Electrochemical behavior of caffeic acid on carbon nanomaterials: a contribution to the optimization of electroanalytical methods for determination of natural reducers : diploma thesis

U ovom radu su predstavljeni rezultati istraživanja ponašanja kofeinske kiseline na različito modificiranim elektrodama od staklastog ugljika. Elektrokemijska ispitivanja su vršena u tri različite puferske otopine (acetetnom, otopini model vina, Britton-Robinson puferu) te pri različitim pH vrijednostima (2,6 – 3,6 u Britton-Robinson puferu). Uočena je znatna ovisnost elektrokemijskog ponašanja kofeinske kiseline na modificiranim elektrodama u ovisnosti o puferu u kojima su mjerenja vršena. Kao najpogodniji pufer pokazao se Britton-Robinson pufer, dok su značajna kinetička ograničenja zabilježena u acetatnom pufer. Ove pojave su pripisane Frumkinovom efektu, koji je posebno naglašen na elektrodama modificiranim s ugljikovim nanocijevčicama. Nadalje, kinetička ograničenja vezana za prijenos elektrona kroz heterogenu granicu faza ispitivana su u širokom području brzina posmika. Na osnovu analize izračunati su koeficijenti prijelaza (α), kao i konstante brzine prijenosa elektrona za sve modificirane elektrode i u svim puferima. Povišenjem pH vrijednosti dolazi do pomaka potencijala strujnih pikova, ali i do smanjenja osjetljivosti. Ove pojave objašnjene su u kontekstu predloženih mehanizama oksidacije/redukcije kofeinske kiseline. Kao najoptimalniji sustav za određivanje kofeinske kiseline, na osnovu analize, isprofilirale su se elektrode modificirane ugljikovim nanocijevčicama u Britton-Robinson puferu, pri pH 3,6. Rezultati ovog diplomskog rada, zajedno s rezultatima dobivenim s drugim polifenolima na istim elektrodama mogu pomoći u prevladavanju interferencija, povećanju osjetljivosti i razvoju nove metode za određivanje polifenola u realnim uzorcima.This graduate thesis presents the results of research on the behavior of caffeic acid on variously modified glassy carbon electrodes. Electrochemical tests were performed in three different buffer solutions (acetate, wine model solution, Britton-Robinson buffer) at different pH values (2,6 – 3,6 in Britton-Robinson buffer). A significant dependence of the electrochemical behavior of caffeic acid on the modified electrodes was observed depending on the buffer in which the measurements were performed. Britton-Robinson buffer proved to be the most suitable buffer, while significant kinetic limitations were noted in acetate buffer. These phenomena are attribute to Frumkin effect, which is particularly pronounced on electrodes modified with carbon nanotubes. Furthermore, the kinetic constraints related to electron transfer across the heterogeneous phase boundary were investigated over a wide range of scan rates. Based on the analyses, the transition coefficients (α), and constant electron transfer rates for all modified electrodes in all buffers were calculated. Increasing the pH value shifts the potential of current peaks, but also reduces the sensitivity These phenomena are explained in the context of the proposed mechanisms of oxidation / reduction of caffeic acid. Based on analyses most optimal system for the determination of caffeic acids are modified electrodes with carbon nanotubes in Britton-Robinson buffer, at pH 3,6. The results of this thesis, together with the results obtained with other polyphenols on the same electrodes can help to overcome interference, increase sensitivity and develop new methods for the determination of polyphenols in real samples