A review of a new voltammetric method for determining acids

Takamura, Kiyoko; Fuse, Tetsuo; Arai, Kensuke; Kusu, Fumiyo

doi:10.1016/s0022-0728(99)00049-2

Cited by 54 publications

(40 citation statements)

References 19 publications

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“…26 The occurrence of the prepeak is ascribed to the increased proton availability of the added acid compared to the solvent molecules, leading to the reduction potential shift to a more positive direction depending on the pKa of the added acid. 25 The prepeak height was found to be proportional to the acetic acid concentration from 0.05 to 2.7 mM (r = 0.999) and propionic, butyric, and lactic acids concentrations from 0.05 to 2.5 mM (r >0.999). 29 Based on these findings, acid in the eluate from the separation column in the HPLC system was detected by measuring the current height of a flow signal at the fixed potential.…”

Section: Determination Of Scfas By Hplc-ecdmentioning

confidence: 95%

“…We previously developed a new method for determining acids by voltammetry using a quinone reagent. 25 Since the method was shown to be quite sensitive and selective for acids, the method was successfully applied to the determination of the free fatty acid (FFA) content of fats and oils, 26-28 the total acid content of vinegar, 29 and the FFA concentrations of plasma. In the present study, an HPLC system with electrochemical detection (HPLC-ECD) was fabricated for determining SCFAs in rat and human feces.…”

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confidence: 99%

“…The choice of VK3 as a quinone reagent for preparing the quinone solution was favorable, as it facilitated this determination owing to its reduction potential, stability and solubility in ethanol. 25 SCFAs' determination was carried out using the ion exclusion column, the mobile phase of the 0.1 mM HClO4 and the quinone solution. After a 20-μL standard acid solution aliquot was injected into the column, the eluate was mixed with quinone solution and SCFAs were detected with ECD at -0.9 V vs. Ag/AgCl.…”

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Determination of Short-chain Fatty Acids in Rat and Human Feces by High-Performance Liquid Chromatography with Electrochemical Detection

et al. 2009

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A simple method for determining short-chain fatty acids (SCFAs) in rat and human feces was developed using high-performance liquid chromatography with electrochemical detection (HPLC-ECD). A two-channel HPLC-ECD system was fabricated using an ion exclusion column and an electrochemical detector with a glassy carbon working electrode. Aqueous solutions of 0.1 mM HClO4 and of ethanol containing 2-methyl-1,4-naphthoquinone served as a mobile phase and a quinone solution, respectively. Peak areas for lactic, acetic, propionic, butyric, isovaleric, and valeric acids at a detection potential of -0.9 V vs. an Ag/AgCl electrode showed a linear relationship with the acid amount in the range 0.1 to 40 nmol. Standard acids at 4 nmol were determined ten times with relative standard deviations (RSD) of less than 2.0%. The analytical results of healthy human feces were measured within 35 min. RSD (n = 5) in all SCFAs were less than 2.7%, and recoveries of SCFAs were more than 92%. The present method was characterized by reproducibility with the simple and rapid procedure without derivatization of analytes, and it has the potential for clinical and biomedical applications. IntroductionThe bacteria in human colon obtain energy for growth by fermenting carbohydrates in the colonic lumen, mainly polysaccharides of plant cell walls (dietary "fiber") and some starch. The end-products include around 200 to 400 mmol day -1 of short-chain fatty acids (SCFAs) such as acetic, propionic, and butyric acids. Over 90% are absorbed and used by host, contributing 2 to 10% of daily energy requirements. 1,2 This is particularly important in premature babies with lactose malabsorption. 3 An extensive disease of the bowel, surgical bypass, prolonged antibiotic therapy, total parenteral nutrition, malabsorption, immaturity 4,5 and wide variation in dietary fiber intake may all disturb this important host/bacterial symbiosis. 1,2Since fecal SCFAs reflect colonic fermentation, 6 they are measured in studies to investigate and manipulate such disturbances. Moreover, fecal SCFA composition ratio of ulcerative colitis patients remarkably changes in comparison with that for a healthy human. In particular, the composition of lactic acid, called non-volatile fatty acid (NVFA), increased in comparison with that of acetic, propionic, and butyric acids, called volatile fatty acid (VFA), in feces of ulcerative colitis patients. [7][8][9][10][11][12] Thus, the determination of fecal SCFAs is significant to examine homeostasis, characteristics, and metabolism of intestinal bacterial flora, and it would be useful for monitoring of and diagnostic strategy against diseases in the colon.The determination of SCFAs has been carried out by gas chromatography (GC) [13][14][15][16][17][18] and high-performance liquid chromatography with ultraviolet detection (HPLC-UV), fluorescent detection (HPLC-FL), or mass spectrometric detection (LC-MS). [19][20][21][22][23][24] The fecal analysis by GC required the complicate cleanup of the sample, and it was hard to detect NVFAs ...

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Section: Determination Of Scfas By Hplc-ecdmentioning

confidence: 95%

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confidence: 99%

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Determination of Short-chain Fatty Acids in Rat and Human Feces by High-Performance Liquid Chromatography with Electrochemical Detection

et al. 2009

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“…[9][10][11] Valuable electroanalytical methods for vegetable oils may be derived by preparing the samples as w/o MEs. Considering that species different from triglycerides in edible oils constitute minor components, 12,13 the maximization of oil amount in a ME is desirable. On the other hand, the increase of the oil content affects expressively the electrical conductivity of these systems.…”

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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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“…in vegetable oils. 27,28 Since these species constitute minor components in edible oils, both a maximum amount of oil in the ME is desirable and the standard addition calibration technique should be employed, in order to increase the analysis sensitivity. …”

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Water in soybean oil microemulsions as medium for electrochemical measurements

Mendonça¹,

Bica²,

Piatnicki³

2003

J. Braz. Chem. Soc.

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Microemulsões de água em óleo de soja (w/o ME) foram preparadas com dodecil sulfato de sódio (SDS) como surfactante e com os álcoois amílico ou isoamílico, como co-surfactantes. A composição 40,0% de óleo, 43,2% de álcool, 10,8% de SDS e 6,0% de água, em massa, na razão 1:4 [SDS]: [álcool], apresentou a maior estabilidade termodinâmica. O tamanho das gotículas e seu coeficiente de difusão nas microemulsões, D w/o , foram determinados por medidas de espalhamento de luz dinâmico (DLS). As reações de oxidação de ferroceno (Fc) e de água, e a redução de ácido oleico foram observadas nas ME por voltametria em um ultramicroeletrodo (ume) de disco de Pt. Os valores de D w/o determinados a partir de medidas eletroquímicas são menores do que os calculados a partir daquelas por DLS. Isto indica que a oxidação da água requer a difusão para o eletrodo tanto das gotículas como das moléculas de água nelas contidas. Os resultados evidenciam a possibilidade de determinação de analitos em óleos vegetais por métodos eletroanalíticos.Microemulsions of water in soybean oil (w/o ME) were prepared with sodium dodecyl sulfate (SDS) as surfactant and amyl or isoamyl alcohol, as co-surfactants. Microemulsions containing 40.0% oil, 43.2% alcohol, 10.8% SDS and 6.0% water in weight, in the ratio 1:4 [SDS]: [alcohol] showed the highest thermodynamic stability. The aqueous droplet size and its diffusion coefficient D w/o in the ME were determined through dynamic light scattering (DLS). Voltammetric measurements in the ME at a Pt disk ultramicroelectrode (ume) evidenced the oxidation of both water and ferrocene (Fc), and the reduction of oleic acid. The D w/o values calculated from the limiting current being lower than the ones obtained from DLS indicate that water oxidation probably requires diffusion towards the electrode of both the droplets and the water molecules from inside the droplets. The results show that electroanalytical determinations can be carried out in w/o ME. Keywords: microemulsions, soybean oil, voltammetry, ferrocene, oleic acid IntroductionEquilibria in water-oil interfaces have been studied in order to quantify solvent extraction as well as charge transfer processes. In this sense new analytical methodologies such as slow extrusion of water into a nonaqueous phase (and vice-versa) through a capillary, 1 the use of micrometric electrodes 2-3 and of microemulsions 4,5 (ME) have been proposed recently. Besides a significant decrease in costs and toxicity due to the decrease in organic solvents consumption, 6-8 water in oil ME allow to carry out electrochemical measurements due to the enhanced electrical conductivity imparted to the system by the presence of water.Microemulsions are thermodynamically stable systems composed of water, oil and surfactant, and, in some cases, an alcohol can be added as co-surfactant. 9-12 Their behavior is similar to the one of polar organic solvents and, although apparently homogeneous under visual observation, ME are actually microheterogeneous (perhaps nanoheterogeneous would be a better...

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A review of a new voltammetric method for determining acids

Cited by 54 publications

References 19 publications

Determination of Short-chain Fatty Acids in Rat and Human Feces by High-Performance Liquid Chromatography with Electrochemical Detection

Determination of Short-chain Fatty Acids in Rat and Human Feces by High-Performance Liquid Chromatography with Electrochemical Detection

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

Water in soybean oil microemulsions as medium for electrochemical measurements

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