Research On Submersible Automatic Monitor Device For Total Phosphorus In Water

Phosphorus is the essential element for plankton and aquatic plant growth, but also isnutrient element which limit the growth of phytoplankton.Excessive amounts ofphosphorus in the water lead to the large overgrowth of phytoplankton, which change thewater ecology and even cause the generation of blooms or red tide.Therefore, real-timemonitoring of total phosphorus is very important.The traditional method for thedetermination of total phosphorus is tedious and time-consuming, while most automaticanalyzer for that has major flaw that there will be a large number of reagent consumptionand cross contamination because of its principle (the flow injection analysis). To this end,in this paper, we developed a total phosphorus measuring device which is portable and canwork under water, based on the sequential injection analysis principle.The first step of the research on submersible automatic total phosphorus measuringdevice is the optimization for the orthophosphate chromogenic reaction using thesequential injection analysis. The optimal reaction condition is:26g/L ammoniummolybdate,0.7g/L antimony potassium tartrate,50g/L ascorbic acid,(1+6) volume ratioof added60mL sulfuric acid,50μL/s detection velocity,30s stopping time in storage tubezone. The optimal chromogenic order is Ascorbic acid-Sample–Molybdate. The optimalchromogenic volume is:100μL Molybdate salt solution,100μL ascorbic acid solution,60μL sample solution,100μL carrier liquid injection. The determination of phosphate afterdigestion in the optimal chromogenic condition show that orthophosphate concentration isin the range of0~5mg/L and the absorbance is linear. The correlation coefficient is0.9992，the precision is2.32%, the limit of detection is0.0010mg/L.The second step of the research is about digestion reaction condition.The optimumdigestion conditions was determined: The optimal digestion temperature was80℃; Theoptimal digestion time is180s, the optimal sample and digesting agent volume was300μL;The optimum concentration of digestion agent (potassium persulfate solution) was6g/L.The representative organic phosphorus solution were digest and all the results showed themore than84%digestion efficiency.Using optimized chromogenic and digestionconditions by sequential injection analysis, the total phosphorus in water was measured,the experimental results show that, the linear range is still a good linear in0~5mg/L. Thecorrelation coefficient is0.999， the precision is2.63%, the limit of detection is0.0041mg/L. In the experiment, we also using sequential injection analysis measured total phosphorus where sampled from the network water and park lake water, and we calculatedthe recovery rate is between96%~102%.After determined the chromogenic and digestion reaction optimization conditions, wedesign a set of total phosphorus automatic measuring device which can dive to water. Thispaper introduces in detail the structure of the device, the main hardware and the flowdiagram of device. This method makes a certain basis for the development of submersibletotal phosphorus automatic measuring device.