SOL-GEL COATING TECHNOLOGY FOR THE PREPARATION OF SOLID-PHASE MICROEXTRACTION FIBERS OF ENHANCED THERMAL-STABILITY

A novel sol-gel method is described for the preparation of solid-phase microextraction (SPME) fibers. The protective polyimide coating was r emoved from a 1-cm end segment of a 200 mu m o.d. fused-silica fiber, and the exposed outer surface was coated with a bonded sol-gel layer o f poly(dimethylsiloxane) (PDMS). The chemistry behind this coating tec hnique is presented. Efficient SPME-GC analyses of polycyclic aromatic hydrocarbons, alkanes, aniline derivatives, alcohols, and phenolic co mpounds in dilute aqueous solutions were achieved using sol-gel-coated PDMS fibers. The extracted analytes were transferred to a GC injector using an in-house-designed SPME syringe that also allowed for easy ch ange of SPME fibers. Electron microscopy experiments suggested a porou s structure for the sol-gel coating with a thickness of similar to 10 mu m. The coating porosity provided higher surface area and allowed fo r the use of thinner coatings (compared with 100-mu m-thick coatings f or conventional SPME fibers) to achieve acceptable stationary-phase lo adings and sample capacities. Enhanced surface area of sol-gel coating s, in torn, provided efficient analyte extraction rates from solution. Experimental results on thermal stability of sol-gel PDMS fibers were compared with those for commercial 100-mu m PDMS fibers. Our findings suggest that sol-gel PDMS fibers possess significantly higher thermal stability (>320 degrees C) than conventionally coated PDMS fibers tha t often start bleeding at 200 degrees C. This is due, in part, to the strong chemical bonding between the sol-gel-generated organic-inorgani c composite coating and the silica surface. Enhanced thermal stability allowed the use of higher injection port temperatures for efficient d esorption of less-volatile analytes and should translate into extended range of analytes that can be handled by SPME-GC techniques. Experime ntal evidence is provided that supports the operational advantages of sol-gel coatings in SPME-GC analysis.