Development and Application of the Diffusive Gradients in Thin Films Technique for the Measurement of Nitrate in Soils

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• 作者：Chao Cai ; Paul N. WilliamsHong Li ; William Davison ; Tian-Jiao Wei ; Jun Luo ; Yong-Guan Zhu ; Hao Zhang
• 刊名：Analytical Chemistry
• 出版年：2017
• 出版时间：January 17, 2017
• 年：2017
• 卷：89
• 期：2
• 页码：1178-1184
• 全文大小：347K
• ISSN：1520-6882

文摘

Nitrate (NO₃–N), the main plant/microbial nitrogen source, has a fast turnover in soil driven by species transformation (nitrification/denitrification) and phyto/microbiota assimilation. The technique of diffusive gradients in thin films (DGT) is capable of a robust, low disturbance measurement of NO₃–N but has not been implemented due to the absence of a binding layer suitable for deployment in soils. In this study, a new styrene divinylbenzene-based absorbent with amine functional groups (SIR-100-HP) was cast into an agarose gel support. The NO₃–N ion selectivity of the SIR-100-HP/agarose binding layer was retained in the presence of high multivalent ion concentrations and was used successfully to acquire in situ NO₃–N measurements in bulk soil. The kinetics of binding and the maximum binding capacity were determined. The total capacity of the DGT containing the SIR-100-HP/agarose binding phase was 667 μg of NO₃–N. The performance of DGT was not affected by varying pH (3–8) or ionic strength (0–0.018 mol L^–1), while anion competition effects at concentrations reflecting those in common agricultural soils were found to be negligible. Complete elution (100% efficiency) of NO₃–N from the binding phase was achieved using a solution of 5% NaCl. This technique was validated in three contrasting soils. C_DGT measurements were in excellent agreement with pore water NO₃–N values. Two-dimensional NO₃–N mapping of a profile of flooded rice paddy soil demonstrated the potential of this novel methodology for improved characterization of in situ N speciation for further understanding of bioavailability and biogeochemical processes of NO₃–N in soils.