title: Preparation of organic-inorganic hybrid silica monolith with octyl and sulfonic acid groups for capillary electrochromatograhpy and application in determination of theophylline and caffeine in beverage.
abstract: An organic-inorganic hybrid silica monolithic column with octyl and sulfonic acid groups has been prepared by sol-gel technique for capillary electrochromatograhpy. The structure of hybrid monolith was optimized by changing the composition of tetraethoxysilane (TEOS), octyltriethoxysilane (C(8)-TEOS) and 3-mercaptopropyltrimethoxysilane (MPTMS) in the mixture of precursors. Then, the obtained hybrid monolith was oxidized using hydrogen peroxide (30%, w/w) to yield sulfonic acid groups. The sulfonic acid group, which served as strong cation-exchanger, dominated the charge on the surface of the capillary column and generated stable electroosmotic flow (EOF) in a wide range of pH. The monolithic column was characterized by scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy and elemental analysis (EA), and the performance of column was evaluated in detail by separating different kinds of compounds with column efficiency up to 155,000 plates/m for thiourea. In addition, this monolithic column was also applied in the analysis of theophylline (TP) and caffeine (CA) in beverages. The detection limits were 0.39 and 0.48 microg/mL for theophylline and caffeine, respectively. The method reproducibility was tested by evaluating the intra- and inter-day precisions, and relative standard deviations of less than 3.9 and 8.4%, respectively, were obtained. Recoveries of compounds from spiked beverage samples ranged from 87.2 to 105.2%.
authors.affiliation: Key Laboratory of Analytical Chemistry for Biology and Medicine (Ministry of Education), Department of Chemistry, Wuhan University, Wuhan 430072, China.
authors.forename: Ming-Luan
authors.initials: ML
authors.lastname: Chen
authors.forename: Ming-Ming
authors.initials: MM
authors.lastname: Zheng
authors.forename: Yu-Qi
authors.initials: YQ
authors.lastname: Feng
mesh_terms: D000097:Acetonitriles; D001628:Beverages / Q000032:analysis*; D002110:Caffeine / Q000032:analysis*; D053801:Capillary Electrochromatography / Q000379:methods*; D053841:Electroosmosis; D005504:Food Analysis / Q000379:methods*; D006863:Hydrogen-Ion Concentration; D007287:Inorganic Chemicals / Q000737:chemistry; D016014:Linear Models; D008855:Microscopy, Electron, Scanning; D009930:Organic Chemicals / Q000737:chemistry; D044367:Phase Transition; D010710:Phosphates; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012822:Silicon Dioxide / Q000737:chemistry*; D013451:Sulfonic Acids; D013806:Theophylline / Q000032:analysis*
chemical_list: D000097:Acetonitriles; D007287:Inorganic Chemicals; D009930:Organic Chemicals; D010710:Phosphates; D013451:Sulfonic Acids; D002110:Caffeine; D012822:Silicon Dioxide; D013806:Theophylline; C032159:acetonitrile