Sol-gel zirconia- and titania-based surface-bonded hybrid organic-inorganic coatings for sample preconcentration and analysis via capillary microextraction in hyphenation with gas chromatography (CME-GC)

Novel zirconia- and titania-based sol-gel hybrid organic-inorganic coatings were developed for capillary microextraction (in-tube SPME). Principles of sol-gel chemistry were employed to chemically bind two hydroxy-terminated silicone polymers (polydimethyldiphenylsiloxane, PDMDPS, and polydimethylsiloxane, PDMS) to sol-gel zirconia and titania networks in the course of their evolution from highly reactive alkoxide precursors undergoing controlled hydrolytic polycondensation reactions. A properly designed sol solution was used to conduct the sol-gel reactions inside a fused silica capillary for ∼30 min to create a hybrid organic-inorganic sol-gel coating anchored to the capillary inner walls. The unbonded part of the sol solution was then expelled under helium pressure, and the coated capillary was conditioned under temperature programmed conditions. Aqueous samples containing parts per billion (ppb) level trace concentrations of polar and nonpolar analytes were passed through the sol-gel microextraction capillary using a gravity-fed sample dispenser. This process was continued for 30 min for extraction process to reach equilibrium. As the sample passed through the capillary, the target analyte molecules were sorbed and enriched by the sol-gel coating. The microextraction capillary (with the extracted analytes within the coating) was installed in a GC injection port with its exit end connected to the inlet of a sol-gel GC column. The extracted analytes were transferred from the microextraction capillary to the GC column using a rapid (100°C/min) temperature program in the injection port. The desorbed analytes were swept over by the carrier gas (helium) and were focused at the GC column inlet maintained at 30°C. GC analysis of the focused analytes were then performed by programming the column temperature. Parts per trillion (ppt) level detection limits were achieved for various classes of analytes by coupling CME with GC-FID. The newly developed sol-gel hybrid zirconia- and titania-based coatings demonstrated excellent pH stability, and retained the extraction characteristics intact even after continuous rinsing with a 0.1 M NaOH and/or 0.1 M HCl solution for 24 h. To our knowledge, this is the first report on the use of sol-gel zirconia- and titania-based hybrid organic-inorganic coatings as an extraction media in solid phase microextraction in hyphenation with gas chromatography.