Role of geometrical dimensions in electrophoresis applications with orthogonal fields

The role of geometrical dimensions in electrophoresis applications with axial and orthogonal (secondary) electric fields is investigated using a rectangular capillary channel. In particular, the role of the applied orthogonal electrical field in controlling key parameters involved in the effective diffusivity and effective (axial) velocity of the solute is identified. Such mathematically friendly relationships are obtained by applying the method of spatial averaging to the solute species continuity equation; this is accomplished after the role of the capillary geometrical dimensions on the applied electrical field equations has been studied. Moreover, explicit analytical expressions are derived for the effective parameters, i.e., diffusivity and convective velocity as functions of the applied (orthogonal) electric field. Previous attempts (see Sauer et al., 1995) have only led to equations for these parameters that require numerical solution and, therefore, limited the use of such results to practical applications. These may include, for example, the design of separation processes as well as environmental applications such as soil reclamation and wastewater treatment. An illustration of how a secondary electrical field can aid in reducing the optimal separation time is included.     

Completely hydrogen-bonded interpenetrating networks in low-temperature liquid water: Their geometrical possibility and stability

A random tetrahedral network built around linked eight-member rings is denser than an open one described earlier, and has neighbors near in space that are remoter in bond topology. The properties of amorphous ice and liquid water below 0°C correlate with a glass transition in an open network at ≈ 140 K, while linked rings, which increase enthalpy and density, only appear above about ?40°C.     

Tubing modifications for countercurrent chromatography: Investigation of geometrical parameters

Countercurrent chromatography (CCC) is a separation technique which may be described as a combination of a great number of liquid–liquid distributions of analytes in a two-phase solvent system with liquid chromatography (LC) features. Even optimized CCC separations currently provide a lower number of theoretical plates when compared to LC. For this reason, instrumental advancements are indispensable to, at least partly, overcome this drawback. Recently, we found that improvement of the classic CCC coil, that is using a long hollow tubing, may be achieved by the introduction of tubing crimpings which increase the stationary phase retention. In this study, we systematically investigated the effects of three geometrical parameters (crimping depth, distance between two crimpings as well as partial or complete crimping of the tubing) on the stationary phase retention by a factorial design of experiments approach. Separation efficiency tests were performed with two groups of analytes: fatty acid methyl esters (FAME) in the n-hexane/acetonitrile (HAcn) and alkyl p-hydroxybenzoates in the n-hexane/tert-butylmethylether/methanol/water solvent system. The most narrow crimping distance and the deepest crimping of the tubing were the best configurations in the examined flow rate range.     

Investigation of the separability of thaumatin by capillary electrophoresis

The electrophoretic behaviour of the highly basic protein thaumatin was explored in strongly acid (pH 2) and mildly acid (pH 4.5) separation systems using both bare and coated fused silica capillaries. The separation selectivity for thaumatin I, thaumatin II, and for other sample constituents was insufficient for their baseline separation at pH 2 in an uncoated capillary because the separation efficiency was markedly lower than is common in the electrophoretic separations of proteins. A separation selectivity higher by up to one order of magnitude has been reached at pH 4.5. A pronounced asymmetry of zones, which impaired resolution at this pH, was effectively suppressed by coating of the capillary wall with a polymer. In fact, adsorption on the capillary coating always plays a contributory role whenever a good separation of thaumatin constituents is attained. This indicates that electrochromatographic separation systems based on capillaries coated with the layer of either cationic or hydrophilic uncharged polymer hold promise for the development of methods for thaumatin analysis.     

Investigation on the possibility of cold nuclear fusion in Fe-Zr amorphous alloy

Neutron, and Mössbauer spectroscopy were used to study the possibility of cold nuclear fusion in Fe₉₀Zr₁₀ amorphous ribbon having high hydrogen absorbing ability. No significant changes in the neutron and in the spectra were found at deuterization performed electrochemically at different cathodic potentials. The observed differences between the Mössbauer spectra of samples deuterized in air and in nitrogen atmosphere can be explained by decrease of deuterium uptake as well as by a small heat effect due to reaction of hydrogen with oxygen dissolved in water in the case of electrolysis carried out in air.     

Investigation on possibility of rearrangement of pyrimidine-5-carboxylic acids esters

A previously reported rearrangement of pyrimidine-5-carboxylic acids esters to 5-acylpyrimidones does not, in fact, occur in any of the examples studied by us.     

Investigation of Fasciola hepatica sample preparation for two-dimensional electrophoresis

This paper investigates the preparation of Fasciola hepatica samples for two-dimensional electrophoresis (2-DE). Whole samples were prepared by both hot sodium dodecyl sulfate (SDS) solubilisation and precipitation using trichloroacetic acid (TCA) to remove nonprotein contaminants and to inactivate endogenous proteases. Sample preparation had a marked influence on the 2-DE gel profile. TCA precipitation resulted in no measurable improvement in the profile observed, compared to the untreated control. Solubilisation of sample with hot SDS increased the number of protein spots, as did TCA precipitation with the addition of phosphotungstic acid. The preparation of excretory-secretory (ES) products poses problems due to both high salt concentrations and low protein concentration. All precipitation methods used to overcome this gave similar profiles, except acetone alone, which caused depletion of the larger proteins. TCA in acetone gave the best result, similar to that obtained by centrifugal filtration of the sample. Overcrowding of spots in some regions of the 2-DE gel occurred in the whole Fasciola hepatica sample. This problem was alleviated by differential solubilisation, which also resulted in the enrichment of some proteins.     

Investigation of iron oxide nanoparticles by capillary zone electrophoresis

The electrophoretic behavior of γ-Fe₂O₃ nanoparticles was studied in aqueous solutions of Na₂SO₄-NaOH (pH 10.8) and of Na₂SO₄-Na₃cit (pH 7.1) as running electrolytes. Two electrophoretic zones (smooth and with spikes) due to colloidal and suspended particles of approximately the same size range were formed during the runs. The suspension stability and size distribution were shown to depend on the composition of electrolyte used for dispersing the solids. The effects of electric field strength, injection time, injection pressure as well as sodium citrate concentration were studied and particle electrophoretic mobilities were calculated. Electron micrographs of particles studied were obtained. Preparation of reference samples based on the colloidal γ-Fe₂O₃ has been discussed.     

Investigation of the electroosmotic flow effect on the efficiency of capillary electrophoresis.

The influence of the electroosmotic flow profile on the efficiency and resolution of capillary electrophoresis is studied. The mathematical model is formulated and the set of equations is solved numerically. The results of the analysis are applicable to a wide range of buffer concentrations and capillary diameters. The temperature dependence of electrophoretic mobility, viscosity and thermal conductivity and the dependence of electrical conductivity on temperature and ion concentration in the double layer are taken into account. It is shown that there exists a region of buffer concentrations and capillary diameters where the influence of the electroosmotic flow profile on the efficiency and resolution is much greater than that of the temperature dependence of the electrophoretic mobility. The results are especially essential for small buffer concentrations or capillary diameters comparable with the double electrical layer thickness.     

Investigation of interaction between the drug and cell membrane by capillary electrophoresis

By introducing cell membrane into electrophoretic buffer as pseudo-stationary phase, a novel capillary electrophoresis method was established to explore the interaction between drugs and cell membrane, where the interaction between citalopram and rabbit red blood cell membrane was used as an example. A series of concentrations of cell membrane were suspended into the running buffer by peak-shift method. The binding constant of citalopram to rabbit red blood cell membrane of 0.977 g^?1·L was obtained after treatment of Scatchard plot. This method could provide not only a new way for the investigation on the interactions between drugs and cell membrane, but also a new approach for high throughput screening of the drug membrane permeability, biological activity, and evaluating drugs in vivo.     

药物与细胞膜相互作用的毛细管电泳方法研究

以细胞膜在毛细管内构成假固定相,建立一种基于毛细管电泳测定药物与细胞膜相互作用参数的方法．以西酞普兰和兔红细胞膜为相互作用模型,以不同浓度的细胞膜混悬液为电泳缓冲液,采用峰漂移法,并结合Scatchard分析,测得西酞普兰与兔红细胞膜的结合常数为0．977g^-1·L．该方法简单、快速,为研究药物与细胞膜的相互作用提供了新的技术手段,为高通量筛选药物膜通透性和活性,以及评价药物在体内吸收提供一种新的方法．     

Investigation of the factors that induce analyte peak splitting in capillary electrophoresis

Peak splitting has a detrimental effect on analyses by capillary electrophoresis. Many papers have reported it and several mechanisms have been proposed to explain the phenomenon. We investigated the electrophoretic behavior of an amphoteric analyte, levodopa, in phosphate buffer and observed a peak splitting phenomenon at moderate sample concentrations and under general analytical conditions, even without organic solvent. The dependence of effective mobility on pH was taken into account and pKa values of 2.30, 8.11, and 9.92 were obtained for levodopa. Then, we constructed pH-dependent distribution diagrams of levodopa and phosphate species present in aqueous solution and proposed that the most relevant factors contributing to peak splitting are the presence of ionizable groups in the analyte molecule and the occurrence of ionization, yielding charged species which interacted with buffer electrolyte species in a definite pH range to form complexes. This result is different from those presented in the literature and broadens our understanding of amphoteric analyte peak splitting.     

Investigation of unexpected migration behavior of adenosine in capillary zone electrophoresis

Summary The capillary zone electrophoresis of two common nucleosides, adenosine and inosine, was investigated. Both compounds were resolved in a 0.1 M sodium phosphate buffer, pH 7.5. Contrary to expectations, adenosine behaved at this pH— 5 pH units lower than the literature pK_a— as a negative ion, migrating behind mesityloxide (neutral marker) when working in normal polarity mode. To confirm the migration order, peaks were identified from absorption maxima, by high-speed scanning detector. The change in electrophoretic mobility with pH was investigated for the nucleosides, and 10 other background electrolytes were tried to match the separation capabilities of the sodium phosphate buffer. Most inorganic buffers showed comparable separation, while organic, Good-type buffers lacked selectivity.     

Investigation of solvent effects in capillary electrophoresis for the separation of biological porphyrin methyl esters

The effects of organic solvents on the capillary electrophoresis (CE) separation of a number of important biological porphyrin methyl esters - six weakly basic, hydrophobic cyclic tetrapyrroles possessing two and four to eight methyl ester groups around the periphery of the porphyrin ring - were investigated in the mode of micellar electrokinetic chromatography (MEKC), microemulsion electrokinetic chromatography (MEEKC), and nonaqueous CE. In aqueous MEKC, partial separation of the six neutral porphyrin methyl esters was obtained with an organic modifier (acetonitrile) in the concentration range between 20 and 40%, in which sodium dodecyl sulfate (SDS) molecules might be present in the form of SDS micelles and/or SDS micelle-like aggregates. Relatively stable SDS micelles can be formed in nonaqueous MEKC using formamide as the separation medium, but the separation of the target analytes remained unsatisfactory. Improved resolution of all six porphyrin methyl esters was obtained using MEEKC with the running buffer consisting of 0.8% w/w n-heptane (oil phase), 2.25% w/w SDS and 1.0% w/w Brij 35 (mixed surfactant), 6.6% w/w 1-butanol (cosurfactant), and 30% v/v 2-propanol (second cosurfactant), but reproducibility in terms of peak areas for certain porphyrins (especially uroporphyrin I octamethyl ester) was found to be very poor. Best separation performances were achieved with nonaqueous CE separations in which the weakly basic porphyrin methyl esters were protonated under strongly acidic conditions (e.g., using 10 mM perchloric acid) in mixed organic solvents. For example, using a 50:50 mixture of methanol and acetonitrile as the separation medium, baseline separation of all six (positively charged) porphyrin methyl esters can be obtained within 3 min and the average precision (RSD, N = 13) in terms of migration time and peak area were 0.55 and 2.16%, respectively.     

The geometrical structures of the substituted oxiranes

Conclusions The oxiranecarbaldehydes exist as single conformers in solution. The carbonyl group is rotated out of the plane of the bisector of the oxide ring by some 40°, the carbonyl-group oxygen being thereby separated from the oxide-ring oxygen. This conformation is favored from the standpoint of dipole-dipole interactions.Translated from Izvestiya Akademii Nauk SSSR, Sariya Khimicheskaya, No. 6, pp. 1257–1260, June, 1979.The authors would like to thank V. N. Zinin who prepared the PMR spectra.     

Investigation of fulvic acids from peat using capillary electrophoresis (CE)

The aim of this work was to characterize the fulvic acids (FA) extracted from peat by use of capillary electrophoresis (CE). Two FA extracts have been obtained using two different extractants (0.1 M NaOH and 0.1 M NaOH plus 0.1 M Na₄P₂O₇, Na+PP). The CE runs wre performed using a coated silica capillary, and several buffer solutions at different PH values. The results obtained show that the Fa extracts may be well characterized by CE even if the isolelectric point of the fulvic compounds is very low. The best fractionation has been obtained using a buffer borate at PH 8.9 as funning buffer. The charcterization of the two extracts also showed some important differences between the NaOH extract and the Na+PP extract.     

Investigation on the chiral recognition mechanism between verteporfin and cholate salts by capillary electrophoresis

In this article, capillary electrophoresis was applied to investigate the chiral recognition mechanism for the enantioseparation on a well‐known second‐generation photodynamic therapy drug of benzoporphyrin derivative monoacid ring A, that is, verteporfin. In our previous study, cholate salts have been studied as the chiral selectors, which can realize baseline separation of the four verteporfin isomers. Aiming to reveal the chiral recognition mechanism, the separation effect of several kinds of chiral selectors was discussed. According to the results and references, the chiral separation mechanism of this system was concluded: the analytes selectively combine with the chiral micelles, that is, dynamic H‐bonds interactions occur between the hydroxyl groups on the outer side of the cholate micelles and the ester/carboxy groups of the four isomers. In addition, the role of dimethyl formamide as an organic modifier was also researched, including reducing the effective mobility of the analytes and mobility of electroosmotic flow, and preventing them from adsorbing to the capillary wall and self‐aggregating of verteporfin, which are pretty beneficial for separation. The method used in this article provides a direct and reliable solution to study the mechanism of chiral separation.     

毛细管电泳法考察全氟辛酸与人血清白蛋白的相互作用

利用毛细管电泳（CE）技术建立了全氟辛酸（PFOA,C₈HF₁₅O₂）与人血清白蛋白（HSA）相互作用的分析方法。在生理条件下构建配体（PFOA）-受体（HSA）相互作用模型,通过淌度移动法、区段-区段动力学（plug-plug kinetic,PPK）法、简化的Hummel-Dreyer（HD）法研究其与HSA的相互作用。简化的HD法运用非线性方程、Scatchard方程和Klotz方程获得PFOA-HSA体系的相互作用参数,进而分析了模型适用度。结果表明,淌度移动法、PPK法、简化的HD法均适用于PFOA-HSA体系相互作用的分析,其中简化的HD法最优。模型适用度分析得出非线性回归方程为最适理论模型。相互作用参数测试表明PFOA-HSA相互作用体系之间发生的结合反应只有单一类型的结合位点且结合稳定。相关工作阐明了人血清白蛋白与PFOA的相互作用机制,可为PFOA毒理机制的深入研究提供有益参考。