Quantification of phosphate ions by diffusive gradients in thin films technique using ferrihydrite as a binding gel and application to marine sediments

Abstract

A diffusive gradient in thin films (DGT) is a newly developed analytical technique that can isolate and quantify the phosphate ions. A DGT unit comprises two components: the diffusion and binding layers. The diffusion layer comprises polyacrylamide hydrogel, whereas the binding layer from the oxide gel of ferrihydrite is impregnated with polyacrylamide gel. The technique employs a thin film of diffusive hydrogel in contact with a binding phase (ferrihydrite) that can bind phosphate ions. The diffusive and binding gels were characterized via infrared spectroscopy. The main peaks of the diffusive gel were observed at 3336 and 1636 cm−1, whereas those of the binding gel were observed at 3332 and 1638 cm−1. The DGT technique was evaluated as a way to quantify the amount of phosphate ions present in an aqueous KH2PO4 solution. After a contact time of 24 h, ferrihydrite exhibited a high affinity for phosphate, with an uptake efficiency of 98.17%. A linear relationship (R2 = 0.9938) was found to exist between the contact time (3−24 h) and uptake efficiency. Within the 0.2-1.2-mgL−1KH2PO4 concentration range, a linear relationship existed between analyte concentration and the mass of phosphate salt accumulated in the binding gel (R2 = 0.9748). The phosphate ion was eluted from the ferrihydrite hydrogel using 0.25-M H2SO4 over 30 min. The DGT unit was used to measure the phosphate level in six marine sediment samples from Jakarta Bay. The results revealed mass accumulation of P-containing compounds in the 1.009−2.4676-μg range.