## 4 Conclusions  
The cloud point extraction behavior of Pb\({}^{2+}\) using methyl 4,20-diisobutyl-2,5,8,16,19,22- hexaoxo-7,17-dipropyl-3,6,9,15,18,21-hexaaza-1(2,6)-pyridinacyclo-docosaphane-10-carboxylate (DLNL) as a chelating agent in presence of Triton X-114 was optimized. The extraction recovery was affected by pH, the concentration of the chelating agent, and the surfactant (Triton X-114) concentration. The results obtained showed the utility and validity of the presented method. This method revealed remarkable features such as ease of operation, fast speed, and cost-effectiveness for Pb\({}^{2+}\) separation and pre-concentration in water samples compared with other common pre-concentration methods. Comparison between the presented method and others reported in literature based on the cloud point extraction of lead are summarized in Table 3. It is interesting to note that a comparison of the proposed method along with those reported before (Table 3) clearly indicated good enhancement in the behavior of the proposed method in terms of the detection limit [31; 32; 33; 34; 35; 37; 38; 39; 40], linear range [32; 33; 34; 35; 36; 37; 38; 40], enrichment factor [31; 32; 33; 34; 35; 37; 40], and the relative standard deviation (RSD) [23; 32; 33; 34; 35; 36; 37; 38; 40]. The listed authors contributed to this work as described in the following: A.H.K. gave the concepts of the work, interoperated the results, the experimental part and prepared the manuscript. A.H.K. and A.E.-G.E.A. performed the revision before submission. A.E.A., and M.A.A.-O. are revealed the financial support for the work. All authors read and approved the final manuscript. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multicolumn{2}{c}{**Amount of Pb(II), (ng/mL) \({}^{*}\)**} & \multirow{2}{*}{**Recovery, \%**} \\ \cline{2-3} \cline{5-5}  & **Added** & & & \\ \hline \multirow{3}{*}{**River water**} & – & 25.6 \(\pm\) 0.3 & – \\  & 10 & 35.9 \(\pm\) 1.1 & 101.30 \\ \cline{1-1}  & 20 & 45.2 \(\pm\) 2.2 & 99.10 \\ \hline \hline \end{tabular}  
* Average of six measurements  
\end{table} 
Table 4: Determination of lead ion (ng mL\({}^{-1}\)) in river water samples (n = 5). \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Enrichment Method**} & \multirow{2}{*}{**System**} & \multirow{2}{*}{**Detection Method**} & \multicolumn{2}{c}{**Linear Range, (ng/mL)**} & \multirow{2}{*}{**RSD, \%**} & \multirow{2}{*}{**Detection Limit, (ng/mL)**} & \multirow{2}{*}{**Enrichment Factor**} & \multirow{2}{*}{**Ref.**} \\  & & & & & & & \\ \hline \multirow{3}{*}{CPE} & APDC & FAAS & 5–20 & 6.88 & 1.14 & 56 & \\  & DDTC & FAAS & 1.1–160 & 3.5 & 1.1 & 55.6 & [23] \\  & TAN & FAAS & 7.5–3500 & 1.6 & 5.27 & 30 & [31] \\  & APDC & FAAS & Up to 40 & 4.9 & 4.3 & 39 & [32] \\  & DDTC & FAAS & 0.5–10.0 & 1.7–4.8 & 4.8 & 25 & [33] \\  & TAN & FI-FAAS & 50–250 & 1.6–3.2 & 4.5 & 15 & [34] \\  & BCB & FAAS & – & \(<\)6.4 & 7.5 & 25 & [35] \\  & CPE & 5-Br-PADAP & GFAAS & 0.1–30 & 2.8 & 0.08 & 50 & [36] \\  & Tween 80 & FAAS & 2–12 & \(\leq\)6 & 7.2 & 10 & [37] \\  & PONPE 7.5 & Capillary zone & 12–400 & 3.6 & 11.4 & – & [38] \\  & DETO & FEAS & 20–300 & 2.7 & 8.0 & 50 & [39] \\  & DDTP & FAAS & – & – & 40 ng/g & 18 & [40] \\  & DLNL & FAAS & 7–250 & 1.9 & 4.0 & 50 & Present \\ \hline \multirow{3}{*}{BCB, brilliant cresyl blue; 1-PTSC, 1-phenylthioisemcarbazide; PAN, 1-(2-pyridylazo)-2-naphth; DDTP, O,O-diethylditiphosphate; DDTC, diethyldithiocarbamate; APDC, ammonium pyrrolidine dithiocarbamate; RS-CPE, rapidly synergistic cloud point extraction; TAN, 1-(2-thiazol)-2-naphth; 5-Br-PADAP, 2-(5-bromo-2-pyridylazo)-5-(diethyl-amino)-phenol; PONPE, 7.5-polyethyl enegylylcolmono-p-nonylphenylene;DLNL,methyl 4,20-diisobutyl-2,5,8,16,19,22-hexao-7,17-dipropyl-3,6,9,15,18,21- hexaaza-1(2,6)-pyridinacyclo-docosaphane-10-carboxylate.} & \multirow{3}{*}{**Recovery, \%**} \\  & & & & & \\ \end{tabular}
\end{table} 
Table 3: Comparison of the proposed method with other CPE methods for extraction and determination of Pb(II).