Organic Solvent Layer Research Articles

Selecting Experimental Conditions for Measurement of Rates of Electron-Transfer at Liquid/Liquid Interfaces by Thin-Layer Electrochemistry

The use of thin layers of water-immiscible organic solvents on electrode surfaces to evaluate rates of electron-transfer across liquid/liquid interfaces requires that reactant concentrations in the two adjacent phases be selected to minimize the effects of mass transfer on the measured currents. A general inequality is derived which provides a guide to the selection of suitable concentrations of the coreactants. Experimental tests of the inequality demonstrated its utility and should allay recently expressed concerns about the reliability of the thin-layer methodology.11

Multicomponent sequential injection analysis determination of nitro-phenols in waters by on-line liquid-liquid extraction and preconcentration

An automatic sequential injection analysis (SIA) set-up for the determination of phenolic compounds (2-, 3- and 4-nitrophenol) in waters was designed and evaluated. The system performs an on-line phenol extraction from an aqueous medium to an organic solvent, which enables the analyte isolation and preconcentration. The extracted phenols are on-line back-extracted into a small volume of NaOH solution and conducted to a spectrophotometric detector for quantitative analysis. This methodology is based on the formation of a thin organic solvent layer adhered to the PTFE surface of the extraction coil. In the present work, no reversed-flow was carried out in both the extraction and back-extraction steps. By using a photodiode-array detector, multilinear regression algorithms and first derivative spectroscopic techniques were evaluated in order to perform multicomponent determinations of phenol mixtures. Concentrations within the range 0.4–4.6 mg l −1 of 2-nitrophenol, 0.6–11.2 mg l −1 of 3-nitrophenol and 55.6–938 mg l −1 of 4-nitrophenol have been determined and simultaneously analysed at a frequency of four samples per hour. A R.S.D. of 2.2% was obtained for 2.6 mg l −1 of 2-nitrophenol, 2.3% for 5.3 mg l −1 of 3-nitrophenol and 2.2% for 330.8 μg l −1 of 4-nitrophenol, with preconcentration factors comprised between seven and nine.

Electron Transfer between Reactants Located on Opposite Sides of Liquid/Liquid Interfaces

A recently introduced method for interposing thin layers of organic solvents between graphite electrode surfaces and aqueous solutions was used to examine the effects of the nature and concentration of the supporting electrolytes on electrochemical responses for reactants dissolved in the thin layers of organic solvent. The method was also used to evaluate the rates of electron transfer between coreactants, each of which was confined to one of the two adjoining, immiscible phases. The rates of these electron-transfer reactions were shown not to be influenced by simultaneous cross-phase ion-transfer processes in cases where such processes were forced to proceed. The rates of the electron-transfer reactions exhibited only weak sensitivity to the driving force of the reactions. This insensitivity was tentatively interpreted as an indication that assembly of the reactant pairs into precursor complexes may be the step that limits the rate of the electron-transfer process.

Electrode Processes in a Thin Layer of Organic Solvent Covering a Hanging Mercury Drop Electrode. Effects on Metal Ion and Fullerene (C60) Reduction

A novel approach to electrochemistry in thin layers of organic solvents is presented. These layers are formed in situ from benzene, o-dichlorobenzene, or dichloromethane on a hanging mercury drop electrode (HMDE). Very thin organic layers are formed by the expansion of a mercury drop and an organic layer into an aqueous bulk phase. The process of expansion and formation of the thin organic layer on mercury was studied by optical microscopy. Modification of the HMDE by these thin layers of organic solvents significantly limits the reduction of metal ions from the aqueous bulk solution. The redox behavior of C60 in these thin films is shown to be highly solvent dependent. This dependence is demonstrated by comparison of the cyclic voltammetry of C60 in a benzene layer with that in an o-dichlorobenzene layer. In the potential range from 0 to −1200 mV, two reversible reduction processes are observed for C60. In benzene, with its very low dielectric constant, the electrode processes are complicated by the precipitation of fulleride salts.

A Simple Method for Examining the Electrochemistry of Metalloporphyrins and Other Hydrophobic Reactants in Thin Layers of Organic Solvents Interposed between Graphite Electrodes and Aqueous Solutions

A method is described for the preparation of stable, adherent, thin layers of organic solvents interposed between the surfaces of graphite electrodes and aqueous supporting electrolytes in which they are immersed. The electrochemistry of reactants dissolved in the thin layers is examined and utilized to evaluate surface coverages and formal potentials for molecules, such as cobalt tetraphenylporphyrins, that do not exhibit useful electrochemical responses when adsorbed on graphite. The thin layers of organic solvent can be used to concentrate analytes by extracting them from dilute aqueous solutions to produce enhanced sensitivity in electroanalytical applications. Electron transfer across the liquid/liquid interface created by the presence of the thin layer of immiscible organic solvent is also demonstrated.

Voltammetry at Micropipet Electrodes

The use of micropipet electrodes for quantitative voltammetric measurements of ion-transfer (IT) and electron-transfer (ET) reactions at the interface between two immiscible electrolyte solutions (ITIES) requires knowledge of geometry of the liquid interface. The shape of the meniscus formed at the pipet tip was studied in situ by video microscopy under controlled pressure. The shape of the interface can be changed from a complete sphere to a concave spherical cap by varying the pressure applied to the pipet, and the diffusion current to the pipet changes accordingly. With no external pressure applied, the water/organic interface turned out to be flat, and the voltammetric response of a pipet must follow the well-known theory for a microdisk electrode. The large deviations from this theory observed previously can be attributed to a small amount of the filling aqueous solution which escapes from the pipet and forms a thin layer on its outer wall. This effect can be eliminated by making the outer pipet wall hydrophobic. Procedures have been developed for independent silanization of the inner and outer walls of the pipet. Pipets with a silanized inner wall can be filled with an organic solvent (e.g., 1,2-dichloroethane) and be used for voltammetric measurements in aqueous solutions. Another mode of voltammetry is based on trapping of a thin layer of organic solvent in the narrow shaft of a pipet between the filling solution and the aqueous outer phase. This arrangement is potentially useful for electrochemical catalysis and sensor applications.

Biodegradation of indole at high concentration by persolvent fermentation with Pseudomonas sp. ST-200.

Pseudomonas sp. strain ST-200 grew on indole as a sole carbon source. The minimal inhibitory concentration of indole was 0.3 mg/ml for ST-200. However, ST-200 grew in a persolvent fermentation system containing a large amount of indole (a medium containing 20% by vol. diphenylmethane and 4 mg/ml indole), because most of the indole was partitioned in the organic solvent layer. When the organism was grown in the medium containing indole at 1 mg/ml in the presence of diphenylmethane, more than 98% of the indole was consumed after 48h. Isatic acid (0.4 mg/ml) and isatin (0.03 mg/ml) were produced as the metabolites in the aqueous medium layer.

Solute collection after off-line supercritical fluid extraction into a moving liquid layer

A solute collection method after off-line supercritical fluid extraction using a moving layer of liquid organic solvent flowing down through a fused-silica capillary (0.5 mm I.D.) is proposed. Recoveries of over 90% were measured for selected polycyclic aromatic hydrocarbons (acenaphthene, phenanthrene, fluoranthene, pyrene and benzo[a]pyrene) and s-triazine herbicides when methanol was used as a trapping solvent.

Oxidative Bioconversion of Cholesterol by Pseudomonas sp. Strain ST-200 in a Water-Organic Solvent Two-Phase System

Pseudomonas sp. strain ST-200, which is capable of conversion of cholesterol, was isolated from humus soil. This organism effectively modified cholesterol dissolved in an organic solvent by dehydrogenation and oxygenation. When the organism was grown in a medium overlaid with a 10% volume of a mixed organic solvent (p-xylene and diphenylmethane; 3:7, vol/vol) containing cholesterol (20 mg/ml), the cholesterol concentration in the organic solvent was reduced to only 0.4 mg/ml after 8 days. Although the organism did not assimilate cholesterol, 98% of the cholesterol initially present disappeared. The organic solvent layer contained two major and three minor compounds converted from cholesterol. The major compounds were 6beta-hydroxycholest-4-en-3-one (8.9 mg/ml) and cholest-4-ene-3,6-dione (7.6 mg/ml). The concentrations of these compounds were equivalent to 43 and 37% of the cholesterol initially present. This organism would provide an effective and convenient system to oxidize the C-3 and -6 positions of cholesterol by introduction of a hydroxyl or ketone group.

The ultrapurification of indium-111 for radiotracer studies.

We have developed a procedure for the ultrapurification of 111In. A dried sample of 111InCl3 is dissolved in 1 ml of a freshly prepared KI solution of 4% in 4 N H2SO4. After 3 ml of anhydrous diethylether has been mixed well with the aqueous and centrifuged for 5 minutes at 2000 X g, the iodide salt of 111In is recovered with the organic solvent layer at approximately 92% of the original radioactivity. The organic phase is evaporated under a gentle stream of inert gas. After the sublimation of iodine, 111In is dissolved in a solvent of choice. The extraction is highly selective for In and separates it from, at least, Fe, Al, and Zn, principle associated cationic contaminants.

Light-Induced Potential and Current across a Large Bacteriorhodopsin-Asolectin Planar Membrane Stabilized on a Polyacrylamide Gel Surface

A phospholipid bilayer membrane was spread from an organic solvent solution between a polyacrylamide gel surface and an aqueous buffer solution. The membrane was quite similar to the conventional black lipid membrane, but was of a large size and was stable since it was supported on the gel surface. Bacteriorhodopsin, impregnated into the membrane, generated membrane potential and current upon illumination. The induced current was large, and this was attributed to the large area of the present membrane. Remarkable responses of the light-induced potential and current were also observed with a thick layer of organic solvent containing phospholipids. The effects of applied membrane potential, carbonylcyanide-m-chlorophenyl hydrazone (CCCP) and gramicidin were examined on these photoresponses. Steady-state current, which is due to protons flowing through the membrane, was enormously enhanced by applying membrane potential opposite to the photopotential or by adding gramicidin to the membrane-forming solution.

Failure of phosphatidic acid to translocate Ca2+ across phosphatidylcholine membranes.

The putative role of phosphatidic acid (PA) as a Ca2+ ionophore has offered an attractive explanation for the relationship between Ca2+ influx and the turnover of phosphoinositides in stimulated cells. The ionophoretic properties of PA are evident in its ability to translocate Ca2+ across a layer of organic solvent. When added exogenously to some cells, PA produces a physiological response and in neuroblastoma cells stimulation of Ca2+ uptake can also be detected. It was later shown that low levels of PA added exogenously to, or incorporated endogenously in liposomes, increase their permeability to Ca2+ (refs 7, 8), indicating a direct effect of PA on lipid bilayer properties. We now report, however, that we have not been able to demonstrate facilitation by PA of Ca2+ fluxes across liposomal membranes. Ascribing such a role to PA does not seem compatible with known features of biological membranes or the properties of ionophores known to translocate ions across membranes.

Stationary phase effects in reversed-phase liquid chromatography

In addition to dispersive and non-specific interactions at the surface of the adsorbent in reversed-phase liquid chromatography, specific effects also exist. The latter are mainly due to unreacted silanol groups and to the extracted layer of organic solvent. These specific effects are investigated by comparing capacity factors and liquid—liquid extraction constants, K LLE. When chemically identical LLE and chromatographic systems are compared, plots of log k′ vs. log K LLE allow one to estimate specific stationary phase effects. The rôle of the solute and the solvent composition is discussed.

New Rapid Assay for Nafcillin in Serum by Spectrofluorometry

A new, rapid method for measuring serum levels of nafcillin by spectrofluorometry is described. The method involves extraction of 2 ml of acidified serum with n-butyl chloride, subjecting the organic solvent layer to excitation at 340 nm, and measuring the relative intensity of emission fluorescence at 380 nm. An excellent linear correlation exists between serum levels of nafcillin and the relative intensity in a drug concentration range of 0.25 to 150 mug/ml. The results obtained by this spectrofluorometric technique are in complete accord with those obtained by the conventional microbiological assay using Staphylococcus aureus ATCC 6538P. The method is not interfered with by elevated levels of endogenous metabolic products or the presence of other drugs, including a number of antimicrobial agents. The assay is interfered with, however, by the presence of salicylates, for which appropriate correction can easily be made. A salicylate assay employing a spectrofluorometric technique is also described.

248 - Electric breakdown of bilayer lipid membranes III. Analysis of possible mechanisms of defect origination

Different mechanisms of the defect formation are analyzed. A cylindrical hole was taken as an example of a defect caused by thermal motion. It follows from the analysis of such a defect's energy dependence on its sizes that the most probable way of the through-going pore origination is the formation of narrow and deep holes. It is shown by an estimate that the membrane breakdown due to van der waals forces is possible only when an appreciable area of the membrane surface becomes free of phospholipid molecules, and therefore when a pure organic solvent layer is formed. Thus the Van der waals mechanism is shown to be improbable. The effect of local electric field caused by a single ion is analysed. Approximate calculations have shown that the so called image forces can be significant only on late stages of membrane breakdown, i.e. for relatively wide pores. This result constitutes the basis for further theoretical description of the processes taking place during membrane breakdown.

Determination of cadmium by atomic absorption spectrometry combined with solvent extraction with high molecular weight amines

Cadmium was extracted from 0.5N hydrobromic acid solution with 1 vol.% tri-n-octylamine or trioctylmethylammonium chloride in methyl-isobutyl ketone (MIBK), and quantitation of cadmium in the organic solvent layer was directly performed.In order to know the optimum experimental conditions, various factors such as the settings of the instrument, the conditions of the extraction, etc. have been studied.The optimum conditions were found as follows. Wavelength 2288A, hollow cathode lamp current 6.5 mA, slit width 0.2 mm, air pressure 1.4 kg/cm2, and acetylene pressure 0.3kg/cm2.The absorbance became about 2.5 times higher than that of the complex in aqueous solutions. The method was applied to the determination of trace amounts of cadmium in water, soil and rice and the results were found satisfactory in comparison with DDTC method.

Variation of Nitrate Ion and Nitrite Ion in Foods (1)

The determination method of nitrate nitrogen in foods provided in the A.O.A.C. is based on either the colorimetric method by m-xylenol, or the reduction method by cadmium.However, there are some problems in the reproducibility and simplicity of these methods. The sodium salicylate method was studied and it was found that this method was more excellent than the other methods.The procedure of this method is as follows.Extract nitrate nitrogen in foods with distilled water at room temperature, the added 1ml of 20% phosphotungstic acid solution if the sample has more protein. Take an aliquot of the extracts containing 5-20μg of nitrate nitrogen and add 1ml of 1% sodium salicylate-sodium hydroxide solution, 1ml of 0.1% ammonium sulfamate and 1ml of 0.2% sodium chloride, then heat the mixture to driness on a water bath. Add 2ml of concentrated sulfuric acid and 20ml of distilled water to the residue, extract with 20ml of methyl isobutyl ketone. To the organic solvent layer add 10ml of 1% sodium hydroxide solution and transfer sodium hydroxide layer to a 50ml Nessler tube, then dilute to 30ml with distilled water. Measure the absorbance at the wavelength of 415mμ.The recovery ratio was about 90% in the addition experiment to vegetables and meat products.

Precipitate flotation. V. Extractive solvent sublation

AbstractThe new technique of precipitate flotation of the second kind is unique amongst flotation processes in that it requires no surfactant. This does have the disadvantage that the floated material is not supported on the surface and tends to redisperse into the solution. A layer of immiscible organic solvent containing either a surfactant, a complexing agent, or the original precipitant, leads to solubilisation and retention of the floated material. As this is quantitative, spectrophotometric examination of the organic layer may provide a means of analysis for the ion originally precipitated. Complete removal from solutions as dilute as 10−5 M is possible.

Schotten‐baumann esterification of poly(vinyl alcohol). I.

AbstractThe esterification of poly(vinyl alcohol) by SCHOTTEN‐BAUMANN reaction gave poly(vinyl cinnamate). The proposed method is that cinnamoyl chloride dissolved in the mixture of toluene and methyl ethyl ketone is added to the aqueous mixture of poly(vinyl alcohol) and sodium or potassium hydroxide at low temperatures. Produced poly(vinyl cinnamate) is dissolved in the organic layer. This reaction differs from other SCHOTTEN‐BAUMANN reactions such as the interfacial polycondensation and the production of phenyl benzoate in the point that weak alkalis, for example sodium or potassium carbonate and bicarbonate, etc., have no effects. This fact suggests that the ionization of the hydroxyl groups of poly(vinyl alcohol) plays an important role in the esterification. The addition of surface active agents lowers the yield of the product. The explanation is that the esterification of hemi‐esterified poly(vinyl alcohol) at the late period of the reaction proceeds in the organic solvent layer and the detergents aid only the hydrolysis of chloride.

Determination of Vanadium by the Extraction of Vanadium(III) Thiocyanate with Methyl Ethyl Ketone

AbstractThe spectrophotometric study on the extraction behavior of V(III) thiocyanate complex, with methyl ethyl ketone is described.The greenish yellow color extract shows a absorbance maximum at 395 mμ in 1.0 to 2.8 N HCl solution, and the molar absorbancy index of the extract is 4,313. Beer's Law is valid over a range from 0.01 mg to 0.1 mg of vanadium.The optimum concentration of SnCl2 for the reduction of vanadate was found at the range between 0.2 N and 0.4 N.The minimum variation of the volume of organic solvent layer and aqueous layer after equilibration was found when the solution was 1.8 to 2.4 N in HCl, 0.35 to 0.65 N in SnCl2 and 0.9 to 1.2 M in NH4CNS.