Mercury Determination by New Asymmetric Triazene Ligand, 1-(2-Ethoxyphenyl)-3-(4-Nitrophenyl)Triazene (ENT) ) with Partial Least-Squares Calibration Method (PLS) Method

Synthesis, characterization, spectrophotometric studies of three mercury (II) complexes of 1-(2-ethoxyphenyl)-3-(4-nitrophenyl) triazene (ENT) are reported in this article and it was characterized by means of NMR, FT-IR, UV spectroscopy and CHN analysis, then determination of Hg(II) was performed by spectrophotometric determination using chemo metric techniques and new triazen ligand which was prepared by us. The calibration graphs of individual components were linear in the ranges of 1 -5.25 mg·L. The root means square errors of prediction (RMSEP) were 4.4 х10 The proposed method are simple, fast, inexpensive and do not need to any separation or preparation method.


Introduction
The first extensive investigation of the coordination chemistry of a triazene derivative (1,3-diphenyltriazene) was carried out in 1887 by Meldola [1]. The study of transition metal complexses 1, 3-diaryl triazenide ligands has increased greatly in the past few years, because of their potential reactivity in relation to their coordination modes [2][3][4].
Over the last three decades there has been increasing global concern over the public health impacts attributed to environmental pollution, in particular, the global burden of disease [5].
Mercury is one of the most toxic elements and a threat to wild life [5], therefore determining and analyzing this element is so critical.
In this study a new asymetic triazen ligand was synthesized and characterized with several different methods then chelating agents of the ligand with three kinds of mercury salts were examined then PLS was employed as a simple method for determination of mercury.

Synthesis and Characterization of ENT
The 1-(2-ethoxyphenyl)-3-(4-nitrophenyl) triazene (ENT) used as ligand and its structure is shown in Fig. 1. It was synthesized as follows: A 100 ml flask was charged with 10 g of ice and 15 ml of water and then cooled to 0 °C in an ice-bath. After that, 0.69 g (5 mmol) of para nitroaniline and 3.61 g (0.1 mol) of hydrochloric acid (d=1.18 g mL −1 ) were added to the mixture, and then a solution of NaNO 2 2 Mercury Determination by New Asymmetric Triazene Ligand, 1-(2-Ethoxyphenyl)-3-(4-Nitrophenyl)Triazene (ENT) ) with Partial Least-Squares

Solution Studies
The electronic absorption spectra of the ligand L in the presence of the increasing concentration of mercury (II) ions in acetonitril at room temperature are shown in Fig.2. The absorbance spectrum of the solution was recorded after each addition. Fig.3. shows that, the absorbance band of ENT at wavelength 393 nm decreases and at 402 nm increases by increasing in metal ion concentration and it reveals distinct inflection points at a metal-to-ligand molar ratio of about 1 emphasizing the formation of a 1:1 complexes. The conditional formation constants was evaluated as log K =4.88 ± 0.003 by using a non-linear least-squares curve fitting program KINFIT.   Fig4, shows that, the absorbance band of ENT at wavelength 344 nm decreases and at 350 nm increases by increasing in metal ion concentration of Hg (II) nitrate and it reveals distinct inflection points at a metal-to-ligand molar ratio of about 0.5 emphasizing the formation of a 1:2 complex. The conditional formation constants was evaluated as log K =4.93 ± 0.003 by using a non-linear least-squares curve fitting program KINFIT.
Fig5 shows that, the absorbance band of ENT at wavelength 270 nm decreases and at 290 nm increases by increasing in metal ion concentration of Hg (II) chloride and it reveals distinct inflection points at a metal-to-ligand molar ratio of about 0.5 emphasizing the formation of a 1:2 complex. The conditional formation constants was evaluated as log K =4.56 ± 0.001 by using a non-linear least-squares curve fitting program KINFIT.
Solution studies show that our ligand chelated to mercury nitrate better than the other mercury salts, therefore mercury nitrate was selected for further studies.

Extraction Procedure
Thirty mixtures with different mercury concentration and triazen ligand were selected as the calibration set. Their composition was randomly designed for obtaining more information from calibration procedure. Under this condition, the Calibration model was obtained. The calibration model was validated with 5 synthetic mixtures containing the metal ion in different concentrations. The results obtained are given in Tables 1 and 2. Each solution was prepared to contain combinations of the concentration levels 0.5-10 mg/L of mercury. Twenty seven of these solutions were used as a calibration set for PLS model development. Another 5 calibration mixtures, not included in the previous set were employed as an independent test set called the prediction set. To select the number of factors in the PLS algorithm, the leave one out cross-validation method, was used [20]. The prediction error was calculated for each component in the prediction set. The optimum number of factors (latent variables) was determined by computing the prediction error sum of squares (PRESS) for different numbers of latent variables (1-10 latent variables).  Fig. 6 shows a plot of PRESS against the number of factors for each numbers of components. The 7 factors were selected as the optimum number of factors and the model with these numbers of factors was used for prediction of the test samples (Table 2), Table 3 shows the relative and absolute errors between the actual and prediction concentration by PLS model.

Conclusion
PLS method is a simple, fast and inexpensive method for mercury determination. The results show there's a good Universal Journal of Chemistry 2(1): 1-5, 2014 5 reaction between triazen ligand and mercury ions, in comparison of three different formation constants of three mercury salts we can conclude that mercury nitrate has the highest interaction with our triazen ligand because of its highest formation constant, mercury nitrate and choloride gave us the ML 2 complexes but mercury acetate gave us ML complex.