Voltammetric determination of cholecalciferol at glassy carbon electrode performed in water ethanol mixture

To confirm or disprove previous hypotheses, cyclic voltammetry of 0.5 mM cholecalciferol (vitamin D3) at glassy carbon electrode (GCE) and platinum disk electrode (PtE) in pure acetonitrile and water‑ethanol mixture at 50 mV·s‑1 has been used to investigate the oxidation mechanism. The oxidation occurs in two one-electrone steps. According to calculation of the highest electron density in cholecalciferol molecule which is evidently delocalized over carbon atoms of the three conjugated double bonds (C19, C10, C5-C8) points to part of the molecule involved in oxidation processes. An oxidation peak (at +0.925 V vs. Ag/AgCl) was used to develop direct voltammetric method based on differential pulse voltammetry for the vitamin D3 determination at GCE performed in 40% ethanol containing 0.1 M LiClO4. Under optimization of analytical procedure, it was found that a composition of the supporting electrolyte used significantly affects a current response of oxidation peak obtained. Satisfactory sensitivity was achieved in the 1:1 water‑ethanol mixture containing 0.05 M lithium perchlorate as as supporting electrolyte. The linear range for vitamin D3 determination was2.4 × 10-6 - 3.5 × 10-4 M with the detection limit of 8.0 × 10-7 M. This work demonstrates a fact that the GCE is suitable electroanalytical device for analysis of various food supplements and medicaments

Electrochemical Study and Determination of All-trans-Retinol at Carbon Paste Electrode Modified by a Surfactant

U radu je cikličkom voltametrijom istražen mehanizam oksidacije trans-retinola (vitamina A1) i nekoliko njegovih estera u organskom otapalu, miješanoj otopini voda/organsko otapalo i vodenoj otopini. Proces oksidacije odvijao se u nekoliko ireverzibilnih koraka. Najveća gustoća elektrona u retinoidnoj molekuli delokaliziranih oko ugljikovih atoma vezanih s pet konjugiranih dvostrukih veza (C5-C14) pronađena je u dijelu molekule koji sudjeluje u oksidaciji. Najviši oksidacijski pik (na +0.8 V prema Ag/AgCl elektrodi) korišten je za određivanje retinola diferencijalnom pulsnom voltametrijom pomoću elektrode od ugljikove paste modificirane površinski aktivnom tvari (natrijev dodecil-sulfat). Rezultati pokazuju da je s dodatkom 30 % (po masi) natrijeva dodecil-sulfata dobivena optimalna osjetljivost elektrode i optimalan oblik voltamograma. U usporedbi s uobičajenom elektrodom od staklastog ugljika, elektroda od ugljikove paste modificirane pomoću natrijeva dodecil-sulfata bitno je pospješila elektroanalizu retinola. Linearan odziv modificirane elektrode od ugljikove paste bio je u rasponu od 1,5·10^−6–1,8·10^−4 M retinola s limitom detekcije 1,3·10^−6 M, dok je elektroda od staklastog ugljika imala linearni raspon 4,4·10^−6–7,0·10^−4 M i limit detekcije 4,6·10^−7 M.The oxidation mechanism of all-trans-retinol (vitamin A1) and its several esters in non-aqueous, aqueous organic mixture, and pure aqueous media was investigated by cyclic voltammetry. The oxidation occurred in several irreversible steps. The calculated highest density of electrons in retinoid molecules which are delocalized over carbon atoms of the five conjugated double bonds (C5-C14) was found in the part of the molecule involved in oxidation processes. The most sensitive oxidation peak (at +0.8 V vs. Ag/AgCl) was used for development of new direct voltammetric method based on differential pulse voltammetry for the determination of retinol at carbon paste electrode modified with surfactant sodium dodecyl sulfate (CPE/SDS). The results show that 30 % (by mass) of modifier SDS exhibited optimal sensitivity and shape of voltammograms. Compared to commonly used glassy carbon electrode (GCE), the CPE/SDS showed significant progress in the retinol electroanalysis. The linear ranges for retinol determination were 1.5·10^−6–1.8·10^−4 M for CPE/SDS and 4.4·10^−6–7.0·10^−4 M for GCE with the detection limits of 1.3·10^−6 and 4.6·10^−7 M, respectively

Determination of trolox equivalent antioxidant capacity in berries using amperometric tyrosinase biosensor based on multi-walled carbon nanotubes

In this contribution, Trolox equivalent antioxidant capacity (TEAC) was determined in various berries using carbon paste tyrosinase biosensor with multi-walled carbon nanotubes (MWCNTs), coated with Nafion((R)) layer. Electrochemical behaviour of the biosensor and influence of MWCNTs on carbon paste surface were studied with respect to the sensitive amperometric detection of total content of phenolic compounds in berries, expressed as concentration equivalent of Trolox. After optimization of key instrumental and electroanalytical parameters, the biosensor was used for determination of TEAC in blackberries, blueberries, cranberries, raspberries and strawberries by method of multiple standard additions. Electrochemical TEAC assays corresponded well with results obtained by spectrophotometric 1,1-diphenyl-2-picrylhydrazyl radical method, known as DPPH assay. Obtained values were compared with those listed in the National Nutrient Database for additional antioxidant capacity assays as well

Bis(2,2-bipyridil)Copper(II) Chloride Complex: Tyrosinase Biomimetic Catalyst or Redox Mediator?

In this article, construction of amperometric sensor(s) based on screen-printed carbon electrodes covered by thin layers of two types of carbon nanomaterials serving as amplifiers, and containing [Cu(bipy)(2)Cl]Cl center dot 5H(2)O complex is reported. Their performance and biomimetic activity towards two selected neurotransmitters (dopamine and serotonin) was studied mainly using flow injection analysis (FIA). The important parameters of FIA such as working potential, flow rate, and pH were optimized. The mechanism of the catalytic activity is explained and experimentally confirmed. It reveals that presence of hydrogen peroxide plays a crucial role which leads to answer the title question: can presented complex really be considered as a tyrosinase biomimetic catalyst or only as a redox mediator

Application of the Enzymatic Electrochemical Biosensors for Monitoring Non-Competitive Inhibition of Enzyme Activity by Heavy Metals

The inhibition effect of the selected heavy metals (Ag+, Cd2+, Cu2+, and Hg2+) on glucose oxidase (GOx) enzyme from Aspergillus niger (EC 1.1.3.4.) was studied using a new amperometric biosensor with an electrochemical transducer based on a glassy carbon electrode (GCE) covered with a thin layer of multi-wall carbon nanotubes (MWCNTs) incorporated with ruthenium(IV) oxide as a redox mediator. Direct adsorption of multi-wall carbon nanotubes (MWCNTs) and subsequent covering with Nafion((R)) layer was used for immobilization of Gox. The analytical figures of merit of the developed glucose (Glc) biosensor are sufficient for determination of Glc in body fluids in clinical analysis. From all tested heavy metals, mercury(II) has the highest inhibition effect. However, it is necessary to remember that cadmium and silver ions also significantly inhibit the catalytic activity of Gox. Therefore, the development of Gox biosensors for selective indirect determination of each heavy metal still represents a challenge in the field of bioelectroanalysis. It can be concluded that amperometric biosensors, differing in the utilized enzyme, could find their application in the toxicity studies of various poisons

Correction: Sýs et al. Bis(2,2′-bipyridil)Copper(II) Chloride Complex: Tyrosinase Biomimetic Catalyst or Redox Mediator? Materials 2021, 14, 113

In the original publication [...

The issue of education for roma children in primary scholls

Tato závěrečná práce z DPS se především zaměřuje na řešení problematiky vzdělávání romských dětí na základních školách v České republice. Existence nejrůznějších vzdělávacích metod a jejich efektivní využívání může mít veliký přínos pro samotné romské děti, tak i pro celou společnost.This final work of the Supplementary Pedagogical Study focuses primarily on solution issues of education of Roma children in primary schools, in the Czech Republic. The existence of many different methods their effective using will have big contribution for Rome children and all society.Dokončená práce s úspěšnou obhajobo

Adsorption of microorganisms on the surface of carbon paste electrode

Diplomová práce se zabývá aktivní přilnavostí buněk k povrchu uhlíkové pastové elektrody a možnostmi elektrochemického studia adheze buňek. Použitou měrnou metodou byla square wave voltametrie. Množství přichycených buněk k povrchu pracovní elektrody bylo stanoveno nepřímo pomocí elektrochemicky aktivního barviva amidové černi. Získané poznatky během samotného experimentu by mohly přispět k objasnění tvorby nežádoucího biofilmu.This thesis deals with the active adhesion of cell to the surface of carbon paste electrode and the possibilities of electrochemical studies of adhesion of cells. Square wave voltammetry was used throughout the study. The adsorption rate of cells on the surface of carbon paste electrode was determined indirectly by electrochemically active dye amide black. The knowledge gained during the experiment itself represents significant contribution to the study of biofilm formation.Katedra analytické chemieStudent přednesl obhajobu své diplomové práce a zodpověděl dotazy zkušební komise.Dokončená práce s úspěšnou obhajobo

Microextraction methods based on the solid sorbents

Tato bakalářská práce je zaměřena na mikroextrakční techniky založené na využití tuhých sorbetů a jejich uplatnění pro analýzu potravin.Použitelnost mikroextrakčních metod pro analýzu potravin je demonstrována pomocí jednotlivých aplikací zaměřených na stanovení různých látek v určité potravině.This bachelor thesis is focused on the microextraction technology based on the use of solid sorbents and their application for analysis of food. Applicability microextraction methods for food analysis is demonstrated through various applications, which are used for the determination of various substances in the food.Katedra analytické chemieDokončená práce s úspěšnou obhajobo