Electrochemical Sensors Modification with Metal Oxide Nanoparticles

Elektrokemijski senzori su zbog svoje jednostavnosti izrade i upotrebe u kontinuiranom razvoju već više od stoljeća te su brojnim modifikacijama dosegli brojna poboljšanja, što se posebno odnosi na povećanje osjetljivosti i selektivnosti, proširenje linearnog dinamičkog područja te sniženje granice dokazivanja analita. Spomenuta poboljšanja posljedica su noviteta u samoj izvedbi i izgledu elektrokemijskih senzora, kao i sve češće uporabe različitih nanomaterijala kao modifikatora. Među najčešće upotrebljavanim modifikatorima su upravo nanočestice metalnih oksida koje se u senzorima pojavljuju samostalno ili u kombinaciji s drugim materijalima. Posebno se ističe kombinacija nanočestica metalnih oksida i grafena ili (reduciranog) grafenova oksida. Navedena dva materijala sinergijski djeluju s obzirom na to da su grafenski slojevi zaduženi za bolju električnu vodljivost, a nanočestice metalnih oksida za sprječavanje njihove agregacije. Također, česta je i kombinacija s višeslojnim ili jednoslojnim ugljikovim nanocjevčicama te nanočesticama metala. Postoje radovi u kojima su kombinirane različite vrste nanočestica metalnih oksida, što je posebno istaknuto kod kombinacije Al2O3 i ZnO. Osim aluminijeva i cinkova oksida, u ovom radu je prikazan pregled literature upotrebljavanih nanočestica željezovih i bakrovih oksida u procesu modifikacije elektrokemijskih senzora. Uz to, prikazani su podatci o analitu, metode određivanja, linearno dinamičko područje senzora te granica dokazivanja analita. Očit je širok spektar vrsta analita čije je određivanje moguće ovakvim vrstama senzora kao i širok spektar elektroanalitičkih metoda koje su prilikom toga primjenjivane. Ipak, među metodama su najzastupljenije voltametrijske, dok je potenciometrijska metoda primjenjivana u svega nekoliko referencija.Due to their simplicity of manufacture and use, electrochemical sensors have been continuously developed for more than a century, and have achieved numerous improvements, particularly related to increasing sensitivity and selectivity, extending the linear dynamic range, and lowering the limit of detection. The mentioned improvements are the result of innovations in electrochemical sensor design, as well as the more frequent use of different nanomaterials as modifiers. Among the modifiers most frequently used are metal oxide nanoparticles, which are founding sensors alone or in combination with other materials. The combination of metal oxide nanoparticles and graphene or (reduced) graphene oxide is particularly noteworthy. These two materials positively influence each other, as the graphene layers are responsible for better electrical conductivity and the metal oxide nanoparticles for preventing their aggregation. Combinations with multi-walled or single-walled carbon nanotubes and metal nanoparticles are commonly described too. There are publications giving the description of combined different types of metal oxide nanoparticles, which is particularly evident in the combination of Al2O3 and ZnO. In addition to aluminium and zinc oxide, this article reviews the literature on iron and copper oxide nanoparticles used in the modification of electrochemical sensors, the analyte, the method of determination, the linear dynamic range of the sensor, and the limit of detection. The types of analytes that can be determined with these sensors are as varied as the methods used. However, among the methods, the voltammetric method is the most represented, while the potentiometric method has been used in only a few references

Potentiometric Sensors for Iron(III) Cations Determination

Elektrokemijski senzori imaju sposobnost pretvorbe elektrokemijske reakcije koja se odvija između analita i elektrode u analitički koristan signal. Potenciometrijski senzori, ionsko-selektivne elektrode, kao važan član obitelji elektrokemijskih senzora, u središtu su brojnih istraživanja već gotovo cijelo stoljeće. Njihov stalni razvoj te kombinacija s razvojem drugih znanstvenih i tehnoloških područja osigurali su im širok spektar primjene. Svojstva ionsko-selektivnih elektroda kao što su jednostavnost metode, niska cijena, mala veličina senzora, kratko vrijeme očitavanja signala i pouzdanost učinila su ih vrijednim konkurentima među brojnim sofisticiranijim metodama za određivanje koncentracije analita u širokom spektru različitih realnih uzoraka bez ili uz minimalnu obradu uzorka. S obzirom na široku distribuciju i visoku važnost željezovih(III) kationa u ljudskom organizmu ali i okolišu, postoji visoka potreba za razvojem analitičkih alata za njihovo brzo i efikasno određivanje. U ovom je radu predstavljen niz literaturnih izvora koji obrađuju razvoj potenciometrijskih senzora upotrijebljenih za određivanje željezovih(III) kationa s naglaskom na znanstvene radove objavljene u posljednjem desetljeću. Iz spomenutih literaturnih izvora uspoređeni su aktivni centri senzora, linearno dinamičko područje, granica detekcije te promjene potencijala u ovisnosti o koncentraciji analita. Također, utvrđeno je kako su Fe3+ kationi uspješno određeni u brojnim realnim uzorcima poput farmaceutskih pripravaka, bioloških uzoraka, različitim uzorcima vode (pitkoj, otpadnoj, mineralnoj…), prehrambenim proizvodima poput zelenog i crnog čaja i dr. Upravo zbog širokog linearnog područja, niske granice detekcije te širokog spektra realnih uzoraka u kojima ih je moguće primijeniti ionsko-selektivne elektrode perspektivni su kandidati za zamjenu nekih sofisticiranijih metoda za određivanje željezovih(III) kationa.Electrochemical sensors have the ability to convert the electrochemical reaction that occurs between the analyte and the electrode into a useful signal. Potentiometric sensors, ion-selective electrodes, an important member of the electrochemical sensor family, have been the focus of much research for almost a century. Their constant development and combination with the development of other scientific and technological fields have given them a wide range of applications. Properties of ion-selective electrodes, such as simplicity of method, low cost, small sensor size, fast response, and reliability, have made them valuable competitors of other methods for determining the concentration of analytes in different real samples with minimal or no pretreatment of the samples. Considering the wide distribution and great importance of iron(III) cations in the human body and environment, there is a great need to develop analytical tools for their rapid and efficient determination. This paper, presents different literature sources dealing with the development of potentiometric sensors for the determination of iron(III) cations, focusing on scientific papers published in the last decade. The active centre of the sensor, its linear dynamic range, the limit of detection, and the change in potential depending on the change in analyte concentration are shown. It has been found that Fe3+ cations can be determined successfully in numerous real samples, such as pharmaceutical preparations, biological samples, different water samples (drinking, waste, mineral...), food products such as green and black tea, etc. Thanks to the wide linear range, low detection limits, and a wide range of real samples in which they can be applied, ion-selective electrodes are promising candidates for replacing some more sophisticated methods for the determination of iron(III) cations

Monitoring of the Forced Hydrolysis of FeCl3 Solutions in the Presence of Sodium Dodecyl Sulphate

Precipitations by the forced hydrolysis of 0.2 M FeCl3 aqueous solutions between 2 and 72 hours in the presence of 1% sodium n-dodecyl sulphate (SDS) were investigated. In the absence of SDS a direct phase transformation b- FeOOH → a-Fe2O3 via dissolution/ recrystallization occurred in the precipitation system. In the presence of SDS small amounts (traces) of a-FeOOH as an intermediate phase precipitated, and with a prolonged time of forced hydrolysis a-FeOOH also transformed to a-Fe2O3 via the dissolution/recrystallization mechanism. On the basis of Mössbauer spectra it was concluded that in the presence of SDS the a-Fe2O3 phase exhibited a lower degree of crystallinity. During the precipitation process in the presence of SDS the competition between the stability of Fe(III)-dodecyl sulphate on one side and the formation of iron oxide phases on the other also played an important role. Thermal field emission scanning electron microscopy (FE SEM) revealed that the big a- Fe2O3 particles possessed a substructure. The elongation of primary a-Fe2O3 particles produced in the presence of SDS was noticed. This effect can be assigned to the preferential adsorption of sulphate groups on nuclei and crystallites of FeOOH and a-Fe2O3 phases during the forced hydrolysis of FeCl3 solutions

Monitoring of the Forced Hydrolysis of FeCl3 Solutions in the Presence of Sodium Dodecyl Sulphate

Precipitations by the forced hydrolysis of 0.2 M FeCl3 aqueous solutions between 2 and 72 hours in the presence of 1% sodium n-dodecyl sulphate (SDS) were investigated. In the absence of SDS a direct phase transformation b- FeOOH → a-Fe2O3 via dissolution/ recrystallization occurred in the precipitation system. In the presence of SDS small amounts (traces) of a-FeOOH as an intermediate phase precipitated, and with a prolonged time of forced hydrolysis a-FeOOH also transformed to a-Fe2O3 via the dissolution/recrystallization mechanism. On the basis of Mössbauer spectra it was concluded that in the presence of SDS the a-Fe2O3 phase exhibited a lower degree of crystallinity. During the precipitation process in the presence of SDS the competition between the stability of Fe(III)-dodecyl sulphate on one side and the formation of iron oxide phases on the other also played an important role. Thermal field emission scanning electron microscopy (FE SEM) revealed that the big a- Fe2O3 particles possessed a substructure. The elongation of primary a-Fe2O3 particles produced in the presence of SDS was noticed. This effect can be assigned to the preferential adsorption of sulphate groups on nuclei and crystallites of FeOOH and a-Fe2O3 phases during the forced hydrolysis of FeCl3 solutions

Chemical vs. Physical Methods to Improve Dermal Drug Delivery: A Case Study with Nanoemulsions and Iontophoresis

So far, various approaches have been proposed to improve dermal drug delivery. The use of chemical penetration enhancers has a long history of application, while methods based on the electrical current (such as iontophoresis) stand out as promising “active” techniques. Aiming to evaluate the contribution of different approaches to dermal delivery, in this work curcumin-loaded nanoemulsions with and without monoterpenes (eucalyptol or pinene) as chemical penetration enhancers, and a custom-made adhesive dermal delivery system based on iontophoresis were designed and assessed. In an in vivo study applying skin bioengineering techniques, their safety profile was proven. Three examined iontophoresis protocols, with total skin exposure time of 15 min (continuous flow for 15 min (15-0); 3 min of continuous flow and 2 min pause (3-2; 5 cycles) and 5 min of continuous flow and 1 min pause (5-1; 3 cycles) were equally efficient in terms of the total amount of curcumin that penetrated through the superficial skin layers ( in vivo tape stripping) (Q3-2 = 7.04 ± 3.21 μg/cm2; Q5-1 = 6.66 ± 2.11 μg/cm2; Q15-0 = 6.96 ± 3.21 μg/cm2), significantly more efficient compared to the referent nanoemulsion and monoterpene-containing nanoemulsions. Further improvement of an efficient mobile adhesive system for iontophoresis would be a practical contribution in the field of dermal drug application

The New Ion-Selective Electrodes Developed for Ferric Cations Determination, Modified with Synthesized Al and Fe−Based Nanoparticles

The solid-state ion-selective electrodes presented here are based on the FePO4 :Ag2S:polytetrafluoroethylene (PTFE) = 1:1:2 with an addition of (0.25–1)% microwave-synthesized hematite (α-Fe2O3 ), magnetite (Fe3O4 ), boehmite [γ-AlO(OH)], and alumina (Al2O3 ) nanoparticles (NPs) in order to establish ideal membrane composition for iron(III) cations determination. Synthesized NPs are characterized with Fourier-Transform Infrared (FTIR) spectroscopy, Powder X-Ray Diffraction (PXRD), and Scanning Electron Microscopy (SEM) with Energy Dispersive Spectroscopy (EDS). The iron oxides NPs, more specifically, magnetite and hematite, showed a more positive effect on the sensing properties than boehmite and alumina NPs. The hematite NPs had the most significant effect on the linear range for the determination of ferric cations. The membrane containing 0.25% hematite NPs showed a slope of −19.75 mV per decade in the linear range from 1.2·10−6 to 10−2 mol L−1 , with a correlation factor of 0.9925. The recoveries for the determination of ferric cations in standard solutions were 99.4, 106.7, 93.6, and 101.1% for different concentrations

Synthesis and Properties of Ni-doped Goethite and Ni-doped Hematite Nanorods

Ni-doped goethite (α-FeOOH) nanorods were synthesized from mixed Fe(III)-Ni(II) nitrate solutions with various Ni/(Ni+Fe) ratios (0, 5, 10, 20, 33 and 50 mol % Ni) by hydrothermal precipitation in a highly alkaline medium using the strong organic alkali, tetramethylammonium hydroxide (TMAH). Ni-doped hematite (α-Fe2O3) nanorods were obtained by calcination of Ni-doped goethite nanorods at 400 °C. The Ni 2+ -for-Fe 3+ substitution in goethite and hematite was confirmed by determination of the unit cell expansion (due to the difference in the ionic radii of Fe 3+ and Ni 2+ ) using XRPD and determination of the reduction of a hyperfine magnetic field (due to the difference in magnetic moments of Fe 3+ and Ni 2+ ) using Mössbauer spectroscopy. Single-phase goethite nanorods were found in samples containing 0 or 5 mol % Ni. A higher Ni content in the precipitation system (10 mol % or more) resulted in a higher Ni 2+ -for-Fe 3+ substitution in goethite, and larger Ni-doped goethite nanorods, though with the presence of low crystalline Ni-containing ferrihydrite and Ni ferrite (NiFe2O4) as additional phases. Significant changes in FT-IR and UV-Vis-NIR spectra of prepared samples were observed with increasing Ni content. Electrochemical measurements of samples showed a strong increase in oxygen evolution reaction (OER) electrocatalytic activity with increasing Ni content. © 2018 Croatian Chemical Society. All Rights Reserved

Ružička days : International conference 16th Ružička Days “Today Science – Tomorrow Industry” : Proceedings

Proceedings contains articles presented at Conference divided into sections: open lecture (1), chemical analysis and synthesis (3), chemical and biochemical engineering (8), food technology and biotechnology (8), medical chemistry and pharmacy (3), environmental protection (11) and meeting of young chemists (2)

The Content of Biogenic Amines in Croatian Wines of Different Geographical Origins

Samples of white and red wines produced in two different wine-growing regions, coastal (Dalmatia) and continental (Hrvatsko zagorje) of Croatia, were analysed for biogenic amines content. Biogenic amines content was determined, and its concentration levels were associated with the geographical origin of the wine. Due to its high sensitivity, HPLC method with ultraviolet detector was used, including the derivatisation step with dansyl chloride. The method was applied to detect and quantify 11 biogenic amines in 48 red and white wines. It was found that both Dalmatian red and white wines are characterised by tryptamine (0.23–1.22 mg L−1), putrescine (0.41–7.5 mg L−1) and ethanolamine (2.87–24.32 mg L−1). White wines from the Hrvatsko zagorje region are characterised by content of isopentylamine (0.31–1.47 mg L−1), putrescine (0.27–1.49 mg L−1) and ethanolamine (3.80–17.96 mg L−1). In contrast to white wines from the Hrvatsko zagorje region, in the red wines, all biogenic amines except ethylamine, were found and equally presented