Academic literature on the topic 'Silver Amalgam Paste Electrode'

Determination of 6-nitrobenzimidazole by differential pulse voltammetry at a hanging mercury drop electrode, a polished silver solid amalgam electrode and a mercury meniscus modified silver solid amalgam electrode was studied in the presence of the surfactants Triton X-100, cetyltrimethylammonium bromide and sodium dodecyl sulfate. It was found that only cetyltrimethylammonium bromide at polished silver solid amalgam electrode increases the voltammetric signal. This fact was used for the determination of 6-nitrobenzimidazole in the concentration range from 1 × 10–7 to 1 × 10–4 mol l–1 by differential pulse voltammetry at polished silver solid amalgam electrode in the presence of cetyltrimethylammonium bromide (concentration 1 × 10–4 mol l–1).

Milkfish (Chanos chanos) gelatin was successfully developed as biosensor material. The milkfish bone was obtained from local restaurants in Tarakan, North Borneo, Indonesia. Gelatin was extracted from milkfish bone using acid method at 55°C. Characterization by FTIR showed that milkfish gelatin had similar functional group with commercial gelatin. The gelatin was used as biosensor material for detecting chromium. The gelatin was mixed with carbon in 1:1 ratio to form gelatin/carbon paste modified silver electrode. Electrochemical impedance spectroscopy (EIS) analysis of the gelatin/carbon paste modified silver electrode showed a better conductivity than paraffin/carbon paste modified silver electrode. Performance of the gelatin/carbon paste modified silver electrode in chromium (III) solution was conducted using cyclic voltammetry technique. Measurement was carried out at -1 V to +1 V with scan rate of 100 mV/s in acid and base condition. The best result was shown by gelatin/carbon paste modified silver electrode. It can detect chromium (III) ions at reduction potential of -0.78 V in alkaline condition. Unspecific responses were observed from silver electrode, paraffin/silver electrode, carbon/silver electrode, gelatin/silver electrode and paraffin/carbon paste modified silver electrode. This result can be concluded that the milkfish gelatin obtained have a potential to be developed as chromium (III) biosensor.

This work reports a comparative electrochemical behaviour study and p-nitrophenol analytical detection using silver solid amalgam, hanging dropping mercury, and silver electrodes. For this, square wave voltammetry was employed, where the analytical responses and the redox mechanisms could be compared for reduction processes of 4-nitrophenol by analysis of the voltammetric responses. The analytical performance of the electrode was evaluated and detection and quantification limits, recovery percentages, repeatability, and reproducibility for the silver solid amalgam and hanging dropping mercury electrodes presented similar values; the results presented for the silver electrode indicated worse analytical parameters than the other electrodes. The results indicate that the silver solid amalgam electrode can be considered a suitable tool and an interesting alternative for the analytical determination of 4-nitrophenol, as well as for the determination of other biological and environmentally interesting compounds that present analytical responses on mercury surfaces.

Danas, u raznim analitičkim laboratorijama postoji veći broj analitičkih protokola,zasnovanih bilo na izuzetno sofisticiranim ili jednostavnijim tehnikama, koji služe zaodređivanje različitih ciljnih analita od farmakološkog značaja. Među tim grupama ciljnih analita pripadaju i antibiotici koji predstavljaju veliko otkriće u oblasti medicine i zahvaljujući njima spašeno je više od sedam miliona života, ali pored navedenih koristi, antibiotici mogu da izazovu  veliki broj neželjenih efekata i žučne kiseline zajedno sa svojim derivatima, koji su fiziološki deterdženti, mogu biti citotoksične za organizam ako se njihova koncentracija ne kontroliše. U ovoj doktorskoj disertaciji prikazan je razvoj analitičkih metoda pre svega voltametrijskihmetoda u kombinaciji sa jednostavnim i savremenim elektrodama/senzorima za određivanje  odabranih analita kao što je antraciklični antibiotik doksorubicin (DOX), makrolidni antibioticieritromicin-etilsukcinata (EES), azitromicina (AZI), klaritromicina (CLA) i roksitromicina  (ROX) i 3-dehidro-deoksiholne kiseline.Voltametrijska karakterizacija i određivanje gore navedenih antibiotika primenom obnovljive srebro-amalgam film elektrode (Hg(Ag)FE)rađena je direktnom katodnom  voltametrijom sa pravougaonim talasima (SWV) i visoko osetljivom adsorptivnom voltametrijom sa pravougaonim talasima (SW-AdSV) u Briton-Robinson puferu, kao pomoćnom elektrolitu, obuhvatajući širok opseg pH vrednosti. Odgovor DOX-a primenom  Hg(Ag)FE praćen je u intervalu potencijala od -0,20 do -0,80 V.  Za analizu tragova, optimizacija metode ukazuje da su optimalni parametri za analitički pik na potencijalu (Ep ) -0,57 V u odnosu na zasićenu kalomelovu elektrodu (ZKE): pH 6,0, potencijal  akumulacije -0,20 V i vreme  akumulacije 140 s. U model rastvoru, DOX je određivan u koncentracionom opsegu 4,99-59,64  ng mL^-1. Razvijena SW-AdSV metoda je primenjena za određivanje DOX-a u obogaćenom uzorku humanog urina. Niža koncentracija DOX-a 9,89ng mL^-1 u voltametrijskoj  ćeliji je određivana sa relativnom standardnom devijacijom (RSD) manjom od 6,0%. Što se ispitivanih makrolida tiče oni su pokazali redukcione signale u dalekoj negativnoj oblasti potencijala. Ispitivanja direktnom katodnom SWV rađena su u opsegu potencijala od -0,75 V do -2,00 V u odnosu na ZKE, pri čemu su dobijena jedan ili dva redukciona pika u opsegu potencijala od -1,5 V do -1,9 V. Oblik i intenzitet signala zavisi od primenjene pH vrednosti u širokoj pH oblasti. Za analitičke svrhe, radi razvoja direktne katodne SWV i adsorptivne inverzne/striping SWV metode, pogodnim su se pokazale neutralna i slabo alkalna sredina tj. pH 7,0 sa  E_p na -1,67 V u odnosu na ZKE za ROX i EES i pH 7,2 sa E_p na -1,85 V u odnosu na ZKE za AZI i pH 7,4 sa E_p na -1,64 V u odnosu na ZKE za CLA. Na osnovu snimljenih cikličnih voltamograma na  optimalnim pH vrednostima, može se predložiti adsorptivno-kontrolisan kinetički proces na elektrodi u slučaju sva  četiri ispitivana jedinjenja. Takođe,  ¹H NMR merenja uz potiskivanje  signala vode u pH oblasti između pH 6,0 i 10,5 ukazuju na to da su makrolidni molekuli pri optimalnim analitičkim uslovima predominantno u protonovanoj formi preko tercijerne amino grupe što potpomaže, u sva  četiri slučaja, njihovu adsorpciju na odgovarajuće polarizovanoj Hg(Ag)FE. Optimizovane direktne katodne SWV metode  pokazuju dobru linearnost u koncentracionom opsegu 4,81-23,3  µg mL^-1 , 4,53-29,8  µg mL^-1 , 1,96-28,6  µg mL^-1 i 1,48-25,9 µg mL^-1 za AZI, EES, CLA odnosno ROX. Razvijene SW-AdSV metode rezultiraju u linearnom odgovoru pri nižim koncentracionim intervalima 1,0-2,46 µg mL^-1 ,  0,69-2,44  µg mL^-1, 0,05-0,99 µg mL^-1 i 0,10-0,99  µg mL^-1 , za AZI, EES, CLA i ROX. RSD za sve razvijene metode nije veća od 1,5% izuzev SWV metode u slučaju AZI-a gde je 4,5%. Direktna katodna SWV metoda  je uspešno primenjena za određivanje EES-a u farmaceutskom proizvodu Eritromicin^® dok SW-AdSV metoda je primenjena u slučaju određivanja EES-a u obogaćenom uzorku humanog urina i za određivanje ROX-a u farmaceutskom proizvodu Runac^® . U svim pomenutim slučajevima, primenjena je metoda standardnog dodatka. Pouzdanost i tačnost elaboriranih procedura u slučaju određivanja EES-a u model sistemu i  farmaceutskom proizvodu Eritromicin^® su potvrđena poređenjem sa rezultatima dobijenim primenom HPLC-DAD metode.Nakon preliminarnih studija 3-dehidro-deoksiholne  kiseline/3-dehidro-deoksiholata primenom elektrode od staklastog ugljenika (GCE), gde je uočeno da ne dolazi do formiranja redukcionog signala u Briton-Robinson puferu između pH 5,0 i 11,8 primenom direktne katodne SWV, bizmut-film je izdvojen  ex situ na površini iste elektrode od staklastog ugljenika (BiF-GCE) iz uobičajeno korišćenog rastvora za elektrodepoziciju (0,02 mol L^-1 Bi(NO₃)₃, 1,0 mol L^-1 HCl i 0,5 mol L^-1 KBr) i tako pripremljena elektroda je primenjena za karakterizaciju i određivanje pomenutog jedinjenja u alkalnoj sredini. Redukcioni signal ispitivanog analita od analitičkog značaja je uočen jedino primenom BiF-GCE u Briton-Robinson puferusa pH vrednostima između 9,5 i 11,8 u režimu adsorptivne inverzne/stripingvoltametrije sa pravougaonim talasima, dok u slučaju direktnih katodnih SWV eksperimentalnih uslova uočen je slab redukcioni pik sa niskom strujom maksimuma pika. Optimizovani eksperimentalni uslovi za određivanje 3-dehidro-deoksiholata obuhvataju odgovarajuće kondicioniranje elektrode uključujući kondicioniranje  ex situ pripremljene BiF-GCE u Briton-Robinson pomoćnom elektrolitu pH 11,8 do stabilizacije struje bazne linije elektrohemijskim cikliranjem potencijala radne elektrode u potencijalskom opsegu između -1,00 i -2,00 V u odnosu na ZKE (blizu 15 puta) i primenu dva ključna parametara adsorptivne voltametrije sa pravougaonim talasima: vreme akumulacije od 30 s i potencijal akumulacije  -1,00 V u odnosu na ZKE. Zbog relativne asimetričnosti dobijenih redukcionih signala ispitivanog analita sa  E_p na -1,35 V u odnosu na ZKE, što je takođe prisutno i u slučaju primene SW-AdSV, određivanje ispitivanog analita je zasnovano na linearnoj zavisnosti između površine pika redukcionog signala  spitivanog analita i njegove odgovarajuće koncentracije i postignuta granica detekcije je 1,43 µg mL^-1 sa dva linearna opsega kalibracione krive od 4,76 µg mL^-1 do 13,0 µg mL^-1 i od 13,0 µg mL^-1 do 23,1 µg mL^-1 za razvoj analitičke metode. RSD metode je 3,22%. Dodatni eksperimenti, elektroliza ispitivanog analita na potencijalu -1,55 V (blizu maksimuma pika ciljnog analita) u odnosu na ZKE su rađeni primenom GCE u obliku ploče (površina 33,52 cm 2 ) modifikovane sa  ex situ pripremljenim bizmut-filmom. Rastvor od interesa uzorkovan je na početku eksperimenta, nakon 2,5 h i nakon 4,5 h tretmana. Ovakvi uzorci su analizirani primenom ¹H NMR merenja uz potiskivanje signala vode u puferskom rastvoru pH 11,8. Može se pretpostaviti da tokom elektrolize 3-dehidro-deoksiholata dolazi do redukcije keto grupe prisutne u strukturi ispitivanog analita.Na osnovu literaturnih podataka da neki od ciljnihmakrolidnih antibiotika kao što je npr. azitromicin pokazuju oksidativno ponašanje na elektrodi od ugljenične paste i elektrodi od zlata deteljna karakterizacija i određivanje  četiri makrolidna antibiotika rađena je primenom  asične elektrode od ugljenične paste (CPE) koja se sastoji samo od grafitnog praha i parafinskog ulja sa optimizovanih direktnih anodnih SWV metoda. U slučaju EES-a i AZI-a diferencijalna pulsna voltametrija (DPV) je testirana za iste svrhe. Ključni  parametar u slučaju razvoja analitičkih voltametrijskih metoda je odabir pH vrednosti pomoćnog elektrolita gde je oblik/simetričnost i intenzitet oskidacionog pika glavni kriterijum prilikom odabira. Kao odgovarajuće pH vrednosti za voltametrijsko određivanje EES-a primenom SWV metode odabrana je pH 8,0 sa E_p na 0,83V u odnosu na ZKE, dok u slučaju DPV metode pH 12,0 sa  E_p na 0,55 V u odnosu na ZKE je bila najpogodnija za analitičke svrhe. Za određivanje AZI-a, u slučaju obe SWV i DPV metode pH 7,0 se pokazala najpogodnijom sa E_p analitičkog signala na 0,85 V odnosno 0,80 V u odnosu na ZKE, dok u slučaju CLA i ROX koji su ispitivani samo primenom SWV metode za analitičke svrhe pH 12,0 je bila najpogodnija sredina sa E_p analitičkog signala na 0,65 V odnosno na 0,63 V u odnosu na ZKE. Postignute granice detkcije primenom nemodifikovane CPE i direktne anodne SWV su uglavnom u submikrogramskom koncentracionom opsegu 0,17 µg mL^-1 , 0,32  µg mL^-1 i 0,30  µg mL^-1, u slučaju EES-a, AZI-a i ROX-a i u niskom mikrogramskom koncentracionom opsegu 1,43  µg mL^-1 za CLA. Razvijena SWV metoda sa jednostavnom CPE pokazala se pogodnom za određivanje ROX-a u komercijalnom proizvodu Runac^® tableti. U slučaju optimizovanih DPV metoda postignute granice detekcije za EES i AZI su u niskom mikrogramskom  koncentracionom opsegu 1,03  µg mL^-1 odnosno 1,53  µg  mL^-1 . U želji da se postigne niža granica detekcije za AZI, DPV metoda  je testirana u kombinaciji sa  CPE radnom elektrodom površinski modifikovanom sa zlatnim nanočesticama  prečnika 10 nm (Au-CPE) i  postignuta granica detekcije je 0,95  µg mL^-1 sa  E_p analitičkog signala na 0,80 V u odnosu na  ZKE. RSD metode u slučaju Au-CPE je 3,5%, dok je u slučaju nemodifikovane CPE 6,0%.  Linearnost analitičke metode zasnovane na primeni Au-CPE je dva puta šira nego u slučaju  primene nemodifikovane CPE.Na osnovu dobijenih rezultata može se zaključiti da  odgovarajuće kombinacije  optimizovanih voltametrijskih tehnika sa ekološki prihvatljivim i lako primenljivim radnim  elektrodama, kao što su Hg(Ag)FE, BiF-GCE i CPE zajedno sa Au-CPE, rezultuju razvojem  pouzdanih analitičkih metoda, kako u oksidacionim tako i u redukcionim proučavanjima, koje  često omogućuju  određivanje tragova analita od farmakološkog značaja u jednostavnim, a u nekim slučajevima i u složenim sistemima. 
Nowadays in different analytical laboratories there is the increasing number of analytical protocols, either based on highly sophisticated or simpler measurements techniques, which serving for determination of different target analytes of pharmacological importance. Among such target groups of the analyte belongs the antibiotics which present a great discovery in the field of medicine and thanks to them were saved more than seven million people but beside to the mentioned great benefits, antibiotics can cause a large number of side effects and bile acids together with their derivatives which are physiological detergents but if their concentration is notcontrolled they can be cytotoxic to the body. In the present doctoral dissertation the development of analytical methods, primarily analytical voltammetric methods in combination with simple and contemporary electrodes/sensors, for the determination of selected analytes as antracycline antibiotic doxorubicin (DOX), macrolide antibiotics erythromycin ethylsuccinate (EES), azithromycin (AZI), clarithromycin (CLA) and roxithromycin (ROX) and 3-dehydrodeoxycholic acid were performed.Voltammetric characterization and determination of the above mentioned antibiotics using a renewable silver-amalgam film electrode (Hg(Ag)FE) was performed by direct cathodic square-wave voltammetry (SWV) and by highly sensitive adsorptive square-wave voltammetry (SW-AdSV) in aqueous Britton-Robinson buffer solutions as supporting electrolyte covering the wider pH range. The Hg(Ag)FE response of DOX was monitored in the potential range between -0.20 and -0.80 V. For the trace level analysis the method optimization showed that the optimal conditions for the analytical peak with peak potential (E_p) at -0.57 V vs. SCE were: the pH 6.0, the accumulation potential -0.20 V, and the accumulation time 140 s. In the model solutions, DOX was determined in the concentration range of 4.99-59.64 ng mL^-1. The developed SWAdSV method was applied for the determination of DOX in spiked human urine sample. The lowest concentration of DOX of 9.89 ng mL^-1 in voltammetric vessel was determined with the relative standard deviation (RSD) less than 6%. As for the investigated macrolides, they showed reduction signals in fairly negative potential range. During direct cathodic SWV investigations conducted over the potential range from -0.75 V to -2.00 V vs. SCE, either one or two reduction peaks were obtained in the  potential range from -1.5 to -1.9 V. For analytical purposes concerning the development of direct cathodic SWV and adsorptive stripping SWV methods the neutral  and slightly alkaline media were suitable as pH 7.0 with E_p at -1.67 V vs.  SCE for ROX and EES and pH 7.2 and pH 7.4 with E_p at -1.85 V and -1.64 V vs. SCE for AZI and CLA, respectively. Based on the cyclic voltammograms recorded at these pH values, adsorptioncontrolled electrode kinetics process can be proposed for all four investigated compounds. The water suppressed ¹H NMR measurements in the pH range between 6.0 and 10.5 indicated that the macrolide molecules at the optimal analytical conditions are predominantly in protonated form via their tertiary amino groups which supported in all four cases their adsorption on the appropriately polarized Hg(Ag)FE electrode. The optimized direct cathodic SWV methods showed good linearity in concentration ranges 4.81-23.3 μg mL^-1, 4.53-29.8 μg mL^-1, 1.96-28.6  μg mL^-1, and 1.48-25.9 μg mL^-1 for AZI, EES, CLA and ROX, respectively. The SW-AdSV methods resulted in the linear responses at lower concentration ranges as 1.0-2.46 μg mL^-1, 0.69- 2.44 μg mL^-1, 0.05-0.99 μg mL^-1 and 0.10-0.99 μg mL^-1, for AZI, EES, CLA and ROX, respectively. The RSD for all developed methods was not higher than 1.5% except the SWV method for AZI with 4.7%. The direct cathodic SWV method was successfully applied for the determination of EES in the pharmaceutical preparation Eritromicin^®, while SW-AdSV was tested in the case of the spiked urine sample and for determination of ROX in pharmaceutical preparation Runac^®. In all above cases, the standard addition method was used. The reliability and accuracy of the above procedures in the case of EES determination in model system and pharmaceutical preparation Eritromicin^® were validated by comparing them with those obtained by means of HPLC-DAD measurements.After initial study of 3-dehydro-deoxycholic acid/3-dehydro-deoxycholate by glassy carbon electrode, where the absence of any reduction peak was observed in the Britton-Robinson buffer solutions between pH 5.0 and 11.8 by direct cathodic SWV, a bismuth-film was electrodeposited ex situ on the same glassy carbon electrode surface (BiF-GCE) from the usually used plating solution (0.02 mol L^-1 Bi(NO₃)₃, 1.0 mol L^-1 HCl and 0.5 mol L^-1 KBr) and such prepared film-electrode was applied for the characterization and determination of the the target analyte in alkaline media. The reduction signal of analytical importance was observed only by BiF-GCE in Britton-Robinson buffer solutions with pH values between 9.5 and 11.8 in adsorptive stripping square-wave voltammetry working regime, while in the case of the direct cathodic SWV experimental protocol only a very poor reduction peak was obtained. The optimized experimental conditions for the 3-dehydro-deoxycholate determination consist of the optimized electrode conditioning including the electrochemical cycling of the ex situ prepared BiF-GCE potentials in the potential span between -1.0 and -2.0 V vs. SCE (nearly 15 times) in the Britton-Robinson supporting electrolyte pH 11.8 till the stabilization of the baseline current, and the application of two key parameters of the adsorptive square-wave voltammetric protocol: the accumulation time as 30 s and accumulation potential as -1.0 V vs. SCE. Because of the relative asymmetry of the obtained reduction signals of the target analyte with peak E_p at -1.35 V vs. SCE, which is still present in the case of the SW-AdSV, the quantification of the target analyte was based on the linear correlation between peak area of the reduction signal and its appropriate concentrations, and reached limit of detection is 1.43 μg mL^-1 and with two linear ranges of calibration curve from 4,76 μg mL^-1 to 13.0 μg mL^-1 and from 13,0 μg mL^-1 to 23,1 μg mL^-1 for the development of analytical method. The RSD of the method  was 3.22%. Additional experiments were performed applying GCE with rectangular form (area 35.32 cm²) modified with ex situ prepared bismuth-film for the electrolysis of the target analyte which was performed at the potential -1.55 V (nearly the peak maxima of the target analyte) vs. SCE. The solution of interest was sampled at the beginning of the experiment, after 2.5 h and after 4.5 h of treatment. Such samples were analysed by simply water suppressing ¹H NMR measurements in the buffered solution at pH 11.8. It can be assumed that during electrolysis of 3-dehydrodeoxycholate the reduction of the keto group present in the structure of the target analyte can be occurred.Driven by earlier literature data about the fact that some of the target macrolide antibiotics as e.g. azithromycin showed oxidation behavior at a carbon paste and gold working electrodes detailed characterization and determination of four target macrolide antibiotics were performed on classical carbon paste electrode (CPE) constituted only from graphite powder and paraffin oil with optimized direct anodic SWV methods. In the cases of EES and AZI differential pulse voltammetric (DPV) methods were tested for the same purpose as well. The key parameter in the case of the development of the analytical voltammetric methods is the selection of the pH value of the supporting electrolyte where the shape/simmetry and intensity of the oxidation peak were the criteria. As the appropriate pH value for determination of EES by SWV method the pH 8.0 was selected with E_p at 0.83 V vs. SCE while in the case of the DPV method the pH 12.0 with E_p at 0.55 V vs. SCE was the most suitable for analytical  purpose. As for AZI determination, in the case of both SWV and DPV methods the pH 7.0 was the most appropriate supporting electrolyte with the Ep of analytical signal at 0.85 V and 0.80 V vs. SCE, respectively, while in the case of CLA and ROX which were investigated only with SWV method for the analytical purposes the pH 12.0 was the most suitable with E_p at 0.65 V and at 0.63 V vs. SCE. The obtained detection limits applying the bare CPE and the direct anodic SWV are mainly  in submicrogram concentration range as 0.17 μg mL^-1; 0.32 μg mL^-1 and 0.30 μg mL^-1 for EES, AZI, and ROX and in the low microgram concentration range as 1.43 μg mL^-1 for the CLA, respectively. The developed method succesfully tested for the determination of ROX in the commercial formulation, Runac^® tablet. In the case of the optimized DPV methods the obtained detection limits for EES and AZI are in the low microgram concentration range 1.03 μg mL^-1 and 1.53 μg mL^-1, respectively. For the improvement of the sensitivity for AZI the DPV method was tested in combination with a  CPE working electrode surface modified with gold nanoparticles with diameter of 10 nm (Au-CPE) and reached the limit of detection was 0.95 μg mL^-1 at E_p of 0.80 V vs. SCE. The RSD of the method in the case of the Au-CPE is 3.5% while in the case of the native CPE 6.0%. The linearity of the Au-CPE based analytical method is twice wider then it is case with the bare CPE applying protocol.Based on the obtained results it can be conclude that the appropriate combination of the optimized voltammetric pulse techniques and the environmentally friendly and easy to use working electrodes as Hg(Ag)FE, BiF-GCE and CPE together with Au-CPE resulted in the development of reliable analytical method either in the oxidation or reduction studies, often allowing trace level determination of pharmacological importance target analytes in simpler and in some case complexes systems.

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CoordenaÃÃo de AperfeÃoamento de Pessoal de NÃvel Superior
The aim of this work was to study the electrochemical behavior of antifungal ketoconazole on polished Silver Solid Amalgam Electrode (p-AgSAE).The study began with the evaluation of the best electrolyte for ketoconazole (KC) electrochemical reduction and the BrittonâRobinson buffer solution at pH 12 was selected as the best support electrolyte. In the following, with a constant ketoconazole concentration (1.0x10-5 mol L-1) the square wave voltammetric parameters were optimized for the p-AgSAE. The best experimental responses were achieved with 100 s-1 frequency, 25 mV of amplitude and 2 mV of scan increment. The results showed that ketoconazole is reduced in a quasi-reversible process, with one reduction peak at -1.50 V vs. Ag/AgCl/Cl- reference system. After optimized the SWV parameters, the analytical studies were developed in accord to ANVISA for validation the methodology. Linearity range, detection and quantification limits, precision, robustness and accuracy were evaluated. An analytical curve was constructed, that presented a linear region to 4.97x10-7 a 4.30x10-6 mol L-1 with a correlation coefficient to 0.9989. The detection limits for the concentration range were determined as 63.4 μg L-1 while the quantification limits were to 211.5 μg L-1. Studies of accuracy of the methodology were made in different formulations: tablet, cream and shampoo. The values obtained were to 100.8% for the electrolyte, 91% for the tablet, 104% for the cream and 103% for the shampoo. The Relative Standard Deviation (RSD) for the accuracy was less than 5.0%. Quantum chemical calculations were also made with the aim of studying the electronic characteristics of the molecule, and predicting which region of the molecule occurs a electrochemical reduction. It was investigated the distribution of charge on the molecule and the molecular orbital (HOMO and LUMO), which are possible sites of oxidation and reduction, respectively. The LUMO was located on the imidazole ring. In the sequence of the mechanistic elucidation, it was made an exhaustive electrolysis (E = -1,8V during six hours) with monitoring by UV-Vis, being used in the studies that identify the products, the technique of nuclear magnetic resonance espectroscopy, NMR H1. In accord to the study, the reduction of KC occur between the C-N bond on the imidazole ring.
No presente trabalho foi investigado o comportamento eletroquÃmico do antifÃngico Cetoconazol (CTZ) sobre o Eletrodo SÃlido de AmÃlgama de Prata (p-AgSAE). A otimizaÃÃo das condiÃÃes de reduÃÃo foi obtida por voltametria de onda quadrada (VOQ), onde foram analisadas as condiÃÃes mais adequadas para a realizaÃÃo dos experimentos. O meio de trabalho escolhido foi TampÃo BR 0,04 mol L-1. Foi avaliada a influÃncia do pH, onde o valor escolhido para estudar a reduÃÃo do analito foi 12. Os parÃmetros da VOQ otimizados foram frequÃncia (100 s-1), amplitude (25 mV) e incremento de potencial (2 mV). De acordo com os resultados, foi observado que o CTZ sofre um processo de reduÃÃo em -1,5 V vs. Ag/AgCl/Cl-. A concentraÃÃo de CTZ utilizada nos estudos de otimizaÃÃo foi de 1,0x10-5 mol L-1. ApÃs estabelecimento dos parÃmetros experimentais, foram estudadas as figuras de mÃrito especificadas pela ANVISA para validaÃÃo de mÃtodos analÃticos na anÃlise de fÃrmacos. Assim, foram avaliados regiÃo de linearidade (4,97x10-7 a 4,30x10-6 mol L-1 com R = 0,9993), limites de detecÃÃo(1,19x10-7 mol L-1 - 63,4 μg L-1) e de quantificaÃÃo (3,98x10-7 mol L-1 - 211,5 μg L-1), precisÃo e robustez. Os estudos de exatidÃo da metodologia foram feitos em diferentes produtos comerciais: comprimido, creme e xampu. Para fins de comparaÃÃo e avaliaÃÃo de possÃvel influÃncia do meio eletroquÃmico na resposta, foi feito o estudo de exatidÃo utilizando curvas de recuperaÃÃo para o eletrÃlito de suporte, onde o valor da taxa de exatidÃo foi de 100,1%. Assim, os valores das taxas de exatidÃo para as amostras foram de 91% para a amostra de comprimido, 104% para a amostra de creme e 103% para a amostra de xampu. Os valores de RSD para as amostras foram inferiores a 5%. CÃlculos quÃmico-quÃnticos tambÃm foram feitos com o objetivo de estudar as caracterÃsticas eletrÃnicas da molÃcula, e prever qual regiÃo tem maior probabilidade de sofrer a reduÃÃo. De fato, foram investigadas as distribuiÃÃes de carga na molÃcula, bem como os orbitais de fronteira (HOMO e LUMO), que sÃo possÃveis sÃtios de oxidaÃÃo e reduÃÃo, respectivamente. O LUMO foi localizado sobre o anel imidazÃlico. Na sequÃncia da elucidaÃÃo mecanÃstica, foi feita uma eletrÃlise exaustiva (E = -1,8V durante seis horas) com acompanhamento por espectroscopia UVVis, sendo utilizada nos estudos de identificaÃÃo do produto a tÃcnica de espectroscopia de ressonÃncia magnÃtica nuclear, RMN H1. Com base neste estudo, foi constatado que o CTZ sofreu uma reduÃÃo na dupla ligaÃÃo entre C-N do anel imidazÃlico da molÃcula de CTZ.

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This work concern to the characterization of the silver nanoparticles electrodeposition process into a carbon paste (CP), made by mixing carbon powder and mineral oil in the rate of 70/30, respectively. This electrode was used to investigate the dopamine oxidation and its quantification. Voltammetric studies of the electrodeposition process indicated that the silver reduction occurred by two different processes at potentials more negatives than 0.000 V and -0.150 V and it exhibited only one anodic peak to silver metallic oxidation. These two processes were dependent of the silver ion concentration into the CP. In addition, the reduction occurred mainly in the nearest layer of the carbon paste/aqueous solution interface which was strongly influenced by added NaCl into the CP. Scan electron microscopy (SEM) photographs indicated that the silver electrodeposition occurred on some flakes of carbon powder with a homogeneous silver nanoparticles layer, regardless of the composition of the modified CP. X ray diffraction analysis not showed diffraction lines to silver metallic that indicated silver nanoparticles or amorphous formation. The dopamine oxidation during the voltammetry at the carbon paste electrode containing AgNO3, without and with NaCl, occurred in parallel to silver oxidation at the same range of potential, which was aqueous solution composition dependent. The graphic of the anodic charger to the dopamine and silver oxidations obtained in NaCl solution exhibits linear relation in the range of 2.50 × 10-5 – 1.50 × 10-4 mol L-1, with linear regression equations qa = 2.77 + 4.50 × 10-3 [DA], but when sodium disulfite was added to the solution, it was not obtained a good reproducibility of the curve. In this case, this system was not satisfactory to determine dopamine in pharmaceutic formulations.
Este trabalho trata da caracterização do processo de eletrodeposição de nanopartículas de prata dentro de uma pasta de carbono (PC) feita pela mistura de pó de grafite e óleo mineral na razão de 70/30, respectivamente. Este eletrodo foi usado para investigar a oxidação de dopamina e sua quantificação. O estudo voltamétrico do processo de eletrodeposição indicou que a redução de prata ocorreu por dois processos diferentes a potenciais mais negativos que 0,000 V e -0,150 V e exibiu somente um pico anódico para oxidação da prata metálica. Estes dois processos foram dependentes da concentração de íons prata na PC. Ademais, a redução ocorreu principalmente na camada mais próxima da interface PC/solução aquosa, a qual foi fortemente influenciada pelo NaCl adicionado dentro da PC. Fotografias obtidas por microscopia eletrônica de varredura (MEV) indicaram que a eletrodeposição de prata ocorreu sobre algumas placas de grafite com uma camada homogênea de nanopartículas de prata, independentemente da composição da PC modificada. Análises por difração de raios X não mostraram linhas de difração para a prata metálica, indicativo da formação de nanopartículas de prata ou prata amorfa. A oxidação de dopamina durante a voltametria no eletrodo de pasta de carbono contendo AgNO3, sem e com NaCl, ocorreu em paralelo a oxidação de prata na mesma faixa de potencial, a qual foi dependente da composição da solução. O gráfico das cargas anódicas para a oxidação de dopamina e prata, obtido em solução de NaCl exibiu relação linear na faixa de 2,50 × 10-5 – 1,50 × 10-4 mol L-1, com equação de regressão linear qa = 2,77 + 4,50 × 10-3 [DA], porém quando se adicionou bissulfito de sódio à solução, não se obteve uma boa reprodutibilidade para a curva. Neste caso, este sistema, não foi satisfatório para a determinação de dopamina em formulações farmacêuticas.

RESUME

Le travail de thèse porte sur le développement d’électrodes sélectives originales et performantes pour l’analyse de composés d’intérêt pharmaceutique.

La partie introductive traite des notions relatives à l’électrochimie mais également de notions sur les molécules médicamenteuses étudiées, en l’occurrence les principes antipaludéens et l’iode.

La partie expérimentale se subdivise en deux parties distinctes selon le type d’électrodes sélectives auxquelles font appel les techniques électrochimiques.

La première partie concerne l’élaboration, la caractérisation et l’application des électrodes potentiométriques à membrane polymérique incluant une paire d’ions et sélectives à diverses molécules organiques pharmacologiquement actives (antipaludéens). Leur application aussi bien en analyse pharmaceutique qu’en cinétique de dissolution est décrite.

La deuxième partie est consacrée à l’élaboration d’un type de senseur ampérométrique original à pâte de carbone à base d’argent micronisé ou colloïdal et à la comparaison de ses performances avec l’électrode d’argent métallique. L’intérêt analytique est mis en évidence par la détermination quantitative des iodures.

Les différents aspects susceptibles d’influencer leur comportement, dont la nature des agents précipitants (tétraphénylborate de sodium et le tétrakis (4-chlorophényl) borate de potassium) et de plastifiants ont été investigués.

Les bonnes performances des ces électrodes en analyse quantitative ont permis d’explorer les possibilités de leur utilisation à l’étude de la cinétique de dissolution.

L’ampérométrie à électrode à pâte de carbone modifiée à base d’argent à l’échelle micronisée (35% m/m) couplée à la chromatographie liquide ionique s’est avérée très sensible vis-à-vis des iodures en particulier et des halogénures en général. Les facteurs susceptibles d’influencer les grandeurs de séparation et la réponse de l’électrode ont été investigués et l’exploitation du signal ampérométrique permet le dosage sélectif et rapide de faibles concentrations en iodures. Les informations fournies par les mesures réalisées en voltampérométrie cyclique à l’aide des mêmes électrodes permettent une bonne compréhension mécanistique quant au mode de détection ampérométrique évitant ainsi toute confusion à ce sujet et permettant l’optimisation du processus de détection.

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ABSTRACT

This thesis describes the development of original and high performance selective electrodes for the analysis of several pharmaceutical compounds.

The introduction describes the pharmaceutical compounds of interest (antimalarial drugs and iodine) and provides an overall understanding of the electrochemical groundwork pertaining to their analysis.

The experimental aspect of the thesis is divided into two parts, each according to the type of electrode and electrochemical technique used for the analysis.

The first part describes the design, characterization, and application of polymer membrane based ion selective potentiometric electrodes. Selectivity was provided by including ion pairs of several antimalarial drugs into the membrane. The feasibility of use of these electrodes in pharmaceutical analysis as well as in dissolution trials is also described in this part.

The second part describes the design of an original silver-modified carbon paste amperometric sensor and compares its performances to those of a plain metallic silver electrode. The electrode has been modified by silver microparticles or by silver nanoparticles. Quantitative iodine determination serves to prove the usefulness of this new sensor in analytical chemistry.

Different aspects, such as the nature of the counter ions (sodium tetraphenylborate and potassium tetrakis (4-chlorophenyl) borate) and the plastifying agents that are likely to influence electrode behaviour have been investigated.

Since the electrodes have been shown to perform well in quantitative analysis, the possibility of use in dissolution trials was explored.

Micronized silver-modified carbon paste electrode (35% Ag m/m) coupled to anionic-exchange liquid chromatography with amperometric detection was shown to be very sensitive with regards to the assay of halogenides in general and iodide in particular. After having investigated the various factors likely to influence chromatographic separation and electrode response, it was shown that the sensor could be used to rapidly and selectively determine low iodide concentrations in complex samples. Cyclic voltammetric analysis provided information concerning the mechanisms allowing amperometric detection, thus allowing an optimisation of the detection procedures.

Doctorat en Sciences biomédicales et pharmaceutiques
info:eu-repo/semantics/nonPublished

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 ≈...

碩士
南臺科技大學
化學工程與材枓工程系
107
Nowadays sometimes preservatives are used in food industry. For example, hydrogen peroxide is one of the preservatives. Hydrogen peroxide has the effect of sterilization and preservation. Therefore, developing a sensor which can detect the amount of hydrogen peroxide rapidly is an important research subject. The Copper Hexacyanoferrate and Nano Silver Powder possess the effect of elevating the responding current of detecting hydrogen peroxide. They can be used with the carbon powder which possesses conductivity to make the carbon paste electrode. At 30 ℃ and 700 rpm stirring rate, a factorial design involving three factors[(A)operating potential (B)Copper Hexacyanoferrate : Nano Silver Powder (C)pH value of phosphate solution] and two levels was conducted to analyze the effect of operating parameters on the sensitivity and average responding current of detecting hydrogen peroxide. The results of analysis of variance showed that the main effects of operating potential (F=113.554, p value < 0.05), Copper Hexacyanoferrate : Nano Silver Powder (F=169.823, p value < 0.05) and pH value of phosphate solution(F=631.982, p value < 0.05) were significant on the sensitivity. The results of factorial design showed that the optimum operating conditions for this study were operating potential = -300 mV, Copper Hexacyanoferrate : Nano Silver Powder = 3 : 2, and the pH value of phosphate solution = 7.4. At 30℃, 700 rpm stirring rate, and the pH value of phosphate solution = 7.4, the carbon paste electrode was modified by Copper Hexacyanoferrate and Nano Silver Powder [ Copper Hexacyanoferrate：Carbon Powder：Carbon Paste：Nano Silver Powder = 3：7：10：2 ] to detect the sensitivity and average responding current of hydrogen peroxide. At the optimum operating conditions, the detection limit was 0.03 mM H2O2, the linear range was 0.03 ~ 2.0 mM H2O2, R2 = 0.9914 and the sensitivity was 299.50 μA / cm2．mM H2O2.

碩士
南臺科技大學
化學工程與材枓工程系
104
Hydrogen peroxide is widely used in many fields and sometimes it was used in the food industry for the purpose of sterilization and bleaching. Therefore, it is an important research subject to develop a rapid, economical, and convenient hydrogen peroxide sensor. The Chromium Hexacyanoferrate and Nano Silver Powder possess excellent catalytic characteristic and the carbon powder and carbon paste possess the conductivity. In this study, Chromium Hexacyanoferrate and Nano Silver Powder were used as the mediator and were used with the carbon powder and carbon paste to make the carbon paste electrode and to elevate the catalytic ability of reducing the hydrogen peroxide. A study of factorial design involving three factors（operating potential, Chromium Hexacyanoferrate：Nano Silver Powder and pH value of phosphate solution）and two levels was performed to analyze the effect of reaction parameters on the sensitivity and average responding current of detection of hydrogen peroxide for the carbon paste electrode modified with the Chromium Hexacyanoferrate and Nano Silver Powder. The results of analysis of variance showed that the main effects of operating potential (F = 168.748, p value＜0.05), Chromium Hexacyanoferrate：Nano Silver Powder (F = 465.298, p value＜0.05), and pH value of phosphate solution (F = 61.901, p value＜0.05) were significant on the sensitivity. The results showed that the optimum operating conditions for this research were operating potential = -200 mV, Chromium Hexacyanoferrate：Nano Silver Powder = 3：3 and pH value of phosphate solution = 7.4. At 30℃, the operating conditions of carbon paste electrode（Chromium Hexacyanoferrate：carbon powder：carbon paste：Nano Silver Powder = 3：7：10：3）were -200 mV operating potential, pH value of phosphate solution = 7.4, and 700 rpm stirring rate. The detection limit was 0.02 mM H2O2, the linear range was 0.02 ~ 3.2 mM H2O2, R2 = 0.9979, the sensitivity was 236.48 µA/cm2．mM H2O2, and average responding current was 3.885 µA.

碩士
南臺科技大學
化學工程與材枓工程系
105
Hydrogen peroxide is widely used in daily life. The food safety has attracted more attention nowadays, in the food industry, hydrogen peroxide is used for the purpose of sterilization, and preservation. Hydrogen peroxide is also widely used in cosmetic. Therefore, developing a rapid and convenient hydrogen peroxide sensor is an important research subject. The Nickel Hexacyanoferrate and Nano Silver Powder possess the catalytic characteristic of reducing hydrogen peroxide. They can be used with the carbon powder and carbon paste which possess conductivity to make the carbon paste electrode and elevate the responding current of detecting hydrogen peroxide. A study of experimental design involving three factors (operating potential, Nickel Hexacyanoferrate : Nano Silver Powder and pH value of phosphate solution) and two levels was conducted to analyze the effect of operating parameters on the sensitivity and average responding current of detection of hydrogen peroxide for the carbon paste electrode modified by Nickel Hexacyanoferrate and Nano Silver Powder. The results of analysis of variance showed that the main effects of operating potential (F= 167.32, p value < 0.05), Nickel Hexacyanoferrate : Nano Silver Powder (F= 859.92, p value < 0.05), and pH value of phosphate solution (F= 147.579, p value < 0.05) were significant on the sensitivity. The results of experimental design showed that the optimum operating conditions for this study were operating potential = -250 mV, the optimum ratio was Nickel Hexacyanoferrate : Carbon Powder : Carbon Paste : Nano Silver Powder = 3：7：10：3, and the pH value of phosphate solution = 7.4. At the optimum operating conditions, and at 30 ℃, stirring rate = 700 rpm, and in 0.05M phosphate solution, the detection limit was 0.01 mM H2O2, the linear range was 0.01 ~ 4.4 mM H2O2, R2 = 0.9989 and the sensitivity was 294.14 μA / cm2．mM H2O2.

碩士
南臺科技大學
化學工程與材枓工程系
104
The research of sensor is an important research subject. Hydrogen peroxide is widely used in industry. Especially in the food industry, hydrogen peroxide is used for the purpose of sterilization, bleaching and preservation. The food safety has attracted more attention nowadays, and therefore, developing a rapid and convenient hydrogen peroxide sensor is an important research subject. The Cobalt Hexacyanoferrate and Nano Silver Powder possess the catalytic characteristic and they can be used with the carbon powder and carbon paste which possess the high conductivity to make the carbon paste electrode and elevate the responding current of detecting hydrogen peroxide. A study of experimental design involving three factors (operating potential, Cobalt Hexacyanoferrate : Nano Silver Powder and pH value of phosphate solution) and two levels was conducted to analyze the effect of operating parameters on the sensitivity and average responding current of detection of hydrogen peroxide for the carbon paste electrode modified with Cobalt Hexacyanoferrate and Nano Silver Powder. The results of analysis of variance showed that the main effects of operating potential (F= 92.337, p value < 0.05) and Cobalt Hexacyanoferrate : Nano Silver Powder (F= 96.248, p value < 0.05) were significant on the sensitivity. The pH value of phosphate solution (F= 0.818, p value > 0.05) was not significant on the sensitivity. The results of experimental design showed that the optimum operating conditions for this study were operating potential = -200 mV, the optimum ratio was Cobalt Hexacyanoferrate : Carbon Powder : Carbon Paste : Nano Silver Powder = 3：7：10：2, and the pH value of phosphate solution = 7.4. At the optimum operating conditions, and at 30 ℃, stirring rate = 700 rpm, the detection limit was 0.06 mM H2O2, the linear range was 0.06 ~ 4.0 mM H2O2, R2 = 0.9976 and the sensitivity was 356.65 μA / cm2．mM H2O2.

The electrochemic's behaviour of the bile acids (cholic, glycocholic, deoxycholic, ursodeoxycholic and lithocholic acid) was studied on the meniscus-modified silver solid amalgam electrode (m-AgSAE) by differential pulse voltammery. Bile acids provide in the solution of the Britton - Robinson buffer and methanol (9:1) in the pH range 3.0 to 12.0 a cathodal signal in the high negative potentials: cholic acid, deoxycholic acid, ursodeoxycholic acid and lithocholic acid about −1400 mV and glycocholic acid, which alone is the conjugate with glycine, about −1500 mV. Cholic acid, glycocholic acid, deoxycholic acid and ursodeoxycholic acid provide the highest peaks to pH 5.0, approximately in their pKa values. Lithocholic acid provides peaks from pH 7.0. It was demonstrated by the cyclic voltammetry that the electrochemical behavior is influenced by the adsorption of the bile acids to the electrode; presumed reaction at the working electrode - a reduction of a proton of a carboxylic group, is controlled by the diffusion and the process is quasireversible. Utilization of the electrochemical reduction of bile acids for the voltammetric determination does not seem very suitable. It has been proven that the presence of the methanol deteriorates the measuring results for glycocholic acid. In the presence of...

Various types of electrochemical sensors based on the inhibition of butyrylcholinesterase (BChE) have been presented for the analysis of organophosphates (OPC). A special design of thick film sensors and electrochemical detector for cholinesterases assay and their inhibitors in aqueous samples has been developed. For this assay, thiol sensitive sensors based on screen printed graphite electrode modified with nanoparticles of manganese dioxide were used. High sensitivity of manganese dioxide modified thick film sensors towards thiocholine and therefore low detection limit of BChE (1 pM) enabled their use for subnanomolar detection of an organophosphate pesticide diazinon, and other irreversible inhibitors of BChE. This work also presents modern innovative approach for the analysis of BChE by Raman spectroscopy. New SERS-substrates based on silver paste for sensitive quantification of BChE activity were obtained, characterized and applied to thiocholine detection, with LOD (TCh) being 260 nM. Real samples of human plasma were analyzed; a good correlation between spectrophotometric detection and Raman detection was shown. The developed technique is inexpensive and easy-to-use and has promising potential for analysis of OPC.

Various types of electrochemical sensors based on the inhibition of butyrylcholinesterase (BChE) have been presented for the analysis of organophosphates (OPC). A special design of thick film sensors and electrochemical detector for cholinesterases assay and their inhibitors in aqueous samples has been developed. For this assay, thiol sensitive sensors based on screen printed graphite electrode modified with nanoparticles of manganese dioxide were used. High sensitivity of manganese dioxide modified thick film sensors towards thiocholine and therefore low detection limit of BChE (1 pM) enabled their use for subnanomolar detection of an organophosphate pesticide diazinon, and other irreversible inhibitors of BChE. This work also presents modern innovative approach for the analysis of BChE by Raman spectroscopy. New SERS-substrates based on silver paste for sensitive quantification of BChE activity were obtained, characterized and applied to thiocholine detection, with LOD (TCh) being 260 nM. Real samples of human plasma were analyzed; a good correlation between spectrophotometric detection and Raman detection was shown. The developed technique is inexpensive and easy-to-use and has promising potential for analysis of OPC.

This paper presents the fabrication of ITO nanofibers as gas sensor. ITO nanofibers are fabricated by electrospinning process. Sensors based on ITO nanofibers were prepared on Si substrate and silver paste was used as electrode. The morphology and crystal structure of ITO nanofibers were studied by SEM and XRD, respectively. The optimal working temperature and sensitivity of ITO nanofiber sensors were investigated. The sensitivity of ITO nanofiber sensor has been found to increase to a peak of 9.8 at 160°C for 50 ppm NO2, which suggests that ITO nanofibers sensor provides significantly better sensitivity for NO2 at lower temperature.