Investigations on online monitoring of ammonia nitrogen based on distillation-potentiometric titration

Abstract

Water sample pretreatment system and titration detection system were intensely studied based on National environmental protection standards HJ 537-2009 'Water quality-Determination of ammonia nitrogen-Distillation-neutralization titration'. These studies pointed out several problems and difficulties, such as an accurate sampling of water, automatically regulate pH, the low efficiency of distillation, short stabilization time of mixing indicator, and the challenge in determining titration endpoints. Some technical solutions exist, and a new on-line monitor of ammonia nitrogen base on distillation-potentiometric titration was designed to measure metering performance indexes, method detection limit (MDL), and limit of quantitation (LOQ). The results showed a maximum absolute error of 0.0398 mg/L on low concentration sample analysis (≤2 mg/L), the relative error reached 1.4% on high concentration sample analysis (>2 mg/L). The method detection limit and limit of quantitation were 0.025 mg/L and 0.17 mg/L, respectively, which could satisfy both A class and B class instruments of metering performance requirements in verification regulation of ammonia nitrogen automatic monitor.