## 3 Results
### Analytical Figures of Merit  
Analytical figures of merit for the suggested procedure under the optimum conditions (Section 2.4) were determined from results of the analyses. The linear calibration equations for Pb(II) and Cd(II) were A = 0.0011C + 0.0047 (R\({}^{2}\) of 0.988) and A = 0.0112C \(-\) 0.0172 (R\({}^{2}\) of 0.998), respectively. Linearity of dynamic range (LDR) for Pb(II) (5.0 \(\times\) 10\({}^{-6}\)-4.0 \(\times\) 10\({}^{-4}\) g L\({}^{-1}\)) and Cd(II) (5.0 \(\times\) 10\({}^{-6}\)-15 \(\times\) 10\({}^{-5}\) g L\({}^{-1}\)) were recorded. In these equations, A is the absorbance of ions and C expresses as their concentrations in initial sample solutions. The limits of detection (LOD), expressed as 3S\({}_{\rm b}\)/m (S\({}_{\rm b}\) is blank standard deviation and m is slope of the calibration plot), were found as Pb(II) 1.2 \(\times\) 10\({}^{-6}\) g L\({}^{-1}\) and Cd(II)  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Ions**} & \multirow{2}{*}{**Ratio of Coexisting Ions**} & \multicolumn{2}{c}{**Recovery (\%)**} \\ \cline{3-4}  & & **Pb(II)** & **Cd(II)** \\ \hline Na(I) & 10,000 & 96.03 \(\pm\) 0.12 & 98.14 \(\pm\) 0.09 \\ K(I) & 10,000 & 98.12 \(\pm\) 0.27 & 97.43 \(\pm\) 0.11 \\ Li(I) & 800 & 99.17 \(\pm\) 0.14 & 99.14 \(\pm\) 0.08 \\ Ca(II) & 500 & 100.56 \(\pm\) 0.21 & 99.17 \(\pm\) 0.05 \\ Mg(II) & 300 & 98.08 \(\pm\) 0.18 & 96.13 \(\pm\) 0.04 \\ Cr(II) & 200 & 97.03 \(\pm\) 0.24 & 99.94 \(\pm\) 0.18 \\ Pd(II) & 800 & 97.26 \(\pm\) 0.19 & 98.32 \(\pm\) 0.11 \\ Zn(II) & 250 & 102.45 \(\pm\) 0.11 & 100.32 \(\pm\) 0.10 \\ Al(III) & 700 & 99.69 \(\pm\) 0.27 & 98.71 \(\pm\) 0.07 \\ Mn(II) & 500 & 97.34 \(\pm\) 0.18 & 96.52 \(\pm\) 0.04 \\ Co(II) & 100 & 98.98 \(\pm\) 0.35 & 101.43 \(\pm\) 0.01 \\ Cu(II) & 100 & 96.15 \(\pm\) 0.28 & 96.83 \(\pm\) 0.04 \\ Ni(II) & 100 & 95.28 \(\pm\) 0.17 & 99.54 \(\pm\) 0.9 \\ SO\({}_{4}\)\({}^{2-}\) & 1000 & 95.35 \(\pm\) 0.31 & 98.18 \(\pm\) 0.13 \\ Cl\({}^{-}\) & 1000 & 97.53 \(\pm\) 0.24 & 100.32 \(\pm\) 0.15 \\ NO\({}_{3}\)\({}^{-}\) & 1000 & 99.18 \(\pm\) 0.19 & 99.54 \(\pm\) 0.09 \\ CO\({}_{3}\)\({}^{2-}\) & 1000 & 101.37 \(\pm\) 0.20 & 100.91 \(\pm\) 0.11 \\ \hline \hline \end{tabular}
\end{table}
Table 3: The interfering effect of various ions on preconcentrating Pb(II) and Cd(II) (n = 3).  
47 \(\times\) 10\({}^{-8}\) g L\({}^{-1}\) for five measurements of the blank. The limits of quantification (LOQ) were Pb(II) 3.9 \(\times\) 10\({}^{-6}\) g L\({}^{-1}\) and Cd(II) 1.5 \(\times\) 10\({}^{-6}\) g L\({}^{-1}\). LOQ was defined as 3.33 LOD. The preconcentration factor (PF) of 50 was calculated as the concentrations of ions before and after preconcentration. The reproducibility of the preconcentration method (relative standard deviation (RSD)) was determined by performing five experiments from solutions containing Pb(II) and Cd(II) (50 mL, 5.0 \(\times\) 10\({}^{-5}\) g L\({}^{-1}\)). The results showed 1.27% for Pb(II) and 0.94% for Cd(II).  
Table 5 shows a comparison among EgLiCl-mGO with some new adsorbents. EgLiCl-mGO has an important development in MSPE including decreasing adsorbent amount and RSD as well as widening LDR. Additionally, EgLiCl-mGO was performed in semi-neutral pH, reducing the usage of materials to pH adjustment. More importantly, EgLiCl-mGO is a green, safe, and earth-friendly adsorbent and its preparation is fast without consumption of any dangerous material. The preconcentration time is about six minutes, which is another advantage of this method.