Study On The Sensitivity Of Total Nitrogen Measurement Influenced By The SuspendedParticles

The Yuqiao Reservoir is the main water source for water supply in Tianjin City and high water quality in Yuqiao Reservoir is an important safeguard to the sustainable development of Tianjin City.In the recent years,the concentration of total nitrogen(TN)was always higher than the value of IV class in the Surface Water Environment Quality Standard.The comprehensive nutrition state index TLI showed that this reservoir had become eutrophicated.It was reported that nitrogen was the limiting factor in this reservoir.Thus,it is necessary to analyze TN concentration accurately.There are several approach to determining TN concentration,such as spectrophotometric method with Na2S2O3 + NaOH and flow injectionspectrophotometry method(FISM).With the development of technology,automatic measurement methods were preferred to reduce a lot of labours.However,these automatic methods lost efficacy sometimes because of the disturbances of suspended particles(SS)in the water samples.In the current study,the TN concentration of water samples collected from Yuqiao Reservoir and some sites in the Luan River to Tianjin City Water Diversion Project were measured to analyze effects of SS and algae cell density on the results of different measuring approaches.This study could illustrate the most appropriate methods in different seasons and sites.Our results showed that spectrophotometric method with Na2S2O3 + NaOH was the best method while SS>300 mg/L.FISM could be used when algal cell density was below 8×107cells/L.When algal cell density was higher than 1.6×108cells/L,spectrophotometric method with Na2S2O3 + NaOH must be used.Our results are helpful to improve accuracy of the routine monitoring work for TN.