A rapid, automated gradient flow injection-spectrophotometric technique for study of metal complexation reactions

摘要

Controlled dispersion as generated in flow injection analysis (FIA) essentially permits an infinite variety of known compositional gradients. Using this unique advantage of FIA, the stability constants of metal complexation are calculated by injecting an aliquot of metal solution into the flow of ligand solution in a single-line manifold. While the ligand dilution is negligible, the concentration gradient of injected metal ion can be calculated from the dispersion pattern which is calibrated previously using a dye solution. To show the simplicity, versatility and ease of instrumental setup over approaches based on the classical titration, the method was applied to determine stability constants of murexide with several metal ions. The SQUAD computer program was used for fitting the predefined complexation model to the spectral-mole ratio data. The proper selection of the chemical model was verified by the determination of the number of absorbing species by using a singular value decomposition of each data set. The stability constants obtained for murexide and metals including Cu~(2+),Cd~(2+), Pb~(2+), Ca~(2+) and Co~(2+) are 4.35, 4.27, 4.50, 2.55 and 2.57, respectively. The formation constants determined here are in good agreement with those previously reported and with those obtained from conventional batch titrations. The main advantage over the classical batch titration method is that by utilizing just one injection per sample, the proposed method reduces experimental error by reducing the experimental steps needed to obtain the required spectral-mole ratio data. The details of the proposed method are discussed.