Flow-injection analysis applied to the kinetic determination of reactive (toxic) aluminium: comparison of chromophores

A comparison of chrome azurol S (CAS), eriochrome cyanin R (ECR) and pyrocatechol violet (PCV) was made for the estimation of kinetically-labile Al(III) in a series of complexes with model ligands. Flow-injection analysis was used with short reaction times (ca. 10 s). All chromophores differentiated between Al(III) bound in strong and weak complexes, and were suitable for ordering soil solutions and natural waters for relative Al(III) toxicity. By analysing solutions at an isosbestic point at λ>λmax, measurements of “kinetically-labile” (10 s reaction) and “equilibrium-reactive” (10 min reaction) Al(III) were obtainable from a single injection into ECR or CAS. A method is proposed using 0.05 M KCl carrier and CAS (35 μM at the detector) at pH 5.50 in a low sample-dispersion manifold. Kinetically-labile and equilibrium-reactive Al( III) can be determined with a detection limit of 60 nM. The response is linear to 30 μM. The determination of Al(III) in soil solution samples is reported.