Weidong Qin

1, 3-Dialkylimidazolium-based room-temperature ionic liquids as background electrolyte and coating material in aqueous capillary electrophoresis

The 1-ethyl-3-methylimidazolium (EMIM) cation was found to have constant mobility of 4.5 x 10(-4) cm2 V(-1) s(-1) over the pH range of 3 to 11. The electroosmotic flow of bare silica capillary was reversed by the covalently bonded room-temperature ionic liquid (RTIL) coating. With run buffer of 5 mM EMIM (pH 8.5), NH4+ in human urine was separated from the K+ matrix and was detected to be 0.37 +/- 0.012%. K+, Na+, Li+, Ca2+, Mg2+ and Ba2+ were baseline separated in RTIL-coated capillary with run buffer of 10 mM EMIMOH-acetic acid at pH 5, and the concentration of the above ions in a red wine were detected to be 907, 27.9, 0, 71.0, 83.4 and 31.1 microg/ml, respectively. The RTIL-coated capillary showed stable electroosmotic flow for at least 80 h in the run buffer.

Electrophoresis of DNA in ionic liquid coated capillary

An ionic liquid (IL) coated capillary was prepared and investigated for DNA separation. The electroosmotic flow of the capillary was reversed between pH 4.5 and 9. Below 900 base pairs the larger DNA fragment suffered more retardation in the IL coated capillary due to the increasing charge density of the fragment with size. In the presence of 4% hydroxyethylcellulose, the phiX174 DNA-Hae III digest fragments were baseline separated in both IL- and polyacrylamide-coated capillary except for the fragments of 271 and 281 base pairs; while the analysis time was shorter in the IL-coated capillary. Our experiments indicated that the IL-coated capillary could work stably in the run buffer for at least 96 h with no notable deterioration in performance.

Capillary electrophoresis-chemiluminescence determination of norfloxacin and prulifloxacin.

A capillary electrophoresis (CE)-chemiluminescence (CL) method for determining norfloxacin (NFLX) and prulifloxacin (PFLX) was developed based on the enhanced CL intensity of the cerium(IV)-sulfite-fluoroquinolone (FQ) reaction sensitized by terbium(III). The separation was conducted in buffer composed of 20 mM sodium citrate, 4 mM citric acid and 10 mM sodium sulfite at pH 6.1. The CL reagent solution consisted of 2 mM cerium(IV), 4 mM terbium(III) and 1.1 mM hydrochloric acid. NFLX and PFLX were baseline separated within 11 min with detection limits (S/N=3) of 0.057 and 0.084 microg mL(-1), respectively. The maximum intra- and inter-day relative standard deviations (R.S.D.s) of migration time of the analytes were less than 4.0% and 4.2%, respectively. The proposed method was applied to detect NFLX and PFLX in fortified urine sample and the results were comparable to high-performance liquid chromatography (HPLC)-UV method. Moreover, the high selectivity of the CL detection and the high-separation efficiency of CE render the method the potential of quick analyzing fluoroquinolones in real complex matrix.

Separation of ionic liquid cations and related imidazole derivatives by α-cyclodextrin modified capillary zone electrophoresis

The separation and detection of 1-alkyl-3-methylimidazolium, including isomers, and related imidazole derivatives was performed by alpha-cyclodextrin (alpha-CD) modified capillary zone electrophoresis. The separations were carried out in a running buffer comprising 5.0 mM triethylamine and 2.0 mM alpha-CD adjusted to pH 4.5 by acetic acid. All the analytes were baseline separated within 8 min and the detection limits (signal-to-noise ratio = 3) ranged between 0.42 and 1.36 ppm. The method showed good linearity (within 3-50 times the detection limits, r > 0.99) and reproducibility (relative standard deviation < 0.8% for migration times and < 3% for peak areas), which should make it suitable for routine analysis. It was employed in detecting impurities in commercial chemicals, and 0.27% 1-methylimidazole in 1-ethyl-3-methylimidazolium chloride and 0.55% imidazole in 2-ethylimidazole were found. In addition, it was employed in process analysis during synthesis of ionic liquids and demonstrated a potential to provide information on the reaction mechanism.

Polyamidoamine-grafted silica nanoparticles as pseudostationary phases for capillary electrochromatographic separation of proteins.

Polyamidoamine-grafted silica nanoparticles were synthesized, characterized and investigated for the feasibility as pseudostationary phases in alkaline buffer for separation of cationic and anionic proteins, viz., lysozyme, cytochrome C, gamma globulin, and myoglobin. Neither bare silica nanoparticles nor polyamidoamines nor their mixtures as pseudostationary phases could lead to simultaneous separation of the four proteins. However, polyamidoamine-grafted silica nanoparticles not only suppressed the irreversible wall adsorption of the cationic lysozyme and cytochrome C, but also provided selectivity toward all the proteins. We found that polyamidoamine generation two-modified silica nanoparticles were the optimum pseudostationary phases with respect to detection sensitivity and separation efficiency; presence of the nanoparticles at 0.01% in the running buffer of 12.5 mM tetraborate/phosphate at pH 9.1 resulted in baseline resolution of the four proteins.

Incorporation of polyamidoamine sweeping and electrokinetic supercharging for in-line DNA fragment preconcentration

We report an approach for in-line preconcentration of DNA fragments using dendritic polyamidoamine generation 2.0 (PAMAM G 2.0) as sweeping agent. During the experiment, a plug of PAMAM G 2.0 was hydrodynamically injected first, followed by field-amplified sample injection (FASI) of DNA fragments, which were concurrently swept by PAMAMs via DNA-PAMAM complexation. Then, a segment of releasing agent, sodium dodecyl sulfate (SDS), was hydrodynamically introduced and subsequently electrophoretically driven to interact with the DNA-PAMAM complexes, forming more stable supramolecular SDS-PAMAM complexes and releasing the initially bound DNA fragments. The excess dodecyl sulfate anion also acted as terminating electrolyte in the separation, thereby the DNA fragments were enriched by the joint effects of FASI, sweeping and transient isotachophoresis. We term the approach PAMAM sweeping-electrokinetic supercharging (EKS). Because the mobility of the DNA-PAMAM complex was very low, the proposed method allowed long-time sample injection without notable loss in separation efficiency. Under the optimum conditions, the PAMAM sweeping-EKS strategy improved the detection sensitivity of DNA fragments by more than 30 folds relative to the conventional FASI. Moreover, due to the sweeping process incorporated, the approach can be applied to enrichment of DNA fragments in highly saline matrix.

Cationic poly(amidoamine) dendrimers as additives for capillary electroseparation and detection of proteins

We examine the influence of cationic poly(amidoamine) (PAMAM) dendrimers on capillary electroseparation–UV analysis of proteins. PAMAMs adsorbing to the capillary surface suppressed the wall‐adsorption of proteins; meanwhile, PAMAMs added to the buffer exhibited selectivity toward proteins. Presence of 3×10−4 g/mL PAMAM generation one (G 1.0) in 30 mM phosphate, at pH 2.6, rendered significant enhancement in separation efficiency; the merged peaks of myoglobin and trypsin inhibitor were separated. Moreover, the protein–dendrimer interactions changed the inherent UV absorbance profiles of proteins. UV–Vis study showed that the absorbance of cytochrome C and transferrin increased at the detection wavelength of 214 nm; their detection sensitivity enhanced by 2.44 and 2.01‐folds, respectively, with addition of 5×10−4 g/mL PAMAM G 1.0.

Polyamidoamine dendrimers as sweeping agent and stationary phase for rapid and sensitive open-tubular capillary electrophoretic determination of heavy metal ions

Polyamidoamine (PAMAM) dendrimer generation 2.5 was synthesized and evaluated as sweeping agent for in-column enrichment and as stationary phase for capillary electrochromatographic separation of heavy metal ions, viz., Pb(II), Cu(II), Hg(II), Zn(II) and Co(II), in a running buffer containing 4-(2-pyridylazo)resorcinol (PAR) as a chromogenic reagent. During experiment, a plug of aqueous PAMAM generation 2.5 solution was first introduced to the capillary, followed by electrokinetic injection of the heavy metal ions under a positive voltage. In this step, PAMAM acted as a sweeping agent, stacking the metal ions on the analyte/PAMAM boundary by forming metal ion-PAMAM complexes. The second preconcentration process occurred when PAR, a stronger ligand, moving toward the injection end under the electric field, reached and re-swept the metal ion-PAMAM zone, forming metal ion-PAR complexes. During separation, the neutral PAMAM moved toward the detector with the electroosmotic flow, dynamically coating the capillary wall, forming stationary phases that affected the separation of the metal ions. Due to the function of PAMAM, the detection sensitivity and resolution of the heavy metal ions improved significantly. Under the optimum conditions, the detection limits were 0.299, 0.184, 0.774, 0.182 and 0.047 μg/L for Pb(II), Cu(II), Hg(II), Zn(II) and Co(II), respectively. The method was successfully applied to the determination of heavy metals in snow, tap and rain water samples.

Cyclodextrin-functionalized silica nanoparticles with dendrimer-like spacers for enantioselective capillary electrochromatography.

In this report, β‐cyclodextrin (β‐CD)‐functionalized silica nanoparticles (SNPs) with dendrimer‐like spacers were synthesized by first grafting the SNPs with different generations of polyamidoamines (PAMAMs), followed by modifying the grafted SNPs with mono‐6‐deoxy‐(p‐tolylsulfonyl)‐β‐CD. The β‐cyclodextrin‐modified silica nanoparticle‐cored PAMAMs (SNP‐PAMAM‐β‐CDs) were studied as chiral pseudostationary phases for separating three racemic drugs, namely, chlorpheniramine, nefopam, and verapamil. The β‐CD‐functionalized SNPs with dendrimer‐like spacers were more enantioselective than native β‐CD, and the structures of the dendritic spacers were highly influential on the separation. In 20 mM NaH2PO4, addition of 4.00 mg/mL SNP‐G1.0‐β‐CD (corresponding to 1.12 mM β‐CD) could baseline separate the enantiomers of chlorpheniramine and nefopam, and introduction of 7.00 mg/mL SNP‐G0‐β‐CD (corresponding to 1.68 mM β‐CD) resulted in enantioseparation of the verapamil racemates. On the contrary, the enantiomers of nefopam and verapamil could not be resolved in the presence of 15 mM native β‐CD. Our results suggest that SNP‐PAMAM‐β‐CDs hold great promise for enantioselective separations.

CE determination of quinolones in the presence of bovine serum albumin.

This article describes the influence of bovine serum albumin (BSA) as an additive on the capillary electrophoresis-potential gradient determination of five quinolones, enoxacin, norfloxacin, ofloxacin, fleroxacin, and pazufloxacin. With 10 mg/L of BSA present in the buffer of 30 mM Tris and 3 mM phosphoric acid at pH 9, the detection limits of the five quinolones were in the range of 0.24-0.68 mg/L, i. e. 5.8-16.5-fold lower than those obtained with the buffer devoid of BSA, and the analysis time was shortened. We suggest that the inner wall-adsorbed BSA suppresses the adsorption of quinolones and simultaneously enhances the electroosmotic flow rate. Our experiments indicated that adopting the potential gradient detection technique could eliminate the interference of the UV-active proteins on the detection of quinolones that would occur with conventional optical detection, and therefore offer high detection sensitivity. As a demonstration, the method was applied to the determination of QNs in fortified chicken muscle sample with satisfactory results.