The Determination of Quickly Reacting Aluminium in Natural Waters by Kinetic Discrimination in a Flow System

Abstract

Different aluminium species react with oxine at different rates, a behaviour that we have used as the basis of an analytical method. The reaction is performed in a FIA system and is terminated by extraction of the excess oxine, together with the aluminium trioxinate formed, into chloroform. The reaction time is 2.3 sec, much shorter than that used normally. After separation, the amount of aluminium trioxinate in the organic phase is determined spectrophotometrically.

The system has been validated using model substances with known complexation constants. Al³⁺, AlOH²⁺, probably Al(OH)₂ ⁺, aluminium sulphato complexes and, to some extent, some of its weakest organic complexes are included in the measured fraction, whereas fluoro complexes, citrato complexes and Al₁₃O₄(OH)⁷⁺ ₂₄ are excluded. Complexes with fulvic and humic acid cause a reduction of the signal. The detection limit is at best about 5 μg/L (ca. 0.2 μM), and we can make 60 measurements per hour. Results from measurements made on natural waters are presented.

Key Words:

• Aluminium
• speciation
• natural waters
• flow injection
• oxine
• kinetics