The aim of this dissertation is the development of a new type of modified electrode based on glassy carbon, and its optimization for the determination of trace elements in environmental samples. This ...electrode would be used without prior preparation for the determination of trace elements in water, and in biological and soil samples prepared with microwave digestion. The development of such electrode would improve the present electroanalytical technique, which are based on the determination of trace elements on the hanging mercury drop as working electrode, and thin film of mercury electrode, although these electrodes have very low detection limit and excellent reproducibility. Because of the toxicity of mercury and its salts, mercury electrodes are less and less is use as working electrodes, and in some countries the use of mercury is completely forbidden. Now is a number of different types of modified electrodes in develop, that may eventually replace mercury electrode, and have the same or better performance, primarily related to the detection limit, sensitivity and greater selectivity (due to the specificificity of modified electrode). The most common example of modified electrodes are electrodes modified with organic compounds, which can be specific and selective ionophore, embedded in the polymer matrix. Such ionophores can be used as sensitive elements of the working electrodes in electroanalytical measurements. Based on this, a new type of electrode was developed. Nafion was used as polymer matrix, and as a selective ionophore for modification a complex methyl-3 ,5- bis (di (2-pikolil) amino) methyl benzoate with copper (Cu-DPABA) on a glassy carbon electrode was used (Cu-DPABA-NA/GCE). In order to achieve optimal results, especially in terms of detection limits and selectivity, following parameters were investigated: - Thickness of the film, - The potential of deposition, - Time of deposition, and - pH range, the electrolyte and electrode stability.
Cilj ove doktorske disertacije jeste razvoj novog tipa modifikovane elektrode na bazi staklastog ugljenika i njene optimizacije za odredjivanje sadržaja mikroelemenata u uzorcima iz životne sredine. Ova elektroda bi se bez prethodne pripreme koristila za određivanja sadržaja mikroelemenata u vodi, kao i u biološkim uzorcima i uzorcima zemljišta nakon mikrotalasne digestije.Razvoj ovakve elektrode unapredio bi današnje elektroanalitičke tehnike koje se zasnivaju na određivanju sadržaja mikroelemenata na visećoj kapi žive kao radnoj elektrodi, kao i na elektrodi od tankog živinog filma, iako ove imaju veoma nisku granicu detekcije i odličnu reproduktivnost. Zbog toksičnosti žive i njenih soli, elektrode od nje sve manje se koristi kao radne elektrode, a u nekim zemljama upotreba žive je potpuno zabranjena. Zbog toga se danas razvija veliki broj različitih tipova modifikovanih elektroda koje bi u budućnosti mogle da zamene živine electrode, a koje bi imale iste ili bolje karakteristike od ovih, što se pre svega odnosi na granicu detekcije, osetljivost i postizanje veće selektivnosti (zbog specifičnosti modifikovanih electroda). Najčešći primer modifikovanih elektroda predstavljaju elektrode modifikovane organskim jedinjenjima, koja mogu biti specifične i selektivne jonofore, ugrađene u polimernu matricu. Takve jonofore se mogu koristiti kao senzitivni elementi na radnim elektrodama prilikom elektroanalitičkih merenja. Na ovom principu razvijen je novi tip elektrode gde je kao polimerna matrica korišćen nafion a kao selektivna jonofora za modifikaciju kompleks metil-3,5-bis(di(2- pikolil)amino)metilbenzoata sa bakrom (Cu-DPABA) na elektrodi od staklastog uglejnika (Cu-DPABA–NA/GCE). U cilju postizanja optimalnih rezultata, prvenstveno u pogledu granice detekcije i selektivnosti, ispitani su sledeći parametri: – debljina filma, – potencijal depozicije, – vreme depozicije i – pH opseg, elektrolit i stabilnost elektrode.
Glass-like carbon (GC) is an isotropic material. Good mechanical properties and electrical conductivity, corrosion resistance, as well as impermeability to gases and liquids are essential properties ...which make GC a very useful material, especially as an electrode material in electrochemical reactions. Different mechanical, chemical and/or electrochemical treatment of GC surface can be applied to increase its electrochemical activity. In the present thesis activation of the GC electrode by anodic or cathodic electrochemical polarization was studied. The influence of electrolyte composition, potential and duration of polarization on double layer charge, as a measure of electrode activity has been investigated. Glass-like carbon surface can be easily modified by silver or copper, simply by exposing it to the corresponding metal salt solution. Auger electron spectra - AES and X-ray photoelectron spectra - XPS of such an electrode show that the metal is present on the surface and in the near surface region in the form of zero-valent state. Electrochemical characterization of silver modified GC electrodes is presented. The influence of concentration of AgNO3 solutions, the time of immersion, the pre treatment and/or activation of glass-like carbon electrode, as well as the influence of oxygen presence in AgNO3 solution was determined. In addition, ultra high vacuum - UHV methods of surface analysis, AES and XPS, and scanning tunneling microscopy - STM were applied for examination of modified electrodes. The results obtained suggest that functional groups, formed on the GC surface during electrochemical activation, participate in modification as active sites. The modified electrode is catalytically active in the electrooxidation of small organic molecules, and can be used as an indicator electrode in electroanalytical techniques.
Stаklаsti kаrbоn је izоtrоpnа, nеgrаfitаbilnа fоrmа uglјеnikа. Nјеgоvе dоbrе mеhаničkе оsоbinе, visоkа еlеktričnа prоvоdnоst, hеmiјskа inеrtnоst, kоrоziоnа оtpоrnоst, kао i nеprоpustlјivоst zа tеčnоsti i gаsоvе, оmоgućаvајu mu širоku primеnlјivоst, pоsеbnо kао еlеktrоdnоg mаtеriјаlа. Еlеktrоhеmiјskа аktivnоst stаklаstоg kаrbоnа sе pоvеćаvа rаzličitim mеhаničkim, hеmiјskim i/ili еlеktrоhеmiјskim pоstupcimа. Prеdmеt оvе disеrtаciје је istrаživаnjе аktivаciје stаklаstоg kаrbоnа еlеktrоhеmiјskоm, аnоdnоm ili kаtоdnоm pоlаrizаciјоm. Ispitаn је uticај rаzličitih еlеktrоlitа u kојimа је vršеnа pоlаrizаciја, kао i utucај pоtеnciјаlа i vrеmеnа pоlаrizаciје nа kоličinu nаеlеktrisаnjа u dvојnоm slојu, kао mеrе аktivnоsti еlеktrоdе. U drugоm dеlu disеrtаciје istrаžеn је fеnоmеn mоdifikаciје stаklаstоg kаrbоnа bаkrоm i srеbrоm, јеdnоstаvnim pоtаpаnjеm uzоrаkа u rаstvоrе kојi su sаdržаvаli јоnе pоmеnutih mеtаlа - AgNO3, оdnоsnо CuSO4. Auger (Оžе) еlеktrоnskоm spеktrоskоpiјоm - AES i fоtоеlеktrоnskоm spеktrоskоpiјоm X-zrаcimа - XPS, ustаnоvlјеnо је dа su nа pоvršini i u pоdpоvršinskim slојеvimа stаklаstоg kаrbоnа, nаkоn mоdifikаciје prisutni mеtаli u еlеmеntаrnоm, nulа vаlеntnоm stаnju. U pоsеbnоm dеlu disеrtаciје dеtаlјnо је izvršеnа еlеktrо-hеmiјskа i pоvršinskа (AES, XPS i STM) kаrаktеrizаciја srеbrоm mоdifikоvаnih uzоrаkа stаklаstоg kаrbоnа. Ispitаni su uticајi trајаnjа mоdifikаciје, kоncеntrаciје јоnа srеbrа u еlеktrоаnаlitičkim tеhnikаmа.
