| This project aimed to improve the digestion technology of the in-situ nutrient analyzer.The combined digestion laboratory method of total nitrogen(TN)and total phosphorus(TP)was successfully applied to an in-situ online monitoring instrument for the first time to achieve simultaneous digestion and sequential detection of TN and TP in water samples,which greatly improved the efficiency of in-situ detection.The project adopted orthogonal design methods to perform manual digestion experiments and determined the parameters of combined digestion according to existing in-situ detection methods.The experimental results showe that the optimal conditions for the combined digestion are that the ratio of the water sample and the digestion solution is10 m L: 5 m L;the ratio of the potassium persulfate and sodium hydroxide in the digestion solution is 5.00%: 1.25%;the digestion temperature is 120 ° C;the digestion time is 30 min.The test was performed on an in-situ detection instrument according to the experimentally verified combined digestion conditions.Among them,0.50 mg / L potassium nitrate and potassium dihydrogen phosphate solutions were used to prepare a TN / TP standard solution;0.50 mg / L glycine and sodium fosfomycin were used to prepare a TN / TP mixed water samples,and combined digestion test was performed by online instrument.In the test results,the digestion rate of TN was 94.19%,and the digestion rate of TP was 93.65%.It was verified that the combined digestion method can better achieve the in-situ nutrient analyzer to detect TN and TP in water.Through the combined digestion technology,the detection time of TN and TP is only 65 min,and the detection time of TN / TP alone digestion is 120 min,which shortens the detection time by nearly half.Therefore,the method established in this project can significantly improve the detection efficiency of the instrument,reduce the energy consumption of the in-situ detection instrument,and help improve the overall performance of the instrument,thereby extend its service life.Finally,in order to verify the reliability of the combined digestion,the combined digestion experiments on the accuracy and precision of actual seawater samples were carried out to further test the adaptability of the combined digestion technology.The project collected and tested water samples from two different sea areas in Dapeng New District,Shenzhen,and conducted standard recovery experiments at the same time.The experimental results showed that the relative standard deviations of the measured values of TN and TP concentrations were all lower than 5%,and the recoveries of the spiked standards were between 90% and 110%.The precision and accuracy are in accordance with the relevant national quality control requirements of water quality monitoring instruments for detecting water quality parameters.According to this,the in-situ nutrient combined digestion technology researched and improved by the project has certain feasibility and practicability. |
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