For the first time, germania-based hybrid organic-inorganic sol-gel materials were developed for analytical sample preparation and chromatographic separation. Being an isostructural analog of silica (SiO₂), germania (GeO ₂) is compatible with silica network. This structural similarity, which is reflected by the relative positions of germanium and silicon in the periodic table, stimulated our investigation on the development of germania-based sol-gel hybrid organic-inorganic coatings for analytical applications.

Sol-gel sorbents and stationary phases reported to date are predominantly silica-based. Poor pH stability of silica-based materials is a major drawback. In this work, this problem was addressed through development of germania-based organic-inorganic hybrid sol-gel materials. For this, tetramethoxygermane (TMOG) and tetraethyoxygermane (TEOG) were used as precursors to create a sol-gel network via hydrolytic polycondensation reactions to provide the inorganic component (germania) of the organic-inorganic hybrid coating. The growing sol-gel germania network was simultaneously reacted with an organic ligand that contained sol-gel-active sites in its chemical structure. Hydroxy-terminated polydimethylsiloxane (PDMS) and 3-cyanopropyltriethoxysilane (CPTES) served as sources of nonpolar and polar organic components, respectively. The sol-gel reactions were performed within fused silica capillaries. The prepared sol-gel germania coatings were found to provide excellent pH and thermal stability. Their extraction characteristics remained practically unchanged after continuous rinsing of the sol-gel germania-PDMS capillary for 24 hours with highly basic (pH = 13) and/or acidic (pH = 1.3) solution. They were very efficient in extracting non-polar and moderately polar analytes such as polycyclic aromatic hydrocarbons, aldehydes, ketones. Possessing the polar cyanopropyl moiety, sol-gel germania cyanopropyl-PDMS capillaries were found to effectively extract polar analytes such as alcohols, fatty acids, and phenols. Besides, they also showed superior thermal stability compared with commercial cyano-PDMS coatings thanks to the covalent attachment of the coating to capillary surface achieved through sol-gel technology. Their extraction characteristics remained unchanged up to 330 °C which is significantly higher than the maximum operation temperature (< 280 °C) for commercial cyano-PDMS coatings. Low ng/L detection limits were achieved for both non-polar and polar test solutes. Our preliminary results also indicated that sol-gel hybrid germania coatings have the potential to offer great analytical performance as GC stationary phases.