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Voltametrické stanovení vybraných nitroimidazolových léčiv / Voltammetric Determination of Selected Nitroimidazole DrugsŠkvorová, Lucie January 2012 (has links)
The aim of presented Diploma Thesis was to study an electrochemical behavior of nitroimidazole drugs metronidazole and ornidazole and to find optimal conditions for their voltammetric determination at a mercury meniscus modified silver solid amalgam electrode using DC voltammetry (DCV) and differential pulse voltammetry (DPV). Voltammetric behavior of selected drugs was investigated in dependence on the pH of the medium used (realized using a Britton-Robinson buffer (BR buffer)) and a mechanism of the reduction of both drugs was investigated using cyclic voltammetry (CV). The optimum medium for voltammetric determination of studied nitroimidazole drugs at the m-AgSAE in a region of cathodic potentials was found to be the BR buffer of pH 8.0. Then, the concentration dependences were measured in this optimum medium in the concentration range from 2·10-7 mol/L to 1·10-4 mol/L. The limits of quantification (LQs) for both metronidazole and ornidazole were found in the concentration order of 10-7 mol/L by using DCV and DPV at the m-AgSAE. The applicability of the newly developed voltammetric methods of the determination of nitroimidazole drugs was verified on the model samples of drinking and river water, with LQ ≈ 2·10-7 mol/L for both DC voltammetry and differential pulse voltammetry at the m-AgSAE....
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Elektrochemická impedanční spektroskopie jako charakterizační metoda modifikovaných nanostrukturovaných elektrod / Electrochemical impedance spectroscopy as a nanostructured bioelectrodes characterization methodVrbová, Eva January 2015 (has links)
Diploma thesis deals of nanostructured surfaces, nanoparticles and electrochemical characterization methods such as cyclic voltammetry, differential pulse voltammetry and electrochemical impedance spectroscopy. The aim of this thesis is a theoretical research issues of production and characterization nanostructured modified electrodes. The practical part is the production of biomodified nanostructured electrodes by anodi- zation W/Al layers with galvanic deposition of gold or deposition of mercury, a modifi- cation of the electrodes by 11-mercaptoundecanoic acid and by bovine serum albumin (BSA). The thesis includes SEM images of nanostructured electrodes contact angle mea- surements of these electrodes and form an electrical circuit with subsequent simulation waveforms.
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Voltametrické stanovení 5-nitrobenzimidazolu za využití netradičních elektrodových materiálů / Voltammetric Determination of 5-Nitrobenzimidazole Using Non-Traditional Electrode MaterialsChládková, Barbora January 2012 (has links)
5 Abstract This Diploma Thesis is targeted on the determination of 5-nitrobenzimidazole (5-NBIA) using following techniques: DC voltammetry (DCV) and differential pulse voltammetry (DPV). As working electrodes, a silver amalgam paste electrode (AgA-PE), which was constructed for this determination in the form of a new prototype, a bismuth film electrode (BiFE), at which the optimum conditions for the deposition of the bismuth film at a suitable substrate (glassy carbon electrode and gold electrode were tested for this purpose) were initially optimized, and a glassy carbon electrode (GCE) were used. The optimum conditions for the voltammetric determination of 5-NBIA at the AgA-PE (in a medium of Britton-Robinson buffer (BR-buffer) of pH 7.0 for both DCV and DPV), at the BiFE with gold substrate (BR-buffer of pH 9.0 for both DCV and DPV; the film was deposited "ex situ" in a stirred plating solution (1000 mg L-1 Bi(III) solution in 0.1 mol L-1 acetate buffer of pH 4.5) for 300 s), and at the GCE (BR-buffer of pH 5,0 for both DCV and DPV). Under these conditions, calibration dependences were measured in the concentration ranges of 0.1 - 100 µmol L-1 (pro DCV a DPV na AgA-PE) and 1 - 100 µmol L-1 (pro DCV a DPV na BiFE a GCE), and the limits of quantification (LQs) were calculated for particular methods: LQ ≈...
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Voltametrické stanovení herbicidu Aclonifenu pomocí rtuťových elektrod / Voltammetric Determination of Herbicide Aclonifen Using Mercury ElectrodesMurcková, Klára January 2012 (has links)
Presented Diploma Thesis is focused on electroanalytical determination of the herbicide Aclonifen, which belongs to a group of herbicides derived from diphenylether. These herbicides are used due to their effects - inhibition of protoporfyrinogen oxidase synthesis and also inhibition of biosynthesis of carotenoids. Due to its widespread use in agricultural, toxical effects on humans and because of its negative impacts particularly on aquatic ecosystems there is a need for methods capable of determining the presence of Aclonifen in the environment to monitor its ecological impacts. Optimal conditions for the determination of Aclonifen have been investigated in BR buffer - methanolic solution and in BR buffer. Electrochemical behavior of the substance has been studied using direct current voltammetry (DCV), differential pulse voltammetry (DPP) and adsorptive stripping voltammetry (AdSV) on the hanging mercury drop electrode (HMDE) and by using TAST polarography and differential pulse polarography (DPP) on the dropping mercury electrode (DME). UV/VIS spectrophotometric detection was used for comparison to electrochemical detection. Used wavelengths were 308 nm and 388 nm. For electrochemical determination of Aclonifen the above mentioned techniques were used and following results were obtained: DCV...
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Využití potenciálových programů při průtokovém elektrochemickém stanovení biologicky aktivních organických látek / Utilization of potential programs in flow electrochemical determination of biologically active organic compoundsBavol, Dmytro January 2018 (has links)
9 Abstract In this Ph.D. thesis possibilities of using our proposed potential programs for a multiple-pulse amperometry and a fast scan differential pulse voltammetry in combination with flow systems are presented. The development of new sensitive amperometric and voltammetric methods for the determination of oxidisable biologically active organic compounds is another aim of this work. In the first part of the work, the flow injection system and multiple-pulse amperometric detection were employed to develop and optimize a simple, low-cost, and rapid method for the simultaneous determination of natural and synthetic antioxidants. This technique involves the application of an appropriate potential waveform consisting of a suitable sequence of pulses on a single working electrode, thus allowing distinguish the analytes in a mixture with no need of separation. Conditions for the determination of antioxidants and modelling of the potential program were tested and studied, respectively. Second part of the work describes and characterizes the application of the fast scan differential pulse voltammetry (FSDPV) in combination with the flow systems. FSDPV is the electroanalytical technique that use high scan rate to record voltammograms within several milliseconds and ensures high temporal resolution. This technique...
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Voltametrické a amperometrické stanovení nitrofenolů pomocí borem dopované diamantové filmové elektrody / Voltammetric and Amperometric Determination of Nitrophenols Using Boron-Doped Diamond Film ElectrodeKaraová, Jana January 2018 (has links)
Presented Ph.D. Thesis is focused on the use of the boron-doped diamond (BDD) electrodes for voltammetric and amperometric determination of selected nitrophenols: 2-nitrophenol (2NP), 4-nitrophenol (4NP), and 2,4-dinitrophenol (2,4DNP). These compounds are listed as "priority pollutants" by United States Environmental Protection Agency (US EPA) due to their negative impact on living organisms and are mainly used in agriculture as plant growth stimulators. BDD electrodes are used for determination of wide range of electrochemically both reducible and oxidisable organic compounds and have become a popular electrode material thanks to its commercial availability and excellent mechanical and electrochemical properties. A differential pulse voltammetric method was developed for the determination of 2NP, 4NP and 2,4DNP at a BDD film electrode using electrochemical reduction and of 4NP and 2,4DNP using electrochemical oxidation. The method was successfully applied for the direct determination of these compounds in drinking and river water in the concentration range from 4×10-7 to 2×10-5 mol.L-1 . To improve the limit of quantification, a preconcentration by solid phase extraction from 100 mL (drinking and river water) and 1000 mL (drinking water) of water samples was used with limit of determination...
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Vývoj nových elektrochemických metod s využitím různých membránových materiálů pro sledování vybraných protinádorových léčiv a fytochelatinů / Development of Novel Electrochemical Methods Using Various Membrane Materials for Monitoring of Selected Anticancer Drugs and PhytochelatinsSkalová, Štěpánka January 2019 (has links)
Present Ph.D. Thesis is focused on the development of electrochemical methods for determination of anticancer drugs using various types of membranes for their preliminary separation. Furthermore, this Thesis reports the study of transport mechanisms of heavy metals in the presence of phytochelatins across biological membranes. Sodium anthraquinone-2-sulphonate (AQS) was used as a model compound for its similar structure with anthraquinone-based (AQ-based) anticancer drugs (doxo/daunorubicin) and also due to its better availability. All these compounds can be easily electrochemically oxidized and/or reduced. Redox behaviour of AQS was investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) in a cathodic region on mercury meniscus modified (m-AgSAE) and polished silver solid amalgam (p-AgSAE) electrodes, Obtained results were used for the development of a micro-volume voltammetric cell (MVVC). Its applicability for voltammetric determination of anticancer drugs was verified by using doxorubicin (DX) as a model substance. The second part of this Thesis deals with therapeutic monitoring of anticancer drugs in the blood circulation of the patients. For pilot experiments, a liquid-flow system with dialysis catheter and amperometric detection was used. The flow rate of carrier...
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Voltametrické a amperometrické stanovení homovanilové, vanilmandlové a 5-hydroxy-3-indoloctové kyseliny / Voltammetric and amperometric determination of homovanillic, vanillylmandelic, and 5-hydroxyindole-3-acetic acidNěmečková, Anna January 2020 (has links)
Presented dissertation thesis is focused on the development of electrochemical methods for the determination of three important tumour biomarkers, namely homovanillic acid (HVA), vanillylmandelic acid (VMA), and 5-hydroxyindole-3-acetic acid (5-HIAA). First part of the study is focused on electrochemical behaviour of these analytes in batch arrangement using differential pulse voltammetry (DPV) at screen-printed carbon electrodes (SPCEs). It has been proved that presented method is sufficiently sensitive for monitoring above mentioned analytes. Moreover, it can be used for determination of HVA and VMA in mixture. Obtained limits of detection (LODs) were 0.24 µmol·L-1 for HVA, 0.06 µmol·L-1 for VMA, and 0.12 µmol·L-1 for 5-HIAA. The requirements to speed up the analysis and at the same time to reduce its price initialized our study of the determination of tested biomarkers in flow systems. Firstly, flow injection analysis with amperometric detection was investigated for the determination of all three biomarkers at the same SPCE, and then an analogous determination of structural more similar pair, HVA and VMA, was performed at a boron doped diamond electrode (BDDE). Obtained LODs of optimized methods were as follows: at SPCE 0.07 µmol·L-1 for HVA, 0.05 µmol·L-1 for VMA, and 0.03 µmol·L-1 for 5-HIAA,...
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Využití potenciálových programů při průtokovém elektrochemickém stanovení biologicky aktivních organických látek / Utilization of potential programs in flow electrochemical determination of biologically active organic compoundsBavol, Dmytro January 2018 (has links)
9 Abstract In this Ph.D. thesis possibilities of using our proposed potential programs for a multiple-pulse amperometry and a fast scan differential pulse voltammetry in combination with flow systems are presented. The development of new sensitive amperometric and voltammetric methods for the determination of oxidisable biologically active organic compounds is another aim of this work. In the first part of the work, the flow injection system and multiple-pulse amperometric detection were employed to develop and optimize a simple, low-cost, and rapid method for the simultaneous determination of natural and synthetic antioxidants. This technique involves the application of an appropriate potential waveform consisting of a suitable sequence of pulses on a single working electrode, thus allowing distinguish the analytes in a mixture with no need of separation. Conditions for the determination of antioxidants and modelling of the potential program were tested and studied, respectively. Second part of the work describes and characterizes the application of the fast scan differential pulse voltammetry (FSDPV) in combination with the flow systems. FSDPV is the electroanalytical technique that use high scan rate to record voltammograms within several milliseconds and ensures high temporal resolution. This technique...
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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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