Study And Application Of Determination Methods Of Nutrients In Aquatic Environment With Flow Analysis And Spectrophotometry

Nutrients play important roles in the biogeochemical cycles of aquatic ecosystems.It is well known that biogeochemical cycle study and environmental pollution management all need scientific data support,therefore,it is very important to accurately and rapidly determine the nutrients in environmental waters.Although methods for the determination of main nutrients and trace nutrient elements have been relatively mature,the automation analysis technique still needs to be continuously improved.In this study,for the purpose of being fast and convenient,of environmental friendly and possible for multi-analyte detection,several methods of nutrients determination based on flow analysis and spectrophotometry have been established to overcome the shortcomings in current analysis methods,and applied to the analysis of practical samples.The main contents and results are as the follows:(1)Simple and rapid analysis methods for determination of several typical nutrients(NO2-,NO3-,PO43-,SiO44-)in environmental water were established by combining continuous flow analysis with spectrophotometry.The methods could effectively avoid the influence of air bubbles on the detection signal by using a 1.2-cm laboratory-made anti-bubble flow cell.The method detection limits(MDLs)of NO2-,NO3-,PO43-,SiO44-were 0.06 ?mol·L-1,0.27 ?mol·L-1,0.08 ?mol·L-1,0.11?mol·L-1,and the liner ranges were 0.2-40 ?mol L-1,5-180 ?mol L-1,0.3-14 ?mol·L-1,0.5-80 ?mol·L-1,respectively.The proposed methods could meet the requirement of environmental water detection.The relative standard deviations and recoveries were satisfied,and results had no significant difference compared with reference methods.The proposed methods had the advantages of simple structure,fast analysis speed and convenient operation,and the laboratory-made anti-bubble flow cell might avoid the interference of the bubble on the detection signal.The proposed methods were successfully applied to a shipboard underway analysis of nutrients in the Jiulong River Estuary and Xiamen coastal area.(2)An automated method for the determination of NH4+ in natural water was established using reverse flow injection analysis(rFIA)based on indophenol blue colorimetric method with less toxicity o-phenylphenol as reagent instead of phenol.The salinity effect on sensitivity was examined and corrected,which made the method be suitable for analysis of NH4+ in fresh water and estuarine and coastal seawater with large changes in salinity.The MDL of the proposed method was 0.07 ?mol·L-1 and 0.08 ?mol·L-1,and the liner range was 0.5-50 ?mol·L-1 and 0.5-35 ?mol·L-1 for fresh water and seawater,respectively.The recoveries varied from 90.0±1.0%to 106.0±2.7%.The analytical results obtained with the proposed method showed good agreement with those using reference methods.The proposed method has been successfully applied in-field in the Jiulong River for a 24 h on-line monitoring of NH4+ concentration in surface water,and also used in the laboratory for analysis of NH4+ in estuarine and coastal water samples.(3)A rFIA method for simultaneous determination of NO2-and NO3-in natural water was established and using vanadium(III)chloride as a reductant instead of the toxic cadmium column for reducing NO3-to NO2-.The MDLs were 0.06 ?mol·L-1 and 0.13 ?mol·L-1,and linear analytical ranges were 0.5-20 ?mol·L-1 and 1-80 ?mol·L-1 for NO2-and NO3-,respectively.The recoveries varied from 100.0±2.5%to 107.5±2.5%for NO2-and 90.7±0.3%to 98.0± 1.0%for NO3-.The analytical results obtained with the proposed method showed good agreement with those using reference methods.The proposed method was successfully applied for the determination of NO2-and NO3-in Jiulong River Estuary and Xiamen coastal water samples.(4)A rFIA method combined with spectrophotometric detection was developed for sequential determination of main nutrients(NO2-,NO3-,PO43-)and trace nutrient elements(Fe(II),Fe(III),Mn(II)).The MDL of NO2-,NO3-,PO43-,Fe(II),Fe(III),Mn(II)were 0.03 ?mol·L-1,0.70 ?mol·L-1,0.30 ?mol·L-1,0.03 ?mol·L-1,0.03?mol·L-1,0.20 ?mol L-1,and linear analytical ranges were 0.2-20 ?mol·L-1,5-200?mol·L-1,1-12 ?mol L-1,0.5-5 ?mol·L-1,0.5-5 ?mol·L-1,0.5-9 ?mol· L-1,respectively.The proposed methods could meet the requirement of environmental water detection.The relative standard deviations and recoveries of proposed method were satisfied,and results had no significant difference compared with reference methods.The proposed method was applied for the determination of multi-nutrient elements in natural water samples.(5)A flow injection method combined with an on-line UV and thermal digestion for simultaneous determination of total dissolved nitrogen(TDN)and total dissolved phosphorus(TOP)in natural waters was established.The method of alkaline persulfate combined with UV light was used for sample digestion.Two flow cells aligned in the same cell support,and reaction products were measured with one spectrophotometer.The MDL were 0.8 ?mol·L-1 and 0.2 ?mol L-1,and linear analytical ranges were 5-300 ?mol·L-1 and 1-25 ?mol·L-11 for TDN and TDP,respectively.The recoveries of spiked natural water samples varied from 86.8±4.8%to 102.6±0.5%for TDN and 88.0±2.0%to 102.0±4.0%for TDP.The analytical results obtained with the proposed method showed good agreement with those using reference methods.The proposed method was successfully applied for the determination of TDN and TDP in natural water samples.