Separation and Spectrophotometric Determination of Iron (III) and Mercury (II) via Cloud Point Extraction with New Azo- Derivative

A new coupled cloud point extraction (CPE) was developed as prompt, easy and economical preconcentration technique for spectrophotometric determination of tiny amounts of Fe3+ and Hg2+ in real samples. A modern thiazolylazo ligand [methyl phenyl thiazolyl azo]-3-methyl-4-methoxy-2-naphthol (MPTAN) was done for the CPE method in the preconcentration of Fe3+ and Hg2+ as an earlier step to its characterization by UV-VIS spectrophotometry. The analytical manner includes the formation of under study metals complex with new ligand and quantitatively extracted to the Cloud point layer (CPL) of TritonX-100 after heating. The concentration of MPTAN, metals, pH, thermodynamic data and volume of surfactant was optimized. The investigation of stoichiometry has the ratio of metal to ligand of 1:1. Under finest settings and conditions, the calibration curve was found to be linear in the concentration range of two ions (0.05-10) ppm and the limit of detection for Fe3+ and Hg2+ are (0.016 and 0.041) ppm respectively. The suggested CPE has an excellent methodology for characterization of trace metal ions in surrounding samples with a complex matrix as in soils, water, vegetable, meats, and fruits.


INTRODUCTION
Trace determination of biometals is one of the greatest issues of chemical analysis.Cloud point extraction has many advantages using a small amount of surfactant without using an organic solvent to limit environmental pollution.The small volume of CPL allows a design extraction plans and holds lower toxicity than those using organic solvents.Also, it attaches the green chemistry ideas.There are many applications for sensitive cloud point extraction methods, especially for separation of a micro amount of metal ions such as Mg(II), Zn(II) and others.Feasibly used CPL method is an indirect method of extraction that involves aqueous and surfactant phases.After heating these two phases separated by aggregation micelles, CPL can be in high density and small volume [1][2][3][4].Special work has been conducted about separation and spectrophotometric characterization of iron in nutrient and water samples by CPE method as an innovative complexing agent forming a compound with pH of 4.5, that isolated in non-ionic X-114 Triton surfactant [5].Trace components can be extracted to CPL layer ordinarily after the realization of a hydrophobic compound with a favorable chelating agent [6].CPE has productively used for extraction and preconcentration Vitamins B1 and B2 [7] Dyes such as Malachite green, Crystal violet, Rhodamine B [8], Azo Dyes [9] and many trace elements from various samples [10,11].CPE can be coupled with onium system to determine Fe 3+ and Hg 2+ in real samples [12].There are several studies for determination of a lower amount of iron by using different organic reagents in the minor amount of the surfactant-rich phase [13][14][15][16][17][18][19][20].Mercury is a heavy hazardous poisoning metal that can arise from exposing to water-soluble forms of mercury as in mercuric chloride or methylmercury by breathing mercury vapor, or by taking in any form of mercury [21][22][23].CPE 2 / 11 methodology is feasibly used for Hg 2+ determination in different matrices, coupled with spectrophotometric technique and different surfactants as in (TritonX-100 and Triton X-114) and organic reagents as in (DDTP, 4-(2pyridylazo) resorcinol, and ThioMichler's Ketone).These studies include numerous investigational parameters as in pH, the concentration of chelating agent and surfactant [24][25][26][27].The development of a new analytical method employing ultrasound assisted-cloud point extraction (UA-CPE) for the extraction of CH3Hg + and Hg 2+ species from fish samples has been achieved in [28].The UA-CPE method has shown to be a suitable method.The results were in a good agreement (with Student's t-test at 95% confidence limit) with the certified values, and the relative standard deviation was lower than 3.2%.The limits of detection were 0.27 and 1.20 μg L −1 for Hg 2 + from aqueous calibration solutions and matrix-matched calibration solutions were spiked before digestion, respectively, while it was 2.43 μg L −1 for CH3Hg + from matrix-matched calibration solutions.A significant matrix effect was not observed from comparison of slopes of both calibration curves to represent the sample matrix.In [29], a new cloud point extraction procedure has been optimized for the selective determination of trace amounts of total iron in some environmental samples without using organic reagents.The determination of mercury via sensor in real aqueous along with real samples has been also reported as in [30,31].
Since our survey through literature did not find any synthesis or using of [methylphenyl thiazolyl azo]-3methyl-4-methoxy-2-naphthol (MPTAN) as a chelating agent for metal ions in CPE or other methods.This study explains the synchronous preconcentration of Fe 3+ and Hg 2+ , after the construction of ion-pair association complex with MPTAN and then analyzes the spectrophotometry employing TritonX-100 as a surfactant.This study presents the determination of iron and mercury separation through cloud point extraction as flexible and accurate technique that can be utilized for characterization of metal ions in meat, vegetable, soil, water, and fruit.

Reagents
Each solution has been formulated with deionized water.An analytical grade of acids, salts, bases and other materials employed in this paper has been gotten from Merck, Darmstadt, Germany.Stock solution of 1mg/mL of Fe 3+ ion was prepared by dissolving 0.2880g of FeCl3 in 100mL and for Hg 2+ ion dissolved 0.1353g of HgCl2 in 100 mL of purified water.Other employed solutions have been prepared by dilution technique with purified water in an appropriate volumetric flask.The MPTAN ligand as presented in Scheme 1 was created in relation to [32] by reacting methyl phenyl thiazolyl amine with 3-methyl-4-methoxy-2-naphthol after controlling all conditions as reported in [32].Consequently, 1×10 -2 M of MPTAN was prepared by dissolving 0.363g in 100mL distilled water containing Triton X-100.

Comprehensive Method
10mL aqueous solutions containing 50µg of metal ion under study Fe 3+ or Hg 2+ have been taken with optimal HCl concentration and 1×10 -4 M MPTAN in the presence of the optimal volume of surfactant with 1% TritonX-100.The solution has been heated in an electrostatic water bath for proper temperature up to the period of cloud point layer formation.At that point, it disjointed CPL from aqueous solution and liquefied CPL in 5mL ethanol.The absorption of an alcoholic solution was determined at λmax=485nm for Fe 3+ and λmax=497nm for Hg 2+ ion in Eurasian J Anal Chem 3 / 11 contradiction of blank arranged in the similar method without metal ions.Nevertheless, aqueous solution for Fe 3+ ion has been handled along with thiocyanate method but Hg 2+ ion has been handled according to Dithizone spectrophotometric process [33] to regulate the remainder amount of metal ions in aqueous solution along with extraction as in Figure 1.This quantity has been subtracted from the primary quantity of 50µg to evaluate the transferred quantity to CPL to extract ion-pair association complex.Then, distribution ratio (D) can be calculated according to Equation (1):

Spectroscopy
For identification of new azo derivative reagent [methyl phenyl thiazolyl azo]-3-methyl-4-methoxy-2-naphthol, (MPTAN) Uv-Vis and IR spectrums in Figures 2 and 3 prove and put forward the true structure of new organic reagent with a wavelength of maximum absorbance equal to 475nm.IR spectrum shows a peak at a wave number of 3420 cm -1 belongs to stretching vibration -OH group but aromatic C-H appears at wave number more than 3000 cm -1 .Bending vibration for ether C-O giving a peak at 1262 and 1159 cm -1 , as well as the weak peaks at 1450-1350 cm -1 , belong to N=N, while at 1510-1100 cm -1 region belongs to all peaks for vibration of bridge azo group.The UV-VIS spectrophotometric investigations about extracted ion-pair association complexes of Fe 3+ and Hg 2+ are shown in Figures 4 and 5.The UV-VIS spectrum reveals that red shift in the bands and the complexes have less energy than reactants.

Variation of pH
According to the comprehensive method, 50µg for each metal ion was extracted alone from 10mL aqueous solutions at different pH values in the existence of 1×10 -4 M MPTAN and 0.5mL of 1% TritonX-100 after heating the solution in an electrostatic water bath at 90ᵒC for 15 minutes.Up to realization of CPL, it was separated from the aqueous phase and liquefied in 5mL ethanol to complete the procedure.The results were shown in Figures 6.These results showed that optimum pH for extraction was pHex=9 for both ions.At this pH, the best rate was reached for thermodynamic formation ion-pair complex and partitioning to CPL.At pH less than the optimum value, the rate of complex formation was decreased but at more than optimal value, a side effect of OH -ion has appeared in aqueous solutions with decreased extraction efficiency.

Effect of Surfactant Volume
By following comprehensive method, 50µg of Fe 3+ and Hg 2+ was extracted each one alone in 10mL aqueous solutions at pHex of 9 in the existence of 1×10 -4 M MPTAN with rising volume of a surfactant of 1% TritonX-100.The resultant absorbance curves were shown in Figure 7.The optimum surfactant volume giving higher extraction efficiency was 0.5mL for Fe 3+ ion and 0.4mL for Hg 2+ ion.This volume formed the best CPL for partitioning complexes and contributed to the formation of CMC state.Any volume less than optimal level was not suitable to form CMC and make the volume more than the finest volume effect to increase diffusion of micelles.

Effect of Temperature
Depending on the comprehensive method of extraction to determine rising temperature for Fe 3+ and Hg 2+ , the absorbance results are shown in Figure 8.The finest temperature of two ions is 90ᵒC that formed suitable CPL layer with more hydrophobic and smaller volume.By application of mathematical thermodynamic relation below to calculate extraction constant Kex at each temperature, the extraction consequences were depicted in Figure 9.The results explained that extraction method was endothermic with an optimum temperature of extraction (90ᵒC) for both metal ions.The high value of entropy reflected the dependency of extraction method on entropy to form new stable system.It could be extracted quantitatively which was the ion-pair association complex for each metal ions.
From the slope of straight relation above and relations below, calculated thermodynamic data of extraction results are shown in Table 1.

Effect of Heating Time
50µg of each ion alone was extracted from 10mL aqueous solutions at the optimum condition and at different heating times.Accordingly, the absorbance consequences were shown in Figure 10.The results showed that the most probable heating time for bath metal ions was 15 minutes.Giving best extraction efficiency at this time reached the cave of CMC in the formation of CPL with very good properties to give higher quantitatively partitioning of ion-pair complexes of metal ions under study.At less than optimum heating time, it was not able to reach to CMC state.However, at more than the optimum value, it increased the diffusion of micelles went far away from the optimum state and CMC formation.

Stoichiometry
The most probable structure of ion-pair complex of both metal ions under study can be identified using two spectrophotometric methods which were slope ratio, slope analysis, mole ratio and continuous variation approaches.The results were explained in Figures 11 and 12.The results showed the metal to ligand ratio of 1:1 for all used methods.Accordingly, Schemes 2 and 3 show a more probable structure of ion-pair association complex extracted to CPL.

Effect of Electrolytes
50µg of each metal ions alone has been extracted from 10mL aqueous solutions at the optimal situation in the presence 0.01M of some electrolyte salts according to an inclusive method.The results of electrolyte on extraction efficiency of Fe 3+ or Hg 2+ ions have been summarized in Table 2.These results show increased extraction efficiency by the presence of electrolyte salts in aqueous solutions and this increasing differs with different electrolyte salts dependent on nature and behavior of electrolyte in aqueous solutions which motivate water molecular withdrawing from hydration shell of metal ions and increases the chances of binding with MPTAN organic reagent to increase formation and stability of extracted ion-pair complex.The finest electrolyte salt was LiCl for the reason that it has a smaller ionic radius of a metal cation and more water molecular has been withdrawn from hydration shell of metal ions under study.

Spectrophotometric Determination
By comprehensive application method at the optimum condition to determine Fe 3+ and Hg 2+ in different samples, a calibration curve for spectrophotometric determination was prepared to calculate analytical data for a calibration curve for a new sensitive method as illustrated in Table 3.The corresponding results in Figure 13 consist of the linear relationship between concentration and absorbance.Table 4 presents analytical results for the determination of analytes in different samples (n=5) by using this new method.

CONCLUSION
The speedy, reliable, economical and accurate method is applied in this work in presence of a new ligand MPTAN that has more selective Fe 3+ and Hg 2+ .This method increases the extraction efficiency by the presence of electrolyte salts in aqueous solutions and this increasing differs with diverse electrolyte salts reliant on nature and performance of electrolyte in aqueous solutions that assists to withdraw water molecular from hydration shell of metal ions and increases the likelihoods of binding with MPTAN organic reagent to increase formation and stability of extracted ion-pair complex.The best electrolyte salt was LiCl since it has a smaller ionic radius of a metal cation.More water molecular has withdrawn from hydration shell of metal ions under study.TritonX-100 has been used as a non-ionic and green extractant solvent.The values of ∆Hex of the resultant reaction were endothermic and the values of ∆Gex showed that the reaction occurs spontaneously.Computerized genetic algorithms can be used in this study as future work to further optimize the desired analytical chemical outcomes using these algorithms with expected interesting performances.

Figure 1 .
Figure 1.Calibration curve for determination Fe(III) and Hg(II) in aqueous solution

Figure 6 .Figure 7 .
Figure 6.Effect of pH on formation and stability of ion-pair complex

Figure 8 .Figure 9 .
Figure 8. Consequence of temperature on the formation and quantitation partitioning of complexes

Figure 10 .
Figure 10.The consequence of heating time on formation CPL and partitioning of complexes

Figure 12 .
Figure 12. Results of mole ratio method

Scheme 3 .
Scheme 3.More probable structure of Hg 2+ ion pair extracted complex

Figure 13 .
Figure 13.Calibration curve for spectrophotometric determination of Fe(III) and Hg(II) in different samples

Table 1 .
Thermodynamic details of extraction Hg

Table 2 .
The consequences of electrolyte on extraction efficiency of Fe 3+ or Hg 2+ ions

Table 3 .
The analytical parameter of merit for CPE extraction of Fe and Hg

Table 4 .
Fe 3+ and Hg 2+ content (ppm) in different samples * Given values represent the average of five analyses of each sample