Guichen Ping

Rapid separation of nucleosides by capillary electrochromatography with a methacrylate-based monolithic stationary phase

SummarySeparation of nucleosides by capillary electrochromatography with a methacrylate-based monolithic column is described. Because the nucleosides are relatively hydrophilic compounds, chromatographic parition is very weak on non-polar stationary phases. A small quantity of organic modifier is usually required to increase their retention factars but, because the wettability of the stationary phase by the mobile phase is rather poor, bubble formation can be a significant problem. This situation was improved by use of a polymeric monolithic column with higher level charged monomer in the polymerization mixlure, because of the presence of charged moieties on the surface of the monolithic stationary phase. The very high stability under conditions of very low organic modifier concentration used in the experiment showed that the wettability of the stationary phase by the mobile phase was satisfactory. The effect of pH, orgonic modifier content, and applied voltage on the separation was investigated. Baseline separction of six nucleosides was achieved within 4.5 min on this type of column. Because of the presence of charged moieties and butyl groups on the surface of the monolithic column, the mechanism of separation might involve both ion-exchange and hydrophobic interactions.

Study on the multiple sites binding of human serum albumin and porphyrin by affinity capillary electrophoresis

Equations to describe the two sites binding between proteins and ligands were deduced. According to these equations, not only the binding constants, but also the mole fraction of proteins in different forms could be obtained. Using the published data on the interaction between human serum albumin (HSA) and three kinds of porphyrin (coproporphyrin (CP), uroporphyrin I (UP) and protoporphyrin (PP)), a further study on their binding was carried out. It was concluded that there may exist two binding sites with the binding constants at the first site, proved to be the preferential one, being 6.50 x l0(5), 1.94 x 10(6) and 8.94 x 10(5), respectively. In addition, it was also demonstrated that the two binding sites of HSA with CP and UP might be of different kinds, though those of HSA and PP were of the same kind but at different positions.

Migration of neutral solutes by double stepwise gradient elution in capillary electrochromatography.

Characteristics of electroosmotic flow (EOF) and the migration of neutral solutes under double stepwise gradient elution in capillary electrochromatography were studied systematically. EOF velocity proved to be the function of operation time changing with the introduction of the second mobile phase. Accordingly, the retention of components also changed. The migration of neutral solutes was studied under the following three situations; A, components eluted when the column was filled only with the first kind of mobile phase; B, solutes eluted still in the first kind of mobile phase while at that time two kinds of mobile phase coexisted in the column and C, samples eluted in the second kind of mobile phase. Equations to describe the retention times of components under these three kinds of conditions were deduced and applied to predict the retention times of 12 aromatic compounds. Relative errors between experimental and calculated values were below 5.0%, which proved the reliability of the equations. In addition, parameters that might affect the retention time of solutes, such as the transferring time of mobile phase vials, the capacity factors of components and EOF velocities two steps were studied systematically.

Abnormal phenomenon of the dependence of the retention factors for uncharged species on applied voltage in capillary electrochromatography

SummaryPolymethacrylate-based monolithic columns were prepared for capillary electrochromatography (CEC) byin situ copolymerization of butyl methacrylate (BMA), 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS), and ethylene dimethacrylate (EDMA) in the presence of a porogen in fused-silica capillaries of 100 μm I.D. The abnormal phenomenon that retention factors for neutral species decreases with applied voltage in CEC was observed. Capillary electrophoresis (CE) instruments usually require a period of time to increase voltage from 0 kV to desired value, which is called as ramp time. Such ramp time and any error in the determination of dead time should be taken into account during the accurate calculation of retention factors. After the correction of the retention factors, the plots of the corrected factors for alkylbenzene versus applied voltage were made, the absolute value of the plot slopes are less than 1.8×10−4, which indicates that the corrected retention times for neutral species do not show any dependence on applied voltage. Further, the plats of the corrected retention times for acidic and basic compounds versus the reciprocal of applied voltage were drawn, where the target compounds were eluted in neutral form. The very nice linearity of the plots was obtained. The linear correlation coefficients are over 0.999. Here, the slopes of the plots represent

On-line concentration of neutral and charged species in capillary electrochromatography with a methacrylate-based monolithic stationary phase

\frac{{L_{eff} \cdot L_{tot} \cdot \left( {l + k} \right)}}{{\mu eo}}

Analysis of aromatic amines by high-performance liquid chromatography with pre-column derivatization by 2-(9-carbazole)-ethyl-chloroformate

, which indicates that retention factors for the test compounds are constants under a given separation condition.

Preparation and characterization of monolithic columns for capillary electrochromatography with weak electroosmotic flow

A theoretical study on the velocity of electroosmotic flow (EOF) and the retention times of neutral solutes under multiple‐step gradient of capillary electrochromatography (CEC) was carried out, focusing on that with three kinds of mobile phases. Through the model computations, the detaining time of the second kind of mobile phase in the column was proved to play an important role in affecting EOF. The variation speed of EOF was shown to be determined by the differences among dead times in different steps. In addition, the prediction of the retention times of 13 aromatic compounds under gradient mode was performed with the deduced equations. A relative error below 3.3% between the calculated and experimental values was obtained, which demonstrated the rationality of the theoretical deduction. Our study could not only improve the comprehension of stepwise gradient elution, but also be of significance for the further optimization of separation conditions in the analysis of complex samples.