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

摘要

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 1.3mL urea at three different concentrations: 50gL(-1), 100gL(-1) and 200gL(-1) urea-N. In addition, five concentrations of urease were tested, ranging from 0.1UmL(-1) to 4UmL(-1). Samples were hydrolysed for various time periods ranging from 5 to 120min. A urease concentration of 0.4UmL(-1) and a hydrolysis period of 120min gave the best results, with 99.6-101% recovery of urea-N in samples spiked with 100 or 200gL(-1) urea-N. The level of accurate quantification of ammonia using the method is 50gL(-1) NH4+-N, and the detection level is 5-10gL(-1) NH4+-N.