Zhichao Zhang

Separation of peptides by pressurized capillary electrochromatography

A pressurized electrochromatography (pCEC) instrument with gradient capability was used in this work for separation of peptides. Three separation modes, namely, pCEC, high-performance liquid chromatography and capillary electrophoresiscan be carried out with the instrument. In pCEC mode, the mobile phase is driven by both electroosmotic flow and pressurized flow, facilitating fine-tuning in selectivity of neutral and charged species. A continuous gradient elution can be carried out conveniently on this instrument, which demonstrates that it is more powerful than isocratic pCEC for separation of complicated samples. The effects of applied voltage, supplementary pressure and ion-pairing agents on separation of peptides in gradient pCEC were investigated. The effects of flow-rate of the pump and the volume of the mixer on resolution were also evaluated.

Fast and precise determination of phenthoate and its enantiomeric ratio in soil by the matrix solid-phase dispersion method and liquid chromatography.

A fast and precise method was developed for the determination of phenthoate and its enantiomeric ratio (ER) in three soil samples. A recently developed sample pretreatment technology--matrix solid-phase dispersion (MSPD) was used to extract phenthoate simply and effectively. MSPD conditions, i.e. solid-phase Florisil amount, water content of Florisil-soil mixture, the constituent and volume of the eluting solvent, were optimized stepwise. The MSPD extract was directly used for quantitative determination of phenthoate by silica-based high-performance liquid chromatography (HPLC) with UV detection. The recoveries of phenthoate from three different types of soils fortified at three levels of 0.1, 1, 10 microg/g ranged from 75 to 94% with RSDs of 1.5-6.5%. On this basis, phenthoate was further isolated from the remainder of MSPD extract by silica-based HPLC and then ER determined on HPLC with cellulose tris-3, 5-dimethylphenylcarbamate as chiral stationary phase. The ERs determined in the soils spiked with racemic or enantiomer-enriched phenthoate agreed sufficiently well with those in the corresponding standard solutions. Finally, the proposed method was successfully applied to the study of enantioselective degradation of phenthoate in the three soils under laboratory conditions. High enantioselectivity was observed in the two alkaline soils with (+)-enantiomer degrading faster than the (-)-enantiomer, while there was little to no enantioselectivity in the acidic soil. The methodology can be used to study the enantioselective environmental behavior of chiral pollutants.

Optimization stacking by transient pseudo-isotachophoresis for capillary electrophoresis: example analysis of plasma glutathione.

Low concentrations of both reduced form glutathione (GSH) and oxidized form glutathione (GSSG) in diabetic nephropathy (DN) patients plasma were measured with transient pseudo-isotachophoresis. The plasma samples were deproteined with acetonitrile and centrifuged. The method was performed at constant voltage of 5 kV using a 300 mM borate buffer (pH 8.0), with a fused-silica capillary of 21 cm x 75 microm. The sample length can reach 25% of the efficient length of the capillary, and the sensitivities of GSH and GSSG increased 15-20-fold. The method was also systematically optimized, and the results show that this type of stacking offers good repeatability for routine clinical assay of glutathione in DN plasmas.

High-performance capillary zone electrophoretic assay for markers of diabetic nephropathy in plasma and urine.

A new high-performance capillary zone electrophoretic assay for creatine (Cr), creatinine (Cn), urea (U) and uric acid (Ua), markers of human diabetic nephropathy, both in plasma and urine has been developed with UV detection at 200 nm. The plasma sample was deproteinized with trichloroacetic acid and centrifuged at 10 000 rpm for 10 min. The urine sample was diluted 20-fold with buffer before analysis. The optimum separation conditions for the markers was investigated with respect to the concentration of the buffer, the pH, the voltage and the capillary temperature. Baseline separation was achieved in 25 mmol/L phosphate buffer (pH 3.45) using a 21 cm x 75 microm I.D. fused-silica capillary at 40 degrees C with an electric field of 1190 V/cm. The calibration curves showed good linearity in the range 3.5-1000, 0.18-700, 500-5000 and 2-800 microM (r2 min > 0.998) for Cr, Cn, U and Ua, respectively. The proposed method also has a high reproducibility (peak area RSD max < 3%) and has been successfully applied to the determination of clinical samples.

SHORT, HIGHLY CROSS-LINKED, POLYMER BASED, MONOLITHIC COLUMN FOR CAPILLARY ELECTROCHROMATOGRAPHY

ABSTRACT Capillary electrochromatography with a short and highly cross-linked butyl methacrylate based negative charged monolith as stationary phase was developed. The reproducibility of the column in different kinds of mobile phase was investigated. Moreover, the effects of the operational parameters such as, applied voltage, salt concentration, pH, and organic modifier content in the mobile phase on EOF, as well as the retention mechanism of small neutral compounds on such a column were studied systematically. It was found that the reproducibility and stability of the column is satisfactory in the buffer with very extreme pH values. The retention mechanism of neutral solutes on such a column proved to be similar to that of reversed-phase high performance liquid chromatography.

Mixed Mode of Hydrophilic and Ionic Interaction Pressurized Capillary Electrochromatography for Separation of Basic Compounds

Abstract The separation of six basic compounds was obtained using a mixed mode of hydrophilic interaction and strong cation exchange (SCX), pressurized capillary electrochromatography (pCEC) on a novel pCEC instrument. The effects of organic modifier concentration, ionic strength, and pH value in the buffer on retention behaviors of solutes were investigated. The effects of pressure and voltage on separation also were evaluated. Moreover, the separation result was compared with that in reversed phase pCEC, and the separation mechanism was discussed. A satisfactory reproducibility and stability in the separation system was also achieved in our study. This paper demonstrates the mixed mode pCEC is potentially applicable for separation of basic compounds.

Cinnamic Acid Polymer-Based Monolithic Column for Capillary Electrochromatography

SummaryCapillary electrochromatography has been performed with a cinnamic acid polymer-based monolithic stationary phase. The reproducibility and stability of the column in buffers of very extreme pH were found to be satisfactory. The effects on electroosmotic flow of operating conditions such as applied voltage, salt concentration, pH, and mobile phase organic modifier content were investigated. The retention mechanism of small neutral compounds on such a column was shown to be similar to that in reversed-phase high-performance liquid chromatography.