## 3 Results and Discussion
### Performance of the Proposed Approach  
To verify the performance of the proposed CE approach, the calibration graph was constructed in the range of 0.5 to 10.0 \(\upmu\)M. Table 1 summarizes the analytical characteristics and method validation including linear range, linearity, LOD (S/N = 3), LOQ (S/N = 10), repeatability (intraday precision), and reproducibility (interday precision). A good linear response was observed in all cases (R\({}^{2}\) > 0.990). To evaluate the reproducibility of our approach and ensure acceptable precision in terms of peak heights, the relative standard deviations (RSD, \(n\) = 3) for intraday and interday analyses were carried out. The results were revealed to be less than 2.90% and 4.61%, respectively. The LODs and LOQs of the analytes ranged from 0.11 to 0.61 \(\upmu\)M and 0.38 to 2.03 \(\upmu\)M, respectively. Table 2 summarizes the comparison of the analytical characteristics of different CE methods from previous literature. The advantages of the proposed approach include high efficiency, fast analysis time and cost-effectiveness.  
Figure 3: Electropherograms showing the effect of SDS on the separation of the nine analytes: SDS of (**A**) 15 mM, (**B**) 20 mM, (**C**) 25 mM, and (**D**) 30 mM. Other conditions were the same as shown in Figure 2C.  
Figure 2: Effect of the pH on the separation of the nine analytes. The capillary was filled with 5 mM phosphate buffer at a pH of (**A**) 3.0, (**B**) 3.5, (**C**) 3.7, and (**D**) 4.0 containing 20 mM SDS before the sample was injected. Other conditions were the same as shown in Figure 1B.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Analy** & **Linear Range (uM)** & **Regression Equation** & \(\mathbf{R^{2}}\) & **Repeatability (\%) 3 ** & **Reproducibility (\%) 4 ** & **LQ (uM)** & **LOD (uM)** \\ \hline T & 1.0–10.0 & y = 0.147\(\sim\) 0.048 & 0.9904 & 1.93 & 4.12 & 2.03 & 0.61 \\ S-HT & 1.0–10.0 & y = 0.195\(\sim\) 0.031 & 0.9921 & 0.68 & 3.46 & 1.50 & 0.45 \\ TA & 0.8–10.0 & y = 0.348\(\sim\) 0.111 & 0.9917 & 1.23 & 2.10 & 0.91 & 0.27 \\ DA & 0.55–10.0 & y = 0.437\(\sim\) 0.059 & 0.9959 & 1.99 & 2.90 & 0.48 & 0.15 \\ Trp & 1.0–10.0 & y = 0.176\(\sim\) 0.047\(\sim\) 0.0936 & 1.56 & 3.24 & 1.58 & 0.48 \\ E & 0.55–10.0 & y = 0.478\(\sim\) 0.111 & 0.9964 & 2.90 & 4.61 & 0.41 & 0.12 \\
5-HTP & 0.8–10.0 & y = 0.223\(\sim\) 0.044 & 0.9956 & 0.70 & 3.33 & 1.04 & 0.31 \\ NE & 0.55–10.0 & y = 0.500\(\sim\) 0.105 & 0.9924 & 1.89 & 4.29 & 0.38 & 0.11 \\ Tyr & 0.55–10.0 & y = 0.275\(\sim\) 0.028 & 0.9954 & 1.86 & 3.14 & 0.45 & 0.13 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Linearity, precision, accuracy, LOQs, and LODs of the proposed method.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Method** & **Time (min)** & **LODs** & **Reference** \\ \hline CE-ECL & Spd, His, Tyr, Phe, Put & 30 & \(6.0\times 10^{-4}-9.6\times 10^{-2}\) mg/L & [22] \\ CE-C4D & Spd, Put, His, Cad, Tyr & 6 & \(4.1\times 10^{-2}-9.8\times 10^{-2}\) mg/L & [23] \\ CE-UV & Spd, Put, His, Cad, Phe, TA, Tyr, DA, S-HTP, OA, NE, E & 8.5 & \(0.4-0.6\) uM & [17] \\ CE-IIF & Hut, Cad, SD, Step, Tyr, Phe, Tyr & 28 & \(0.5-10\) uM & [32] \\ CE-UV & 3-MT, HVA, DOPAC, 5-HLA, NE, S-HTP, DA, Trp, DHBA, Tyr, NA, DOPA & 40 & N.P. & [27] \\ MEKC-UV & T, S-HT, TA, DA, Trp, E, S-HTP, NE, Tyr & 11 & \(0.11-0.61\) uM & This work \\ \hline \hline \end{tabular}
\end{table}
Table 2: Comparison of the developed method with previously reported capillary electrophoresis (CE) methods for the determination of biogenic amines.