Sol-gel coatings with covalently attached methyl, octyl, and octadecyl ligandsfor capillary microextraction. Effects of alkyl chain length and sol-gel precursorconcentration on extraction behavior

摘要

Fused silica capillaries with surface-bonded sol-gel coatings containing covalently attached octade-cyl, octyl, and methyl groups were prepared for capillary microextraction (CME) hyphenated on-linewith high-performance liquid chromatography (HPLC). For this, octadecyltrimethoxysilane (CIO-MS),octyltrimethoxysilane (C8TMS), or methyltrimethoxysilane (MTMS) was used as the respective sol-gelprecursor. Hydrolytic polycondensation of these precursors led to the formation of surface-bondedsol-gel sorbents with pendant alkyl groups ready to serve as the extraction medium: no additional sur-face derivatization reactions were needed to anchor these ligands to the surface. Extraction behaviorsof two sets of microextraction capillaries with alkyl-bonded sol-gel coatings were investigated: (a) cap-illaries prepared with a constant molar concentration of these precursors in the sol solution, and (b)capillaries prepared with varied molar concentrations of C8TMS in the sol solution. Among the capillar-ies prepared using sol solutions with the same molar concentration of sol-gel precursor, the detectionlimits for nonpolar and polar analytes ranged from 0.3 ng/L to 213.9 ng/L. The sol-gel octadecyl-coatedcapillaries were found to be the most efficient at extracting these analytes, followed by the sol-gel octyl-coated capillaries, followed by the sol-gel methyl-coated capillaries. The results of this study point to thepossibility that polar analytes are extracted through synergistic molecular level interactions of the polarand nonpolar parts of the analyte molecules with the alkyl chains and silanol groups within the sol-gelcoatings. These coatings also demonstrated run-to-run and capillary-to-capillary reproducibility, withHPLC peak area RSD values ranging from 1.1% to 9.6% and 1.3% to 10.0%, respectively. In the set of sol-geloctyl capillaries with varied molar concentrations, the capillaries prepared with 0.514 M concentrationof C8TMS in the sol solution were most efficient in extracting nonpolar and polar analytes. When higheror lower concentrations of C8TMS were used in the sol solution, the resulting sol-gel coated capillarieswere less efficient in extracting nonpolar and polar analytes.