Haifeng Han

Synthesis of ionic liquid‐bonded organic‐silica hybrid monolithic column for capillary electrochromatography

An ionic liquid (IL) was introduced into the organic-silica hybrid monolithic column as the stationary phase for capillary electrochromatography (CEC). The monolithic silica matrix containing chloropropyl functional group was prepared by the in situ co-condensation of tetramethoxysilane and (3-chloropropyl)-trimethoxysilane via a sol-gel process and chemical modification with N-methylimidazole. The electroosmotic flow of the IL-modified hybrid monolithic column was reversed at acidic pH and the morphology of the column was characterized by scanning electron microscope. Four aromatic hydrocarbons were completely separated with 40% acetonitrile phosphate buffer as the mobile phase and seven inorganic ions were efficiently separated with the phosphate buffer on the column in CEC. Reproducibilities of migration time for four aromatic hydrocarbons (benzene, naphthalene, anthracene, chrysene) were acceptable on IL-modified hybrid monolithic columns. Relative standard deviations of run-to-run (n=5), peak area-to-peak area (n=5), day-to-day (n=3) and column-to-column (n=3) were in the range of 0.72-0.88, 1.47-5.40, 2.44-4.99 and 3.01-8.11%, respectively.

Polymeric ionic liquid modified organic-silica hybrid monolithic column for capillary electrochromatography

A polymeric ionic liquid (PIL) modified hybrid monolithic column for CEC was synthesized on the basis of mercaptopropy-functionalized (MP-silica) hybrid monolithic column which was prepared by the in situ co-condensation of tetramethoxysilane and 3-mercaptopropyltrimethoxysilane via a sol-gel process. The PIL modified (PImC₈-silica) hybrid monolithic column, which was characterized by FT-IR and X-ray Photoelectron spectroscopy (XPS), generated a strong reversed and relatively stable EOF in a wide range of pH (3.0-8.0). The PImC₈-silica hybrid monolithic column was evaluated by the separation of three aromatic hydrocarbons (AHs), four alkylbenzenes and five phenols, respectively, with phosphate buffers containing different ratios of acetonitrile as mobile phase. Reproducibilities of the column were also investigated by measuring RSDs of the migration time for AHs. RSDs of run-to-run (n=5), day-to-day (n=3) and column-to-column (n=3) were in the range of 0.26-0.87%, 0.90-3.2% and 1.5-5.7%, respectively.

Polymeric ionic liquid as a dynamic coating additive for separation of basic proteins by capillary electrophoresis

A simple and economical capillary electrophoresis method has been developed for the analysis of four model basic proteins by employing a polymeric ionic liquid (PIL), poly(1-vinyl-3-butylimidazolium) bromide, as the dynamic coating additive. When a small amount of PIL was present in the background electrolyte, a cationic coating on the inner surface of fused-silica capillary was established. These PIL modified capillaries not only generated a stable reversed electroosmotic flow, but also effectively eliminated the wall adsorption of proteins. Several important parameters such as the PIL concentration in the background electrolyte, pH values and concentrations of the background electrolyte were optimized to improve the separation of basic proteins. Consequently, under the optimum conditions, a satisfied separation of basic proteins with peak efficiencies ranging from 247,000 to 540,000 (plates m(-1)) had been accomplished within 11 min. The run-to-run RSDs (n=3) of the migration times for the four basic proteins were all less than 0.37%.

Polymeric ionic liquid-coated capillary for capillary electrophoresis

A new application of the polymeric ionic liquid (PIL) in capillary electrophoresis is reported. Poly(1-vinyl-3-butylimidazolium bromide) was physically adsorbed on silica capillary as the simple and effective coating for capillary electrophoresis (CE) analysis, in which the PIL is not present in the background electrolyte. The electroosmotic flow (EOF) of the PIL-coated capillary as compared with that of the bare fused-silica capillary shows a different dependence on electrolyte pH values. The EOF is reversed over a wide pH range from 3.0 to 9.0 and shows good repeatability. It is also found that the coated capillary has a good tolerance to some organic solvents, 0.1 M NaOH and 0.1 M HCl. The PIL-coated capillary has been employed in different areas. Both the basic proteins and anionic analytes can be well separated by PIL-coated capillaries in a fast and easy way. The PIL-coated capillary is also able to separate organic acid additives in a grape juice. The results showed that this type of coating provides an alternative to the CE separation of anions and basic proteins.

Preparation and characterization of dipyridine modified hybrid-silica monolithic column for mixed-mode capillary electrochromatography

A new mixed-mode organic–silica hybrid monolithic column for capillary electrochromatography was synthesized via a sol–gel process and a following post-modification with 4,4′-dipyridine. Characterization by SEM shows that the hybrid monolith has homogenous macroporous morphology and it is well attached to the inner wall of the capillary. A stable and reversed electroosmotic flow (EOF) was generated at acidic pH due to the pyridinium groups on the surface of the stationary phase. The column performance was evaluated by separating various kinds of compounds, such as polycyclic aromatic hydrocarbons (PAHs), alkylbenzenes, phenols, inorganic anions and organic acids. Multiple retention mechanisms including hydrophobic, π–π and anion-exchange interactions were exhibited at separation of the analytes. The monolithic stationary phase exhibited reversed-phase chromatographic behavior toward neutral solutes. Meanwhile, inorganic anions and organic acids can be separated by the mixed-mode mechanism comprising electrophoresis, hydrophobic and anion-exchange interactions. Good performance and repeatability showed that this new hybrid column can be used in the analysis of various compounds with great prospects.

Novel approach to improve the detection of colchicine via online coupling of ionic liquid‐based single‐drop microextraction with capillary electrophoresis

A novel approach based on ionic liquid-single-drop microextraction (IL-SDME) online coupling with capillary electrophoresis (CE) was used to determine a toxic alkaloid--colchicine. The IL-SDME procedure was optimized by extraction solvent, drop volume controlling, sample volume and pH, extraction time, and ionic strength. Under optimum conditions, enrichment factor was as much as 41-fold with a relative standard deviation of 2.8% (n = 3). Linear range of response was observed from 1 to 100 μg/mL, with detection limit of 0.25 μg/mL and correlation coefficient (R(2) ) of 0.9994. The extraction of colchicine from spiked Lanzhou lily sample was performed and obtaining good result with an average recovery rate of 102.4 and 98.8% at 5 and 50 μg/mL, respectively. Comparing with the previous methods, IL-SDME-CE is really a convenient, economical, and environmentally benign way for determining colchicine.

Polymeric ionic liquid as additive for the high speed and efficient separation of aromatic acids by co-electroosmotic capillary electrophoresis

A simple and reliable co-electroosmotic capillary electrophoresis system for the fast determination of aromatic acids has been developed by employing poly (1-vinyl-3-butylimidazolium bromide) as the background electrolyte modifier. The polymeric ionic liquid was synthesized by the conventional radical polymerization. The reversed electroosmotic flow was obtained by adding a small amount of the polymeric ionic liquid (0.0006%, w/v) to the electrolyte. To further improve the resolution of aromatic acids, conditions including the concentration of polymeric ionic liquid and pH of background electrolytes were optimized. All eight aromatic acids were baseline resolved in one measurement in a short time (less than 3.5 min) under optimized conditions, 100 mM NaH(2)PO(4) buffer containing 0.006% (w/v) polymeric ionic liquid, pH 6.0. Separation efficiencies were in the range from 355,000 to 943,000 (plates/m). Satisfactory reproducibility on the basis of the migration time of analytes was achieved. RSDs (n=3) were less than 0.33% except the p-aminobenzoic acid (0.9%). The applicability of the present method has been demonstrated for the determination of water-soluble aromatic acids in a common drug for external use.

Polymeric ionic liquid as a background electrolyte modifier enhancing the separation of inorganic anions by capillary electrophoresis

A novel and easy method for the separation of inorganic anions by capillary electrophoresis using a polymeric ionic liquid (PIL), poly(1-vinyl-3-butylimidazolium bromide) as a background electrolyte modifier has been developed. The PIL has been proved to generate a reversed electroosmotic flow which reduces the analysis time and improves the separation significantly. Effects of the PIL concentration and buffer composition (pH and concentration) were evaluated on basis of the resolution and efficiency of the sample. Under optimum conditions, good separation of six model inorganic anions was achieved with high efficiency and excellent reproducibility within 3 min. The results obtained indicate that the combination of reversed EOF and the association between the analytes and the PIL on the capillary wall or BGE play a prominent role in the separation of anions. Therefore, the PIL presents a useful alternative for the BGE modifier in the study of inorganic anions by CE.

A versatile polar-embedded polyphenyl phase for multimodal separation in liquid chromatography

A new polar-embedded aromatic stationary phase has been prepared by covalently attaching p-biphenylacetamide silane to silica spheres. The retention behavior of this phase was compared with an alkylamide counterpart and octadecyl phases using different classes of analytes, including geometric isomers and congeners from Standard Reference Materials 869b, 870 and 1647e, positional isomers of electron-deficient benzenes, as well as alkylbenzenes and alkylbiphenyls. The relationship between shape selectivity and surface chemistry of stationary phase was comparatively studied. Influences of the embedded group and ligand length and/or size on the chromatographic selectivity towards various congeners were established. The new polar-embedded aromatic phase possessed unique benzenoid affinity, enhanced aromatic selectivity, distinct charge-transfer properties, as well as good water-wettablity, as a result it can be employed in normal phase, reversed-phase and per-aqueous modes.

Highly efficient and rapid capillary electrophoretic analysis of seven organic acid additives in beverages using polymeric ionic liquid as additive

A new capillary electrophoretic method for the rapid and direct separation of seven organic acids in beverages was developed, with poly (1-vinyl-3-butylimidazolium bromide) as the reliable background electrolyte modifier to reverse the direction of anode electroosmotic flow (EOF) severely. Several factors that affected the separation efficiency were investigated in detail. The optimal running buffer consisted of 125 mmol/L sodium dihydrogen phosphate (pH 6.5) and 0.01 g/L poly (1-vinyl-3-butylimidazolium bromide). Highly efficient separation (105,000 to 636,000 plates/m) was achieved within 4 min and standard deviations of the migration times (n=3) were lower than 0.0213 min under optimal conditions. The limits of detection (S/N = 3) ranged from 0.001 to 0.05 g/L. The present method was applied to determine a beverage sample (Mirinda) for sodium citrate, benzoic acid and sorbic acid with concentration of 2.64, 0.10 and 0.08 g/L, respectively. The recoveries of the three analytes in the sample were 100.3%, 100.7% and 131.7%, respectively. The method is simple, rapid, inexpensive, and can be applied to determine organic acids as additives in beverages.