Basic Magnesium Carbonate-Based DGT Technique for in situ Measurement of Dissolved Phosphorus in Eutrophic Waters
Abstract A technique of diffusive gradients in thin films (DGT) was developed for the in situ measurement of reactive phosphorus (P) species in natural waters, sediments and potentially soils. Polyacrylamide/basic magnesium carbonate was firstly used as the novel binding phase of DGT. Various factors which would affect the adsorption of phosphate to the DGT, such as initial concentration, deployment time, pH value and ionic strength, were investigated. 10 mL of 0.25 M H 2 SO 4 was used for elution of phosphate from the binding gel, and an elution efficiency of 85% ± 5% was obtained. The DGT measurement was independent of ionic strength (0.001−0.05 M) and pH value (4.10−9.15). The results indicated that the maximum adsorption capacities of DGT were limited to 20.4 μg per disc ( T = 25 °C, pH 7.0, [P] = 2 mg L −1 ). Good agreement was obtained between measurement results of DGT and molybdenum blue method in the P concentration from 0.001 mg L −1 to 20 mg L −1 . The method detection limit (MDL) was 102.4 ng L −1 . Field performance of DGT in synthetic seawater, the coastal seawater of Xiamen, Yihai Lake, Chaohu Lake and Nanfei River indicated that the basic magnesium carbonate-DGT method was more reliable than the commonly used ferrihydrite-DGT method.