# Fabric Sol-gel Phase Sorptive Extraction Technique: A Review
## 1 Introduction
FPSE successfully combines the advantages of sol-gel derived sorbents used in microextraction and the wide variety of fabric substrates, resulting in a highly efficient and green sample pretreatment technique [13; 17]. Two main limitations of sorptive extraction techniques have been addressed by FPSE, the low sorbent capacity and long sample preparation time. The inherent porous surface of cellulose or polyester used as fabric substrate together with the strength of sol-gel derived hybrid sorbents uniformly dispersed as an ultra-thin film within the fabric substrate, results in a plethora of sorbent materials with significant analyte retention capacity and very fast extraction equilibrium. In comparison with a typical SPME fiber, the sorbent loading in FPSE media is about 400-times higher Also unlike SPME, the extraction sorbent is dispersed homogeneously on the surface of nanometer size polyester/cellulose micro-fibrils of FPSE [13]. Regarding the elution of the retained analytes from the FPSE media in organic solvents, this is also fast without the potential carryover risk. Highly acidic or basic chemical environments as well as any organic solvent can be used as eluents. The advantages of the FPSE technique include: (a) simplicity, low cost, minimal consumption of solvents; (b) sample preparation can be completed by directly introducing the FPSE media into the vessel containing the sample matrix; (c) enhanced efficiency by sonication, magnetic stirring; (d) a plethora of organic solvents can be used as eluent; (e) minimization of sample preparation steps, reducing potential sources of errors; (f) a variety of effective sol-gel coatings can be employed as sorbent; (g) high analyte preconcentration factors; (h) high chemical resistance of the FPSE media thanks to a strong chemical bonding between the sorbent phase and the substrate. Typically, the FPSE procedure starts with the immersion of the FPSE medium in a solvent system to clean any unwanted residue, followed by subsequent rinsing with deionized water to remove residual organic solvents. An amount of sample containing the target analytes is taken into a screw-capped glass vial. The FPSE medium is inserted into the vial along with a clean Teflon-coated magnetic stir bar. The sample solution is stirred for a defined extraction time for the sorption of the analytes. The FPSE medium is then removed from the extraction vial and is inserted into another vial containing the eluting solvent, for 4-10 min. Finally, the eluent is centrifuged and filtered to remove any particulate matter prior to injection into HPLC or other systems [18]. The FPSE procedure is shown in Figure 1. The FPSE medium can be reused by washing with the solvent system or it can be left to dry on a watch glass and stored in an air-tight glass container for future use. The recent trend of solid-phase extraction and microextraction is related to the development and characterization of new sorbent materials. The main targets in the search of novel sorbents depend on the extraction mode as well as on the analytes and samples, including better selectivity (or even specificity towards definite target species), improved sorptive or adsorptive capacity, as well as enhanced thermal, chemical or mechanical stability of the extractive media [19]. Sol-gel technology has many features in producing new materials of high purity and homogeneity, in forms of bulk, fibers, sheets, coating films as well as particles [20]. In analytical chemistry, the sol-gel process is commonly used in the synthesis of materials as sorbents for sample preparation techniques like SPE, SPME, and SBSE. The first demonstration of sol-gel technology for preparation of SPME fibers was presented by [PERSON] and co-workers [21]. Since then, a wide variety of sol-gel sorbents with high selectivity, extraction sensitivity and FPSE applications have been presented. In FPSE, a large pool of sol-gel sorbent materials with unique properties is available including a variety of polymers coated on either hydrophilic or hydrophobic substrates.