Comparison of Phenate and Salicylate Methods for Determination of Total Ammonia Nitrogen in Freshwater and Saline Water

A study was conducted to compare the precision and accuracy of the phenate method and the salicylate method for determining total ammonia nitrogen concentration in water over a wide range of salinities. The two methods provided results that were highly correlated (P < 0.01) as follows: freshwater, n = 29, r = 0.996; low salinity (>> 4 ppt), n = 17, r = 0.994; high salinity (>> 24 ppt), n = 11, r = 0.981. Considering all samples the regression equation for the two methods was Y = 0.939X + 0.0038 where X = salicylate method (mg/L) and Y = phenate method (mg/L); the r value was 0.984 (P < 0.01), the slope differed from 1.0 (P < 0.05), but the intercept was not different from 0.0 (P > 0.05). In replicate analyses of the same samples, the salicylate method often gave a higher mean concentration of total ammonia nitrogen than was obtained with the phenate method. Also, precision was usually better for the salicylate method. Accuracy, as determined by spike recovery, was slightly superior for the salicylate method. The findings suggest that the salicylate method is a preferable alternative to the phenate methods for use in freshwater and saline water aquaculture applications.