High pH-resistant, surface-bonded sol–gel titania hybrid organic–inorganic coating for effective on-line hyphenation of capillary microextraction (in-tube solid-phase microextraction) with high-performance liquid chromatography

Sol–gel titania–poly(dimethylsiloxane) (TiO2–PDMS) coating was developed for capillary microextraction (CME) to perform on-line preconcentration and HPLC analysis of trace impurities in aqueous samples. A method is presented describing in situ preparation of the titania-based sol–gel PDMS coating and its immobilization on the inner surface of a fused silica microextraction capillary. To perform CME-HPLC, the sol–gel TiO2–PDMS capillary was installed in the HPLC injection port as an external sampling loop, and a conventional ODS column was used for the liquid chromatographic separation. The target analytes were extracted on-line by passing the aqueous sample through this sampling loop. The sol–gel titania–PDMS coated capillaries were used for on-line extraction and HPLC analysis of polycyclic aromatic hydrocarbons, ketones, and alkylbenzenes. The extracted analytes were then transferred to the HPLC column using an organic-rich mobile phase followed by HPLC separation via gradient elution. To our knowledge, this is the first report on the use of sol–gel titania-based organic–inorganic material as a sorbent in capillary microextraction. The newly developed sol–gel titania-based CME coatings demonstrated excellent pH stability and enhanced extraction capability over the commercial GC coatings that are conventionally used for the same purpose. Extraction characteristics of a sol–gel titania–PDMS capillary remained practically unchanged after continuous rinsing with a 0.1 M NaOH solution (pH 13) for 12 h.