Preparation and application of a carbon nanotube reinforced polyamide-based stir bar for sorptive extraction of naproxen from biological samples prior to its spectrofluorometric determination

Abstract

A novel method for simple, fast and reproducible preparation of a reinforced polyamide (PA)-based stir bar was presented. The carbon nanotube/polyamide stir bar was prepared by dispersion of an appropriate amount of oxidized multiwalled carbon nanotubes (MWCNTs) in a solution of PA in formic acid (FA) followed by dipping the stainless steel substrate of stir bar into the prepared solution. Finally, dipping the CNT/PA coated substrate into water causes the diffusion of formic acid into water and remaining CNT/PA forms a homogenous layer on the stainless steel substrate. The surface characteristics of PA and CNT/PA coated stir bars were investigated using scanning electron microscopy (SEM). The prepared CNT/PA nanocomposite-based stir bar was used as an extraction device for stir bar sorptive extraction (SBSE) of naproxen (NAP) from biological samples followed by fluorimetric detection. The effect of CNT doping level on the extraction capability of the prepared coating was investigated. Important parameters influencing the extraction and desorption processes including extraction time, salt content, pH, desorption solvent, its volume and desorption time were optimized using response surface methodology (RSM). The limit of detection (LOD) was 2 ng mL⁻¹ and the method precision (RSD%) with three replicates was 3.4%. The linearity of the method was 7–1000 ng mL⁻¹. The reproducibility of the presented method was evaluated by preparing eight stir bars using a unit solvent and performing eight extractions from the aqueous solution applying different stir bars under the same extraction and desorption conditions. The obtained RSD% was 3.0% at 1 μg mL⁻¹. The developed method was successfully applied to the biological and tap water samples, while the relative recovery percentages (RR%) were obtained to be 99%, 96% and 95% for urine, plasma and tap water samples, respectively.