A novel solid-phase microextraction technique using a hollow fiber-supported sol–gel combined withmulti-walled carbon nanotubes was employed in the determination of phenobarbital in wastewater. In this new technique, a silica-based, organic–inorganic polymer containing functionalized multi-walled carbon nanotubes(MWCNTs)was prepared with sol–gel technology via the reaction of tetraethylorthosilicate (TEOS) with an acidic catalyst (HCl). This sol was injected into a polypropylene hollow fiber segment for in situ gelation. This device operated in direct immersion sampling mode. The experimental setup is simple and affordable, and the device is disposable, so there is no risk of cross-contamination or carryover. Parameters affecting extraction such as pH of the aqueous solution, ageing and extraction times, aqueous sample volume, agitation speed and carbon nanotube amount were optimized. Linearity was observed over a range of 0.50–5000 ngmL−1, with an estimation coefficient (r2) higher than 0.982. The limit of detection (LOD) was 0.32 ngmL−1 (n = 5), and repeatability (RSD% = 2.9) was from the average of three levels of analyte concentrations (1, 1000 and 4500 ngmL−1) with three replicates for each within a single day. Finally, a pre-concentration factor of 2100 was obtained for phenobarbital.

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