An optimized and simplified method for analysing urea and ammonia in freshwater aquaculture systems

Aquaculture Research, Wiley, ISSN 1365-2109

Volume 46, 7, 2015

DOI:10.1111/are.12314, Dimensions: pub.1041195337,



  1. (1) Technical University of Denmark, grid.5170.3, DTU






This study presents a simple urease method for analysis of ammonia and urea in freshwater aquaculture systems. Urea is hydrolysed into ammonia using urease followed by analysis of released ammonia using the salicylate-hypochlorite method. The hydrolysis of urea is performed at room temperature and without addition of a buffer. A number of tests were performed on water samples obtained from a commercial rainbow trout farm to determine the optimal urease concentration and time for complete hydrolysis. One mL of water sample was spiked with 1.3 mL urea at three different concentrations: 50 μg L−1, 100 μg L−1 and 200 μg L−1 urea-N. In addition, five concentrations of urease were tested, ranging from 0.1 U mL−1 to 4 U mL−1. Samples were hydrolysed for various time periods ranging from 5 to 120 min. A urease concentration of 0.4 UmL−1 and a hydrolysis period of 120 min gave the best results, with 99.6–101% recovery of urea-N in samples spiked with 100 or 200 μg L−1 urea-N. The level of accurate quantification of ammonia using the method is 50 μg L−1 NH4+-N, and the detection level is 5–10 μg L−1 NH4+-N.

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