## 2 Results and Discussion
### Optimization of Extraction Parameters
#### 2.1.2 Solid-Phase Extraction
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**SPE-Based Extraction Procedures**} & \multicolumn{2}{c}{**DHPG**} & \multicolumn{2}{c}{**MHPG**} & \multicolumn{2}{c}{**VMA**} \\ \cline{2-7}  & **R \(\pm\) SD (\%)** & **EF** & **R \(\pm\) SD (\%)** & **EF** & **R \(\pm\) SD (\%)** & **EF** \\ \hline \multirow{2}{*}{Sorbent} & \multicolumn{2}{c}{Eluent} & & & & & \\ \cline{2-7}  & MeOH & \(59.5\pm 2.7\) & - & _no_ & - & \(69.8\pm 6.3\) & - \\ \cline{2-7}  & Aceton & \(86.8\pm 2.8\) & - & _no_ & - & \(83.4\pm 2.8\) & - \\ \cline{2-7}  & ACN:MeOH & \(50\):50 & \(18.2\pm 1.4\) & - & _no_ & - & \(37.6\pm 2.5\) & - \\ \hline \multirow{2}{*}{C18} & \multicolumn{2}{c}{MeOH} & \(239.9\pm 8.6\) & 2.4 & \(153.2\pm 3.9\) & 1.5 & \(300.5\pm 12.7\) & 3.0 \\ \cline{2-7}  & Aceton & \(120.4\pm 4.8\) & 1.2 & \(41.8\pm 2.9\) & - & \(152.4\pm 3.4\) & 1.5 \\ \cline{2-7}  & ACN:MeOH & \(50\):50 & \(111.3\pm 6.3\) & 1.1 & \(62.2\pm 2.7\) & - & \(190.8\pm 9.5\) & 1.9 \\ \hline \multirow{2}{*}{CN} & \multicolumn{2}{c}{Acent} & \(121.6\pm 5.7\) & 1.2 & \(52.1\pm 4.0\) & - & \(67.8\pm 4.4\) & - \\ \hline \multirow{2}{*}{ABN} & \multicolumn{2}{c}{MeOH} & \(11.1\pm 1.3\) & - & _no_ & - & \(21.2\pm 2.6\) & - \\ \hline \multirow{2}{*}{AX} & \multicolumn{2}{c}{MeOH:FA 98:2} & \(9.1\pm 2.3\) & - & _no_ & - & \(53.4\pm 3.7\) & - \\ \cline{2-7}  & \multicolumn{2}{c}{MeOH:NH\({}_{4}\)OH} & \multirow{2}{*}{_no_} & \multirow{2}{*}{-} & \(30.5\pm 3.9\) & - & \(12.8\pm 3.5\) & - \\ \cline{2-7}  & \multicolumn{2}{c}{25\% 95:5} & & & & & & \\ \hline \multirow{2}{*}{Styre DVB} & \multicolumn{2}{c}{Aceton} & \(140.4\pm 3.5\) & 1.4 & \(50.5\pm 2.9\) & - & \(67.5\pm 4.1\) & - \\ \cline{2-7}  & ACN:MeOH & \(50\):50 & \(no\) & - & _no_ & - & _no_ & - \\ \cline{2-7}  & DCM:IPA:NH\({}_{4}\)OH & \(no\) & - & _no_ & - & _no_ & - \\ \hline \hline \end{tabular}
\end{table} 
Table 4: The results of extraction efficiency (R) with SD value and enhancement factor (EF) for SPE-based extraction procedures depending on sorbent and eluent (n = 3). \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Type of Sorbent**} & \multirow{2}{*}{**Activation Step**} & \multirow{2}{*}{**Washing Step**} & \multirow{2}{*}{**Elution Step**} \\ \hline HLB & & & 1 mL of ACN:MeOH (50:50, \(v/v\)) or \\ \hline C18 & 1 mL of MeOH followed by & 1 mL of mixture water:MeOH (9:1, & 1 mL of acetone or \\ \cline{2-5}  & 1 mL of DI water & \(v/v\)) & 1 mL of MeOH \\ \cline{2-5}  & CN & & 1 mL of acetone \\ \hline AX & - & 1 mL of 0.05 M ammonium & 1 mL of MeOH:formic acid (98:2, \(v/v\)) \\ \hline CX & - & acetate pH6:MeOH (95:5, \(v/v\)) & 1 mL MeOH:ammonium hydroxide 25\% (95:5, \(v/v\)) \\ \hline Evolute ABN & - & 1 mL of water:MeOH (95:5, \(v/v\)) & 1 mL of MeOH \\ \hline Styren DVB & - & 1 mL of DI water & 1 mL of CH\({}_{2}\)Cl\({}_{2}\):IPA:NH\({}_{4}\)OH (78:20:2, \\ \(v/v/v\)) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The SPE extraction conditions depending on the type of the sorbent. any signal enhancement. The better extraction efficiency for VMA is likely due to its lower hydrophilicity (log P 0.43) compared to DHPG (log P \(-\)0.72) or MHPG (log P 0.11). Cyanopropyl (CN) sorbents, due to their strong and reversible interactions, allow for the extraction of polar compounds. Acetone was the only eluent used, providing a 1.4-fold signal enhancement for DHPG. However, unsatisfactory extraction efficiency was observed for MHPG and VMA, with values of 52.1 \(\pm\) 4.0% and 67.8 \(\pm\) 4.4%, respectively. The higher extraction efficiency and signal enhancement for DHPG can be attributed to its more polar properties. Polymeric SPE for acidic, basic and neutral analytes (ABN) sorbents are a modified polymer phase of PS-DVB, consisting of a polystyrene divinylbenzene polymer for reversed-phase (hydrophobic) retention, with non-ionizing hydroxyl groups that ensure wettability without secondary interactions. ABN cartridges can be used to extract a wide range of acidic, basic, and neutral analytes from aqueous matrices, including biological fluids.