电解质溶液组成对低分子量阴离子毛细管电泳分离的影响

研究了毛细管电泳间接紫外检测法测定低分子量阴离子时电解质溶液中背景电解质、电渗流改性剂、ｐＨ值、有机溶剂等对分离的影响；比较了铬酸根、邻苯二甲酸根、苯甲酸根３种背景离子对不同迁移率阴离子分离的影响，并对间接紫外检测的定量基础及灵敏度进行了讨论；考察了３种不同长链烷基三甲基季铵盐电渗流改性剂浓度对阴离子迁移时间和电渗迁移率的影响，结果表明电渗流的改性效果与烷基链的长度有关；ｐＨ影响阴离子的有效迁移率     

A New Method to Measure Electroosmotic Flow Mobility of Capillary Electrophoresis by Abrupt Change of Current De‐noising via Wavelet Transform

The electroosmotic flow mobility has been measured by the combination of monitoring the change in electric current during electrophoretic run and operating the wavelet transform. Once the sample solvent zone with different ionic strength from background electrolyte migrated from the capillary, a sudden change in current could be observed from the electric current record of time history. The exact time (in the middle of abrupt range) corresponding to the abrupt change in current was determined by wavelet transform. This work showed that the electroosmotic flow mobility determined by the proposed method was in a good agreement with the neutral marker method commonly used.     

Parameters influencing separation and detection of anions by capillary electrophoresis

Electrolyte composition is critical in optimizing separation and detection of ions by capillary electrophoresis. The parameters which must be considered when designing an electrolyte system for capillary electrophoresis include electrophoretic mobility of electrolyte constituents and analytes, detection mode, and compatibility of electrolyte constituents with one another. An electrolyte system based on pyromellitic acid is well suited for use with indirect photometric detection, and provides excellent separations of anions. The ability to modify the electrophoretic mobility of pyromellitic acid as a function of ph provides flexibility in matching electrophoretic mobilities of analytes. Additionally, the use of alkyl amines as electroosmotic flow modifiers allows the rapid separation of anions by reversing the direction of electroosmotic flow in a fused-silica capillary. The optimization of a capillary electrophoresis electrolyte for anion analysis is also discussed in terms of pH, ionic strength and applied voltage. The effect of organic solvent on separation selectivity is also discussed.     

样品带示踪法测定毛细管电泳过程中的电渗流

电渗流在毛细管区带电泳（CZE）和胶束电动力色谱（MEKC）中具有重要作用,通过控制电渗流可以提高分辨率或加快分析速度,因而控制和测定电渗流已成为毛细管电泳领域重要的研究课题．SalomonK．［'j建立了一种电渗流近似模型,但因影响因素复杂,电渗流还无法从理论上计算,只能通过实验测定．目前常用的测定法有中性示踪剂法［'－"、称量法［'和电泳电流监测法［'j本文提出一种新的电渗流测定法--样品带示踪法,该法不必另加示踪剂,利用样品带中的基体介质即可示踪电渗流．该法适用于较宽的I。H范围及多种检测器,对于某些样品（与…     

Impact of organic solvents on the resolution of synthetic peptides by capillary electrophoresis

The effect of variations in the concentrations of different organic solvents, including acetonitrile, methanol, ethanol, propanol and isopropanol, with aqueous buffer electrolytes of defined composition and pH on the electroosmotic flow velocity, v(EOF), of uncoated fused silica capillaries and on the electrophoretic mobility, mu(e), of synthetic peptides in high-performance capillary electrophoresis (HPCE) has been systematically investigated. In these experiments, the volume fractions of the organic solvent in the aqueous buffer electrolyte were changed from psi = 0.0 to 0.80. The addition of these organic solvents to the aqueous buffer electrolyte reduced the electroosmotic flow (EOF) of the system, but to significantly different extents. For the protic solvents as the alkyl chain of the alcohol increased, at the same volume fraction the greater was the influence on the electroosmotic flow. However, for the aprotic solvent, acetonitrile, the EOF did not change substantially as the volume fraction was varied. The electrophoretic mobility of synthetic peptides under the different buffer electrolyte conditions showed similar trends, confirming that the content and type of the organic modifier can be rationally employed to subtly manipulate the separation selectivity of synthetic peptides. These results, therefore, provide fundamental insight into the experimental options that can be used to maximise resolution of synthetic peptides in HPCE with aqueous buffer-organic solvent mixtures as well as a basis to select optimal binary or ternary buffer electrolyte compositions for the analysis of peptides when hyphenated techniques, such as HPCE-electrospray ionisation mass spectrometry (ESI-MS), are contemplated for the analysis of peptide samples of low abundance as can often be experienced in proteomic investigations.     

Discontinuous electrokinetic chromatography of parabens using different substituted resonances as pseudostationary phases

Resorcarene derivatives, negatively charged even at moderate pH, were synthesized and employed as pseudostationary phases to achieve mobilities exceeding that of the electroosmotic flow. Under these conditions, a discontinuous electrolyte system was developed which allows the separation of four uncharged homologous 4-hydroxybenzoic esters (parabens) within a zone of resorcarene electrolyte, and the detection of these UV active compounds in a resorcarene-free zone, free from the high UV background absorbance of the resorcarenes. Resorcarenes, with differently charged functionalities (carboxylate and phosphate groups) to provide the electrophoretic mobility and with alkyl residues of different chain lengths responsible for the chromatographic interactions with the analytes, were tested and compared in terms of mobility and selectivity. Only the resorcarene phosphates exhibited sufficient mobilities at low pH exceeding the mobility of the electroosmotic flow (EOF). Retention factors of the parabens were found to increase with increasing chain length of the alkyl residues attached to the resorcarene. However, maximum selectivity was observed for an intermediate chain length (C8). An equation for the calculation of retention factors in discontinuous electrokinetic chromatography (EKC) is presented.     

Separation of anions by ion chromatography-capillary electrophoresis

Capillary electrophoresis (CE) with a water-soluble ion-exchange polymer in the background electrolyte is very efficient for the separation of organic and inorganic anions because the ion-exchange selectivity, as well as differences in electrophoretic mobility, can be used for separating sample ions. Poly(diallyldimethylammonium chloride) (PDDAC) was employed for this purpose. A very stable electroosmotic flow was obtained between pH 2.3 and 8.5 due to the strong adsorption of PDDAC onto the capillary wall. The effect of ion exchange on the migration of sample anions and their separation was controlled by varying the concentration of PDDAC, the concentration and the type of salt used in the CE background electrolyte. Addition of organic solvent (e.g., acetonitrile) could also modify the sample migration and the separation. Baseline separations were obtained for anions with very similar mobilities, such as bromide and iodide, naphthalenesulfonates, and bi- and tricarboxylic acids. Typical separation efficiencies were between 195,000 and 429,000 theoretical plates per meter. Ten replicate separations gave an average RSD of 1.0% for migration times of the sample anions studied. Excellent separations were obtained for a variety of samples, including a separation of 17 inorganic and organic anions in less than 6 min.     

Method development approaches for capillary ion electrophoresis

Capillary ion electrophoresis (CIE) is a capillary electrophoretic technique optimized for rapid determination of low-molecular-mass inorganic and organic ions. CIE predominantly employs indirect UV detection since the majority of the analytes lack specific chromophores. Described are three methods for detection and electrolyte optimization. The first method discussed approaches for optimizing sensitivity, selectivity and peak confirmation using a chromate electrolyte and selected detection wavelengths. Peak confirmation is aided by using both direct detection of analytes. The second and third methods involve an unattended electrolyte development approach for instruments that only provide fresh electrolyte on the injection side of the capillary. The electrolyte composition is changed in both the injection side vial and in capillary before each sample injection while leaving the receiving side electrolyte vial constant at the initial electrolyte composition. In one mode, the concentration of the electroosmotic flow (EOF) modifier used to induce anodic flow is varied while keeping the background electrolyte composition constant. In a second experiment, the background electrolyte co-ion is sequentially changed from high mobility to low mobility while keeping the EOF modifier concentration constant. The end effect is to achieve a broad range of controlled peak symmetry for analytes in a simple matrix. The results are compared to separations obtained when the injection side and receiving side electrolytes are manually matched.     

Scaling behavior in on‐chip field‐amplified sample stacking

Field amplified sample stacking (FASS) uses differential electrophoretic velocity of analyte ions in the high‐conductivity background electrolyte zone and low conductivity sample zone for increasing the analyte concentration. The stacking rate of analyte ions in FASS is limited by molecular diffusion and convective dispersion due to nonuniform electroosmotic flow (EOF). We present a theoretical scaling analysis of stacking dynamics in FASS and its validation with a large set of on‐chip sample stacking experiments and numerical simulations. Through scaling analysis, we have identified two stacking regimes that are relevant for on‐chip FASS, depending upon whether the broadening of the stacked peak is dominated by axial diffusion or convective dispersion. We show that these two regimes are characterized by distinct length and time scales, based on which we obtain simplified nondimensional relations for the temporal growth of peak concentration and width in FASS. We first verify the theoretical scaling behavior in diffusion‐ and convection‐dominated regimes using numerical simulations. Thereafter, we show that the experimental data of temporal growth of peak concentration and width at varying electric fields, conductivity gradients, and EOF exhibit the theoretically predicted scaling behavior. The scaling behavior described in this work provides insights into the effect of varying experimental parameters, such as electric field, conductivity gradient, electroosmotic mobility, and electrophoretic mobility of the analyte on the dynamics of on‐chip FASS.     

毛细管电泳法测定阿霉素脂质体药物中的微量硫酸根离子

建立了以硝酸钾作为背景电解质测定阿霉素脂质体药物中微量硫酸根离子的毛细管电泳分析法。考察了分离电压、背景电解质、电渗流改性剂浓度、pH值对分离测定的影响。结果表明,当毛细管长度为60 cm(有效长度51.5 cm)、分离电压为~15 kV、缓冲溶液采用20 mmol/L硝酸钾(pH 7.0)、电渗流改性剂采用0.4 mmol/L十六烷基三甲基氯化铵(CTAC)、检测波长为202 nm时,阿霉素脂质体破乳液中硫酸根离子和氯离子在3 min内得到了基线分离,硫酸根离子迁移时间和峰面积的相对标准偏差分别小于0.01%和1.0%,检出限为5 μg/L。用该方法对阿霉素脂质体样品中的微量硫酸根离子进行了分析测定,结果令人满意。     

Prediction of Migration Times of Organic Ions in Capillary Zone Electrophoresis

The electrophoretic mobility ratio (R value) of any two ions is constant and independent of the capillary type and electrophoretic conditions if their electrical charges and hydration radii are constant. The use of strong acid salts and quaternary ammonium salts is therefore proposed for the determination of R values. Such analytes are called markers. The following determinations can be carried out: (i) the determination of the migration time corresponding to the electroosmotic flow (EOF) in any capillary under any electrophoretic condition by measuring the migration times of two markers in the condition studied (useful when the EOF is weak); (ii) the determination of the migration time of an analyte in any capillary by knowing the migration time of the markers in the capillary studied. If the pH is changed and the ionization of the analyte is pH dependent, the resulting migration time for the analyte can be calculated. The constancy of the mobility ratios of seven markers was checked experimentally at eight different pH values (between pH 3 and 10), at three temperatures, and for two buffer concentrations. The predicted and experimental migration times were also compared in two different types of capillaries.     

Optimization of separation and migration behavior of cephalosporins in capillary zone electrophoresis

The influences of buffer pH, buffer concentration and buffer electrolyte on the migration behavior and separation of 12 cephalosporin antibiotics in capillary zone electrophoresis using three different types of buffer electrolyte, including phosphate, citrate, and 2-(N-morpholino)ethanesulfonate (MES), were investigated. The results indicate that, although buffer pH is a crucial parameter, buffer concentration also plays an important role in the separation of cephalosporins, particularly when cefuroxime and cefazolin, cephalexin and cefaclor, or cefotaxime and cephapirin are present as analytes at the same time. The electrophoretic mobility of cephalosporins and electroosmotic mobility measured in citrate and MES buffers are remarkably different from those measured in phosphate buffer. With citrate buffer, optimum buffer concentration is confined to a small range (35-40 mM), whereas buffer concentrations up to 300 mM can be used with MES buffer. Complete separations of 12 cephalosporins could be satisfactorily achieved with these three buffers under various optimum conditions. However, the separability of 12 cephalosporins with citrate or MES buffer is better than that with phosphate buffer. As a consequence of a greater electrophoretic mobility of cephalosporins than the electroosmotic mobility with citrate buffer at pH below about 5, some cephalosporins are not detectable. The cloudiness of the peak identification and of the magnitudes of the electrophoretic mobility of cefotaxime and cefuroxime reported previously are clarified. In addition, the pKa values of cephradine, cephalexin, cefaclor, and cephapirin attributed to the deprotonation of either an amino group or a pyridinium group are reported, and the migration behavior of these cephalosporins in the pH range studied is quantitatively described.     

Electrophoresis of soft particles at high electrolyte concentrations: an interpretation by the Henry theory

The existence of electrophoretic mobility at high electrolyte concentrations defines a remarkable peculiarity in the electrosurface characteristics of soft particles. According to Ohshima [H. Ohshima, Colloids Surf. 103 (1995) 249], this effect is caused by the electroosmotic flow within the soft particle shell. An explanation supporting Ohshima's conclusion can be derived from classic electrokinetic theories. Based on the Henry theory [D.C. Henry, Proc. R. Soc. London Ser. A 133 (1931) 106], we demonstrate that the electrophoretic mobility of soft particles does not disappear at decinormal concentration.     

Transient electrophoresis of dielectric spheres

The dynamic electrophoretic response of a spherical dielectric particle suspended in an electrolyte solution to a step change in the applied electrics field is analytically studied. The electrical double layer surrounding the particle may have either a small but finite thickness or a very large thickness relative to the particle radius. For the case of electrophoresis of a particle with a thin double layer, the local electroosmotic velocity at the outer edge of the double layer evolving with time after the external field is imposed is used as an apparent slip boundary condition at the particle surface so that the unsteady equation of motion for the fluid flow outside the double layer is solved. Closed-form formulas for the transient electrophoretic mobility of the particle are derived as functions of relevant parameters. The results demonstrate that, when the double layer surrounding the particle is relatively thin, the normalized electrophoretic mobility at a given dimensionless time decreases monotonically with a decrease in the parameter kappaa, where kappa(-1) is the Debye screening length and a is the particle radius. When the double layer of the particle is relatively thick, the particle mobility can have magnitudes comparable to those for a particle with a thin double layer in the initial stage, but will become much smaller afterward. In general, the effect of the relaxation time for transient electrophoresis is negligible, regardless of the value of kappaa.     

The application of spline wavelet transform to the determination of electroosmotic mobility in capillary electrophoresis

The rule of current change was studied during capillary electrophoresis (CE) separation process while the conductivity of the sample solution was different from that of the buffer. Using a quadratic spline wavelet of compact support, the wavelet transforms (WTs) of capillary electrophoretic currents were performed. The time corresponding to the maximum of WT coefficients was chosen as the time of current inflection to calculate electroosmotic mobility. The proposed method was suitable for different CE modes, including capillary zone electrophoresis, nonaqueous CE and micellar electrokinetic chromatography. Compared with the neutral marker method, the relative errors of the developed method for the determination of electroosmotic mobility were all below 2.5%.     

Separation of bacteria by capillary electrophoresis

Differences in the surface charges of bacteria can be exploited for their separation by capillary electrophoresis. Because of their low electrophoretic mobility, the separation is not always easy to perform, especially in the presence of the electroosmotic flow. Elimination of electroosmotic flow by capillary wall modification with γ‐(trimethoxysilyl)propyl methacrylate followed by acrylamide bonding permits separation over a distance of 8.5 cm.     

Effects of double-layer polarization and electroosmotic flow on the electrophoresis of an ellipsoid in a spherical cavity

The electrophoresis of a rigid, positively charged ellipsoidal particle at the center of a spherical cavity is investigated theoretically under the conditions where the effects of double-layer polarization and the presence of an electroosmotic flow can be important. The equations governing the problem under consideration and the associated boundary conditions are solved numerically, and the influences of the key parameters on the electrophoretic mobility of the particle are discussed. We show that if the cavity is uncharged, the effect of double-layer polarization yields a local minimum in the electrophoretic mobility as the thickness of the double layer varies. This local minimum disappears if the cavity is also positively charged. In addition to reducing the scaled mobility of an ellipsoid, the presence of the boundary is also capable of influencing the relative magnitudes of the scaled mobility for particles of various shapes. For instance, if the volume of an ellipsoid is fixed, the scaled mobility ranks as prolate > sphere > oblate if the boundary effect is unimportant, but that order is reversed if the boundary effect is important.     

Investigations on the behaviour of acidic, basic and neutral compounds in capillary electrochromatography on a mixed-mode stationary phase

This work describes the separation of acidic, basic and neutral organic compounds as well as inorganic anions in a single run by capillary electrochromatography employing a stationary phase which exhibits both strong anion-exchange and reversed-phase chromatographic characteristics. The positive surface charge of this stationary phase provided a substantial anodic electroosmotic flow. The analytes were separated by a mixed-mode mechanism which comprised chromatographic interactions (hydrophobic interactions, ion-exchange) as well as electrophoretic migration. The influence of ion-exchange and hydrophobic interactions on the retention/migration of the analytes could be manipulated by varying the concentration of a competing ion and/or the amount of organic modifier present in the background electrolyte. Additionally the effects of pH changes on both the chromatographic interactions as well as the electrophoretic migration of the analytes were investigated.     

Ion association with alkylammonium cations for separation of anions by capillary electrophoresis

A background electrolyte (BGE) containing a 100 mM concentration of an alkylammonium cation with ethyl, propyl or butyl groups provides an excellent medium for separation of anions by capillary electrophoresis (CE). Two major effects were noted. Use of one of a series of alkylammonium cations in the BGE at a selected pH provides a simple and effective way to vary and control electroosmotic flow (EOF) over a broad range. It is believed that the alkylammonium cations are coated onto the capillary surface through a reversible dynamic equilibrium. Secondly, alkylammonium cations modify the electrophoretic migration of sample anions and the electroosmotic migration of neutral organic analytes by association interaction. This selective interaction results in improved anion separations and permits the simultaneous separation of neutral analytes. The degree of association interaction varies with the bulk and hydrophobicity of the alkylammonium cations. Incorporation of an aliphatic amine salt of moderate molecular weight in the running electrolyte provides a valuable new way to vary the migration times of sample anions and to optimize their resolution. The interactions between alkylammonium cations and sample anions or neutral organics appear to take place entirely within the liquid phase and do not require a polymeric or micellar pseudo phase.     

Electrophoretic mobility of poly(acrylic acid)-coated alumina particles

The effect of poly (acrylic acid) (PAA) adsorption on the electrokinetic behavior of alumina dispersions under high pH conditions was investigated as a function of polymer concentration and molecular weight as well as the presence, concentration and ion type of background electrolyte. Systems of this type are relevant to nuclear waste treatment, in which PAA is known to be an effective rheology modifier. The presence of all but the lowest molecular weight PAA studied (1800) led to decreases in dynamic electrophoretic mobility at low polymer concentrations, attributable to bridging flocculation, as verified by measurements of particle size distribution. Bridging effects increased with polymer molecular weight, and decreased with polymer concentration. Increases in background electrolyte concentration enhanced dynamic electrophoretic mobility as the polymer layers were compressed and bridging was reduced. Such enhancements were reduced as the cation was changed from K(+) to Na(+) to Cs(+).