| Total phosphorus(TP)is a term to describe all forms of phosphorus in water,and serves as a significant water quality index.It is very important to rapidly and accurately determine TP in water bodies and water samples.However,there are many factors affecting the determination of TP,and the recognized effective methods of on-line and off-line analysis still have great limitations.The traditional off-line analytical methods are cumbersome,non-automated,and having large errors.On the other hand,the existing commercial instruments for on-line determination of TP suffer shortages of bulky size,low sample throughput,short-term reagent supplement,easily aged and damaged connector,and cannot meet the demand of long-term application in-field.To overcome the above shortcomings,new off-line or on-line analytical methods and automatic analytical instruments for determination of TP in water and water samples have been developed in this study.These methods are of simple operation,high sensitivity,good reliability,fully automated,and can provide new methods for laboratory off-line determination and on-line real-time monitoring of TP.The main contents and results are as follows:(1)The core components of flow analysis,including pump,valve,light source,and detection unit,were modularized and packaged in software and hardware to form a series of standard equipments.Based on the design method of distributed control systems and modular instruments,a general hardware framework employing the standard equipment components,CAN bus and a bus topology,was established.An integrated universal platform comprising the general hardware framework and a selfdesigned general upper computer software with self-adaptive capabilities was developed for general methods of flow analysis-photometric determination.On the basis of the integrated universal platform,an on-line and rapid analyzer was developed for real-time determination of TP that represented phosphonates in industrial circulating cooling water system(CCWS).Measurement of TP was based on colorimetric method with vanadomolybdophosphoric(VMP)acid,after being converted to orthophosphate with ultraviolet(UV)photooxidation digestion.The detection linear range was 4.3-1940 μmol L-1,while the limit of detection(LOD)was 1.3 μmol L-1.The analyzer had a high sample throughput of 20 samples per hour.The recoveries of several real samples at different concentrations were ranged from 91.5%to 104%.Owing to fully automation and long-term reagent supplement,the proposed method and analyzer had been successfully applied in a CCWS.(2)Based on the results described in(1),a low-power ring-shaped UV on-line digester operating at normal temperature/pressure and a dual-spectrophotometer detector were manufactured.Combined with flow batch analysis technique,an antichloride interference and high sensitivity on-line analyzer for analysis of TP in CCWS water was developed,which could monitor water treatment reagent with phosphorus at normal concentration and low concentration,or even with phosphorus-free formulations.The method had a wide linear range(0.360-160 μmol L-1)and a low LOD(0.11 μmol L-1),which could eliminate the negative effects of chloride ion at a concentration of up to 700 mg L-1.The relative standard deviations of the determination results of high(60.0 μmol L-1)and low(4.0 μmol L-1)concentration samples were 0.83%and 3.2%(n=11),respectively,indicating good precision.The analyzer was deployed in a CCWS in a natural gas purification plant.The TP concentration was analyzed every hour over for 12 d.The results obtained with the on-line system well agreed with those of discrete samples collected at the same time and analyzed using a conventional analytical method in the factory laboratory.(3)Aiming at the TP in natural water,especially seawater,a two-step digestion method was proposed.The two-step on-line digestion device was composed of a homemade high temperature/pressure on-line digester and a ring-shaped UV on-line digester.A digestion efficiency model of phosphorus compounds was established to obtain the optimal digestion conditions.The digestion efficiencies of 17 phosphorus compounds were higher than 85%(86.2%-99.3%)in both fresh water and seawater matrices.A flow analysis design was hyphenated with hydrophilic-lipophilic balance(HLB)solid phase extraction(SPE)technique,thus a two-step digestion-HLB SPE-spectrophotometric method,which is suitable for determination of TP in natural waters,was established.In addition,based on the integrated universal platform mentioned in(1),a two-step digestion TP analyzer was developed.The proposed method was free of salinity effect,and had good precision and accuracy.The LOD and linear range could be adjusted according to the requirements of analysis of different natural waters.The analytical results of the proposed method obtained with the underway measurement in-field and measurement in laboratory well agreed with those using a reference method by a third party.(4)In accordance with the laboratory operation process of the standard analytical methods of TP in fresh water and seawater,mechanized devices with functions of sample bottle grabbing,capping,reagent injection,shaking,and sample injection were built.A high temperature/pressure digestion device,a sample cooling device,and a dual-spectrophotometer detector were made.Based on above devices,an automatic laboratory analyzer for determination of TP in water samples was structured to realize the mechanization and automation of the entire analysis processes of two national standard methods.The operation procedures of the national standards include digestion,dechlorination,color development,determination and report output,etc.The performance of the "fresh water analysis method" and "seawater analysis method" of the analyzer were superior to the corresponding standard methods.The linear ranges were 0.080-20.0 μmol L-1 and 0.040-8.00 μmol L-1,respectively,and the LODs were 0.02 μmol L-1 and 0.01 μmol L-1,respectively.The digestion efficiencies of 17 phosphorus compounds in different matrices(fresh water and seawater)were all higher than 85%(85.7%-99.9%).There was no significant difference between the measured values and the certified values of various TP reference materials.The analyzer was successfully applied to the determination of TP in fresh water and seawater samples. |
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