## 3 Results
### Adsorption Isotherm  
The isotherm study shows the adsorption behavior of a system such as homogenous or heterogenous distribution of the analyte onto the surface of the adsorbent. In this article, five isotherm models were applied to investigate the adsorption of Pb(II) and Cd(II) on the surface of EgLiCl-mGO. This study was conducted in the presence of EgLiCl-mGO (1.0 \(\times\) 10\({}^{-2}\) g) in the sample solution containing the analytes (50 mL) during 5 min shaking at room temperature. According to Figure S1, increasing the initial concentration of ions has a direct effect on adsorption capacity (\(q_{e}\)) of EgLiCl-mGO, because by increasing \(C_{e},q_{e}\) increases. \(q_{e}\) is calculated using the following equation. \[q_{e}=\frac{(C_{0}-C_{e})}{W}\times V \tag{3}\] \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & **Spiked** & **Found** & **Recovery (\%)** & **Found** & **Recovery (\%)** \\ \cline{3-6}  & **(g L\({}^{-1}\))** & & **Cd(II)** & & **Pb(II)** \\ \hline \multirow{2}{*}{Kidney bean} & 0 & 1.84 & - & 2.46 & - \\  & 5.0 \(\times\) 10\({}^{-5}\) & 52.91 & 102.14 & 54.26 & 103.43 \\ \hline \multirow{2}{*}{Cowpea} & 0 & 1.34 & - & 1.76 & - \\  & 5.0 \(\times\) 10\({}^{-5}\) & 49.65 & 96.97 & 49.64 & 97.79 \\ \hline \multirow{2}{*}{Pinto bean} & 0 & 3.11 & - & 2.95 & - \\  & 5.0 \(\times\) 10\({}^{-5}\) & 51.98 & 97.87 & 50.75 & 95.84 \\ \hline \multirow{2}{*}{Navy bean} & 0 & 0.95 & - & 4.76 & - \\  & 5.0 \(\times\) 10\({}^{-5}\) & 52.04 & 102.15 & 54.38 & 99.30 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Analytical results of Pb(II) and Cd(II) quantified by EgLiCl-mGO (n = 3). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Method** & **Amount (g)** & **LOD (g L\({}^{-1}\))** & **RSD (\%)** & **PF** & **LDR (g L\({}^{-1}\))** & **Reference** \\ \hline SPE & - & \(6\times 10^{-6}\)-12 \(\times 10^{-6}\) & 1.0–2.2 & 100 & 0.5 \(\times\) 10\({}^{-6}\)–100 \(\times\) 10\({}^{-6}\) & [32] \\ MSPE & 5.0 \(\times\) 10\({}^{-2}\) & \(0.06\times 10^{-6}\)-0.76 \(\times\) 10\({}^{-6}\) & 0.18–3.10 & 150 & 0.1 \(\times\) 10\({}^{-6}\)–200 \(\times\) 10\({}^{-6}\) & [33] \\ LLE & - & \(0.38\times 10^{-6}\)-0.42 \(\times\) 10\({}^{-6}\) & 3.6–5.2 & - & 1.0 \(\times\) 10\({}^{-6}\)–40 \(\times\) 10\({}^{-6}\) & [34] \\ SPE & 4.0 \(\times\) 10\({}^{-3}\) & \(2.74\times 10^{-6}\)-3.10 \(\times\) 10\({}^{-6}\) & 3.2–3.5 & 50 & - & [35] \\ SPE & - & \(0.031\times 10^{-6}\)–0.043 \(\times\) 10\({}^{-6}\) & 2.44–4.68 & & 0.25 \(\times\) 10\({}^{-6}\)–25 \(\times\) 10\({}^{-6}\) & [36] \\ MSPE & 1.0 \(\times\) 10\({}^{-2}\) & \(47\times 10^{-8}\)–1.2 \(\times\) 10\({}^{-6}\) & 0.94–1.27 & 50 & 5.0 \(\times\) 10\({}^{-6}\)–4.0 \(\times\) 10\({}^{-4}\) g L\({}^{-1}\) & This work \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Comparison of the proposed technique with several recent methods for simultaneous determination of heavy metals (FAAS was used for all detections). \(C_{0}\) is the initial concentration of the analyte, \(C_{e}\) is the equilibrium concentration of the analyte, \(V\) is the volume of the sample solution, and \(W\) is the amount of the adsorbent [37; 38]. Langmuir is a monolayer adsorption model. It shows that the adsorbate molecules are adsorbed onto the homogeneous surface of the adsorbent. After the first layer of the analyte, no more analyte will be adsorbed onto the surface of the adsorbent. Equation (4) shows the linear form of this model. \[\frac{1}{q_{e}}=\frac{1}{q_{0}K_{L}C_{e}}+\frac{1}{q_{0}} \tag{4}\]  
\(C_{e}\) is the equilibrium concentration of heavy metals adsorbed by EgLiCl-mGO, \(q_{e}\) is the retention capacity of analytes, \(K_{L}\) is the Langmuir constant, showing the binding energy between the adsorbate and adsorbent; \(q_{max}\) is the maximum adsorption capacity of the adsorbent. The straight line was obtained when \(1/q_{e}\) was plotted against \(1/C_{e}\) as shown in Figure S2. The slope and intercepts show the \(q_{max}\) and \(K_{L}\), respectively [38; 39; 40].