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Determination of propyl gallate on carbon paste electrode
Vysoká, Marie ; Fischer, Jan (referee) ; Zima, Jiří (advisor)
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 0,6110-7 moldm-3 was obtained. Using HPLC with a mobile phase consisting of 0,01 moldm-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 moldm-3 for HPLC-ED and 4,95 moldm-3 for HPLC-UV. After verification of the extraction procedure PG was determined in vegetable oil. The resulting value of 3,2 mgkg-1 corresponds with permited limits.
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Determination of Selected Nitrophenols Using Modified Carbon Paste Electrodes
Hranická, Zuzana ; Barek, Jiří (advisor) ; Zima, Jiří (referee)
The voltammetric behavior of selected nitrophenols (2-nitrophenol, 4-nitrophenol, 2,4-dinitrophenol and 2,4,6-trinitrophenol) was investigated by differential pulse voltammetry (DPV) and by adsorptive stripping voltammetry (AdSV) at an unmodified electrode (CPE) and a clay-modified carbon paste electrodes modified by montmorillonite (MMT-CPE) and sepiolite (SEP-CPE) using electrochemical reduction and oxidation in Britton-Robinson buffer. For reduction, optimum conditions have been found at pH 2 for 2-NP and 4-NP, at pH 3 for 2,4-DNP and at pH 4 for 2,4,6-TNP. For oxidation, optimum conditions have been found at pH 2 for 2-NP and 4-NP and at pH 5 for 2,4-DNP. Voltammetric determination using electrochemical oxidation is not a suitable method for 2,4,6-TNP. The lowest detection limits were obtained for 2-NP using cathodic AdSV on SEP-CPE with 2,9·10-7 mol.dm-3 , for 4-NP using cathodic DPV on MMT-CPE with 2·10-6 mol.dm-3 , for 2,4-DNP using cathodic AdSV on SEP-CPE with 2,7·10-7 mol.dm-3 and for 2,4,6-TNP using cathodic DPV on unmodified electrode with 4,8·10-7 mol.dm-3 . Determination of mixture 2-NP and 4-NP and the possibility of the selective determination using open circuit sorption with DPV detection was further studied.
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Use of Chiral Separations for the Determination of Enzyme Enantioselectivity
Břicháč, Jiří ; Zima, Jiří (advisor) ; Tesařová, Eva (referee) ; Flieger, Miroslav (referee)
Conclusion Enantioselective enzymes pray important rore in metaboric pathways of chirar compounds. Enantioselective metabolism of lipid peroxidation product HNE was studied using measurement of enzyme kinetics. Difference in ability to detoxiý individua| HNE enantiomers by rat brain mitochondriar ALDHs was found. Based on kinetic parameters of purified recombinant enz),Ťnes' it was concluded, that rat ALDH5A enantioselective|y oxidized (R)-HNE' whereas rat ALDH2 was not enantioserective. Moreover, direct and indirect RP-HPLC methods for the separation of HNEA enantiomers were deveroped and validated. The indirect method involved pre-corumn derivatization with a chiral amino agent ANPAD' and subsequent separation ofdiastereomers on a Spherisorb oDS2 column. The direct separation of HNEA enantiomers was performed using the porysacharide-based CSP, Chiralpak AD-RH. Enantioserective enzymes are useful biocatalyzators a'owing cheap preparation of optically pure chemicals. screening of epoxide hydrolases produced by various microorganisms was performed and enantioselective enzymes were found using chiral GC on cyclodextrin-based CSps. In summary, this thesis describes development and optimization of the analytical methods for determination of various chiral compounds implicated in enzyme enantioselectiviý. All...
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