Sol–gel immobilized cyano-polydimethylsiloxane coating for capillary microextraction of aqueous trace analytes ranging from polycyclic aromatic hydrocarbons to free fatty acids

Sol–gel coating containing highly polar cyanopropyl and nonpolar poly(dimethylsiloxane) components (sol–gel CN-PDMS coating) was developed for capillary microextraction (CME). The sol–gel chemistry provided an efficient means to immobilize the CN-PDMS coating by establishing chemical anchorage between the coating and the fused silica capillary inner surface. This chemical bond provided excellent thermal and solvent stability to the created sol–gel coating. For the extraction of polar and nonpolar analytes, the upper allowable conditioning temperatures were 330 °C and 350 °C, respectively. To our knowledge, this is the first time when a CN-PDMS thick coating survived such a high operation temperature. The prepared sol–gel CN-PDMS coating provided effective extraction of polar and nonpolar analytes simultaneously from aqueous samples. The cyanopropyl moiety in sol–gel CN-PDMS coatings provided effective extraction of highly polar analytes such as free fatty acids, alcohols, and phenols without requiring derivatization, pH adjustment or salting out procedures. The PDMS moiety, on the other hand, provided efficient extraction of nonpolar analytes. The extraction properties of the sol–gel CN-PDMS coatings can be fine tuned via manipulation of relative proportions of 3-cyanopropyltriethoxysilane and hydroxy-terminated PDMS in the sol solution used to create the coatings. Detection limits of nanogram/liter (ng/L) were achieved for both highly polar and nonpolar analytes directly extracted from aqueous media using sol–gel CN-PDMS coated microextraction capillaries followed by GC analysis.