## 6 FPSE Method Development
### Selection of FPSE Substrate  
FPSE is the only microextraction technique that exploits the substrate surface chemistry to compliment to the overall selectivity and the extraction efficiency of an FPSE membrane. The surface property of the fabric substrate substantially impacts on the selectivity and extraction efficiency of an FPSE membrane. The dependence of the analytes' polarity (logKow) on the nature of different fabric substrates has been estimated using a compound mixture consisting of furfural alcohol (FA, logKow 0.3), piperonal (PIP, logKow 1.05), phenol (PHE, logKow 1.5), benzodiazole (BDO, logKow 2.08), 4-nitrotoluene (4 NT, logKow 2.45), 9-anthracene methanol (9 AM, logKow 3.04), 1,2,45-tetramethyl benzene (TMB, logKow 4.0), triclosan (TCL, logKow 4.53), and diethylstilbestrol (DES, logKow 5.07). As can be seen from Table 3, for the sol-gel PTHF sorbent, cellulose fabric is favored for polar analytes extraction, whereas fiber glass fabric is suitable for nonpolar analyte extraction. Between sol-gel PDMDPS sorbents coated on polyester fabric and cellulose fabric, polyester is better for nonpolar analyte extraction. Since PDMDPS is a nonpolar polymer, extraction of polar analytes is not favored in either polyester fabric or in cellulose fabric. As expected, the organic/inorganic polymer plays the most significant role in the overall selectivity and extraction efficiency of FPSE membrane. However, the role of the fabric substrate cannot be ignored.  
\begin{table}
\begin{tabular}{l c} \hline \hline \multicolumn{1}{c}{**Sorbent (Substrate)**} & \multicolumn{1}{c}{**Equation for Recovery\% Calculation**} \\ \hline Si-CW20M (Cellulose) & 4.2977487 + 22.823041 log Kow \(-\) 3.1343544 (log Kow \(-\) 2.737)\({}^{2}\) \\ \hline Si-PEG1000 (Cellulose) & \(-\)11.53483 + 20.950137 log Kow \(-\) 0.4017218 (log Kow \(-\) 2.737)\({}^{2}\) \\ \hline Si-PEG300 (Cellulose) & 14.758805 + 16.309632 log Kow \(-\) 5.5504622 (log Kow \(-\) 2.737)\({}^{2}\) \\ \hline Si-CN-CW20M (Cellulose) & \(-\)24.39275 + 23.940499 log Kow \(+\) 1.247171 (log Kow \(-\) 2.737)\({}^{2}\) \\ \hline Si-PPG-PEG-PPG (Cellulose) & \(-\)3.648816 + 21.546191 log Kow \(-\) 2.878525 (log Kow \(-\) 2.737)\({}^{2}\) \\ \hline Si-PEG-PPG-PEG (Cellulose) & \(-\)7.680093 + 23.069108 log Kow \(-\) 1.7262745 (log Kow \(-\) 2.737)\({}^{2}\) \\ \hline Si-PTHF (Cellulose) & 12.40054 + 17.848979 (log Kow + 17.848979 (log Kow \(-\) 2.737)\({}^{2}\) \\ \hline Si-PTHF (Fiber Glass) & \(-\)28.44237 + 20.9507 log Kow \(+\) 3.3273496 (log Kow \(-\) 2.737)\({}^{2}\) \\ \hline Si-C18 (Cellulose) & \(-\)2.274875 + 20.816015 log Kow \(-\) 4.1478973 (log Kow \(-\) 2.737)\({}^{2}\) \\ \hline Si-C8 (Cellulose) & \(-\)3.392783 + 21.261305 log Kow \(-\) 3.7724155 (log Kow \(-\) 2.737)\({}^{2}\) \\ \hline Si-PDPS (Cellulose) & \(-\)10.30009 + 17.450029 log Kow \(-\) 0.2880039 (log Kow \(-\) 2.737)\({}^{2}\) \\ \hline Si-PDMDPS (Polyester) & \(-\)9.185327 + 17.815515 log Kow \(-\) 1.9655752 (log Kow \(-\) 2.737)\({}^{2}\) \\ \hline Si-PDMDPS (Cellulose) & \(-\)19.60225 + 15.453851 log Kow \(-\) 1.62186 (log Kow \(-\) 2.737)\({}^{2}\) \\ \hline \hline \end{tabular}
\end{table}
Table 2: Absolute recovery calculator for selected FPSE membranes.