海洋生态系统中，尿素是最主要的小分子溶解态有机氮，主要来源于浮游生物的代谢和吸收，以及有机物的矿化作用，在全球海洋碳、氮的生物地球化学循环过程中扮演重要的角色。本项目研究人员针对海水样品中尿素的显色反应条件进行系统的研究和优化，建立标准化的手动分析方法，克服了以往分析方法重现性差的问题。针对寡营养海区海水痕量尿素样品，结合液芯波导毛细管流通池（光程1 m），有效地提高分析方法的灵敏度（1.2 nM），该检测限远低于目前已有文献报道的最低值，同时，首次获得南中国海高精度的痕量尿素分析剖面，为海洋氮循环的研究提供有力的技术支持。

图、                                                                           2014年6月南海SEATS站温盐（a）和痕量尿素（b）垂直剖面

      Chen L., J. Ma, Y. Huang, M. Dai, X. Li. Optimization of a colorimetric method to determine trace urea in seawater.2015. Limnol. & Oceanogr.-Meth. Accepted.

Abstract: AQ3 This study optimized the experimental conditions for the analysis of dissolved urea in seawater. The kinetics of the colorimetric reaction of urea with diacetyl monoxime were studied under different conditions: reagent stability, pH, and reaction temperature and time, based on which robust procedures were developed for both normal (> 100 nmol L21, using a five centimeter cuvette) and trace (< 100 nmol L21, using a one meter path length capillary cell) levels of dissolved urea. Our trace level method showed very high sensitivity (detection limit of 1.2 nmol L21) and high reproducibility (relative standard deviations were 0.29–1.09%), which was a significant improvement as compared to what was reported previously. The current method afforded a more stable colorimetric product, which provided better reproducibility when a large number of samples were analyzed. The normal-level method was applied to studying the urea distribution in estuarine surface water, and the trace-level method was applied to studying the vertical distribution of urea in the South China Sea basin (> 4000 m).