[On-line enrichment and separation of glycoprotein by capillary electrophoresis based on pH response coating column].

A capillary column coated with 3-aminophenylboronic acid (APBA)-functionalized gold nanoparticles (AuNPs@APBA) was prepared via electrostatic self-assembly. The coated column exhibited anti-nonspecific adsorption of glycoproteins, enabling selective online enrichment during capillary electrophoresis (CE). First, gold nanoparticles (AuNPs) were synthesized using the sodium citrate reduction method. Then, APBA was self-assembled electrostatically on the surface of the AuNPs to obtain AuNPs@APBA. This nanomaterial was bonded to the inner wall of a capillary through ion adsorption to produce a AuNPs@APBA-coated capillary column. Glycoproteins were adsorbed via bond formation with boric acid groups under alkaline conditions (pH 8) to generate borate esters. Under acidic conditions (pH 3), the borate esters dissociated to release the glycoproteins, thereby achieving the selective online enrichment and separation of glycoproteins. The AuNPs and AuNPs@APBA were characterized using Fourier transform infrared spectroscopy, and their sizes and Zeta potentials were determined. In addition, the electroosmotic flow (EOF) of the AuNPs@APBA-coated capillary column was measured. The results showed that the surface of the AuNPs was successfully modified with APBA and that AuNPs@APBA was adsorbed on the inner wall of the capillary. The peak area of ovalbumin (OVA) on the AuNPs@APBA-coated column was 26.46 times higher than that on a bare column via conventional electrophoresis. In contrast, the peak area of bovine serum albumin (BSA) only increased by 8.47 times, indicating that the AuNPs@APBA coated column selectively enriched glycoproteins. Evaluation of the reproducibility and stability of this method revealed that the AuNPs@APBA coated capillary column could be used continually for 33-67 h. The relative standard deviations (RSDs) of the peak areas for intra-day (n=5) and inter-day (n=6) analyses were 2.2% and 3.0%, respectively. The developed method was successfully applied to enrich glycoproteins in a 1×106-fold diluted egg white sample. Glycoproteins were not detected using conventional electrophoresis on the bare column, whereas the AuNPs@APBA-coated capillary column effectively enriched and separated glycoproteins, resulting in a peak area of 10469 mAU·ms. Furthermore, the entire enrichment and separation process was completed within 3 min. This new online enrichment and separation method for glycoproteins has the advantages of low sample consumption, simple operation, and high separation efficiency.

Specific enrichment of caffeic acid from Taraxacum mon-golicum Hand.-Mazz. by pH and magnetic dual-responsive molecularly imprinted polymers.

Specific recognition of caffeic acid (CA) from Taraxacum mon-golicum Hand.-Mazz. was successfully performed using a new pH responsive magnetic molecularly imprinted polymers (pH-MMIPs) by simple surface molecular imprinting polymerization. The pH-MMIPs were prepared on the surface of the Fe3O4@SiO2@MPS particles using CA as a template, 2-(dimethylamino) ethyl methacrylate (DMA) as the pH responsive functional monomer, 4-vinylpyridine (4-VP) as an assisting functional monomer, ethylene glycol dimethyl acrylate (EGDMA) as cross-linker, 2,2'-azobisisobutyronitrile (AIBN) as initiator and methanol-H2O (1:1, v/v) as the porogen. The resultant polymers were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), dynamic light scattering (DLS), Fourier transform infrared spectroscopy (FT-IR), thermal gravimetric analysis (TGA), vibrating sample magnetometry (VSM) and x-ray diffraction (XRD). The adsorption experiments revealed that the pH-MMIPs performed high adsorption ability (11.5 mg g-1) by changing solution pH. Successful selective adsorption of CA was achieved with distribution coefficient of 0.12 and 0.21 towards ferulic acid and chlorogenic acid. Furthermore, pH-MMIPs were employed as adsorbents for extraction and enrichment of CA from Taraxacum mon-golicum Hand.-Mazz. extract. The recoveries of CA in the Taraxacum mon-golicum Hand.-Mazz. ranged from 90.47% to 98.97%. The results proved that the polymers have the potential to provide a selective recognition of CA in complex samples by simple pH regulation.