A Flow-injection System for Monitoring of Total Nitrogen and Control of Eutrophication in an Aquatic Environment

Abstract

A flow-injection system was described for continuous monitoring of total nitrogen in water samples. The present method exploited a series of chemical reactions to transform all nitrogen compounds into nitrite that is then coupled with N-(1-naphthyl) ethylenediammonium dichloride to form a highly colored diazodye and selectively monitored at 540 nm. When 200 μl of standard solution (potassium nitrate) was injected at a sampling frequency of 20/h, the determination range was 0.02-10 mg/l nitrogen. The detection limit and relative standard deviation of the method were 0.02 mg/l nitrogen and 1.2% (n=12), respectively. Utilization of a high-purity distilled water attained a detection limit of 0.002 mg/l and determination range of 0.002-10 mg/l nitrogen. Since the flow-injection system was operated by a high-precision pump in a reproducible manner and any vaporization, loss and matrix effect of samples can be perfectly prevented in the system, the reliability of monitoring results appeared to be far better than that obtained by the standard manual method. The flow-injection system, which is coupled with a sampling system, fulfills the essential functions of continuous monitoring in near-real time. The monitoring system has been designed with emphasis on high sampling rate, long-term stability, low reagent consumption and minimum maintenance, and is therefore suitable for use in water quality management to control eutrophication in an aquatic environment.