A new DGT technique comprised in a hybrid sensor for the simultaneous measurement of ammonium, nitrate, phosphorus and dissolved oxygen

A new diffusive gradients in thin films technique (ZrO-AT DGT) with zirconium oxide, A-62 MP and T-42H resins containing in a single binding gel was developed for simultaneous measurement of nitrate (NO₃-N), ammonium (NH₄-N) and phosphate (PO₄-P). The DGT uptake was found to be independent of pH variation from 3.2–8.7. Ionic strengths below 5, 10 and 750 mmol·L⁻¹ NaCl did not affect DGT uptake of NH₄-N, NO₃-N and PO₄-P, respectively. This new DGT was deployed in natural freshwater environments, with in situ measurements of the three nutrients found to be accurate. It ensured that rinsing the exposed surface of the DGT device at 3-day intervals can prevent biofouling. Additionally, a hybrid sensor comprising the novel DGT binding layer overlying an O₂ planar optrode was tested in sediments to evaluate the dynamics of O₂ and the three nutrients. Results showed that PO₄-P and NO₃-N fluxes decreased while fluxes of NH₄-N increased under aerobic conditions. Nearly simultaneous variation in O₂ and NO₃-N was observed at the sediment-water interface (SWI) and transformation of NO₃-N and PO₄-P was found to be sensitively influenced by O₂ dynamics.