Abstract
2-(ο-Hydroxyphenyl)-benzoxazole (abbreviated to oxazole) forms a yellow colored 1:2 chelate with copper ion in acidic solution. Since the selectivity of the reaction with copper is high, studies on the gravimetric determination of copper in copper or aluminum alloys have been carried out. The copper oxazole chelate is dissolved into various kinds of organic solvents. The absorption curve of the chelate extracted into organic solvents shows an absorption maximum at 370 nm in carbon tetrachloride, benzene and toluene and at 365 nm in chloroform and methyl isobutyl ketone, whereas the reagent blank has an absorption maximum at 345 nm and a slight absorption at 370 nm against the respective organic solvents. In this paper, a highly sensitive and selective method of spectrophotometric determination of copper has been achieved by extraction of the chelate into carbon tetrachloride.
Since oxazole is only slightly souble in water, carrier precipitation of a minute amount of copper has also been investigated using oxazole as a collector organic reagent. A single precipitation of 0.01 g of oxazole in each case collects 9858% of copper in 1005000 ml of aqueous solution at pH 5.57.0. The relationship between the concentration of copper in the aqueous solution vs. the amount of copper coprecipitated with oxazole in equilibrium is quite similar as that obtained by solvent extraction. The distribution ratio of copper in this case has been caluculated to be 7.0×105 (ml/g) at 20°C.
The precipitate of oxazole which collects coprecipitated copper is dissolved in hydrochloric acid, followed by carbon tetrachloride extraction and spectrophotometric determination of copper. These experiments were applied to the separation, concentration and determination of copper of an amount below 3 ppb in water samples.
The recommended procedure for the spectrophotometric determination of copper is as follows:
To a sample containing less than 40 μg of copper in a 100 ml separatory funnel, add 1 M acetic acid and 1 M sodium acetate solution to adjust pH 6.0, 1 ml of 0.5% ethanolic oxazole solution and 10.0 ml of carbon tetrachloride. Shake the liquids for 2 min, separate the organic phase and dried with anhydrous sodium sulfate. Measure the absorbance at 370 nm against the reagent blank as a reference. Beer's law is obeyed up to 40 μg of copper in 10 ml of the extract and the molar absorptivity is 2.5×104. A constant absorbance was obtained in the range 5.37.0 of pH, 50300 ml of the aqueous layers and 13 min of the shaking time.
Intreference by hydrolysis of iron(III) up to 20 ppm can be avoided by an addition of 5 ml of 10% ammonium tartrate solution per 100 ml of the aqueous solution. By an addition of 0.01 g of oxazole per 1000 ml sample solution, 88% of copper in the precipitate was recovered from 10005000 ml of water samples, followed by the determination of 0.230 μg of copper using the calibration curves obtained by the similar procedure.
