The problem of metal speciation analysis as a tool to differentiate toxicity and mobility of metal ions in natural waters has long been an illusive one. The use of operationally defined methods and mathematical models has resulted in substantial progress in understanding systems containing metal ions, but the accuracy of the resultant determinations is problematic. In response to this difficulty a high performance liquid chromatographic (HPLC) method was developed to more accurately examine the concentrations of complexed and free aluminum (AL) species at the low micromolar concentrations characteristic of natural waters. Subsequently the method was used to examine the equilibrium binding of several aluminum complexes and to investigate aluminum binding to a fulvic acid and to naturally occurring dissolved organic materials in lake waters.

Al (III) was chosen as it is toxic to a variety of aquatic organisms in acid-impacted ecosystems but forms nontoxic complexes with dissolved naturally occurring materials. Initially a flow injection analysis (FIA) technique was developed which quantitatively determined monomeric forms of aluminum. The method had a detection limit of 3.7 nanoM with a linear range to 37 microM. The subsequent HPLC method used a cation exchange column and gradient flow to determine the concentration of a variety of aluminum species including Al (III) with a detection limit of 7 nM. In both methods aluminum was detected using a post column lumogallion reaction. Concentrations of aluminum citrate and aluminum fluoride complexes at equilibrium with free aluminum agreed very favorably with concentrations determined by equilibrium calculations. No dissociation of complexes was apparent. Although previously undetected by HPLC, several aluminum acetate complexes and an aluminum silicate complex were also analyzed. Formation constants for these were determined and compared to literature results.

The applicability of the HPLC method to the determination of limnologically relevant samples was demonstrated by analyzing equilibrium solutions of aluminum with Suwannee River Fulvic Acid (SRFA) and samples from acid impacted Adirondack lakes. SRFA showed significant pH-dependent binding to aluminum at pH 4.0, 5.5, 7.0 and 8.2. Although slightly less binding occurred at the higher pH values, SRFA complexes at and above pH 5 were significantly more concentrated than anticipated. By modeling the binding of SRFA to aluminum, concentrations of complexed aluminum could be estimated in acid lake waters based on pH, organic carbon content and free Al (III). Comparison of predicted values to observed lake water and literature values showed good agreement.

Although aluminum is a toxic in low pH waters, an important implication of this research was not directly related to the use of aluminum as the metal ion of choice. Other metal ions occur in freshwaters via mining and indiscriminate polluting. Many of these also exist in toxic (free) and nontoxic (complexed) forms. The successful determination of aluminum species directly by HPLC leads one to believe that the kinetic lability of some metal complexes may be less than previously postulated.