A Novel Gully-like Surface of Stainless-Steel Fiber Coated with COF-TPB-DMTP Nanoparticles for Solid-Phase Microextraction of Phthalic Acid Esters in Bottled Tea Beverages  
[PERSON]  
1 Department of Environmental Science and Engineering, North China Electric Power University,  
Baoding 071003, China; yynkyda@163.  
nient, fast and green sample pretreatment technique that integrates collection, extraction, desorption and injection into one step, solid-phase microextraction (SPME) was developed by [PERSON] and [PERSON] in 1990 [PERSON] and [PERSON] in 1990 [PERSON] and [PERSON] (1990), which has been widely employed in various fields, such as food [PERSON] and [PERSON] (1990), biomedicine [PERSON] et al. (2016) and the environment [PERSON] et al. (2016). SPME usually consists of a substrate and a coating that mainly includes the physical coating mode and the chemical grafting one. The traditional fiber substrate is made of quartz, which is easily broken [PERSON] et al. (2016). Therefore, stainless-steel [PERSON] et al. (2016), titanium [PERSON] et al. (2016), copper foam [PERSON] et al. (2016) and aluminum [PERSON] et al. (2016) substrate fibers were explored to overcome the disadvantage of quartz fiber. Furthermore, a variety of coating materials were explored to expand the applications of the metal fibers, including carbon nanotubes [PERSON] et al. (2016), metal organic frameworks [PERSON] et al. (2016); [PERSON] et al. (2016); [PERSON] et al. (2016), covalent organic frameworks (COFs) [PERSON] et al. (2016); [PERSON] et al. (2016); [PERSON] et al. (2016), ionic liquids [PERSON] et al. (2016); [PERSON] et al. (2016); [PERSON] et al. (2016) and molecularly imprinted polymers [PERSON] et al. (2016); [PERSON] et al. (2016).  
COFs, discovered by [PERSON] (1999) in 2005, are porous organic materials composed of ordered organic monomers. Owing to their merits of excellent thermal stability, controllable size and great chemical stability, COFs have been widely used in gas adsorption [PERSON] et al. (2016); [PERSON] et al. (2016), energy storage and conversion [PERSON] et al. (2016), pollutant removal [PERSON] et al. (2016), sensing [PERSON] et al. (2016), catalysis [PERSON] et al. (2016), etc. Currently, a variety of COFs are employed as the coatings of SPME fibers. [PERSON] and his co-workers [PERSON] and his co-workers [PERSON] and others (2016) developed COF-immobilized SPME fibers by chemically bonding SNW-1 on stainless-steel fiber, while the prepared fiber was used to extract phenolic compounds from honey samples with limits of detection from 0.06 ng\(\cdot\)g\({}^{-1}\) to 0.2 ng\(\cdot\)g\({}^{-1}\).  
However, no matter how the coating was applied to the metal fiber (i.e., physical mode or chemical mode), the coatings of the metal fiber were easily exfoliated due to the repeated thermal expansions and contractions and the friction between the coating and the syringe during the extraction procedure. Consequently, the metal fiber coating could suffer from worse reproducibility and a shorter service time. To solve this problem, some researchers began to create fibers with rough surfaces via chemical and electrochemical etching methods [PERSON] and others (2016); [PERSON] and others (2016); [PERSON] and others (2016). [PERSON] and his co-workers [PERSON] et al. (2016) fabricated one kind of robust coating fiber to improve the service time and extraction efficiency via binding COF-TpBD into the arrayed nanopores of stainless-steel fibers.  
In this study, the COF-TPB-DMTP was physically filled into the gully-like surface of SSF prepared with a two-step electrochemical etching method. The TPB-DMTP-coated gully-like surface SSF was used to pretreat the PAEs in a bottled tea beverage prior to the GC-FID separation and detection. For only the physical coating, the prepared TPB-DMTP-GS-SSF exhibited a sound service time and reproducibility thanks to the firm combination between the COFs coating and the gully-like surface of the SSF.