**1. Introduction**

The objectives of a sample preparation technique in Analytical Chemistry are twofold; transformation of a sample into a form that is suitable for instrumental analysis and to ensure that the sample is at the detection level for the instrument of choice. Solid phase extraction (SPE) is a popular sample preparation technique for liquid samples with subsequent chroma‐ tographic analysis [1]. SPE is employed with the aim of either reducing interferences or achieving analyte preconcentration in order to enhance instrumental detection. Although SPE can be described as a physical extraction process involving a liquid phase and a solid phase (that can be packed or free flowing sorbent), the increased use of packed sorbent formats seems to have led to a bias towards packed sorbent SPE devices [2]. One of the first applications of packed sorbent SPE was reported in 1951, when Braus and co-workers packed 1.2-1.5 kg of granular activated carbon into an iron cylinder for the isolation of organic compounds [3]. Since then, there has been significant progress in SPE technology, as evidenced by reports on new formats and sorbents covering a wide range of morphologies and chemistries [1].

SPE research and developments have progressed with a focus on SPE device fabrication or SPE method development. In principle, the heart of the SPE technique is the sorbent material as it has a direct influence on the selectivity, sorptive capacity and the format or the configu‐ ration of the resultant SPE device (s).

To predict and optimize extraction, it is important to be aware of the nature of the sorbent used with respect to physicochemical characteristics. The most important physicochemical charac‐ teristics for optimal extraction are porosity, specific surface area and surface chemistry.

Given that there will always be a need for new sorbent materials, it is imperative to focus research efforts on versatile sorbent fabrication techniques that could address current and anticipated challenges. Electrospinning is seen as having great potential as a sorbent fabrica‐ tion technique, given its versatility [4].

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The objective of the chapter is to equip the readers with sufficient knowledge that would enable them to fabricate and employ electrospun nanofibers as sorbents not only for SPE but for a wide range of applications. A discussion of the fundamental principles of SPE, the challenges associated with further research efforts and the unlimited potential that lies in electrospinning to address SPE will be presented. The use of electrospun nanofibers for SPE is an area that is still at its infancy (Scifinder scholar search of the words *"Electrospinning*"*and*"*Solid Phase Extraction"* showed 34 hits which consisted of 30 papers, 2 review articles, 2 patents and 0 books/book chapters) thus the chapter will be presented mostly in a postulative manner on the basis of the experiments conducted in the authors' research lab as well as literature reports.

thus the general term *sorption* is often used to refer to a combination of these processes. Despite the uncertainty of the extent of contribution of adsorption or absorption mechanisms in extraction, fundamentally, all sorbent based extraction techniques are guided by the thermo‐ dynamic partition or distribution coefficient *K*, which is usually expressed as the ratio of

For adsorption, surface structure (porosity and surface area governing the available sites for analyte retention) is the more important sorbent characteristic compared to chemical compo‐ sition. While the chemical composition (governing the diffusion coefficient of the analyte into

Sorption from the sample phase is essentially a dynamic process in a heterogeneous system in which transport of the analytes between the sorbent and the sample phase is achieved. The process proceeds by a decrease in free energy until it reaches the minimum value (that is equilibrium). The mechanism of analyte adsorption or absorption is governed by the charac‐ teristics of interactions between the analyte and active sites of the sorbent. Therefore, sorbent selection is based on the binding mechanisms between the sorbent and analyte of interest.

The process of analyte sorption can be assumed to consist of multiple steps. Any of the steps may become rate limiting in controlling sorption of an analyte. The analyte may interact with

**1.** Through absorption, the analyte may interact with the sorbent by penetrating its three dimensional structure. Three dimensional penetration into the sorbent is a particularly dominating process for solid supported liquid phases. In the absorption process, analytes do not compete for sites; therefore, absorbents can have a high capacity for the analyte.

**2.** The analyte may interact two dimensionally with the sorbent surface through adsorption due to intermolecular forces [10]. Surface interactions may result in displacement of water

Table.1. shows different interaction mechanisms with their corresponding energies.

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Electrospun Nanofiber Based Solid Phase Extraction

http://dx.doi.org/10.5772/57100

analyte concentration in the sorbent phase, *Csorbent* to that in the sample phase, *Csample*;

*<sup>K</sup>* <sup>=</sup> *Csorbent Csample*

the sorbent) of the liquid phase is the more important for absorption.

**Interaction mechanism Energy (kJ/mol)**

Van der Waals 1-5 Dipole-induced dipole 2-7 Dipole-dipole 5-10 Hydrogen bonding 5-10 Ionic 50-200 Covalent 100-1000

**Table 1.** Energies of interaction mechanisms [9].

a sorbent in at least four ways:
