Development of bromide-selective Diffusive Gradients in Thin-Films for the measurement of average flow rate of streams.

Diffusive Gradients in Thin-Films (DGT) have traditionally been used to measure time-weighted average concentration in water. We tested whether Br--DGT in combination with the trace-dilution flow rate method, could be used as a new approach for measuring water flow rate. A novel bromide selective DGT based on the Purolite Bromide Plus anion exchange resin (Br--DGT) was developed, which provided environmental bromide concentrations comparable to grab samples. The Br--DGT provided quantitative bromide concentrations at a range of pH, competing ion concentrations, and in synthetic natural solution. The uptake efficiency was 95.7 ± 3.4%, and the elution efficiency was 95.5 ± 4.7%. The absorption maximum/saturation point of each binding disk was 0.684 ± 0.001 mg. Bromide adsorption to the binding layer was linear to 44.1% of the total binding capacity, 0.302 mg. The determined diffusion coefficient through the agarose cross-linked polyacrylamide (APA) hydrogels was 1.05 × 10-5 cm2 s-1 at 17.9 °C, temperature corrected to 25 °C was 1.29 × 10-5 cm2 s-1. DGT flow rates were between -14.7 and 6.50% of the flow independently monitored flow rate (weir). In comparison, grab sample flow rates diverged by 5.52 to 58.9% from the weir flow rate.