# Fabric Sol-gel Phase Sorptive Extraction Technique: A Review
## 1 Introduction  
In modern analytical methods, sensitive techniques as well as new analytical instruments are used for the determination of various analytes in a plethora of different and complex matrices. However, the direct determination of very low concentrations has been broadly recognized as the Achilles heel of the analysis and is mainly associated with matrix interferences or inadequate sensitivity. On the other hand, it is well known that sample preparation is a key step of chemical analysis and somehow is considered as the bottleneck of the whole analytical cycle being the most tedious and time consuming stage and affecting significantly the precision as well as the accuracy of the overall analysis [1; 2]. Thus, a preliminary step of preconcentration and separation of analytes from the original sample matrix or matrix simplification is usually required. Among sample pretreatment techniques which are used prior to determination, solid-phase extraction (SPE) is recognized as an advantageous alternative to classic liquid-liquid extraction (LLE), which is undesirable due to the recent green analytical chemistry (GAC) regulations, regarding the use of organic solvents [3; 4]. SPE has been widely accepted thanks to several inherent advantages like simplicity, the ability to extract polar compounds, no requirement of phase separation, lower volumes of organic solvent which can be reached even at microliter level (50-100 \(\mu\)L) in automated procedures, lower sample pretreatment time, as well as lower cost of analysis. Moreover, SPE facilitates miniaturization and automation [5; 6]. Following the trends of analytical chemistry on miniaturization, several approaches of sorbent microextraction have been developed such as solid-phase microextraction (SPME) [7; 8; 9], stir-bar sorptive extraction (SBSE) [10], thin film microextraction (TFME) [11] and related techniques as well as magnetic solid-phase extraction (MSPE) [12]. Despite the fact that SPME is a well-established microextraction technique, in some applications, it may not provide the desired sensitivity due to the small sorbent mass and sample capacity as well as mechanical distortion resulting in poor precision and sensitivity [13]. In order to increase the volume of the extraction phase as well as the active surface area, [PERSON] et al. proposed a TFME approach based on a thin sheet of a polydimethylsiloxane (PDMS) organic polymer membrane as an extraction phase [11]. The membrane was attached to a stainless-steel rod which was immersed into the sample solution containing the target analytes. The extraction procedure took place in both direct and headspace extraction mode. After the extraction procedure, the membrane was rolled around the rod and placed into a gas chromatography (GC) injector for thermal desorption. In comparison with SPME, it presents higher extraction efficiency as well as shorter equilibrium time, thanks to the larger extraction phase (25-125 times more than a fiber). In 2012, [PERSON] and [PERSON] reported a modification of TFME based on the distribution of a polymeric sorbent consisting of a mixed carboxen/polydimethylsiloxane (CAR/PDMS) and polydimethylsiloxane/divinylbenzene (PDMS/DVB), spread onto a glass wool fabric support as the substrate [14]. The extraction procedure was similar to TFME for GC-MS analysis. The resulted samplers presented better stability and robustness thanks to the incorporation of the fabric substrate in their thin film structure. Recently, a carbon mesh support was presented by [PERSON] et al., as an alternative substrate for the TFME technique [15] for GC-toroidal ion trap MS (GC-TMS) analysis. The proposed carbon substrate seems to be more durable than other TFME designs. In 2014, [PERSON] and [PERSON] [16] developed a novel highly promising and versatile sample preparation sorbent extraction technique named as fabric phase sorptive extraction (FPSE).