DETERMINATION OF THE ALUMINUM COMPLEXING CAPACITY OF FULVIC-ACIDS ANDNATURAL-WATERS, WITH EXAMPLES FROM 5 NEW-ZEALAND RIVERS

An FIA technique with 7 s reaction time was used to analyse free plus labile Al in fulvic acid (FA) solutions and natural waters at pH 4.7, without the need for separation procedures. Titrations of these soluti ons using incremental pH or total Al were used to determine pH binding curves or estimates of the 'kinetic' Al complexation capacity (Al-CCk ) respectively. The operational definition of Al-CCk relates to the ca pacity of a humic substance or natural water to bind Al through a 7-s FIA reaction time under defined experimental conditions of chromophore (GAS) concentration, ionic strength, and pH. Both Al binding strength and complexation capacity were greater than the corresponding Cu-CC ( ISE) values. The Al-CCk measurements at pH 4.7 were 710 mu mol Al g(-1 ) v. 590 mu mol Cu g(-1). Al-CCk results (pH 4.7) were higher for soil FA (710 mu mol g(-1)) than for aquatic FA (390 mu mol g(-1)). AI-CC, results (pH 4.7)for five unfiltered river waters from different catchm ents gave results in the range 6.5-9.8 mu mol Al L(-1). The difference s between total (natural) Al in the samples and Al-CCk were between 2. 7 mu M and 8.6 mu M. Filtration experiments identified fractionation p atterns between total (natural) Al and the fraction of Al-CCk not util ized. The Al titration of alginate, another component of natural organ ic matter, is reported.