Water in soybean oil microemulsions as medium for electrochemical measurements

Mendonça, Carla Rosane Barboza; Bica, Clara Isméria Damiani; Piatnicki, Clarisse Maria Sartori

doi:10.1590/s0103-50532003000400021

Cited by 14 publications

(18 citation statements)

References 32 publications

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“…Also the stability of MEs diminished with the reduction of the cosurfactant:surfactant ratio. 25 As shown in Table 1, MEs prepared with 1-pentanol were the most conductive, followed by those prepared with 3-methyl-1-butanol. MEs prepared with 1-hexanol presented the lowest values of electrical conductivity, about three times lesser than those prepared with 1-pentanol.…”

Section: Physical-chemical Characterization Of Mesmentioning

confidence: 95%

“…This agrees with the smaller refractive index of the alcohols with respect to that of the soybean oil (1.4093, 1.4061 and 1.4179 for 1-pentanol, 3-methyl-1-butanol and 1-hexanol, respectively, but 1.475 for soybean oil). 34,25 Viscosity was not expressively affected by the variation of the alcohol ratio in MEs; however, by comparing MEs with equal SDS:alcohol ratios, the MEs prepared with 1-hexanol showed the largest viscosity. This agrees with the higher viscosity of this alcohol (4.578 cP) with respect to 1-pentanol (3.619 cP) and 3-methyl-1-butanol (3.692 cP).…”

Section: Physical-chemical Characterization Of Mesmentioning

confidence: 96%

“…25 The results of physical-chemical characterization of the MEs are shown in Table 1. It was verified that the droplet hydrodynamic radius (R H ) of the MEs prepared with 1-pentanol tended to become smaller with the increase of concentration of this co-surfactant, while for the other two tested co-surfactants, the reverse effect was observed; however, the differences were not large.…”

Section: Physical-chemical Characterization Of Mesmentioning

confidence: 99%

“…4, 2008 Procedures ME preparation and characterization MEs were prepared by sequentially mixing the surfactant (SDS) with an alcohol co-surfactant and water and, finally, adding soybean oil to the mixture. The proportions of the ME components were taken from a previous work, 25 where the best surfactant/co-surfactant ratios, capable of producing stable thermodynamic systems, were described. However, to acquire a better knowledge about the physical-chemical properties of these MEs, different surfactant/co-surfactant ratios were also tried.…”

Section: Instrumentationmentioning

confidence: 99%

“…Even in this case, an UME has the advantage of a reduced charge time, 22,23 which allows the study of very fast reactions, of the order of microseconds. 24 In this sense, linear voltammetry measurements 25 in resistive media 26 like the w/o MEs employed in this study, can be performed by an UME.…”

Section: Introductionmentioning

confidence: 99%

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Physical chemical properties and kinetics of redox processes in water/soybean oil microemulsions

Mendonça¹,

Bica²,

Simó‐Alfonso³

et al. 2008

J. Braz. Chem. Soc.

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Microemulsões de água em óleo (ME w/o) constituídas de água, óleo de soja, SDS (dodecil sulfato de sódio) e diversos álcoois de cadeia curta foram caracterizadas sob o ponto de vista físico-químico e de propriedades eletroanalíticas. Foram testados diferentes co-surfactantes e razões surfactante:cosurfactante, sendo a ME com a composição mais favorável utilizada para estudar a cinética de processos redox. Para tanto, realizaram-se medidas de voltametria cíclica utilizando como eletrodo de trabalho um ultramicroeletrodo de disco de Pt e, como eletrodo de referência e auxiliar, foram usados Ag/AgCl e Pt, respectivamente, e ferroceno como uma sonda. Verificou-se que a estabilidade termodinâmica das MEs aumenta com o conteúdo de co-surfactante. A estrutura molecular e a solubilidade em água do co-surfactante afetam a condutividade elétrica e o raio hidrodinâmico das MEs. Devido aos baixos coeficientes de difusão observados na ME, foi possível a realização de medidas em estado transiente usando velocidades de varredura convencionais. A oxidação do ferroceno na ME demonstrou ocorrer em condições de quasi-reversibilidade. Assim, foi demonstrada a possibilidade de realizar estudos por voltametria cíclica em óleos vegetais sob a forma de ME w/o.Water/oil microemulsions (w/o ME) constituted by water, soybean oil, SDS (sodium dodecyl sulfate) and several short-chain alcohols were characterized from the viewpoint of its physical-chemical and electroanalytical properties. Different co-surfactants and surfactant:co-surfactant ratios were used, and the ME with the most favourable composition was used to study the kinetics of redox processes. For this purpose, cyclic voltammetry measurements using a Pt disk working ultramicroelectrode, an Ag/AgCl reference electrode and a Pt auxiliary electrode, and ferrocene as a probe, were performed. It was verified that the thermodynamic stability of the MEs increases with the co-surfactant content. The molecular structure and water solubility of the co-surfactant affect the electrical conductivity and the hydrodynamic radio of the MEs. Owing to the low diffusion coefficients verified in the MEs, measurements in transient state using conventional sweeping rates could be performed. Ferrocene oxidation in the ME has been demonstrated to proceed in quasi-reversibility conditions. Thus, the possibility of carrying out studies of cyclic voltammetry in vegetable oils under the w/o ME form was demonstrated.Keywords: w/o microemulsions, physical chemical properties, redox process, cyclic voltammetry, vegetable oils IntroductionValuable information relative to structure evolution, inter-particle interactions and transport data of mass and charge in diverse media, can be obtained by using electrochemical techniques. 1-3 However, the application of these techniques in nanoheterogeneous systems, including microemulsions (MEs), has been scarcely exploited. MEs are optically transparent, isotropic and thermodynamically stable systems. Water in oil (w/o) MEs are formed by water droplets dispersed in an oi...

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Section: Physical-chemical Characterization Of Mesmentioning

confidence: 95%

Section: Physical-chemical Characterization Of Mesmentioning

confidence: 96%

Section: Physical-chemical Characterization Of Mesmentioning

confidence: 99%

Section: Instrumentationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Physical chemical properties and kinetics of redox processes in water/soybean oil microemulsions

Mendonça¹,

Bica²,

Simó‐Alfonso³

et al. 2008

J. Braz. Chem. Soc.

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Carbon Microsphere – Polystyrene Composite Electrode for Three‐Phase Boundary Oil Analysis: Quinizarin in Methyllaurate

et al. 2015

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Quinizarin (see molecular structure and redox processes in Scheme 1) is water-insoluble in the ambient pH range and has been shown to be electrochemically active. In technical application, quinizarin has been proposed as colorant and anti-corrosion coating for anodised aluminium [11].M olecular quinizarin adsorbed onto carbon has been shown to catalyse the oxygen reduction process [12,13].Q uinizarin has also been shown to act as aM ichael-acceptor when oxidised [14] and this has potential implications in electroanalytical detection of sulphur species.W hen examined as aD NA groove-binding redox reagent, quinizarin has been shown to act as af luorescence reporter in biological samples [15] and it has been investigated as am odel system for anti-cancer drug molecules [16].H owever, the main application of quinizarin is as dye-marker additive in hydrocarbon oils [17,18] for safety and tax reasons.Methyllaurate is am ajor component in bio-fuels [19] and employed here as a" model oil" with quinizarin as a" model redox marker". Then ewly developed electroanalytical method based on ac arbon microsphere composite electrode could be applied to aw ider range of oils containing redox active substances such as anti-oxidants. No electrolyte is added to the oil phase which is deposited directly into ap orous carbon electrode made from ac omposite with glassy carbon microspheres and polystyrene.F igure 1s hows as chematic drawing of the electrode with as mall amount (A) and with ah igher amount (B) of oil deposited. Thee lectrochemical reaction is believed to occur at the three-phase boundary.AFaradaic current is anticipated as long as the electro-analyte (quinizarin in oil) can diffuse towards the three-phase boundary,w here ions (here protons) present in the neighbouring phase can balance the build-up of charge resulting from the electron transfer. From an electroanalytical standpoint, not having to alter or prepare the sample before electrochemical analysis is beneficial and developing as imple "dip-probe" method could be very useful.In this study ac ost efficient and easy-to-make (potentially disposable) porous carbon electrode is fabricated to facilitate three-phase boundary electrochemistry.T he Abstract:O il analysis for the case of quinizarin in methyllaurate is demonstrated with ad isposable carbon microsphere -p olystyrene composite electrode.O xidation and reduction of quinizarin are observed as three-phase boundary processes at the immiscible oil j water j carbon interface.R andomly packed glassy carbon microspheres (2-12 mmd iameter) held together with ap olystyrene binder (ca. 0.1 %b yw eight) are immobilized onto ap encil lead electrode and used for electrochemical oil analysis.P orefilling with oil is optimised for voltammetric detection and fluorescence spectroscopy is employed to support the mechanistic analysis based on voltammetry.F uture applications for aw ider range of oils and additives are proposed.

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Electrokinetic capillary chromatography in a polar continuous‐phase water‐in‐oil microemulsion constituted by water, sodium dodecyl sulfate, and n‐pentanol

et al. 2005

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A water-in-oil (w/o) microemulsion (ME) constituted by 15% Tris buffer, pH 8.4, in water and 85% sodium dodecyl sulfate (SDS)/n-pentanol 1:4 mixture, capable of dissolving up to 30% vegetable oils and lard, was used as background electrolyte in reverse microemulsion electrokinetic capillary chromatography (RMEEKC). Owing to the free SDS ions in the continuous phase and some degree of percolation, the ME showed a high conductivity (0.65 mS. cm(-1) at 25 degrees C) and sustained a very stable capillary current. Previous rinsing of the capillary with a quaternary ammonium salt for electroosmotic flow (EOF) reduction, a series of nonionic and anionic solutes dissolved either in the ME or in fat samples diluted with the ME (1:4 ratio), were injected. Using -20 kV, fair separations of the solutes in the migration time order singly charged anions < nonionic solutes < doubly charged anions approximately pyromellitate were obtained, salicylate (I) showing by far the shortest migration time, and phthalate (II) and pyromellitate the longest. Separation was attributed to partition between the aqueous droplets, where pyromellitate and II were assumed to be trapped, and the n-pentanol continuous phase, where the mobilitites could be also modified by association of the solutes with SDS ions. Adequate EOF markers were not found, thus the relative mobility of any solute with respect to the mobility of the droplets, mu(r), was expressed as a fraction of the mobility of I with respect to that of the droplets, being mu(r) = (t(II) - t(R)) t(I) / [(t(II) - t(I)) t(R)], where t(R), t(I), and t(II) are the migration times of the solutes I and II, respectively. The application of RMEEKC to the analysis of both hydrophilic and hydrophobic samples, including edible fats, was demonstrated.

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Water in soybean oil microemulsions as medium for electrochemical measurements

Cited by 14 publications

References 32 publications

Physical chemical properties and kinetics of redox processes in water/soybean oil microemulsions

Physical chemical properties and kinetics of redox processes in water/soybean oil microemulsions

Carbon Microsphere – Polystyrene Composite Electrode for Three‐Phase Boundary Oil Analysis: Quinizarin in Methyllaurate

Electrokinetic capillary chromatography in a polar continuous‐phase water‐in‐oil microemulsion constituted by water, sodium dodecyl sulfate, and n‐pentanol

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