Copper is an important trace element in several branches of science (e.g., medicine, industrial chemistry, and biology) [1]. The trace of copper in a water supply often causes troubles in galvanized cisterns and hot water tanks. A precaution to protect the galvanized steel should be taken if the copper content of the water approaches 0.1 ppm [2]. Copper salts are used in water supply systems for controlling biological growth in reservoirs and distribution pipes. The corrosion of copper-containing alloys in pipe fittings may introduce measurable amounts of copper into the water in a localized pipe system. Copper is essential to humans, and adults daily requirement has been estimated at 2.0 mg [3]. Copper was used as a reagent for the determination of cliquinol in pharmaceutical products [4]. There are a number of chromogenic agents that have been determined by the micro amount of copper [5], those based on bathocuproinc (2. 9-dimethyl-4. 7-diphenyl-1. 10-phenanthrolinc) [6] and neocuproine (2. diphenyl-1. 10-phenathrolineare) [7] considered to be specific. Extraction with dithiozonc (dipheyl thio carbazone) in an acidic solution gives a sensitive color reaction but is not very specific [8]. One of the most widely used methods, however, is still based on dithiocarbamate [9]. In this paper, a simple, sensitive, and selective color reaction for the spectrophotometric determination of copper by means of copper-sulphonazo III is described. The available copper can be determined directly in an aqueous medium with no need for extraction into an organic solvent. It has been satisfactorily applied to the determination of copper in tap water.

Apparatus

The following apparatus was used: a Philips Pv 8800 UV/Vis spectrophotometer. A Philips PW 9421 pH meter with glass calomel electrodes was used. A Perkin-Elmer 2280 atomic absorption spectrometer. And thermo-Jarrell Ash ICAP 61 inductively compiled Arcon plasma-emissions spectrometry.

Reagents

All the reagents used were of analytical-reagent grade. The water used was always twice-distilled.

Copper standard solution 100µg/ml; Dissolve 206.8 mg of CuCI₂ in 1L distilled water. Dilute the stock solution suitably to give a standard solution containing 50µg/ml of copper with water.

Sulphonazo III (SAZIII) Solution (0.757 10^-4 M): Dissolve 54 mg in 1 litre of distilled water.

Buffer solution pH₃: 16.2 ml of 0.1 M chloracetic acid plus 8.8 ml of 0.1 M potassium hydroxide, and dilute to 100 ml with distilled water.

Composed masking agent: It contains 2 mg/ml NaF 2 mg/ml Na₂SQ₄ M, and 0.5 mg of citric acid.

Interfering ion solution: A 1000 mg/mL solution of each ion was prepared.

General Procedure

Place a volume of the working standard solution corresponding to 15 µg of copper in a 25 ml calibrated flask. Add 1 ml of PH₃, buffer solution, 10 ml of (0.787 x 10^-4 M) Sulphonazo III, and 1 ml of the composed masking agent. Dilute with water to the mark. Measure the absorbance at 606 nm against a reagent blank. Carried through the above-described procedure using a 1-cm quartz cell.

UV-visible spectrophotometry is still considered a convenient and low-cost method for the estimation of pharmaceuticals [10–11]. This method is used for the estimation of copper in tap water. Spectral characteristics and effects of experimental variables. The absorbance curves of the reagent and its copper complex are shown in figure 1. The maximum absorbance of the reagent is 540 nm, and that of the Cu-Sulphonazo III system is 606 nm. Variation of the PH of the reaction medium revealed that the complex formation remained maximal and constant over the PH range of 2.8–4.0. Therefore, a pH value of 3.0 was selected for the procedure. The absorption spectrum of the blue-colored complex was recorded between 480 and 750 nm (Figure 1).

Figure 1: Absorption Spectra of 15µgcu (II) /25ml. Measured Against (A) Blank (B) Distilled Water and (C) Blank Against Distilled Water.

At the optimum PH absorbance, measurements were carried out by varying the reagent concentration. It was observed that the addition of more than 8 ml of (0.787 x 10^-4 M) reagent solution was required to obtain a maximum reagent concentration. It was observed that the addition of more than 8 ml of reproducible absorbance for 15 µg of copper smaller amounts were given in complex formation. Therefore, 10 ml of the (0.787 x 10^-4 M) solution of Sulphonazo III were used throughout the study. The minimum time for complex color development of the complex was found to be directly at room temperature (15-30 ⁰C). The absorbance was then stable for at least 6 micrograms of copper, as determined with an accuracy of better than 1.6 % and a relative standard deviation of <2.1 %.

Beer's Law

Once the optimum conditions for the determination of copper with SAZ III were established, the concentration range in which Beer’s Law is obeyed was studied. This range was between 0.0 and 30µg per 25ml (Figure 2), and the molar absorptivity was 12.9 x10⁴ 1/mol.cm, and the sandell sensitivity index was 0.003µg.cm^-2.

Figure 2: Calibration Curve of Copper Determination with SAZIII Reagent.

Table 1: Optical Characteristics and Statistical Data for the Regression Equation of the Proposed Method.

Composition of the metal complex [12]

The continuous variation method and mole-ratio method were employed to establish the composition of the complex. The results indicate the formation of a 1:1 complex between the metal and Sulphonazo III.

Apparent stability constant of the complex [13]

The apparent stability constant of the metal was calculated by the method of Garcia-Vargas et al. The value thus obtained was 0. 24x10⁶ 1/ Mole, indicating the complex is relatively stable.

Interferences

The effects of some ions that often accompany copper were studied by adding different amounts to 10µg/25ml of copper in solution. The species are considered to interfere seriously if they cause a change of more than 2% in the absorbance obtained for copper alone [14,15]. The color was developed as an outline during the procedure. When NaF, kcl. Na₂ SO₄, citric acid were added as masking agents. The following ions did not interfere (amount given in mg). Fe (III) (500), Al (III) (1000), Ba⁺²(1000) , Ca⁺² (1000); Cd⁺² (200),Co⁺² (200), Zn⁺² (600), Cr (III) (700), Bi (III) (700), Si(IV) (800), Ti (IV) (500), pb (1000), Zr (IV) (700), Sn⁺²  (500), Ni⁺² (1500), Cr(VI)(500), Fe⁺² (1500), Na⁺ (2000), K⁺ (2000), Mn⁺² (1000), Li⁺ (2000).

On the basis of these data, the selectivity of the method is very good.

To 100 ml of tap water, 2.5 ml of HCL is added and evaporated to about 5 ml, which is then transferred to a 25 ml calibrated flask, neutralized with NaOH solution, 1 ml of pH₃ buffer solution, 10 ml of reagent (0.787 10^-4M) and 1 ml of composed masking, diluted to the mark of 25 ml, and measured at 606 nm against a reagent blank. The same sample was analyzed by the AAS, ICP, and Na-DDTC methods. The results were compared favorably, as shown in Table 2 below.

Table 2: Determination of copper in tap water.

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