Parts per quadrillion level ultra-trace determination of polar and nonpolar compounds via solvent-free capillary microextraction on surface-bonded sol–gel polytetrahydrofuran coating and gas chromatography–flame ionization detection

Sol–gel polytetrahydrofuran (poly-THF) coating was developed for high-sensitivity sample preconcentration by capillary microextraction (CME). Parts per quadrillion (ppq) level detection limits were achieved for both polar and nonpolar analytes through sample preconcentration on sol–gel poly-THF coated microextraction capillaries followed by gas chromatography (GC) analysis of the extracted compounds using a flame ionization detector (FID). The sol–gel coating was in situ created on the inner walls of a fused silica capillary using a sol solution containing poly-THF as an organic component, methyltrimethoxysilane (MTMOS) as a sol–gel precursor, trifluoroacetic acid (TFA, 5% water) as a sol–gel catalyst, and hexamethyldisilazane (HMDS) as a deactivating reagent. The sol solution was introduced into a hydrothermally-treated fused silica capillary and the sol–gel reactions were allowed to take place inside the capillary for 60 min. A wall-bonded coating was formed due to the condensation of silanol groups residing on the capillary inner surface with those on the sol–gel network fragments evolving in close vicinity of the capillary walls. Poly-THF is a medium polarity polymer, and was found to be effective in carrying out simultaneous extraction of both polar and nonpolar analytes. Efficient extraction of a wide range of trace analytes from aqueous samples was accomplished using sol–gel poly-THF coated fused silica capillaries for further analysis by GC. The test analytes included polycyclic aromatic hydrocarbons (PAHs), aldehydes, ketones, chlorophenols, and alcohols. To our knowledge, this is the first report on the use of a poly-THF based sol–gel material in analytical microextraction. Sol–gel poly-THF coated CME capillaries showed excellent solvent and thermal stability (>320 °C).