This Ph. D. thesis presents new methods for the determination of selected clinically relevant electrochemically active compounds. The first part deals with development of determination of tumour biomarkers homovanillic acid (HVA) and vanillylmandelic acid (VMA) in human urine with the use of hollow-fibre based liquid-phase microextraction (HF-LPME) and differential pulse voltammetry (DPV) at cathodically pre-treated boron doped diamond electrode (BDDE). Optimum conditions for HF-LPME-DPV of HVA and VMA were as follows: butyl benzoate as supported liquid membrane formed on porous polypropylene hollow-fibre, 0.1 mol L−1 HCl as donor phase and 30 min extraction time. Optimum acceptor phases were 0.1 mol L−1 phosphate buffer of pH 6 with ionic strength set to 0.55 mol L−1 for HVAand 0.1 mol L−1 NaOH for VMA, respectively. HF-LPME-DPV concentration dependencies for HVA and VMAwere linear in the range from 0.4 to 100 µmol L−1 and 0.5 to 100 µmol L−1 . Limits of quantification (LOQ)/detection (LOD) were 1.2/0.4 µmol L−1 for HVA and 1.7/0.5 µmol L−1 for VMA, respectively. The applicability of the developed methods was verified by analysis of human urine. In the second part, voltammetric behaviour of heavy metal poisoning antidote 2,3- dimercapto-1-propane-sulfonic acid (DMPS) was investigated with the use...

Propyl gallate (PG) is a significant synthetic antioxidant and preservative. Its determination has been studied at carbon paste electrode (CPE) using differential pulse voltammetry (DPV) and high performance liquid chromatography with electrochemical detection (HPLC-ED) and with UV spectrometric detection (HPLC-UV). Concentration dependences were measured in the media of Britton-Robinson buffer (pH 5) and methanol (20 %, v/v) by DPV and the limit of detection 0,6110-7 moldm-3 was obtained. Using HPLC with a mobile phase consisting of 0,01 moldm-3 phosphate buffer (pH 4) and methanol (50 %, v/v) with potential of working electrode E = +0,8 V and detection wavelength λ = 280 nm, concentration dependences were measured. Limit of detection was determined to 0,39 moldm-3 for HPLC-ED and 4,95 moldm-3 for HPLC-UV. After verification of the extraction procedure PG was determined in vegetable oil. The resulting value of 3,2 mgkg-1 corresponds with permited limits.

4 ABSTRACT Development and testing of novel non-toxic electrode materials, detection arrangements and analytical methods applicable in determination of selected agrochemicals is the main aim of this Ph.D. Thesis. New working electrodes based on silver solid amalgam paste (AgSA-PE) with organic pasting liquid and other based on crystallic silver amalgam (CAgAE) were developed, their electrochemical behaviour investigated and further used in voltammetric determination of widespread and toxic environmental pollutant 4-nitrophenol (4-NP). This analyte could be determined by DPV at AgSA-PE with limit of detection (LD) 1×10í6 mol lí1 and using CAgAE with LD 4×10í7 mol lí1 , both in 0.2 mol lí1 acetate buffer pH 4.8. Attempts to decrease LDs by utilization of adsorptive stripping voltammetry were not successful in either case. Crystallic silver amalgam was also successfully used for construction of microcylindric flow-through cell and tested for amperometric determination of nitrophenol mixture in HPLC-ED system. Both novel electrodes were found to be suitable alternatives to toxic mercury electrodes and the CAgAE seems to be promising working electrode for flowing systems. Method for sample preparation and voltammetric determination of broad-spectrum herbicide Glyphosate in contaminated soil samples was also...

7 ABSTRACT (EN) This dissertation thesis is focused on the study of electrochemical properties of new types of carbon paste electrodes (CPE) and carbon fiber rod electrodes (CFRE), which were used for the development of new highly sensitive and selective voltammetric and amperometric methods for the determination of 5-amino-6-nitroquinoline and trans- and cis- isomers of resveratrol. The carbon paste electrodes were compared in terms of size of the microparticles of glassy carbon contained in the paste (diameters 0.4 - 12 µm; 10 - 20 µm; 20 - 50 µm) in comparison with carbon paste electrode consisting of crystalline graphite and solid glassy carbon electrode. The electrochemical properties were tested using potassium hexacyanoferrate in an aqueous supporting electrolyte and 5-amino-6-nitroquinoline (5A6NQ) in a mixed methanol-water supporting electrolyte. The carbon paste electrode was further used in an amperometric detector of a wall-jet type connected in series with a spectrophotometric detector for the development of a new HPLC method with electrochemical detection and spectrophotometric detection for the determination of trans-resveratrol and cis-resveratrol in samples of grains, hulls and leaves of common and tartary buckwheat. The method was optimized and used for the determination of resveratrol in...

This study investigates electrochemical oxidation of m-cresol on boron-doped diamond electrode using direct current voltammetry (DCV), differential pulse voltametry (DPV) and cyclic voltammetry (CV). In aqueous media in pH range 2.0 - 12.0 m-cresol provides one oxidation peak. The electrode reaction is diffusion-controled. Because of electrode passivation two types of pretreatment were applied for reactivation of electrode surface., i.e. alumina polishing and anodic activation using potential of +2400 mV. Peak heights and potentials are strongly dipending on the type of pretreatment for DCV and DPV - the difference in peak potentials can reach 430 mV. Using optimal conditions for alumina polishing in 0.01 μmol·L-1 NaOH the linear dynamic range is 1.0 - 75 μmol·L-1 for DCV and 0.75 - 75 μmol·L-1 for DPV. And for anodic activation in BR buffer pH 2.0 the linear dynamic range is 0.75 - 75 μmol·L-1 for DCV and DPV. The influence of boron-doping level was investigated using a semiconductive and mettalic-type BDD film. For the latter the sensitivity in DP voltammetry is two times higer and for both types the linear dynamic range is ca 1 - 25 μmol·L-1 . The voltammetric response of m-cresol was further investigated in the presence of cationic surfactants. In the presence of CTAB and CPB the peak current...

This diploma thesis deals withthe studyof electrochemical behaviorand detection of two structurally different neurotransmitters, dopamine (DA) and serotonin (5-HT), in solutions commonly used for neuron cultivation, namely Neurobasal (NB), NB with phenol red and in phosphate buffer (PB) of a pH close to the physiological value. An electrode based on boron-doped diamondwas used for the study, examiningtwo types of surfaces obtained after oxidation (O-BDD) and mechanical polishing (p-BDD). The results were obtained by two voltametric techniques,namely cyclic and differential pulse voltammetry.The studyrevealedthat DA oxidationis a quasi-reversible process,whereas 5-HT oxidizes irreversibly on O-BDD and p-BDD. Nevertheless, for both neurotransmitters their anodic oxidationonboth BDD surfaces is controlledby diffusion. Due to the passivation of the electrode surface by the oxidation products, anodic reactivation(Eact = +2400 mV, t = 30 s) was first testedto regenerate the O-BDD surface during DA and 5-HT measurements. There was no continuous decrease in DA peak currents on O-BDD and the measuredsignals were characterizedby high repeatabilityin all studiedmedia (sr (Ip) 1.1% in PB of pH 7.0, 1.7% in NB of pH 7.34, 0.9% in NB with phenol red of pH 7.48). In the case of 5-HT, the anodic reactivation was...

The aim of this thesis was the development of a voltammetric method for the determination of 7-dehydrocholesterol as a biomarker of congenital disease Smith-Lemli-Opitz syndrome. The concentration of 7-dehydrocholesterol in plasma will increase hundred-fold to hundreds to thousands µmol L-1 in patients suffering from Smith-Lemli-Opitz syndrome. The determination of 7-dehydrocholesterol was carried out in artifical serum in this work, which was prepared to mimic the conditions of postnatal diagnosis of Smith-Lemli-Opitz syndrome. 7-dehydrocholestrol provides a well developed voltammetric signal at approximately +0.8 V vs. Ag/AgNO3 in acetonitrile. Differential pulse voltammetry with optimized parameters was used for the determination of 7-dehydrocholesterol. The presence of protein in artificial serum (human serum albumin) resulted in an unacceptably high detection limit of the method (178 µmol L-1 in artificial serum). Therefore, human serum albumin was eliminated from the artificial serum samples by precipitating it with acetonitrile and subsequently centrifuging the resulting suspension. At the same time, the ratio of aqueous and organic components in the studied medium was also adjusted with acetonitrile to achieve an optimal voltammetric response of 7-dehydrocholestrol. With regard to the...

This thesis is devoted to the study of electrochemical oxidation of meta-substituted phenolic substances on a boron-doped diamond electrode. In the first phase, it was studied the effect of pH on their electrochemical oxidation by the methods of classical "direct current" voltammetry (DCV) and differential pulse voltammetry (DPV). The study was performed on three types of boron doped diamond (BDD) surfaces: polished, anodic and cathodically activated. In the second phase, attention was paid to the Hammett correlation to study the effect of the substituent on the potential of electrochemical oxidation of selected phenolic compounds. Among the substituents studied were (-H, -CH3, -OCH3, -(CH2)2COOH, -COOH a -NO2). In general, the oxidation potentials were lower in the basic medium than in the acidic medium on all studied surfaces. An exception was the studied phenolic acids, which could not be detected in an alkaline medium on the O-terminated BDD, probably due to electrostatic repulsion between the partially negative electrode surface and the acid dianion. The highest correlation coefficient for the dependence composed of all studied phenols was obtained for the polished and H-terminated surface at pH 11, ie the dissociated form of phenolic substances. The high electron density leads to easy...

Cholesterol is an irreplaceable sterol found in animal cells, lathosterol is one of its precursors. The first aim of this Thesis is to develop a method for determining cholesterol after liquid- liquid extraction from milk matrices by differential pulse voltammetry on a boron doped diamond electrode in the presence of perchloric acid in acetonitrile where cholesterol provides an irreversible anodic response at the potential between +1300 and +1600 mV depending on the water content. The second aim is a study of the voltammetric behavior of lathosterol on boron doped diamond and glassy carbon electrodes using cyclic voltammetry and differential pulse voltammetry mainly in perchloric acid but also sodium perchlorate where lathosterol provides an irreversible anodic response at the potential of about +1650 mV on the boron doped diamond electrode and at the potential of +1350 mV on a glassy carbon electrode. The effect of other acids - sulfuric, nitric and phosphoric - on the response of lathosterol was also investigated. The influence of the water content in the measured solution and the influence of the polarization rate on the response of lathosterol were studied. Furthermore, the calibration dependence of lathosterol was measured using differential pulse voltammetry after optimization of its...

The aim of this Thesis is development of electroanalytical methods for determination of cholesterol and 7-dehydrocholesterol on boron doped diamond electrodes based on electrochemical oxidation of products of acid-induced dehydration reaction. Two approches have been applied, relying on their detection in 0,1 mol.l-1 perchloric acid in acetonitril containing variable water content 0,43 % - 40 %. Cyclic voltammetry revealed substantial difference in oxidation peak pontecials for 7-dehydrocholesterol (+850 mV) and cholesterol (+1500 mV) in 0,1 mol.l-1 perchloric acid in acetonitrile containing 5 % of water. The limit of detection using differential pulse voltammetry were 6,19 µmol.l-1 a 19,2 µmol.l-1 for a mixture of 7-dehydrocholesterol and cholesterol, respectively. For flow injection analysis with amperometric detection (FIA-AD) the water content in run buffer, detection potencial and the distance between the capillary outlet and electrode surface in wall-jet arrangement of amerometric flow-through detection cell were optimized. Achieved detection limits are in range of 0,61 - 3,43 µmol.l-1 depending on the detection potencial and water concent in the run buffer. The developed FIA-AD method was used for determination of a model mixture solution of 7- dehydrocholesterol and cholesterol. Key words...