title: Determining time-weighted average concentrations of nitrate and ammonium in freshwaters using DGT with ion exchange membrane-based binding layers.
abstract: Commercially-available AMI-7001 anion exchange and CMI-7000 cation exchange membranes were utilised as binding layers for DGT measurements of NO3-N and NH4-N in freshwaters. These ion exchange membranes are easier to prepare and handle than DGT binding layers consisting of hydrogels cast with ion exchange resins. The membranes showed good uptake and elution efficiencies for both NO3-N and NH4-N. The membrane-based DGTs are suitable for pH 3.5-8.5 and ionic strength ranges (0.0001-0.014 and 0.0003-0.012 mol L-1as NaCl for the AMI-7001 and CMI-7000 membrane, respectively) typical of most natural freshwaters. The binding membranes had high intrinsic binding capacities for NO3-N and NH4-N of 911 ± 88 μg and 3512 ± 51 μg, respectively. Interferences from the major competing ions for membrane-based DGTs are similar to DGTs employing resin-based binding layers but with slightly different selectivity. This different selectivity means that the two DGT types can be used in different types of freshwaters. The laboratory and field experiments demonstrated that AMI-DGT and CMI-DGT can be an alternative to A520E-DGT and PrCH-DGT for measuring NO3-N and NH4-N, respectively, as (i) membrane-based DGT have a consistent composition, (ii) avoid the use of toxic chemicals, (iii) provided highly representative results (CDGT: CSOLNbetween 0.81 and 1.3), and (iv) agreed with resin-based DGTs to within 85-120%.
authors.affiliation: Environmental Futures Research Institute, School of Environment, Griffith University, Gold Coast Campus, QLD 4215, Australia. d.welsh@griffith.edu.au.
authors.forename: Jianyin
authors.initials: J
authors.lastname: Huang
authors.affiliation: Environmental Futures Research Institute, School of Environment, Griffith University, Gold Coast Campus, QLD 4215, Australia. d.welsh@griffith.edu.au.
authors.forename: William W
authors.initials: WW
authors.lastname: Bennett
authors.affiliation: Environmental Futures Research Institute, School of Environment, Griffith University, Gold Coast Campus, QLD 4215, Australia. d.welsh@griffith.edu.au.
authors.forename: David T
authors.initials: DT
authors.lastname: Welsh
authors.affiliation: Environmental Futures Research Institute, School of Environment, Griffith University, Gold Coast Campus, QLD 4215, Australia. d.welsh@griffith.edu.au.
authors.forename: Peter R
authors.initials: PR
authors.lastname: Teasdale
mesh_terms: D064751:Ammonium Compounds / Q000032:analysis*; D004784:Environmental Monitoring / Q000379:methods*; D005618:Fresh Water / Q000737:chemistry*; D007474:Ion Exchange; D007475:Ion Exchange Resins; D009566:Nitrates / Q000032:analysis*; D009589:Nitrogen Oxides; D009994:Osmolar Concentration; D011793:Queensland
chemical_list: D064751:Ammonium Compounds; D007475:Ion Exchange Resins; D009566:Nitrates; D009589:Nitrogen Oxides