A modified method for on-line determination of trace ammonium in seawater with a long-path liquid waveguide capillary cell and spectrophotometric detection
A modified method for on-line determination of trace ammonium in seawater with a long-path liquid waveguide capillary cell and spectrophotometric detection
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DOI：
10.1016/j.marchem.2014.03.011
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发表时间：
2014-05
期刊：
影响因子：
3
通讯作者：
Yong Zhu;D. Yuan;Y. Huang;Jian Ma;Sichao Feng;Kunning Lin
中科院分区：
文献类型：
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作者：
Yong Zhu;D. Yuan;Y. Huang;Jian Ma;Sichao Feng;Kunning Lin
采用流动注射技术和2.5 μ m液体波导毛细管池，建立了海水中痕量铵的在线自动比色测定方法。以低铵海水为载体，将样品注入载体中，与试剂混合形成靛酚蓝染料，在690 nm波长处进行监测。研究了不同的试剂进样策略，以获得更低的试剂空白和更高的检测灵敏度。采用单因素实验设计优化了实验参数，并对海水的基质效应进行了初步研究。该方法灵敏度高，检出限为3.6 nmol·L-1。线性范围为10 ~ 500 nmol·L-1，通过选择较低灵敏度的检测波长或较低的反应温度，检测上限可扩展至30 μmol·L-1。对50 nmol·L-1氨氮的老化海水样品进行了回收率测定，回收率在95.0%~ 104.3%之间，相对标准偏差为4.4%（n = 7）。样品通量为22 h− 1。用所提出的方法得到的分析结果与使用参考荧光法显示出良好的一致性。与靛酚蓝（离线）法相比，该方法具有试剂用量少、操作方便、样品通量高、线性范围宽（10 nmol·L-1 ~ 30 μmol·L-1）、灵敏度高等优点，具有上级优势。将该方法应用于五缘湾表层海水氨氮浓度的现场24 h在线监测。此外，它还被用来分析从中国南海采集的表层海水样品的铵分布的研究。
An automated colorimetric method for the on-line determination of trace ammonium in seawater was established using a flow injection technique coupled with a 2.5-m liquid waveguide capillary cell. Using low ammonium seawater as a carrier, a sample was injected into the carrier and mixed with reagents to form indophenol blue dye, which was monitored at a wavelength of 690 nm. Different strategies of reagent injection were investigated to obtain a lower reagent blank and a higher detection sensitivity. Experimental parameters were optimized using a univariate experimental design, and the matrix effect of seawater was preliminarily investigated. The proposed method had high sensitivity with a detection limit of 3.6 nmol·L− 1. The linearity was 10 to 500 nmol·L− 1and the upper limit could be extended to 30 μmol·L− 1by choosing a less sensitive detection wavelength or lower reaction temperature. The recoveries were between 95.0 and 104.3% and the relative standard deviation was 4.4% (n = 7) for an aged seawater sample spiked with 50 nmol·L− 1ammonium. The sample throughput was 22 h− 1. The analytical results obtained with the proposed method showed good agreement with those using reference fluorescence methods. Compared with the normal indophenol blue (off-line) method, the proposed method was superior due to its lower reagent consumption, greater convenience, higher sample throughput, wider linear range (10 nmol·L− 1to 30 μmol·L− 1), as well as higher sensitivity. The method was applied in-field in Wuyuan Bay for 24 h on-line monitoring of ammonium concentrations in the surface seawater. In addition, it was also used to analyze surface seawater samples collected from the South China Sea for the study of ammonium distribution.