Determination of Traces of Iron, Copper, Zinc, Nickel and Cebalt in Water by Atomic Absorption Spectrometry Using PAN-MIBK Extraction

Abstract

A new method for the determination of trace amounts of iron, copper, zinc, nickel and cobalt has been developed by the combination of solvent extraction and atomic absorption spectrophotometry. These metals produce water-insoluble complexes with 1-(2-pyridylazo)-2naphthol (PAN), which were extracted into methyl isobuthyl ketone (MIBK). Although the optimum pH ranges for the complex-formation with PAN were 3-5.5 for iron and 7-10 for other metals, these complexes were able to form by adjusting the pH of solution to 4-5, then raising it to 8-9, and extracted in MIBK simultaneeusly. These complexes were stable in MIBK for ten days. Lineat calibration curves were obtained up to 70 ppb. The coefficients of variation were 5% at 2 ppb for copper, 3% at 5 ppb for iron, and 6% at 5 ppb for zinc, nickel and cobalt.Based on these data, following procedure was presented for the deterrnination of iren, copper, zinc, nickel and cobalt. Four hundred milliliters of the sample solution containing these metals up te 70 ppb are transferred to a 500 ml separatory funnel, and the pH is adjusted to 4-5 by 5 ml of an acetic acid-ammonium acetate buffer solution. After addition of 2 ml of O. O1 mol/l PAN solution, the solution is shaken for 3 minutes. Further, pH is adjusted to 8-9 by 3 ml of 6% ammonia solutien and the solution is shaken for 3 minutes. Then, 20 ml of MIBK are added and metal-PAN complexes are extracted by shaking for 2 minutes. The organic phase is subjected to the atomic absorption measurement following the condition shown in Table 1.The presence of Pb(II), sulfate, thiosulfate, phosphate, pyrophosphate, ehloride, fluoride, or hydrazihe caused no interference to the determination. Even a small amount of cyanide and a large amount of nitrate interfered the determination (Table 5).