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Antichagásicos potenciais: síntese e estudo do comportamento voltamétrico de bioisósteros do nitrofural / Pontential antichagasic: synthesis and study of voltammetric behavior of biososteres of nitrofurazoneBrito, Charles de Lima 13 October 2011 (has links)
A compreensão do mecanismo de redução de compostos nitroheterocíclicos pode ser um parâmetro importante para correlacionar estudos entre a transferência eletrônica e a atividade biológica. O nitrofural (NF), fármaco pertencente ao grupo químico dos 5-nitro- heterocíclicos é ativo contra o Trypanosoma cruzi, agente etiológico da doença de Chagas, mas sua toxicidade impede o seu uso no tratamento desta parasitose. Desta forma, realizaram-se estudos do comportamento eletroquímico de três bioisósteros de NF, com substituição ora no heteroátomo do anel (O e S) ora na carbonila (O e S). As técnicas eletroquímicas de voltametria cíclica (VC), voltametria de pulso diferencial (VPD) e cronoamperometria (CRO) em meio aquoso e empregando eletrodo de carbono vítreo (ECV) como eletrodo de trabalho. A finalidade deste estudo foi compreender a influência do efeito estrutural sobre a atividade redox dos bioisósteros, pois os respectivos comportamentos eletroquímicos podem estar correlacionados com a ação biológica. Todos os processos de redução foram controlados por difusão, com a formação de único pico de redução (Ecp,1), sendo os análogos NT e NTS reduzidos em potencial ligeiramente mais negativo. A comparação dos resultados voltamétricos de NF com os obtidos para cada análogo demonstraram que todos os compostos apresentaram mecanismo de redução similar, envolvendo quatro elétrons, sendo em meio ácido o derivado hidroxilmina (RNHOH) o principal produto formado. Os dados obtidos por VPD e CRO corroboraram com estes resultados. Em meio alcalino e com prévio tratamento do eletrodo de carbono vítreo, constatou-se a formação de um pico de redução reversível, com envolvimento de um elétron para todos os compostos. Este pico refere-se à formação do nitro radical aniônico (R-NO2•-), mostrando-se estável na escala de tempo de medida da técnica de VC. Ademais, realizou-se estudo comparativo do efeito do polimento mecânico no ECV, com diamante e alumina, onde os dois procedimentos não apresentaram efeitos significativos diferentes sobre o comportamento voltamétrico dos análogos estudados. O nitro radical gerado eletroquimicamente em meio aquoso sofre reação de desproporcionamento com cinética de segunda-ordem, seguindo mecanismo ErCi (reação eletroquímica reversível seguida de uma reação química irreversível). Os valores da constante de velocidade k2 desta reação mostraram-se dependentes do pH, confirmando que o nitro radical aniônico é mais facilmente estabilizado em meio alcalino, uma vez que com a diminuição da acidez do meio, a protonação do radical torna-se mais difícil. O composto com a inclusão de dois átomos de enxofre (NTS) apresentou os menores valores de k2 indicando uma cinética de reação de desproporcionamento mais lenta praticamente em toda faixa de pH, com exceção em pH 8, com o qual os valores de k2 não apresentaram diferenças significativas. Portanto, os resultados obtidos neste estudo indicaram claramente a possibilidade de geração e detecção do nitro radical em meio aquoso a partir de compostos nitro-heterocíclicos, distinguindo-se de dados reportados na literatura em que se realizam estes estudos predominantemente em meio não aquoso ou misto. / The comprehension of the reduction mechanism of nitroheterocyclic compounds is an important study to know the parameters which can establish the correlation between electron transfer and biological activity. Nitrofural (NF), a drug containing the 5-nitro-heterocyclic moiety, is active against Trypanosoma cruzi, which is the etiologic agent of Chagas disease. Unfortunately, as NF toxicity prevents its use for the treatment against this illness, studies on the electrochemical behavior of three NF bioisosteres were performed. These bioisosteres contained substitutions (O and S) on either the heterocyclic atom or the carbonyl group. The electrochemical techniques herein used were cyclic voltammetry (CV), differential pulse voltammetry (DPV) and chronoamperometry (CRO) in aqueous medium employing a glassy carbon (GCE) as the working electrode. The purpose of this study was to understand the structural influence on the redox activity of these bioisosteres and to suggest the correlation possibilities between the electrochemical behavior and the biological activity. The reduction processes were all diffusion controlled in acidic medium, with the formation of a single peak reduction (Ecp,1), being the NT and NTS analogue reduced at a slightly less negative potential. The comparison between the NF voltammetric results and those obtained with each analogue showed that all compounds presented a similar reduction mechanism, involving four electrons, being the hydroxylamine derivative the main product formed. The obtained data by DPV and CRO corroborated these results. Additionally, in alkaline medium and with previous GCE treatment by polishing a reversible reduction peak formation was observed with the involvement of one electron for all compounds. This peak refers to the nitro-radical anion formation ((R-NO2•-), being stable in the CV time scale. Moreover, a comparative study was carried out on the mechanical effect in the GCE by polishing with diamond and alumina, showing that both procedures had no significant effect on the voltammetric behavior of the compounds. The nitro-radical electrochemically generated in aqueous medium undergoes disproportionation reaction with second-order kinetics, following the ErCi mechanism (reversible electrochemical reaction followed by an irreversible chemical reaction). The constant rate values (k2) for this reaction proved to be pH dependent, confirming that the nitro-radical anion is more easily stabilized in alkaline medium, since the decreasing acidity of the medium hinders the radical protonation. Complementarily, NTS compound showed the lowest values of k2, indicating a slower disproportionation reaction in almost all pH values, except at pH 8, in which the k2 values had no significant difference among all bioisosteres. Therefore, the obtained results in this study clearly showed that nitro-radical anion can be detected and formed in aqueous solution in contrast to what is reported in literature, in which it is predominantly stabilized in non-aqueous solution or in solvent mixture.
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Antichagásicos potenciais: síntese e estudo do comportamento voltamétrico de bioisósteros do nitrofural / Pontential antichagasic: synthesis and study of voltammetric behavior of biososteres of nitrofurazoneCharles de Lima Brito 13 October 2011 (has links)
A compreensão do mecanismo de redução de compostos nitroheterocíclicos pode ser um parâmetro importante para correlacionar estudos entre a transferência eletrônica e a atividade biológica. O nitrofural (NF), fármaco pertencente ao grupo químico dos 5-nitro- heterocíclicos é ativo contra o Trypanosoma cruzi, agente etiológico da doença de Chagas, mas sua toxicidade impede o seu uso no tratamento desta parasitose. Desta forma, realizaram-se estudos do comportamento eletroquímico de três bioisósteros de NF, com substituição ora no heteroátomo do anel (O e S) ora na carbonila (O e S). As técnicas eletroquímicas de voltametria cíclica (VC), voltametria de pulso diferencial (VPD) e cronoamperometria (CRO) em meio aquoso e empregando eletrodo de carbono vítreo (ECV) como eletrodo de trabalho. A finalidade deste estudo foi compreender a influência do efeito estrutural sobre a atividade redox dos bioisósteros, pois os respectivos comportamentos eletroquímicos podem estar correlacionados com a ação biológica. Todos os processos de redução foram controlados por difusão, com a formação de único pico de redução (Ecp,1), sendo os análogos NT e NTS reduzidos em potencial ligeiramente mais negativo. A comparação dos resultados voltamétricos de NF com os obtidos para cada análogo demonstraram que todos os compostos apresentaram mecanismo de redução similar, envolvendo quatro elétrons, sendo em meio ácido o derivado hidroxilmina (RNHOH) o principal produto formado. Os dados obtidos por VPD e CRO corroboraram com estes resultados. Em meio alcalino e com prévio tratamento do eletrodo de carbono vítreo, constatou-se a formação de um pico de redução reversível, com envolvimento de um elétron para todos os compostos. Este pico refere-se à formação do nitro radical aniônico (R-NO2•-), mostrando-se estável na escala de tempo de medida da técnica de VC. Ademais, realizou-se estudo comparativo do efeito do polimento mecânico no ECV, com diamante e alumina, onde os dois procedimentos não apresentaram efeitos significativos diferentes sobre o comportamento voltamétrico dos análogos estudados. O nitro radical gerado eletroquimicamente em meio aquoso sofre reação de desproporcionamento com cinética de segunda-ordem, seguindo mecanismo ErCi (reação eletroquímica reversível seguida de uma reação química irreversível). Os valores da constante de velocidade k2 desta reação mostraram-se dependentes do pH, confirmando que o nitro radical aniônico é mais facilmente estabilizado em meio alcalino, uma vez que com a diminuição da acidez do meio, a protonação do radical torna-se mais difícil. O composto com a inclusão de dois átomos de enxofre (NTS) apresentou os menores valores de k2 indicando uma cinética de reação de desproporcionamento mais lenta praticamente em toda faixa de pH, com exceção em pH 8, com o qual os valores de k2 não apresentaram diferenças significativas. Portanto, os resultados obtidos neste estudo indicaram claramente a possibilidade de geração e detecção do nitro radical em meio aquoso a partir de compostos nitro-heterocíclicos, distinguindo-se de dados reportados na literatura em que se realizam estes estudos predominantemente em meio não aquoso ou misto. / The comprehension of the reduction mechanism of nitroheterocyclic compounds is an important study to know the parameters which can establish the correlation between electron transfer and biological activity. Nitrofural (NF), a drug containing the 5-nitro-heterocyclic moiety, is active against Trypanosoma cruzi, which is the etiologic agent of Chagas disease. Unfortunately, as NF toxicity prevents its use for the treatment against this illness, studies on the electrochemical behavior of three NF bioisosteres were performed. These bioisosteres contained substitutions (O and S) on either the heterocyclic atom or the carbonyl group. The electrochemical techniques herein used were cyclic voltammetry (CV), differential pulse voltammetry (DPV) and chronoamperometry (CRO) in aqueous medium employing a glassy carbon (GCE) as the working electrode. The purpose of this study was to understand the structural influence on the redox activity of these bioisosteres and to suggest the correlation possibilities between the electrochemical behavior and the biological activity. The reduction processes were all diffusion controlled in acidic medium, with the formation of a single peak reduction (Ecp,1), being the NT and NTS analogue reduced at a slightly less negative potential. The comparison between the NF voltammetric results and those obtained with each analogue showed that all compounds presented a similar reduction mechanism, involving four electrons, being the hydroxylamine derivative the main product formed. The obtained data by DPV and CRO corroborated these results. Additionally, in alkaline medium and with previous GCE treatment by polishing a reversible reduction peak formation was observed with the involvement of one electron for all compounds. This peak refers to the nitro-radical anion formation ((R-NO2•-), being stable in the CV time scale. Moreover, a comparative study was carried out on the mechanical effect in the GCE by polishing with diamond and alumina, showing that both procedures had no significant effect on the voltammetric behavior of the compounds. The nitro-radical electrochemically generated in aqueous medium undergoes disproportionation reaction with second-order kinetics, following the ErCi mechanism (reversible electrochemical reaction followed by an irreversible chemical reaction). The constant rate values (k2) for this reaction proved to be pH dependent, confirming that the nitro-radical anion is more easily stabilized in alkaline medium, since the decreasing acidity of the medium hinders the radical protonation. Complementarily, NTS compound showed the lowest values of k2, indicating a slower disproportionation reaction in almost all pH values, except at pH 8, in which the k2 values had no significant difference among all bioisosteres. Therefore, the obtained results in this study clearly showed that nitro-radical anion can be detected and formed in aqueous solution in contrast to what is reported in literature, in which it is predominantly stabilized in non-aqueous solution or in solvent mixture.
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Konstrukce měřící cely s elektrodou na bázi uhlíkového filmu / Construction of an electrochemical cell based on carbon film electrodeLibánský, Milan January 2013 (has links)
This Thesis deals with the construction of an electrochemical cell with two types of integrated composite electrodes based on carbon films. Using these electrodes, the voltammetric behavior of environmental pollutant triclosan (5-chlor-2-(2,4- dichlorophenoxy)phenol) was studied. For the construction of composite electrodes, graphite and glassy carbon were used as conductive microparticles. Several types of polymers served as the nonconductive binder. For the measurements, combinations of graphite with polystyrene and graphite with polycarbonate were selected as optimum materials. From the dependence of peak heights on solution composition, a mixture of a buffer of pH 7 and methanol (1:9, V/V) was selected as the optimum medium. In this medium, concentration dependences were measured; calculated triclosan detection limit were 0,49 µmol dm-3 for carbon polystyrene composite electrode and 0,25 µmol dm-3 for carbon polycarbonate composite electrode, respectively. The possibility of further increasing the sensitivity of the determination by the accumulation step was studied. Accumulation of triclosan on carbon polystyrene composite electrode was observed, but the increase in response was connected with the loss of repeatability. Accumulation of triclosan on carbon polycarbonate composite electrode was...
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Voltametrijske metode zasnovane na primeni jednostavnih i savremenih elektroda/senzora na bazi ugljeničnih materijala za određivanje vodonik-peroksida u odabranim uzorcima / Voltammetric methods based on the application of simple and contemporary carbonaceousmaterials-based electrodes/sensors for the determination of hydrogen-peroxide in the selected samplesAnojčić Jasmina 22 November 2018 (has links)
<p>Cilj ove doktorske disertacije je bio razvoj brzih i pouzdanih voltametrijskih metoda zasnovanih na primeni jednostavnih i savremenih elektroda/senzora na bazi ugljeničnih materijala (ugljenične paste napravljene od grafitnog praha i parafinskog ulja i štampanih ugljeničnih elektroda) za određivanje H <sub>2</sub>O<sub>2 </sub>u odabranim složenim model i realnim uzorcima. U tu svrhu, ispitana je primenljivost različitih radnih elektroda. Amperometrijska metoda zasnovana na elektrodi od ugljenične paste (CPE) zapreminski modifikovane sa 5% (m:m) MnO2 je, pri optimizovanim uslovima i pri radnom potencijalu od 0,40 V u odnosu na zasićenu kalomelovu elektrodu (ZKE) u fosfatnom puferu pH 7,50 kao pomoćnom elektrolitu, omogućila kvantifikaciju H <sub>2</sub>O<sub>2</sub> u opsegu koncentracija od 1,4 do 65 µg mL -1 sa relativnom standardnom devijacijom (RSD) manjom od 10%. Ova metoda je primenjena za određivanje sadržaja H <sub>2</sub>O<sub>2 </sub>u uzorcima podzemne vode iz centralnog Banata (Pokrajina Vojvodina, Srbija) tretirane Fentonovim (Fe<sup> 2+</sup> i H <sub>2</sub>O<sub>2</sub> ) i Fentonu-sličnim (Fe <sup>3+</sup> i H <sub>2</sub>O<sub>2</sub> ) reagensima u cilju uklanjanja prirodnih organskih materija (POM) pri čemu su korišćene različite početne koncentracije gvožđa i različiti odnosi molarnih koncentracija gvožđa i H <sub>2</sub>O<sub>2</sub> . Utvrđeno je da oksidaciono stanje gvožđe (Fe<sup> 2+</sup> ili Fe <sup>3+</sup>) i molarni odnos jona Fe i H<sub> 2</sub>O<sub>2</sub> utiču na stepen potrošnje/razgradnje H<sub> 2</sub>O<sub>2</sub><br />u podzemnoj vodi sa visokim sadržajem POM. Takođe, u slučaju Fentonu-sličnog procesa, za sve početne koncentracije Fe <sup>3+</sup> i H <sub>2</sub>O<sub>2 ,</sub> signifikantna količina H <sub>2</sub>O<sub>2 </sub>ostaje neiskorišćena, što ukazuje na nižu efikasnost ovakvog sistema u poređenju sa Fentonovim procesom.Štampana ugljenična elektroda (SPCE) zapreminski modifikovana sa MnO 2 kao medijatorom je primenjena za određivanje sadržaja H<sub> 2</sub>O<sub>2</sub> u toku Fentonovog (Fe <sup>2+</sup> , H<sub>2</sub>O<sub>2</sub> ) i vidljivom svetlošću potpomognutog foto-Fentonovog (Fe<sup> 2+ </sup>, H <sub>2</sub>O<sub>2 </sub>, hν) procesa uklanjanja neonikotinoidnog insekticida acetamiprida (ACT). Pri optimizovanim uslovima (radni potencijal 0,40 V u odnosu na ZKE, fosfatni pufer pH 7,50 kao pomoćni elektrolit) amperometrijskog određivanja H <sub>2</sub>O<sub>2</sub> , postignuta je linearnost u opsegu koncentracija 0,01–1,24 mmol L-1(0,34– 42,2 µg mL -1<br />) i vrednost RSD nije prelazila 4,2%. U ispitivanimuzorcima (nakon odgovarajućeg<br />podešavanja pH vrednosti od 2,8 do 7,5 odmah nakon uzorkovanja radi stopiranja ili maksimalnog usporavanja procesa oksidacije, filtriranja, zamrzavanja i odmrzavanja neposredno pre merenja) sadržaj H <sub>2</sub>O<sub>2</sub> je određen metodom standardnog dodatka analiziranjem odgovarajućih amperometrijskih krivi. Paralelna HPLC-DAD merenja su vršena u cilju praćenja koncentracije/uklanjanja ACT. U slučaju foto-Fentonovog procesa (početne koncentracije 0,31; 2,0 i 3,0 mmol L -1 (70,0; 111,7 i 102,1 µg mL -1 ) za ACT, Fe<br /><sup>2+</sup> i H <sub>2</sub>O<sub>2</sub>, redom) nakon 10 min H <sub>2</sub>O<sub>2 </sub>je izreagovao, a može se smatrati da je ACT uklonjen nakon 5 min. U toku Fentonovog procesa ACT je uklonjen nakon 20 min tretmana i oko 10% početne koncentracije H <sub>2</sub>O<sub>2</sub> je ostalo u sistemu<br />neiskorišćeno.CPE je površinski modifikovane kompozitom na bazi nanočestica Pt (< 5 nm) i grafitizovanog ugljenika (Pt-C, 10% Pt na Vulkanu XC72) etodom nanošenja kapi. Nemodifikovana CPE i modifikovana (Pt-C/CPE) su okarakterisane primenom SEM/EDS i CV merenja. Pt-C/CPE je pokazala izuzetne elektrokatalitičke osobine u pogledu elektrohemijskeredoks reakcije H<br /><sub>2</sub>O<sub>2</sub> u poređenju sa nemodifikovanom CPE u fosfatnom puferu (0,1 mol L -1 ;<br />pH 7,50), a takođe i u acetatnom puferu (0,1 mol L -1 ; pH 4,50) kao pomoćnim elektrolitima. Prilikom amperometrijskog određivanja H <sub>2</sub>O<sub>2</sub> primenom Pt-C/CPE u model sistemima, zadovoljavajuća linearnost je postignuta u koncentracionom opseguH<sub>2</sub>O<sub>2</sub>od 0,15 do 1,45 µg mL -1 ,dok su vrednosti GO iznosile 0,06 µg mL -1 (pH 7,50, radni potencijal 0,20 V) i 0,10 µg mL -1 (pH<br />4,50, radni potencijal 0,50 V). Optimizovane analitičke metode su primenjene za određivanje sadržaja H <sub>2</sub>O<sub>2</sub> u komercijalno dostupnim proizvodima za ličnu negu: rastvoru za dezinfekciju (pH 7,50) i rastvoru za čišćenje kontaktnih sočiva (pH 4,50). Amperometrijski dobijeni rezultati su u dobrom slaganju sa rezultatima dobijenim primenom tradicionalne spektrofotometrijske metode bazirane na titanijum-sulfatu kao reagensu sa određenim koncentracijama 2,91% i 2,94% za<br />dezinfekcioni rastvor i 3,04% i 3,17% za rastvor zakontaktna sočiva, redom. RSD je bila manja od 2%. Postignuti rezultati su u dobrom slaganju sa sadržajem H<br /><sub>2</sub>O<sub>2 </sub>deklarisanim od strane proizvođača (3%) u oba ispitivana uzorka. Pt-C/CPE je takođe testirana za praćenje koncentracije H<sub>2</sub>O<sub>2</sub> u rastvoru za kontaktna sočiva u toku procesa njegove neutralizacije/razgradnje. Nakon 6 h procesa neutralizacije, 24,68 µg mL -1 je bila određena koncentracija H <sub>2</sub>O<sub>2 ,</sub> što je ispod dozvoljene<br />H<sub>2</sub>O<sub>2 </sub>koncentracije u rastvoru za kontaktna sočiva imajući u vidu granicu koja izaziva iritaciju oka. CPE je površinski modifikovana višezidnim ugljeničnim nanocevima (MWCNT) i kompozitima MnO 2 -MWCNT ili Pt-MWCNT metodom nanošenja kapi radi pripreme jednostavnih, osetljivih i pouzdanih voltametrijskih senzora za određivanje H <sub>2</sub>O<sub>2 </sub>u odabranom uzorku. Rezultati SEM/EDS analize kompozitnih materijala su potvrdili da su medijatori, čestice MnO 2 i Pt, nasumično raspoređeni na površini MWCNT i zastupljeni sa blizu 5% (m:m) u kompozitu izraženo<br />preko Mn i Pt. CV merenja su vršena sa pripremljenim radnim elektrodama u acetatnom (pH 4,50), fosfatnom (pH 7,50) i boratnom (pH 9,18) puferu kako bi se okarakterisalo osnovno elektrohemijsko ponašanje H <sub>2</sub>O<sub>2 </sub>i odabrali pogodni radni potencijali za amperometrijsko određivanje ovog ciljnog analita. Pt- WCNT/CPE je primenljiva za rad kako u fosfatnom puferu pH 7,50 tako i u acetatnom puferu pH 4,50 V kako pri negativnim tako i pri pozitivnim radnim<br />potencijalima, pri čemu su vrednosti RSD uglavnom ispod 2,5%. U slučaju MnO 2<br />-MWCNT/CPE, na potencijalu 0,30 V i višim vrednostima, oksidacioni signali H<br /><sub>2</sub>O<sub>2</sub> su signifikantni u blago alkalnoj sredini (pH 7,50), pri pH 4,50 ova elektroda pokazuje nezadovoljavajuće ponašanje, dok pri pH 9,18 ima prihvatljive performanse. Granice određivanja (GO) su bile u oblasti µg mL -1 . H <sub>2</sub>O<sub>2</sub> je određen u spajkovanom uzorku mleka metodom standardnog dodatka nakon odgovarajuće pripreme uzorka (pH podešavanje i centrifugiranje) i primenom optimizovane amperometrijske procedure (acetatni pufer pH 4,50, radni potencijal-0,75 V) koristeći Pt-MWCNT/CPE kao radnu elektrodu. RSD za tri ponovljena merenja je iznosila 2,5%, dok je prinos metode bio nešto veći od 71%.<br />Kompozitni materijali koji se sastoje od MWCNT i čestica na bazi Pd (Pd-MWCNT) ili Pt (Pt-MWCNT) su primenjeni za pripremu zapreminski modifikovanih SPCE (Pd-MWCNT-SPCE i Pt-MWCNT-SPCE) i površinski modifikovane SPCE (Pd-MWCNT/SPCE). Ove elektrode, kao i nemodifikovana SPCE i MWCNT-SPCE, su okarakterisane primenom CV i amperometrije u fosfatnom puferu pH 7,50 radi određivanja H <sub>2</sub>O<sub>2</sub> . Pd-MWCNT-SPCE i Pd-MWCNT/SPCE su se pokazale pogodnim za određivanje H <sub>2</sub>O<sub>2</sub> na radnim potencijalima između -0,50 i 0,50 V, a PtMWCNT-SPCE na ispitivanim radnim potencijalima od -0,80 do 0,70 V. Ove elektrode su zatim modifikovane enzimom glukoza oksidazom (GOx) metodom nanošenja kapi rastvora GOx i Nafion ® -a na njihovu površinu, pri čemu je optimizovana količina nanetog biofilma. GOx/PdMWCNT-SPCE je pokazala bolje analitičke performanse za određivanje glukoze u poređenju sa GOx/Pd- WCNT/SPCE. Kao optimalan radni potencijal GOx/Pd-MWCNT-SPCE je odabrana<br />vrednost potencijala -0,40 V u odnosu na ZKE, sa zadovoljavajućom linearnošću u ispitivanom opsegu koncentracija glukoze od 0,16 do 0,97 mmol L -1 (od 29,1 do 174 µg mL -1), dok je GO iznosila 0,14 mmol L -1 (25 µg mL<br />-1 ). Optimizovana metoda zasnovana na GOx/Pd-MWCNT-SPCE je uspešno primenjena za određivanje glukoze u uzorku livadskog meda. Dobijeni rezultati su u dobroj saglasnosti sa onima dobijenim primenom komercijalno dostupnog aparata za merenje glukoze. Pogodan radni potencijal za GOx/Pt-MWCNT-SPCE je bio -0,50 V u odnosu na ZKE, pri čemu je zadovoljavajuća linearnost postignuta u ispitivanom opsegu koncentracija glukoze od 65,8 do 260,6 µg mL -1 , sa GO 35 µg mL -1 . Optimizovana metoda zasnovana na GOx/Pt-MWCNT-SPCE je uspešno primenjena za određivanje glukoze u u uzorku belog grožđa i uzorku tableta (Traubenzucker-bonbons), pri čemu su dobijeni rezultati u dobroj saglasnosti sa rezultatima dobijenim primenom Accu-Chek aparata.<br />Na osnovu dobijenih rezultata može se zaključiti da su razvijene analitičke metode pre svega jednostavne, pouzdane i pogodne za dobijanje brzih informacija o sadržaju H <sub>2</sub>O<sub>2</sub> u različitim tipovima uzoraka. Svakako odabir pogodne radne elektrode, kao i optimizacija eksperimentalnih uslova su ključni faktori za uspešno određivanje H <sub>2</sub>O<sub>2</sub></p> / null / <p>The aim of this doctoral dissertation was the development of fast and reliable voltammetric methods based on the application of simple and contemporary electrodes/sensors based on carbonaceous materials (carbon paste made of graphite powder and paraffin oil and screen printed carbon electrodes) for the determination of H <span id="cke_bm_571S" style="display: none;"> </span><sub>2</sub><span id="cke_bm_571E" style="display: none;"> </span>O<sub>2</sub> in the selected complex model and real samples.For this purpose, applicability of different working electrodes was investigated.The amperometric method based on carbon paste electrode (CPE) bulk- modified with 5% (m:m) MnO 2 , under optimized conditions, with a working potential of 0.40 V vs. the saturated calomel elect<span id="cke_bm_572E" style="display: none;"> </span>rode (SCE) and a phosphate buffer solution (pH 7.50) as supporting electrolyte, enabled the quantitation of H <span id="cke_bm_577S" style="display: none;"> </span><sub>2</sub><span id="cke_bm_577E" style="display: none;"> </span>O<sub>2</sub>in the concentration interval from 1.4 to 65 µg mL −1 with a relative standard deviation (RSD) of less than 10%. This meth<span id="cke_bm_578E" style="display: none;"> </span>od was applied for the determination of the H<span id="cke_bm_583S" style="display: none;"> </span><sub>2</sub><span id="cke_bm_583E" style="display: none;"> </span>O<sub>2 </sub>consumption in samples of groundwater fro<span id="cke_bm_584E" style="display: none;"> </span>m the Central Banat region (Province of Vojvodina, Serbia) treated by the Fenton (Fe <sup>2+ </sup>and H <sub>2</sub>O<sub>2</sub> ) and Fenton- like (Fe <sup>3+</sup>and H <sub>2</sub>O<sub>2</sub> ) reagents to remove natural organic matter (NOM) at differentinitial concentrations of iron species, and of their molar ratios to the initial concentration of H<sub>2</sub>O<sub>2</sub> . It was found that the form of Fe (Fe <sup>2+</sup> or Fe <sup>3+</sup> )and the molar ratio to H <sub>2</sub>O<sub>2</sub>influenced the degree of the H<sub> 2</sub>O<sub>2</sub> decomposition in the groundwater with high NOM content. Besides, in the case of the Fenton-like process, for all initial doses of Fe <sup>3+</sup> and H<span id="cke_bm_604S" style="display: none;"> </span><sub> 2</sub><span id="cke_bm_604E" style="display: none;"> </span>O<sub>2</sub>, a sign<span id="cke_bm_605E" style="display: none;"> </span>ificant amount of H<span id="cke_bm_610S" style="display: none;"> </span><sub> 2</sub><span id="cke_bm_610E" style="display: none;"> </span>O<sub>2</sub> remained unused, whi<span id="cke_bm_611E" style="display: none;"> </span>ch also indicates a lower efficiency of such system compared to the Fenton process. Screen printed carbon electrode (SPCE) bulk-modified with MnO <sub> 2</sub> as a mediator was applied for amperometric determination of the H <span id="cke_bm_617S" style="display: none;"> </span><sub>2</sub><span id="cke_bm_617E" style="display: none;"> </span>O<sub>2</sub> content during the Fenton (Fe <sup>2+</sup> , H <span id="cke_bm_624S" style="display: none;"> </span><sub>2</sub><span id="cke_bm_624E" style="display: none;"> </span>O<sub>2 </sub>) and <span id="cke_bm_625E" style="display: none;"> </span>visible light-assisted<span id="cke_bm_618E" style="display: none;"> </span>, photo-Fenton (Fe <sup>2+ </sup> , H <span id="cke_bm_631S" style="display: none;"> </span><sub>2</sub><span id="cke_bm_631E" style="display: none;"> </span>O<sub>2</sub> , hν)<span id="cke_bm_632E" style="display: none;"> </span> based removal of neonicotinoid insecticide acetamiprid (ACT). Under optimized conditions (working potential of 0.40 V vs. SCE, phosphate buffer pH 7.50 as supporting electrolyte) amperometric determination of H <span id="cke_bm_637S" style="display: none;"> </span><sub>2</sub><span id="cke_bm_637E" style="display: none;"> </span>O<sub>2 </sub>showed a linear dynamic range from 0.01 to 1.24 mmol L -1 (from 0.34 to 42.2 µg mL -1) and the RSD did not exceed 4.2%. In the investigated samples (after appropriate pH adjustment from 2.8 to 7.5 instantly after the sampling<span id="cke_bm_638E" style="display: none;"> </span> to stop or maximum decelerate the oxidation processes, filtering, and storage of the deep- frozen sample with defrosting immediately before the measurements) the H <span id="cke_bm_643S" style="display: none;"> </span><sub>2</sub><span id="cke_bm_643E" style="display: none;"> </span>O<sub>2</sub> contents were determined by the standard addition method by analyzing the corresponding amperometric curves. Parallel HPLC-DAD measurements were performed to monito<span id="cke_bm_644E" style="display: none;"> </span>r the concentration/removal of ACT. In the case of the photo- Fenton process (initial concentrations: 0.31; 2.0 and 3.0 mmol L -1 (70.0; 111.7 and 102.1 µg mL -1 ) of ACT, Fe<sup> 2+</sup> and H <span id="cke_bm_650S" style="display: none;"> </span><sub>2</sub><span id="cke_bm_650E" style="display: none;"> </span>O<sub>2</sub>, respec<span id="cke_bm_651E" style="display: none;"> </span>tively) after 10 min of irradiation H <span id="cke_bm_656S" style="display: none;"> </span><sub>2</sub><span id="cke_bm_656E" style="display: none;"> </span>O<sub>2</sub> was consumed and it can be consi<span id="cke_bm_657E" style="display: none;"> </span>dered that ACT was removed after 5 min. During the Fenton process ACT was removed after 20 min of treatment and around 10% of the initial concentration of the H 2O2 remained still unused.<br />CPE was surface modified with a composite of Pt nanoparticles (< 5 nm) on graphitized carbon (Pt-C, 10% Pt on Vulcan XC72) by simply dropcoating method. The unmodified CPE and the modified one (Pt-C/CPE) were characterized by EM/EDS and CV measurements. The PtC/CPE showed remarkable electrocatalytic propertiestoward the electrochemical redox reaction of H<span id="cke_bm_662S" style="display: none;"> </span><sub>2</sub><span id="cke_bm_662E" style="display: none;"> </span>O<sub>2</sub> compared to modified CPE in phosphate buffer (0.1 mol L -1 ; pH 7.50), as well in acetatebuffer (0.1 mol L -1 ; pH .50) supporting electrolytes. Amperometry of H2O2 in the concentration range from 0.15 to 1.45 µg mL -1 with the Pt-C/CPE showed acceptable linearity, while the obtained values of LOQs were 0.06 µg mL -1 (pH 7.50, working potential 0.20 V) and 0.10 µg mL -1 (pH 4<span id="cke_bm_663E" style="display: none;"> </span>.50, working potential 0.50 V). The proposed analytical methods were applied to the determination of the H 2O2 content in commercially available personal care products; i.e., disinfection (pH 7.50) and contact lens cleaning solutions (pH 4.50). The obtained amperometric results are in good agreement with those measured by traditional titanium sulfatereagent based spectrophotometric method with determined concentrations as 2.91% and 2.94% for the disinfection product, and 3.04% and 3.17% for the contact lens solution, respectively. RSD was lower than 2%. The obtained results are in a good agreement with the amounts of the H<span id="cke_bm_668S" style="display: none;"> </span><sub> 2</sub><span id="cke_bm_668E" style="display: none;"> </span>O<sub>2 </sub>declared by producers (3%) in the both investigated samples. The Pt-C/CPE was also tested for monitoring of the H<span id="cke_bm_674S" style="display: none;"> </span><sub> 2</sub><span id="cke_bm_674E" style="display: none;"> </span>O<sub>2</sub> residual concentration in contact lens solution during its neutralization/decomposition rocess. At 6 h of<span id="cke_bm_675E" style="display: none;"> </span> neutralization treatment 24.68 µg mL -1 of the H <span id="cke_bm_680S" style="display: none;"> </span><sub>2</sub><span id="cke_bm_680E" style="display: none;"> </span>O<sub>2 </sub>was determined which is almost half of the allowedH2<span id="cke_bm_681E" style="display: none;"> </span>O2 concentration in the case of the contact lens solution concerningthe limit of eye irritation. CPE was surface modified with multiwalled carbon nanotubes (MWCNT) and with composites of MnO<sub> 2 </sub>-MWCNT or Pt-MWCNT by drop coating method to prepare simply, sensitive and reliable volta<span id="cke_bm_669E" style="display: none;"> </span>mmetric sensors for the determination of H <span id="cke_bm_687S" style="display: none;"> </span><sub>2</sub><span id="cke_bm_687E" style="display: none;"> </span>O<sub>2 </sub>in selected sample. The results of the SEM/<span id="cke_bm_688E" style="display: none;"> </span>EDS analysis of composite materials have confirmed that the mediators, MnO <sub>2</sub> and Pt articles, are randomly distributed on the surface of MWCNT and represent nearly 5% (m:m) of the composite expressed as Mn and Pt. CV measurements were performed with prepared electrodes in acetate (pH 4.50), phosphate (pH 7.50) and borate (pH 9.18) buffers to characterize the basic electrochemical behavior of H <span id="cke_bm_694S" style="display: none;"> </span><sub>2</sub><span id="cke_bm_694E" style="display: none;"> </span>O<sub>2</sub> and to select the working potentials suitable for amperometric determination of this target analyte. The Pt-MWCNT/CPE performs well in phosphate buffer pH .50 and acetate buffer solution pH 4.50 in the negative as well as in the positive polarization range with RSD mainly lower than 2.5%. In case of MnO<sub> 2 </sub>-MWCNT/CPE at <span id="cke_bm_695E" style="display: none;"> </span>0.30 V and above the H<span id="cke_bm_701S" style="display: none;"> </span><sub>2</sub><span id="cke_bm_701E" style="display: none;"> </span>O<sub>2 </sub>oxidation signal is rem<span id="cke_bm_702E" style="display: none;"> </span>arkable in slightly alkaline media (pH 7.50), at pH 4.50 this electrode showed poor behavior and at pH 9.18 offered acceptable performance. LOQs were in the µg mL -1 concentration range. H<span id="cke_bm_707S" style="display: none;"> </span><sub>2</sub><span id="cke_bm_707E" style="display: none;"> </span>O<sub>2 </sub>was determined in a spiked milk sample by standard addition method after appropriate sample preparation (pH adjustment and centrifugation) and using optimized amperometric p<span id="cke_bm_708E" style="display: none;"> </span>rocedure (acetate buffer pH 4.50, working potential -0.75 V) by Pt-MWCNT/CPE as a working electrode. RSD for three repeated measurements was 2.5%, while the recovery of the method was a bit higher than 71%. The composite materials consisting of MWCNT and Pd (Pd-MWCNT) or Pt containing particles (Pt-WCNT) were applied to the preparation of bulk- modified SPCEs (Pd-MWCNTSPCE and Pt-MWCNT-SPCE) and surface modifiedSPCE (Pd- MWCNT/SPCE). These electrodes, as well as unmodified SPCE and MWCNT-SPCE, were characterized by CV and amperometry in phosphate buffer solution of pH 7.50 for the H<span id="cke_bm_713S" style="display: none;"> </span><sub> 2</sub><span id="cke_bm_713E" style="display: none;"> </span>O<sub>2 </sub>determination. Pd-MWCNT-SPCE and PdMWCNT/SPCEare convenient for the etermination of H 2O2 at working potentials from -0.50 to 0.50 V, and Pt-MWCNT-SPCE at investigated working potentials in the range from -0.80 to 0.70 V. These electrodes were then modified with glucose oxidase (GOx) by drop coating a solution of GOxand Nafion ® on their surface, whereby the applied amount of biococktail was optimized. GOx/PdMWCNT-SPCE showed better analytical performance for glucose determination in comparison with GOx/Pd-MWCNT/SPCE. The optimal working potential for GOx/Pd-MWCNT- SPCE was -0.40 V vs. SCE and <span id="cke_bm_714E" style="display: none;"> </span>satisfactory linearity was obtained in the investigated glucose concentration range from 0.16 to 0.97 mmol L -1 (from 29.1 to 174 µg mL -1 ), hile the LOQ was 0.14 mmol L -1 (25 µg mL -1 ). The optimized method based on GOx/Pd-MWCNT-SPCE was successfully applied to the determination of glucose in multifloral honey sample. The results are in a good agreement with those obtained by commercially available equipment for determination of glucose. Optimal working potential for GOx/Pt-MWCNT-SPCE was -0.50 V vs. SCE, and the satisfactory linearity was obtained in the investigated concentration range ofglucose from 65.8 to 260.6 µg mL -1 , with LOQ of 35 µg mL -1 . The optimized method based on GOx/Pt- MWCNT-SPCE was successfully applied for determination of glucose in white grape and glucose tablets (Traubenzucker-bonbons) samples, whereby the obtained results were in a good agreement with the results obtained by Accu-Chek device. Based on the results, the developed analytical methods are first of all simple, reliable and suitable for obtaining fast information about the content of H <sub>2</sub>O<sub>2</sub> in different types of samples. Certainly the selection of a suitable working electrode, as well as the optimization of experimental conditions are key factors for the successful determination of H<sub>2</sub>O<sub>2 </sub>.</p>
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