## 4 Discussion
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Complexing Agent** & **Range** & **Correlation Coefficient** & **Wavelength** & **Sample Preparation** & **LOD** & **Reference** \\ \hline
3-mercapto-5-(2\({}^{\prime}\)- & & & & & & \\ hydroxynaphylazo-1\({}^{\prime}\))- & 0.06-2.65 ug/mL & 0.9994 & 530 nm &
\begin{tabular}{c} Dissolution in 0.1 N \\ HCl/no L/L extraction \\ involved \\ \end{tabular} & NR & [47] \\
1,2,4-triazole & & & & & \\ \hline
3-(5\({}^{\prime}\)-mercaptoethanol-1\({}^{\prime}\)/2\({}^{\prime}\),4\({}^{\prime}\)- & & & & \\ triazole-3\({}^{\prime}\)-azo)-2,4- & & & & & \\ dihydroxybenzoic acid & 0.06–2.7 ug/mL & 0.9999 & 480 nm &
\begin{tabular}{c} Dissolution in 0.1 N \\ HCl/no L/L extraction \\ involved \\ \end{tabular} & NR & [47] \\ \hline
2,2A-dipyridyl-2- & 0–10 ug/mL & NR & 448 nm & \
\begin{tabular}{c} Dissolution in 0.1 N \\ HCl/no L/L extraction \\ involved \\ \end{tabular} & 6 ug/L & [48] \\ pyridylhydrazone * & & & & & \\ \hline Xylenol orange * & 10–60 ug/mL & 0.9984 & 568 nm &
\begin{tabular}{c} Dissolution in \\ deionized water/no \\ L/L extraction \\ involved \\ \end{tabular} & 420 ug/L & [49] \\ \hline
2-Benzoylpyridine thiosemicarbazone & 0.26–2.61 ug/mL & NR & 430 nm &
\begin{tabular}{c} Digestion in \\ concentrated \\ HNO\({}_{3}\)/no L/L extraction involved \\ \end{tabular} & 64 ug/L & [50] \\ \hline
1-(2-pyridylazo)-2-naphthol & 0.5–4 ug/mL & NR & 555 nm &
\begin{tabular}{c} Digestion in \\ _regia_/L/L extraction in \\ toluene \\ \end{tabular} & NR & [51] \\ \hline
8-Hydroxy quinoline & 1–5 ug/mL & 0.9979 & 384 nm &
\begin{tabular}{c} Digestion in \\ concentrated \\ HNO\({}_{3}\)/no L/L extraction involved \\ \end{tabular} & 0.381 mg/L & [52] \\ \hline
4,5-diphenyl-2-((1E)-(4-(1-(2-phenylhydrazone)) ethyl)phenyl)diazenyl\({}_{4}\)- & 0.5–27 ug/mL & 0.9997 & 520 nm &
\begin{tabular}{c} Dissolution in 2 N \\ HCl/no L/L extraction involved \\ \end{tabular} & 0.12 mg/L & [54] \\ \hline
1 & NR & NR & 560 nm &
\begin{tabular}{c} Digestion in \\ concentrated \\ extraction in toluene \\ involved \\ \end{tabular} & NR & [39] \\ \hline
7-(4-nitrophenylazo)-8- & & & & & \\ hydroxyquinoline-5- & 0.05–1.0 ug/mL & 0.9996 & 520 nm &
\begin{tabular}{c} Claication and \\ digestion in \\ concentrated HCl/no \\ L/L extraction \\ involved \\ \end{tabular} & 0.015 mg/L & [40] \\ \hline
5,7-dibromo-8- & & & & & \\ hydroxyquinoline & 0.02–4 ug/mL & 0.9998 & 391 nm & \begin{tabular}{c} Digestion with \\ concentrated \\ HNO\({}_{3}\)/no L/L extraction involved \\ \end{tabular} & 5 ug/L & [41] \\ \hline di-2-pyridyl ketone & 0.01308–1.308 & NR & 376 nm & \
\begin{tabular}{c} Digestion in \\ concentrated H\({}_{2}\)SO\({}_{4}\) \\ concentrated H\({}_{2}\)O\({}_{2}\)/no L/L extraction involved \\ \end{tabular} & 4.06 ug/L & [42] \\ \hline di-2-pyridyl ketone & 0.217–4.6 ug/mL\({}^{-1}\) & NR & 376 nm &
\begin{tabular}{c} Digestion in \\ concentrated H\({}_{3}\)O\({}_{4}\)/L/L extraction in toluene \\ involved \\ \end{tabular} & 13.9 ug/L & [43] \\ \hline
2-(2-thienyl) & 0.2–7 ug/mL & NR & 465 nm & \begin{tabular}{c} Digestion in \\ concentrated H\({}_{3}\)SO\({}_{4}\)/L/L extraction in chloroform involved \\ \end{tabular} & 40 ug/L & [44] \\ \hline Xylenol orange & 0.5–1.5 ug/mL & 0.9998 & 560 nm & \
\begin{tabular}{c} Dissolution in \\ HCI/no L/L extraction involved \\ \end{tabular} & 4.93 ug/L &
\begin{tabular}{c} Presented \\ method \\ \end{tabular} \\ \hline \hline \end{tabular}  
NR—not reported. * Flow-injection analytical method; L/L—liquid–liquid.  
\end{table} 
Table 6: _Cont._As presented in Table 6, the proposed method has a comparable range with other published 0 order spectrophotometric methods. The novelty of the method we described consists of a better characterization of the ternary complex (absorption minimum and isosbsite point).