Search

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.

This work describes preparation and application of “homemade” chloride ISE enriched with iron oxides or zinc oxide nanoparticles. The prepared chloride ISE membrane was made of AgCl:Ag2S:PTFE = 1:1:2 and AgCl:Ag2S:PTFE = 2:1:2 enriched with mentioned nanoparticles in ratio 0.5-1.2 wt.%. Prepared membranes were used for chloride determination in perchloric acid (pH = 0-2) and acetic buffer (pH = 4 – 4.75). Due to the low method price, simplicity and a reasonably fast way of usage, it was considered as a possibility for chloride determination in high acid media. Two of prepared membranes (M1 and M4) have shown best characteristics. M1 showed linear response range for chloride between 2.0×10−6 and 1×10−1 mol L−1, with a detection limit of 2.24×10−6 mol L−1 and potential change of 44.39 mV per decade. M4 showed linear response range for chloride between 4.2×10– 6 to 1×10–1 mol L−1, limit of detection of 1.39×10–6 mol L−1 with potential change of 24.79 mV per decade at pH = 0.

The effect of sodium dextran sulphate (Mw = 500,000) on the forced hydrolysis of FeCl3 solutions was investigated using a microwave-assisted method. Reference samples obtained upon 10 to 120 min of forced hydrolysis of the FeCl3 solution showed the presence of an α-Fe2O3 phase alone. After 10 min of the forced hydrolysis of FeCl3 in the solution containing sodium dextran sulphate, α-Fe2O3 and additionally β-FeOOH precipitated. The Mossbauer spectra of α-Fe2O3 precipitated in the presence of sodium dextran sulphate showed a significant broadening of spectral lines accompanied by decreased values of the hyperfine magnetic field. This was explained by lower α-Fe2O3 crystallinity. The FESEM of reference α-Fe2O3 samples showed cube-like particles of good uniformity in the submicrometer range. In the presence of dextran sulphate polymer, the α-Fe2O3 particles of varying sizes and close to egg-like shape were obtained as a result of the specific adsorption of sulphates on the oxide surface and steric conditions created by dextran branches.

The metal content (iron and copper) was potentiometrically analyzed in 44 tea samples. The analyzed samples included chamomile (Matricaria chamomilla), green tea (Camellia sinensis), sage tea (Salvia officinalis L.), linden (Tilia L.) and mint (Mentha piperita) in tea bags and bulk purchased at local supermarkets and marketplaces in Split, Croatia. Tea samples digestion was performed in microwave oven by using nitric acid and hydrogen peroxide mixture. Potentiometric determination was performed by using FISE for Fe3+ and CuISE for Cu2+, respectively, by using potentiometric methods previously developed in our laboratory. The measured results were compared with atomic absorption spectrometric measurements from our previous research and showed notable statistical superposition.

Ionsko-selektivne membrane u svrhu potenciometrijskog određivanja koncentracije željezovih(III) kationa u otopinama, sastavljene su od laboratorijski pripravljenih taloga željezovog(III) fosfata i srebrovog sulfida uz dodatak komercijalnog politetrafluoretilena (PTFE). S obzirom da je senzor (M1) sastava FePO4 : Ag2S : PTFE = 1:1:2 prilikom testiranja u laboratorijski pripremljenoj otopini željezovih(III) kationa prema istima pokazao promjenu potencijala u ovisnosti o promjeni koncentracije Fe3+ kationa u skladu sa zahtjevima Nernstove jednadžbe, membrana je zatim primijenjena za određivanje Fe3+ kationa u otopinama realnih uzoraka lijekova koji se koriste za nadomještanje manjka koncentracije željeza u krvi. Predložena metoda određivanja željeza validirana je usporedbom rezultata s rezultatima predočenim na deklaraciji samog lijeka te određivanjem nasumično pripremljene koncentracije željezovih(III) kationa u laboratorijski pripremljenoj otopini. Tako je mikrovalnom digestijom jedne tablete farmaceutika potenciometrijski potvrđena koncentracija u iznosu od 1, 8൉10-3 molL-1 dok je deklaracijom istaknuto 2, 5൉10-3 molL-1 Fe3+ kationa pri pH vrijednosti 1. S druge strane, određivanjem koncentracije Fe3+ kationa u laboratorijski pripravljenoj otopini, potvrđena je očekivana koncentracija i to uz podudarnost od 100%. Sve navedeno ukazuje kako su ovdje prikazani laboratorijski pripravljeni senzori pogodni za određivanje Fe3+ kationa u realnim uzorcima.

Forced hydrolyses in the precipitation systems (a) Fe(NO3)(3)/Fe-2(SO4)(3) and FeCl3/Fe-2(SO4) (3) and (b) FeCl3/N-guanylurea sulphate were investigated using Fe-57 Mossbauer and FT-IR spectroscopies and scanning electron microscopy (FE SEM). Forced hydrolyses of Fe(NO3)(3)/Fe- 2(SO4)(3) solutions at 90 degrees C yielded superparamagnetic goethite nanorods, whereas in the case of FeCl3/Fe-2(SO4)(3) solutions the clusters of akaganeite nanoneedles were formed. With a prolonged heating time at 90 degrees C the conversion of these akaganeite nanoneedles into goethite nanorods was observed. Forced hydrolysis in the system FeCl3/N- guanylurea sulphate at 160 degrees C generated only hematite and goethite phases and their fractions depended on the concentration of FeCl3 and the amount of N-guanylurea sulphate in the solution. Different shapes of iron(III) oxyhydroxides and hematite in dependence on the experimental conditions were monitored with FE SEM. Specifically adsorbed sulphates on these particles, as shown by FT-IR spectroscopy, served as directing agents in the particle/crystal growth.

Potentiometric ion determination method is very inexpensive, simple and reasonably fast method so due to that it is often applied for different cations or anions determination. “Home-made” ferrous ion-selective electrode has been prepared by constructing a solid membrane disk consisting of

Nanostructural morphology and cation (divalent or tetravalent) doping are known to be important factors for photocatalytic and photoelectrochemical activities of iron oxides. Modifications of iron oxides in an appropriate way could significantly improve these activities. In the present work the effects of Cu doping on the microstructural, thermal, optical and photocatalytic properties of goethite (α-FeOOH) and hematite (α-Fe2O3) 1D nanoparticles were investigated. Goethite and Cu-doped goethite 1D nanoparticles were synthesized by precipitation in a highly alkaline medium. Hematite and Cu-doped hematite 1D nanoparticles were prepared by calcination of goethite samples at 500 °C. Cu2+-for-Fe3+ substitution in goethite and hematite was confirmed by determining the change in unit cell size using X-ray powder diffraction and by measuring the hyperfine magnetic field reduction using Mossbauer spectroscopy. An increased Cu2+-for-Fe3+ substitution in goethite caused a gradual elongation and narrowing of nanorods with the formation of nanoneedles at 3 or 4 mol% Cu. The shape and size of nanoparticles were not changed by thermal transformation of goethite to hematite. Thermal analysis showed a lower temperature of goethite dehydroxylation upon increased Cu doping. Cu2+-for-Fe3+ substitution in goethite and hematite caused increased absorption of visible and near-IR radiation beyond the absorption edge, as well as a slight decrease in direct and indirect optical band gaps compared with pure phases. The visible light photocatalytic activities of Cu-doped goethite and hematite nanoneedles were significantly improved compared with undoped goethite and hematite nanorods, which could be attributed to a combined effect of nanoneedle morphology and Cu doping.

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&ndash, 1.22 mg L&minus, 1), putrescine (0.41&ndash, 7.5 mg L&minus, 1) and ethanolamine (2.87&ndash, 24.32 mg L&minus, 1). White wines from the Hrvatsko zagorje region are characterised by content of isopentylamine (0.31&ndash, 1.47 mg L&minus, 1), putrescine (0.27&ndash, 1.49 mg L&minus, 1) and ethanolamine (3.80&ndash, 17.96 mg L&minus, 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.

This paper describes the preparation and application of “home-made” iodide ISE enriched with ZnO nanoparticles. Iodide ISE membrane was made of AgI:Ag2S:PTFE = 1:1:2 and enriched with ZnO nanoparticles in ratio 1-5.0 wt.%. Prepared membranes were used for penicillamine (Pen) determination in acetic buffer (pH = 4-4.75) and in perchloric acid (pH = 1-2). Due to the low price method, simplicity and relative speed, a possibility for Pen determination was found. Pen determination showed better results in an acetic buffer, pH = 4 than in perchloric acid. All experiments for Pen measurements were done without pretreatment of pharmaceuticals. The determination is based on the reaction between Pen with both Ag+ and Zn2+ from the electrode membrane. A newly described method has linear response range for Pen 2.45×10−6-1×10−2 mol L−1 and a detection limit of 2.24×10−6 mol L−1. The found concentrations of Pen are in a very good agreement with the declared ones with the standard deviation of 2.70 %.

Iron oxides and oxyhydroxides are common and widespread compounds in nature. Goethite (α- FeOOH) and hematite (α-Fe2O3) are the most stable and the most ubiquitous iron oxyhydroxide and iron oxide, respectively. A number of favourable properties (nontoxicity, stability, low cost, band gap in the visible range, etc.) make these compounds promising candidates for different applications (catalysts, photocatalysts, gas sensors, battery electrodes, supercapacitors, etc.). Properties of goethite and hematite can be enhanced by modification of particle size and shape, as well as by incorporation of different metal cations into their crystal structure. For example, elongated (1D) hematite nanoparticles (nanorods) showed higher visible-light photocatalytic activity compared to hematite nanoplates (2D) or nanocubes (3D). Substitution of Fe3+ ions with other metal ions can also significantly modify different properties. Ni-doped goethite (α-FeOOH) nanorods were synthesized from mixed Fe(III)-Ni(II) nitrate aqueous solutions by a hydrothermal treatment in a highly alkaline medium using a strong organic alkali tetramethylammonium hydroxide (TMAH). Small amounts of Ni-containing ferrihydrite and Ni ferrite were present as minor phases in samples with 10 mol% Ni and more. Ni-doped hematite (α- Fe2O3) nanorods were obtained by calcination of Ni-doped goethite nanorods at 400 °C. Ni-for-Fe substitution in the structure of goethite and hematite was confirmed by the determination of the unit cell expansion using XRPD and by the measurement of the hyperfine magnetic field (HMF) reduction using Mössbauer spectroscopy. Ni-doped goethite and hematite nanorods were smaller compared to reference samples for 5 mol % Ni but significantly larger for higher Ni contents. Electrochemical measurements showed significant increase in oxygen evolution reaction (OER) catalytic activity of Ni-doped goethite and Ni-doped hematite nanorods compared to pure phase.

The aim of our work was an implementation of potentiometric determination of copper in samples of the genus Veronica (family Plantaginaceae). Genus Veronica herbs are widely used in e.g. cosmetic, traditional medicine and food industry. The copper content was potentiometrically analysed in 25 herbal samples of genus Veronica and 12 of their hydrolats. The analysed samples were herbal samples of Veronicas harvested mainly in three Croatian regions – Dalmatia, Lika and Slavonia as well as randomly selected samples of theirs hydrolats. Veronicas’ samples were digested in a microwave oven by using nitric acid and hydrogen peroxide mixture. The potentiometric determination was performed by using commercially available CuISE for Cu2+, by using potentiometric methods previously developed in our laboratory.

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 β FeOOH α-Fe2O3 via dissolution/ recrystallization occurred in the precipitation system. In the presence of SDS small amounts (traces) of α-FeOOH as an intermediate phase precipitated, and with a prolonged time of forced hydrolysis α-FeOOH also transformed to α-Fe2O3 via the dissolution/recrystallization mechanism. On the basis of Mössbauer spectra it was concluded that in the presence of SDS the α-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 α-Fe2O3 particles possessed a substructure. The elongation of primary α-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 α-Fe2O3 phases during the forced hydrolysis of FeCl3 solutions. This work is licensed under a Creative Commons Attribution 4.0 International License.