Is three-dimensional nanofiber scaffolds superior over the two-dimensional sorbent for the needle trap microextraction?

In the past decades, electrospinning has been widely used for the production of micro/nanofibers, and led to the development of sorbents with different capabilities[1-3]. In this process by applying a high-power electric field, polymer nanofibers are generated. In spite of the simplicity and effectivity of the conventional electrospinning for fabricating nanofibers, compact structure and small pores of the nanofibers which hinder the efficient analyte infiltration during the extraction process, is one of the main concerns. In order to overcome these problems, an applicable strategy called wet electrospinnig in which a collector is placed at the bottom of a solvent bath, has been employed to enlarge the pore size of the electrospun scaffolds. By applying this technique, a highly porous foam was produced immediately after freeze-drying, while a dense layer was formed using the conventional electrospinning method to obtain two-dimensional (2D) structures[4, 5]. The porosity, morphology, and thermal stability of 3D scaffolds have been characterized using various characterization methods including, Fourier transform infrared spectroscopy, scanning electron microscope (SEM), confocal laser scanning microscope (CLSM) and thermogravimetric analysis. Eventually to ensure the comparative capability and efficiency of the abovementioned 3D scaffolds over 2D ones, both nanofibers types were synthesized using an appropriate polyamide solution and utilized as sorbent in headspace–needle trap devices (HS-NTD). The influencing parameters on this study including the type of solvent bath, the polyamide solution concentration, desorption time and temperature, sample flow rate, stirring rate, extraction time and temperature and ionic strength were optimized. Subsequently, the enrichment of the chlorobenzenes (CBs), as model compounds, from the headspace of some aquatic samples including, Karoon river, Persian Gulf and some other indoor rivers have been investigated. The results indicate that the extraction capability of the 3D scaffolds is 6-8 times greater than the 2D ones which in turn makes the 3D nanofibers more suitable candidate for further extraction investigations. From SEM images of the 2D mats, it is demonstrative that nanofibers are closely packed, while in the 3D ones, they are freely packed, leading to more accessible sites in the extraction process. In addition, random arrangement and irregular orientation of nanofibers could be observed in CLSM images of 3D scaffolds indicating more porous extractive substrate in comparison with 2D ones.