Spectrophotometric Determination of Cu ( II ) by Complex with Ethyl Cyano ( 2-Methyl Carboxylate Phenyl Azo Acetate ) ( ECA )

A new simple and sensitive spectrophotometric method for the determination of trace amount of Cu(II) in the ethanol solution have been developed. The method is based on the complexation of Cu(II) with ethyl cyano(2-methyl carboxylate phenyl azo acetate) (ECA) in basic medium of sodium hydroxide givining maximum absorbance at (λmax = 521 nm). Beer's law is obeyed over the concentration range (5-50) (μg / ml) with molar absorptivity of (3.1773 × 10 L mol cm) and correlation coefficient (0.9989). The optimum conditions for the determination of Cu(II)-complex and have been studied and applied to determine Cu(II) in synthetic water sample using simple and standard addition methods.


Introduction
Copper has Cu symbol, atomic number 29 and atomic mass 63.54 gm mol -1 .Copper is a reddish metal with a face centered cubic crystalline structure [1,2].It is one of the several metals that play an important role in the biological systems, it occurs naturally which in many vegetables, meat and grains [3,4].Copper is a mineral that nowadays possess few problems.It is widely distributed, as a component of various enzymes in foodstuffs of all kinds, at levels between 1 and 5 ppm.Milk is notably low in copper, at a round 2 ppm and mammalian liver is exceptionally high, at a round 80 ppm.The daily in take in normal adult diets is between 1 and 3 mg [5].Methods for determination of copper were studied spectrophotometric in synthetic mixture and water samples [6], natural waters and pharmaceutical samples with chloro(pheny) glyoxime [7], determination of micro amount of copper(II) in different environmental and vital samples by new organic reagent [8], determination of micrograms of copper(II) and platinum(II) [9], complexation of cefixime with copper(II) using acetate NaOH buffer in water:methanol [10], determination of copper(II) using 5-nitrosalicyldehyde semicarbazone (NSS) as an analytical reagent [11], with 2-hydroxy-1-naphthalene carboxaldehyde phenyl hydrozone as an analytical reagent [12].Synthesis of the ligand ethyl cyano(2-methyl carboxylate phenyl azo acetate) (ECA) and the structure of (ECA) in Figure (1) [13].In this work a sensitive and simple method for the determination of trace amounts of Cu(II) by UV-Vis spectrophotometry was described based on the formation of the Cu(II)-ECA complex and the influences of some parameters.

Ethyl cyano(2-methyl carboxylate phenyl azo acetate) (ligand) (1000 μg / ml)
The ligand was prepared as same in paper [13].A stock solution of (1000 μg / ml) of ligand was prepared by dissolving (0.1 gm) in ethanol absolute and then made up to (100 ml) in a volumetric flask and was kept ambient bottle a way from sun light.

Copper(II) (1000 μg / ml)
A stock solution of (1000 μg / ml) of Cu(II) was prepared by dissolving (0.2682 gm) of copper chloride dihydrate (CuCl 2 .2H 2 O) in ethanol absolute and diluted to (100 ml) in a volumetric flask by absolute ethanol.Working solution of (500 μg / ml) was prepared by simple dilution of stock solution with ethanol absolute.

Sodium hydroxide ≈ (0.1 M)
This solution was prepared by dissolving (0.4 gm) of sodium hydroxide in ethanol absolute and diluted to (100 ml) in a volumetric flask by the same solvent.

Hydrochloric acid ≈ (0.1 M)
This solution was prepared by diluting of (1.54 ml) of concentrated hydrochloric acid (37%) and diluted to (250 ml) in a volumetric flask by ethanol absolute.

Absorption spectra
The complex is produced from the reaction between (0.5 ml) of Cu(II) (500 μg / ml) with (0.5 ml) of ligand (1000 μg / ml) in a volumetric flask (5 ml) and diluted to ethanol absolute giving maximum absorbance at λ max = 521 nm an in Figure (2).

Optimum conditions for regulation reaction
There are many parameters affecting on the complexation reaction and absorbance of complex which is produced.

Effect of ligand volume
When a various volumes of ligand solution (0.05, 0.1, 0.15, …..0.6) ml for (1000 μg / ml) were added to (0.5 ml) of (500 (μg / ml) Cu(II), solution was found that (0.5 ml) of ligand is enough to give a maximum absorption and was considered to be optimum for concentration range of (5-50) (μg / ml) of Cu(II).The results were shown in Table (1).

Effect of hydrochloric acid volume
Existence of hydrochloric acid (0.1-1) ml of (0.1 M) in reaction solution effect on decreasing the intensity of absorbance for produced complex.The results were shown in Table (2).

Effect of sodium hydroxide volume
It was found that the presence of base in reaction solution effect on increasing the intensity of absorbance for the produced complex, NaOH was selected and (0.1 ml) of (0.1 M) was found to be the optimum volume.This base gives high sensitivity which was selected in subsequent experiments the results were shown in Table (3).

Effect of order of addition
To obtain optimum results, the order of addition of base should be the first followed by addition of ligand and Cu(II).The results were shown in Table (4).

Effect of temperature
The resulting complex of the proposed method was studied at room temperature (25 ˚C), the absorbance values remain constant.The results were shown in Table (5).

Effect of time on the complex formation
The results show that the complex produced was stable between (5-60) minutes, the absorbance value was stable.The results were shown in Table (6).

Precision and accuracy
Under the optimum condition, the precision and accuracy of the method was calculated.The results were shown in Table (7).

Structure of the complex
The stoichciometry of the complex between Cu(II) and ligand was investigated using Job's method and mole ratio method; the results show that 1:2 Cu(II) to ligand complex was formed.The formation of the complex produced suggest occurring as follows, Figure ( 4) [14].

Application
Two methods were successfully applied, (simple method and standard addition method) for determination of Cu(II) in synthetic a river water.The sample Cu(II) in synthetic a river water (1000 μg / ml) was prepared by taking (0.2682 gm) of CuCl 2 .2H 2 O dissolving in a river water and transferred in a volumetric flask (100 ml) diluted up to the mark with same solvent.Simple method transferred (0.25 ml) of Cu(II) in synthetic a river water (1000 μg / ml) to a volumetric flask (5 ml) contains (0.1 ml) NaOH (0.1 M) and (0.5 ml) ligand (1000 μg / ml) diluted up to mark with ethanol absolute.Taken absorbance of solution in (λ max = 521 nm) against blank.The results were shown in Table (10).Standard addition method transferred (0.25 ml) of Cu(II) in synthetic a river water (1000 μg / ml) to each volumetric flask (5 ml) contains (0.1 ml) NaOH (0.1 M) and (0.5 ml) ligand (1000 μg / ml) and various concentrations of Cu(II) solution (5-50) μg / ml diluted up to the mark with ethanol.Taken absorbance of each solution in (λ max = 521 nm) against blank.The results were shown in Figure (5) and Table (10).

Conclusion
A new simple and sensitive spectrophotometric method for the determination of trace amount of Cu(II) in the ethanol solution.The method is based on the complexation of Cu(II) with ethyl cyano(2-methyl carboxylate phenyl azo acetate) (ECA).