## 1 Introduction  
Organochlorine pesticides (OCPs) are persistent lipophilic organic pollutants that are highly resistant to biodegradation in the environment [1]. These compounds exhibit high toxicity and bioaccumulation and have been demonstrated to be carcinogenic in animals and humans. For these reasons, they have been included in the list of priority pollutants compiled by The United States-Environmental Protection Agency (US-EPA) [2]. Although the application of OCPs has been forbidden for a considerable period in many countries, the residues continue to induce a significant impact on the environment and its ecosystems [3]. The maximum possible limits are 0.1 ug L\({}^{-1}\) for each OCP and 0.5 ug L\({}^{-1}\) for the total concentration of all pesticides based on toxicological considerations [4, 5]. Therefore, it is necessary to develop fast, simple, and valid methods for their determination in different matrices [2]. A variety of sample preparation techniques, such as pressurized liquid extraction [6], in-cell accelerated solvent extraction [7], microsolid-phase extraction [8], magnetic solid-phase extraction (MSPE) [9], vortex-assisted MSPE [10], and SPME [11] coupled with gas chromatography, have been used for the extraction and determination of OCPs in different matrices. Among these methods, SPME was developed in the 1990s by [PERSON] and [PERSON] et al. [12], which satisfies the requirements of green analytical chemistry. Hence, this method has widely been applied for sampling a broad spectrum of analytes from gaseous, liquid, and solid media with diverse matrix compositions [13]. Polydimethylsiloxane (PDMS), divinylbenzene (DVB), carboxen (CAR), polyethylene glycol (PEG), carboxax (CW), polyacrylate, and their combinations, such as PDMS/DVB, PDMS/CAR, CW/DVB, and DVB/CAR/PDMS, are the commercially-available SPME fiber coatings [14; 15]. However, the ordinary SPME fibers suffer from poor mechanical strength, low recommended operating temperature, fragility, restricted lifetime, and limited applicability [16]. To overcome these drawbacks, researchers have tried to synthesize new sorption materials for SPME purposes. In recent years, the use of nanoscale materials with diverse functionalities and polarities for the fabrication of new SPME fiber coatings with enhanced selectivity, sorption capacity, and stability has attracted the attention of researchers [17; 18]. Moreover, nanoscale materials with a high specific surface area can improve the sample loading capacity and extraction efficiency [17; 19; 20; 21]. Therefore, due to the unique features of the nanoscale materials, they have emerged and become important in the analytical detection and remediation of environmental pollutants [22]. Furthermore, in some SPME applications, low-cost metal wires have been replaced with fragile fused silica fibers [23; 24]. The electrospinning method, which is a popular technique for the production of polymeric nanofibers [25], has been widely used as an SPME fiber coating [26; 27; 28; 29]. The polymers can be embedded with different materials to enhance the performance of the coating by increasing the surface area-to-volume ratio and the functionality of the produced nanofibers [30; 31].  
In the present study, an effective head space solid phase microextraction (HS-SPME) adsorbent using electrospun composite nanofibers was used for the extraction of OCPs from aqueous solutions. Accordingly, different PET-based nanofibers, such as PET/nanoclay, PET/nano-SiO\({}_{2}\), and PET/calaxarene, were electrospun on the surface of a stainless-steel wire and tested under the same experimental conditions. To the best of our knowledge, this is the first time that these PET-based composite nanofibers have been fabricated and applied for the extraction of OCPs.