A solid-phase microextraction platinized stainless steel fiber coated with a multiwalled carbon nanotube-polyaniline nanocomposite film for the extraction of thymol and carvacrol in medicinal plants and honey

• It is the first use of the EPD platinization technique, to make the surface of a stainless steel SPME fiber porous and cohesive, for tight attaching of the coating.
• Using the EPD strategy, for coating of the platinized stainless steel wire by MWCNTs/PANI, resulted in an SPME fiber with substantial durability, long lifetime, and acceptable efficiency.
• Comparison of the proposed novel fiber, with commercial fibers, has established its preferences.
• Thymol and carvacrol was successfully extracted by the proposed nanocomposite fiber, through a DI-SPME strategy, from aqueous real samples.

A mechanically hard and cohesive porous fiber, with large surface area, for more strong attachment of the coating was provided by platinizing a stainless steel wire. Then, the platinized stainless steel fiber was coated with a multiwalled carbon nanotube/polyaniline (MWCNT/PANI) nanocomposite using electrophoretic deposition (EPD) method and applied for the extraction of thymol and carvacrol with direct-immersion solid-phase microextraction (DI-SPME) method followed by high-performance liquid chromatography-ultraviolet detection (HPLC-UV) quantification. To provide a larger coarse surface for the tightened attachment of coating on the fiber, a stainless steel wire was platinized using a suitable optimized EPD method. Different experimental parameters were studied and the optimal conditions were obtained as: pH of the sample solution: 2; extraction time: 60 min; salt content in the sample solution: 1% w/v NaNO3; desorption time: 60 min; type and volume of the desorption solvent: acetonitrile, 100 μL. Under the optimized conditions, limits of detection (LODs) were 0.6 and 0.8 μg mL−1 for thymol and carvacrol, respectively. Linear dynamic range (LDR) for the calibration curves of both analytes were 1–80 μg mL−1. Relative standard deviation (RSD%, n = 6) was 6.8 for thymol and 12.7 for carvacrol. The proposed fiber was successfully applied for the recovery and determination of thymol and carvacrol in thyme, savory, and honey samples.