Abstract:There are many interference factors in the process of ammonia nitrogen determination,which will affect the accuracy of the results.Nessler's reagent colorimetric method has been adopted to determinate the ammonia nitrogen content in waste water,and the conditions such as water storage time,sample pretreatment method,pH value,reaction temperature,coloration time and so on were analyzed.Test results show thatit's necessary to deal with the waste water on time.After pretreatment by distillation,good accuracy and repeatability of ammonia nitrogen determination can be obtained under the optimum conditions of the pH value is 9-9.5,the reaction temperature is 20 ℃,and the color reaction time is 15 min.