Yuhua Cao

Rapid determination of water- and fat-soluble vitamins with microemulsion electrokinetic chromatography

A rapid, reliable and reproducible method based on microemulsion electrokinetic chromatography (MEEKC) for simultaneous determination of 13 kinds of water- and fat-soluble vitamins has been developed in this work. A novel microemulsion system consisting of 1.2% (w/w) sodium lauryl sulphate (SDS), 21% (v/v) 1-butanol, 18% (v/v) acetonitrile, 0.8% (w/w) n-hexane, 20mM borax buffer (pH 8.7) was applied to improve selectivity and efficiency, as well as shorten analysis time. The composition of microemulsion used as the MEEKC running buffer was investigated thoroughly to obtain stable separation medium, as well as the optimum determination conditions. Acetonitrile as the organic solvent modifier, pH of the running buffer and 1-butanol as the co-surfactant played the most important roles for the separation of the fat-soluble vitamins, water-soluble vitamins and stabilization of system, respectively. The 13 water- and fat-soluble vitamins were baseline separated within 30 min. The system was applied to determine water- and fat-soluble vitamins in commercial multivitamin pharmaceutical formulation, good accuracy and precision were obtained with recoveries between 97% and 105%, relative standard derivations (RSDs) less than 1.8% except vitamin C, and acceptable quantitative results corresponding to label claim.

Comparison of microstructures of microemulsion and swollen micelle in electrokinetic chromatography

Recently, 1-butanol modified MEKC was proven to be similar to MEEKC in separation performance. In the present work, typical microemulsion containing 0.8% n-octane/3.3% SDS/6.6% 1-butanol/20 mM borax buffer and corresponding swollen micelle without n-octane were used to compare their microdroplet structures including hydrodynamic radius, electrokinetic potential ζ and charge density at the hydrodynamic shear surface, as well as microenvironment polarity in the interior of the microdroplets. Three kinds of corticosteroids were separated with MEEKC and 1-butanol modified MEKC to assess their separation performances. The experiment results showed that both microstructure and separation performance in microemulsion and in swollen micelle systems were alike, no matter whether oil phase n-octane was present. The environment polarity in the core of swollen micelle was slightly higher than in the microemulsions, and both of them were higher than in n-octane medium. Furthermore, the influences of SDS and 1-butanol concentration on microstructures were measured in details. Increasing the amount of SDS, hydrodynamic radius decreased in microemulsion but increased in swollen micelle. On the contrary, ζ and shear surface charge density changed in the reverse trends. With increment of 1-butanol concentration, the hydrodynamic radius increased dramatically in microemulsions, whereas decreased slightly in swollen micelle. Even though using n-octane as oil core was not a key factor, microemulsions and swollen micelle as pseudostationary phase in EKC should not be exactly the same.

Determination of phthalates in food packing materials by electrokinetic chromatography with polymeric pseudostationary phase

Polymeric pseudostationary phase (PSP), formed by random copolymer poly (stearyl methacrylate-co-methacrylic acid) (P(SMA-co-MAA)), was used in electrokinetic chromatography (EKC) to separate 15 kinds of phthalates (PAEs). The organic solvent modifier is a key factor for the separation of PAEs. Without organic solvents, only four kinds of PAEs with smaller molecular weight could be separated in the running buffer containing 1% P(SMA-co-MAA). The other eleven kinds of PAEs with larger molecular weight could be separated within 25 min by adding 40% (v/v) methanol and 2% (v/v) 1-butanol in the running buffer. The linear ranges of 15 kinds of PAEs were between 2 and 200mg/L, and the limit of detection based on the ratio of signal to noise of 3 were between 1 and 3mg/L. The method was applied to determination of PAEs in 6 kinds of food packing materials. The recoveries were between 81% and 118% with the RSD less than 4%.

Amphiphilic polymeric micelle as pseudostationary phase in electrokinetic chromatography for analysis of eight corticosteroids in cosmetics

Amphiphilic polymeric micelle, as a novel pseudostationary phase in EKC was used to determine eight kinds of corticosteroids namely hydrocortisone, prednisolone, hydrocortisone acetate, prednisone, cortisone acetate, prednisolone acetate, dexamethasone, and triamcinolone acetonide in cosmetics. Amphiphilic random copolymer poly(methyl methacrylate‐co‐methacrylic acid) (P(MMA‐co‐MAA)) was micellizated via neutralization in alkaline aqueous solution. The influences of the molar ratio of monomer MMA to MAA, the concentration of polymer and pH on the polymeric micelle microstructure and EKC performances were investigated. As molar ratio of MMA to MAA in P(MMA‐co‐MAA) increased, both CMC and environmental polarity of the inner core in polymeric micelle decreased dramatically. With increasing monomer ratio, the size of polymeric micelles increased firstly, and then decreased, finally increased again. ζ potential of the micelle had a slight decline trend. As increment of polymer concentration, the size of the polymeric micelle increased steadily. By optimizing the monomer ratio, the polymer concentration, and pH of the running buffer, as well as operation conditions such as separation voltage and temperature, the eight analytes could be separated within 16.5 min using 7.5 mg/mL polymer with the monomer ratio of 7:3 dissolved in pH 9.2 borax buffer as the running buffer. The method has been used for analysis of corticosteroids in cosmetic samples with simple extraction; the recoveries for eight analytes were between 85.9 and 106%. This method was of accuracy, repeatability, pretreatment simplicity, and could be applied to the quality control of cosmetics.

Microstructure of microemulsion modified with ionic liquids in microemulsion electrokinetic chromatography and analysis of seven corticosteroids

In this work, the influences of ionic liquid (IL) as a modifier on microemulsion microstructure and separation performance in MEEKC were investigated. Experimental results showed that synergetic effect between IL 1‐butyl‐3‐methylimidazolium tetrafluoro‐borate (BmimBF4) and surfactant SDS gave a decreased CMC. With increment of IL in microemulsion, negative ζ potential of the microdroplets reduced gradually. The influence of IL on the dimensions of microdroplet was complicated. At BmimBF4 less than 8 mM, IL made microemulsion droplet smaller in size. While at BmimBF4 more than 10 mM, the size increased and reached to a maximum value at 12 mM, where the microdroplets were larger than that without IL. After that, the micreodroplet size decreased again. Relative fluorescence intensity of the first vibration band of pyrene to the third one (I1/I3) enhanced as IL was added to microemulsion, which indicated that this addition increased environmental polarity in the inner core of microdroplets. Prednisone, hydrocortisone, prednisolone, hydrocortisone acetate, cortisone acetate, prednisolone acetate, and triamcinolone acetonide were analyzed with MEEKC modified with IL to evaluate the separation performance. Cortisone acetate and prednisolone acetate could not be separated at all in typical microemulsion. The seven analytes could be separated by the addition of 10 mM BmimBF4 into the microemulsion system. The method has been used for analysis of corticosteroids in cosmetic samples with simple extraction; the recoveries for seven analytes were between 86 and 114%. This method provides accuracy, reproducibility, pretreatment simplicity, and could be applied to the quality control of cosmetics.

Electrochemical sensor based on magnetic molecularly imprinted nanoparticles modified magnetic electrode for determination of Hb

A fast and selective electrochemical sensor for determination of hemoglobin (Hb) was developed based on magnetic molecularly imprinted nanoparticles modified on the magnetic glassy carbon electrode. The nanoparticles Fe3O4@SiO2 with a magnetic core and a molecularly imprinted shell had regular structures and good monodispersity. Hb could be determined directly by electrochemical oxidization with the modified electrode. A magnetic field increased electrochemical response to Hb by two times. Imprinting Hb on the surface of Fe3O4@SiO2 shortened the response time within 7min. Under optimum conditions, the imprinting factor toward the non-imprinted sensor was 2.8, and the separation factor of Hb to horseradish peroxidase was 2.6. The oxidation peak current had a linear relationship with Hb concentration ranged from 0.005mg/ml to 0.1mg/ml with a detection limit (S/N =3) of 0.0010mg/ml. The sensors were successfully applied to analysis of Hb in whole blood samples with recoveries between 95.7% and 105%.

Rapid analysis of water- and fat-soluble vitamins by electrokinetic chromatography with polymeric micelle as pseudostationary phase.

A novel polymeric micelle, formed by random copolymer poly (stearyl methacrylate-co-methacrylic acid) (P(SMA-co-MAA)) has been used as pseudostationary phase (PSP) in electrokinetic chromatography (EKC) for simultaneous and rapid determination of 11 kinds of water- and fat-soluble vitamins in this work. The running buffer consisting of 1% (w/v) P(SMA-co-MAA), 10% (v/v) 1-butanol, 20% (v/v) acetonitrile, and 30 mM Palitzsch buffer solution (pH 9.2) was applied to improve the selectivity and efficiency, as well as to shorten analysis time. 1-Butanol and acetonitrile as the organic solvent modifiers played the most important roles for rapid separation of these vitamins. The effects of organic solvents on microstructure of the polymeric micelle were investigated. The organic solvents swell the polymeric micelle by three folds, lower down the surface charge density and enhance the microenviromental polarity of the polymeric micelle. The 11 kinds of water- and fat-soluble vitamins could be baseline separated within 13 min. The method was applied to determine water- and fat-soluble vitamins in commercial vitamin sample; the recoveries were between 93% and 111% with the relative standard derivations (RSDs) less than 5%. The determination results matched the label claim.

Polymeric micelle as the pseudostationary phase in electrokinetic chromatography.

A simple, green, and novel approach to prepare polymeric micelle with amphiphilic random copolymer P (MMA-co-MAA) via neutralization in aqueous medium has been developed, and the polymeric micelle was firstly applied as a pseudostationary phase (PSP) in electrokinetic chromatography (EKC) in the present work. Three structurally similar corticosteroids namely hydrocortisone, prednisolone, and prednisone were separated with EKC using polymeric micelle as PSP to assess the separation performance. The effects of polymeric concentration and pH on micellar microstructure including size, morphology, surface charge density and EKC performances have been investigated. TEM showed that amphiphilic random copolymers were self-assembled via neutralization to form micelles with well-defined size and shape. The size and shape of the micelle depended on the P (MMA-co-MAA) concentration and pH. At the concentration of 0.048 mM and pH 9.2, the polymeric micelles were of monodispersity and perfect spheres. DLS showed the size of micelle was almost equal as polymer concentration in the range of 0.0096-0.048 mM, and then enlarged sharply at the concentration larger than 0.048 mM. However, the zeta potentials of micelle were nearly unchanged. The polymer concentration is also the key parameter for EKC separation. Under the optimum conditions, three analytes could be baseline separated within 7.4 min. Compared with typical MEKC, MEEKC, and MEKC modified with IL ([Bmim]BF₄), the developed method was more rapid, efficient, and higher selective. The separation mechanism using polymeric micelle as PSP was reverse-phase interaction. The actual cosmetic samples were analyzed with recoveries between 97.3% and 113%.

Facile fabrication of a magnetically assembled colloidal photonic crystal film via radical polymerization

A facile, economical and practical technique to fabricate a magnetically assembled colloidal photonic crystal in a polyacrylamide hydrogel matrix was demonstrated by an instant radical polymerization. By taking advantage of the instantaneousness of magnetic assembly, magnetic colloids were successfully assembled into photonic crystal structures with tunable stop bands in aqueous solution. The Bragg diffraction color could be simply controlled by tuning the strength of the external magnetic field to achieve diffraction covering the entire visible spectrum. An appropriate amount of an ionic initiator, APS, was key in the radical polymerization of the photonic crystal hydrogel film. 0.3 mg mL−1 of APS was chosen, not only to allow a rapid formation of the polyacrylamide hydrogel, but also to avoid coagulation of these magnetic colloids in the hydrogel. Due to the significantly instantaneous properties of magnetic assembly and radical polymerization, coagulation of these magnetic assemblies owing to their long exposure time to an external magnetic field could be prevented. Therefore, a photonic crystal hydrogel film with a uniform diffraction color could be obtained. Notably, the flexible hydrogel film displayed obvious deformation responsiveness. The diffraction light got red-shifted as the level of deformation rose. The achievement in immobilization demonstrates the system to be a major stride toward practical applications in responsive photonic materials.

Vesicles formed by mixed catanionic surfactants as novel pseudostationary phase in electrokinetic chromatography

In this paper, a novel pseudostationary phase (PSP), the vesicle formed from octyltriethylammonium bromide (C8NE3Br) and sodium dodecyl benzene sulfonate (SDBS), has been developed in electrokinetic chromatography (EKC). Physicochemical parameters of the mixture of catanionic surfactants such as ζ potential and size of the aggregates were characterized as the molar ratio of C8NE3Br to SDBS varied from 2:8 to 8:2 and total concentration of surfactants fixed at 20mM. At any ratio mentioned above, ζ potential of mixture of catanionic surfactants remained negative. The absolute values of ζ potential were even larger than in only SDBS system as the molar ratio of C8NE3Br to SDBS less than 4:6, and they decreased as increasing the ratio of cationic surfactants. The size of the aggregates became smaller as the ratio was close to 1. Unexpectedly, the size was smallest at ratio of 3:7 and 6:4, instead of at 5:5. Notably, coagulation did not occur in the catanionic system at any proportion of each other. TEM testified the formation of vesicles. The performance of the vesicle as PSP was evaluated by separating eight kinds of corticosteroids with EKC, these analytes were separated completely without any additives. Compared with SDS microemulsion modified with ionic liquid (IL) and polymeric micelle, the novel vesicle PSP had better separation performances.