Study of orthophosphate detection method using DGT (diffusive gradients in thin films) device with modified binding layer Fe-chitosan-bentonite biocomposite in aquatic system

Abstract

In this work, a study of orthophosphate detection technique in the aquatic system has been conducted. The detection technique used in this study was Diffusive Gradients in Thin Films (DGT) with Fe-Chitosan-Bentonite (Fe-CSBent) biocomposite as the binding agent. The phosphate species diffused through the polyacrylamide gel and then bound by Fe-CSBent as the binding agent on the binding layer. The adsorption of phosphate by Fe-CSBent is through electrostatic attraction, inner sphere complexation, and ion-exchanged. The synthesized Fe-CSBent biocomposite was characterized using Fourier Transform Infrared (FTIR), Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Spectroscopy (EDS) and X-Ray Diffraction (XRD) analysis, and the synthesized diffusive gel and binding gel were characterized using FTIR analysis. In this experiment, we examined the DGT-Fe-CSBent capability in orthophosphate binding with parameters such as the deployment time, pH of the solution and the presence of co-existent anion i.e. sodium tripolyphosphate (STPP). The mass of bound orthophosphate can be calculated after eluted the binding gel with acid and then measured with the molybdenum blue method using UV-Vis spectrophotometry. Based on the experiment, DGT-Fe-CSBent bound the orthophosphates more efficiently in concentration of 2.2970 μg/mL with 90.208 % efficiency, compared to DGT-CSBent in concentration of 1.7333 μg/mL with 79.874 % efficiency. It was also known that the presence of STPP influenced the amount of orthophosphate concentration bound by Fe-CSBent in the binding gel. DGT-Fe-CSBent device that was made to be selective in predicting bioavailable phosphate, but the presence of other phosphate species such as sodium tripolyphosphate may be influenced orthophosphate bound by DGT.