Optimization of a colorimetric method to determine trace urea in seawater

Abstract

AbstractThis 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 L−1, using a five centimeter cuvette) and trace (<100 nmol L−1, 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 L−1) 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).