Determination of the aluminium complexing capacity of fulvic acids and natural waters, with examples from five 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 solutions 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 capacity 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 catchments gave results in the range 6.5-9.8 mu mol Al L(-1). The differences 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 patterns between total (natural) Al and the fraction of Al-CCk not utilized. The Al titration of alginate, another component of natural organic matter, is reported.