Spectrophotometric Determination of Metals by pH Scanning Extraction under High-Speed Stirring

Abstract

A “pH scanning technique” was introduced for the liquid-liquid extraction of metal chelates by high-speed stirring. The increase of pH in the aqueous phase containing phosphoric, boric and acetic acids as pH buffer reagents was controlled by addition of a 5 M NaOH solution at the rate of 0.9 ml/min. The relationship between pH change in the aqueous phase and the addition time of the NaOH solution was almost linear in the range of pH 2.5–11. The absorbance of metal complexes extracted into chloroform phase was recorded continuously after the separation of organic phase from the mixture of two liquids by use of a Teflon phase separator under the conditions of high-speed stirring. By the present method, copper(II), cobalt(II) and indiurn(III) were simultaneously determined in the range of 0.1–60 μg with 8-quinolinol. The advantage of the present method was the separation of some metals having rapid-extraction rates from other metals having slower rates.