated. Optimal experimental parameters were defined in two-component systems. Dimensionless factors defining the ratio of proportionality constants of the two elements were calculated for different selenium concentration ranges at different sulphide contents. Sulphide content that was chosen as adequate for selenium concentrations reasonably to be expected in food samples was 500 µg/dm(3). Determined detection limit of chronopotentiometric stripping determination of selenium by using a sulphide as an internal standard was 0.04 µg/dm(3) (RSD=7.6%; n=5). Defined quantification method was confirmed by analysing spiked standard solutions and standard reference material. The method was used for selenium determination in biscuit and pasta samples. Calculated contents were statistically compared with those obtained by using graphite furnace atomic absorption spectrometry.

Determination of α-tocopherol in Cosmetic Products by Chronopotentiometry

Abstract In the present study, a rapid chronopotentiometric method was developed for the determination of α-tocopherol in various cosmetic products. Determination of α-tocopherol is based on its irreverse oxidation by constant current at the planar glassy carbon electrode. The influence of the most important experimental parameters of chronopotentiometry was investigated. After optimization, an appropriate procedure for the sample preparation was developed. Under the defined experimental conditions, a detection limit of 7.5 mg L−1 of α-tocopherol was obtained. The accuracy of the defined method was confirmed by means of recovery assay. The developed method was successfully applied to quantitation of α-tocopherol in various cosmetic products.

Development and Validation of Chronopotentiometric Method for Imidacloprid Determination in Pesticide Formulations and River Water Samples

A new electrochemical method for determination of imidacloprid using chronopotentiometry on thin film mercury and glassy carbon electrode was presented. The most important experimental parameters of chronopotentiometry were examined and optimized with respect to imidacloprid analytical signal. Imidacloprid provided well-defined reduction peak in Britton-Robinson buffer on thin film mercury electrode at −1.0 V (versus Ag/AgCl (KCl, 3.5 mol/L)) and on glassy carbon electrode at −1.2 V (versus Ag/AgCl (KCl, 3.5 mol/L)). The reduction time was linearly proportional to concentrations from 0.8 to 30.0 mg/L on thin film mercury electrode and from 7.0 to 70.0 mg/L on glassy carbon electrode. The detection limits were 0.17 mg/L and 0.93 mg/L for thin film mercury and glassy carbon electrode, respectively. The estimation of method precision as a function of repeatability and reproducibility showed relative standard deviations values lower than 3.73%. Recovery values from 97.3 to 98.1% confirmed the accuracy of the proposed method, while the constancy of the transition time with deliberated small changes in the experimental parameters indicated a very good robustness. A minor influence of possible interfering compounds proved good selectivity of the method. Developed method was applied for imidacloprid determination in commercial pesticide formulations and river water samples.

A simple and rapid electrochemical sensing method for metribuzin determination in tap and river water samples

This paper describes an electroanalytical method for the determination of metribuzin using a thin film mercury electrode by chronopotentiometry. Research included optimization of the most important parameters of chronopotentiometric analysis and the best responses were achieved in Britton–Robinson buffer at pH 5.0, using an initial potential of −0.21 V, ending potential of −1.1 V, and reduction current in the range from −4 μA to −15 μA. Under these conditions, metribuzin was reduced in an irreversible electrode reaction process with one well-defined reduction wave at −0.83 V (vs. Ag/AgCl, KCl, 3.5 mol dm−3). A linear response was observed for three concentration ranges 1–5, 5–15 and 15–30 mg dm−3, with an achieved limit of detection of 0.042 mg dm−3. The precision was determined as a function of repeatability and reproducibility, which showed relative standard deviation values not higher than 3.18%. Various interfering substances did not interfere with metribuzin determination. The proposed method was successfully applied to tap and river water samples. The recovery values obtained for spiked river water samples were in good statistical agreement with those obtained by the LC-MS/MS method. Accordingly, the proposed chronopotentiometric methodology can be conveniently applied in the quality control of environmental water samples as a simple, sensitive, reliable and low cost method.

Direct Determination of Heavy Metals in Honey by Potentiometric Stripping Analysis

Honey is a valuable nutritious food rich in simple sugars, aminoacids, proteins and minerals. In addition, this food product contains natural phenols and flavonoids, responsible for some bioactive properties. Due to known health benefits of honey and its exquisite flavour this foodstuff is readily consumed by children and wide population imposing necessity of strict quality control. One of quality criteria is the content of heavy metals. Elevated content of heavy metals in honey may result from environmental or processing contamination, or may originate from soil or plant species that honey is derived from. In this work twenty five samples of honey from Serbia, Montenegro and Bosnia and Herzegovina were analysed in respect to zinc, cadmium, lead and copper content. Honey samples were analysed directly, without sample preparation, by applying potentiometric stripping analysis. Zinc, cadmium and lead were quantitated by using indium as an internal standard, whereas copper was determined by standard addition method. Method accuracy was confirmed by blind analysis of standard samples and with good recovery results which, for analysed samples, were in the range 91-101%. In all analysed sampled determined metals contents were in the range permitted by Serbian regulations. Cadmium was not detected in any of the analysed samples, whereas the content of other metals were in the range of 0.01-3.6 μg/g for zinc, 0.02-0.8 μg/g for lead and 0.1-2.4 μg/g for copper, respectively.

Novel electrochemical procedure for the determination of metamitron

ABSTRACT In this paper, a chronopotentiometric method for the determination of herbicide metamitron (MTM) using a glassy carbon electrode (GCE) and a thin film mercury electrode (TFME) as working electrodes is presented. MTM provided a well-defined reductive peak in the Britton–Robinson buffer on both working electrodes. Instrumental and chemical factors such as pH of the buffer, initial potential and reduction current influencing MTM chronopotentiometric response were optimised with the Box–Behnken experimental design. Under the optimal combination of factors, the analytical signal was linear in the MTM concentration range of 0.8–30 mg/L, with a detection limit of 68.53 µg/L using a TFME, and in the concentration range of 1–30 mg/L, with a detection limit of 92.91 µg/L using a GCE. The precision of the method was estimated as a function of repeatability and reproducibility, with the value of relative standard deviation lower than 2.6%. The applicability of the method was verified by direct analysis of MTM in spiked water samples and commercial pesticide formulations. The obtained results were in good agreement with those obtained using liquid chromatography/tandem mass spectrometry (LC-MS/MS) method, or with those labelled by the manufacturer. By using chronopotentiometry, neither extraction nor preconcentration procedures are necessary, thus making this method simple, cost-effective and more feasible for analytical routine analysis.

Determination of chromium(VI) by anodic stripping voltammetry using a silver-plated glassy carbon electrode

In this work, differential pulse anodic stripping voltammetry (DP-ASV) for the determination of trace amounts of hexavalent chromium (Cr(VI)) at a silver plated glassy carbon electrode (Ag plated-GCE) is described in detail. A Ag film was prepared by in situ plating of silver on the glassy carbon electrode surface. Several solution conditions and instrumental parameters influencing the electroanalytical response of the Ag plated-GCE were examined and optimized for the determination of Cr(VI). Under the optimized conditions, the calibration curve obtained in CH3COOH/NH3 (aq) medium at pH 5.9 was linear over the wide concentration range of 0.35–40 μM Cr(VI). The present method shows a low limit of detection of 0.10 μM. After evaluation of effects from possible interferences, the proposed method was successfully applied for the quantification of Cr(VI) in real water samples, with satisfactory recovery (97–105%). This method is useful for the determination of chromium in drinking water and achieves sensitivity capable of detecting the limits set by the World Health Organization (WHO).