A modified diffusive gradients in thin films (DGT) technique uses both a mixed binding layer (PrCH and A520E resins for NH4-N and NO3-N, respectively) and multiple binding layers (Metsorb binding layer for PO4-P overlying the mixed binding layer) for the simultaneous measurement of dissolved inorganic nitrogen (nitrate and ammonium) and phosphate in freshwater (INP-DGT). High uptake and elution efficiencies were determined for a mixed (PrCH/A520E) binding gel for dissolved inorganic nitrogen and an agarose-based Metsorb binding layer for PO4-P. Diffusion coefficients (D) obtained from DGT time-series experiments (conductivity 180 μS cm-1) for NH4-N, NO3-N and PO4-P agreed well with those measured using individual DGT techniques in previous studies, but were characterised over a wider range of ionic strengths here. D for NO3-N and PO4-P were constant over a range of ionic strengths (between 100 and 800 μS cm-1) while the diffusion coefficient for NH4-N decreased with increasing ionic strength, as reported previously. The measurement of NH4-N, NO3-N and PO4-P using the INP-DGT was independent of pH (3.5-8.5) and quantitative over varying ionic strength ranges (up to 0.004 mol L-1 NaCl for NH4-N, up to 0.014 mol L-1 NaCl for NO3-N and over 0.1 mol L-1 NaCl for PO4-P) for a 24 h deployment time. Performance of INP-DGT in synthetic freshwaters with differing conductivity indicated the three nutrients were affected differently, with NH4-N measurements being most sensitive. Representative performance was determined for NO3-N (90-330 μS cm-1) and PO4-P (all tested conductivities) over a 72 h deployment period and for NH4-N (<330 μS cm-1) over a 24 h deployment period. Field validations showed that the ratios of INP-DGT concentrations to the average concentrations from grab samples were generally between 0.80 and 1.13 over 24 and 48 h deployment periods. To ensure the representative performance of INP-DGT for all three nutrients, the conductivity should not exceed 400 μS cm-1 and deployment times should be no longer than 24 h. The results of this study have demonstrated that INP-DGT could provide a cost-effective monitoring technique for measuring time-weighted average concentrations of dissolved inorganic nutrients in many freshwaters.

中文翻译：

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一种改进的 DGT 技术，用于同时测量淡水中溶解的无机氮和磷

改进的薄膜扩散梯度 (DGT) 技术使用混合结合层（PrCH 和 A520E 树脂分别用于 NH4-N 和 NO3-N）和多个结合层（用于 PO4-P 的 Metsorb 结合层覆盖在混合结合层上) 用于同时测量淡水中溶解的无机氮（硝酸盐和铵盐）和磷酸盐 (INP-DGT)。对于溶解无机氮的混合 (PrCH/A520E) 结合凝胶和用于 PO4-P 的基于琼脂糖的 Metsorb 结合层，确定了高吸收和洗脱效率。从 DGT 时间序列实验（电导率 180 μS cm-1）中获得的 NH4-N、NO3-N 和 PO4-P 的扩散系数 (D) 与之前研究中使用单个 DGT 技术测量的值非常吻合，但在这里的离子强度范围更广。如前所述，NO3-N 和 PO4-P 的 D 在离子强度范围内（100 到 800 μS cm-1）保持恒定，而 NH4-N 的扩散系数随着离子强度的增加而降低。使用 INP-DGT 对 NH4-N、NO3-N 和 PO4-P 的测量与 pH (3.5-8.5) 和在不同离子强度范围内的定量无关（对于 NH4-N，高达 0.004 mol L-1 NaCl，高达0.014 mol L-1 NaCl 用于 NO3-N 和超过 0.1 mol L-1 NaCl 用于 PO4-P）部署时间为 24 小时。INP-DGT 在具有不同电导率的合成淡水中的性能表明三种营养素受到的影响不同，其中 NH4-N 测量最为敏感。确定了 72 小时部署期间 NO3-N (90-330 μS cm-1) 和 PO4-P（所有测试的电导率）和 NH4-N（< 330 μS cm-1) 在 24 小时部署期间。现场验证表明，在 24 和 48 小时部署期间，INP-DGT 浓度与抓取样品平均浓度的比率通常在 0.80 和 1.13 之间。为确保 INP-DGT 对所有三种营养素的代表性性能，电导率不应超过 400 μS cm-1，部署时间不应超过 24 小时。这项研究的结果表明，INP-DGT 可以提供一种具有成本效益的监测技术，用于测量许多淡水中溶解无机养分的时间加权平均浓度。为确保 INP-DGT 对所有三种营养素的代表性性能，电导率不应超过 400 μS cm-1，部署时间不应超过 24 小时。这项研究的结果表明，INP-DGT 可以提供一种具有成本效益的监测技术，用于测量许多淡水中溶解无机养分的时间加权平均浓度。为确保 INP-DGT 对所有三种营养素的代表性性能，电导率不应超过 400 μS cm-1，部署时间不应超过 24 小时。这项研究的结果表明，INP-DGT 可以提供一种具有成本效益的监测技术，用于测量许多淡水中溶解无机养分的时间加权平均浓度。