Preparation and characterization of new solid-phase microextraction fibers obtained by sol-gel technology and zirconium oxide electrodeposited on NiTi alloy

This study describes the use of zirconium oxide electrolytically deposited onto a NiTi alloy as a new substrate for sol-gel reactions. Polydimethylsiloxane (PDMS) was used to coat the fiber after activation of the NiTi-ZrO(2) surface with sodium hydroxide solution followed by hydrochloric acid solution. Micrographs obtained by scanning electron microscopy (SEM) showed good uniformity of the PDMS coating on the proposed substrate and also permitted the evaluation of coating thickness, being approximately 25 microm. Thermal stability of the coating on the NiTi-ZrO(2) surface was evaluated, showing excellent stability up to 320 degrees C. The applicability of the proposed NiTi-ZrO(2)-PDMS fiber was evaluated through extraction of benzene, toluene, ethylbenzene and o-xylene (BTEX) from the headspace of aqueous samples. Some parameters affecting the extraction efficiency such as the salting-out effect, extraction temperature and extraction time were optimized by two consecutive two-level full-factorial experimental designs. This optimization allowed the experimental domain of maximum response to be attained and also the robustness range for the variables. Excellent detection limits in the range of 0.6-1.6 microg L(-1) were obtained as well as correlation coefficients higher than 0.99994. Precision for one fiber (n=7) was in the range of 1.4-4.0% and fiber-to-fiber reproducibility (n=5) was in the range of 3.9-6.7%. Comparison of the extraction profile of the proposed fiber with those of commercially available 100, 30 and 7 microm PDMS fibers showed that NiTi-ZrO(2)-PDMS had a better response compared to that of the 7 and 30 microm fibers. Such characteristics of the NiTi-ZrO(2)-PDMS fiber suggest that this fiber represents an excellent alternative for gas chromatography sample preparation.