An Automated Determination System Of Nutrients In Seawater Based On Spectrophotometry

Seawater nutrients generally refer to inorganic nitrogen,phosphorus,and silicon in seawater.As the basis of marine primary productivity and food chain,the low-cost,rapid and accurate detection of seawater nutrients is of great significance for the study of geochemistry and marine biology.In this paper,nitrite,phosphate and silicate in seawater nutrient salt were used as detection objects,and an automatic determination system for seawater nutrients based on spectrophotometry and flow batch analysis technology was established.The main research contents are as follows:(1)Design and manufacture of automatic determination system for seawater nutrients.It mainly includes flow path and photoelectric detection part design,data acquisition and drive circuit design,and design for software based on LabVIEW.The high precision injection pump equipped with 2.5 mL glass syringe and six-position distribution valve is selected as the liquid propulsion device in the flow design part.The liquid delivery pipeline is composed of PTFE pipes.The"Z"type flow cell with optical path of 15 mm is designed by AutoCAD software and made of quartz material.The LED light source and photoelectric detector are connected at both ends of the flow cell for photoelectric detection.In the part of data acquisition and driving circuit,the constant current driving circuit is designed based on the constant current source chip,which drives the LED as the light source.The data acquisition circuit is based on 16-bit analog-to-digital converter and STM32 series control chips.It is responsible for collecting the voltage signals from the photoelectric detector.After processing,the data are sent to the upper computer software by the control chip through serial communication.The upper computer software based on LabVIEW is responsible for the operation,suspension,stopping and input of experimental parameters of the whole automatic measurement system.The command of injection pump is sent and the experimental data is received through serial communication.At the same time,the experimental data is processed and converted into real-time curve display.(2)Quantitative determination of nitrite,phosphate and silicate by seawater nutrient automated determination system.The experimental reagents for three substances were prepared and the experimental conditions were optimized.The standard solutions of nitrite(0-12?mol/L),phosphate(0-8?mol/L)and silicate(0-24?mol/L)were determined by automated measuring system for three consecutive days under the optimal experimental conditions,and the working curves were drawn.The results showed that the linear fitness R~2 of the standard working curves of the three substances was greater than 0.998,and the relative standard deviations(RSD)were less than 5%.The detection limits for nitrite,phosphate and silicate were 0.02,0.08 and 0.13?mol/L respectively.The recoveries of nitrite,phosphate and silicate were 102.7%to 106.0%,92.0%to 108.7%and 93.4%to102.2%respectively.