| With development of the society and economy,water pollution has been increasing.Water environment monitoring and water sample analysis are of great significance for pollution control and environment management.Compared with traditional methods of taking water samples back to laboratory for analysis,the in-situ detection/monitoring methods and instruments collect data more rapidly,directly,accurately and in real time,thus attracting great attention in the field of detection/monitoring methods and instruments of water environment.The existing commercial in-situ automatic analyzers and mature laboratory-made instruments are relatively expensive,as they often employ costly pumps,valves and detectors.In addition,a proper way of in-situ storing and accessing reagents during instrument deployment is also one of the critical issues that must be concerned.Adopting low-cost detectors,as well as avoiding the use of pumps,valves and complicate flow manifolds,could significantly simplify the instruments,reduce the cost,and lower the user threshold,hence to achieve wider application.The objective of this study is to create novel low-cost in-situ analyzers for detection of nutrients in environmental waters.The main contents and results of the study are as follows:(1)A practical reagent capsule was created to properly store and protect reagent from contamination or degradation.A prototype device,which adopted a low-cost colorimetric sensor as detector and had a novel mechanical structure,was built.By applying plastic parts and commercial modules,the cost of device was significantly reduced.An analytical method for dynamic colorimetric sensing was proposed using the device.Taking nitrite as an example,an experiment was carried out in the laboratory to demonstrate the performance of device.The practicability of the reagent capsule was preliminarily verified,and it was also proved that the integrated system of chromogenic reaction,colorimetric sensor and dynamic colorimetric sensing method could be used to determine nutrient concentrations in water samples.The experimental results show that the limit of determination of nitrite was as low as 0.01 mg/L.The device can be applied in on-site detection of a variety of water quality parameters and rapid screening of water pollution.(2)Based on the above results,a compact in-situ sensor for nutrient monitoring was developed.For underwater in-situ applications,a novel "Fish-bite" reservoir(sampling/reaction cell)was proposed,and the idea of reagent capsule and the dynamic colorimetric sensing method were inherited.The "Fish-bite" reservoir is low-cost and reliable,and the collected bubble-free water samples are especially suitable for optical measurement.The cells are not to be reused during each monitoring period,therefore,cross-contamination and rinsing during the analysis can be avoided.The sensor can be loaded with multiple reservoirs to meet the needs of continuous in-situ monitoring.The determination range of the device was 0.01-1.00 mg/L for phosphate and 0.010.20 mg/L for nitrite.The device has been successfully applied in an irrigation canal,and the measurement results of phosphate and nitrite were 0.011 mg/L and 0.038 mg/L,respectively.Compared with the results obtained using laboratory standard methods,the relative deviations was 20.2%and 11.7%,respectively,indicating that the device is practicable for rapid water screening.(3)A new low-cost and multi-parameter analyzer was developed for in-situ rapid measurements of typical nutrients(nitrite,phosphate,silicate,ferrous and ferric)in environmental water bodies.A portable document scanner was employed as the detector.With its wide sensing area,the chromogenic images of five sampling/reaction cells could be recorded for simultaneously determination of multiple target analytes.The assorted self-sampling/reaction cell was enabled by the cooperative application of the dissolvable thread and rubber bands.Without external forces,the cell automatically collected sample immediately after being immersed into water body.Glass wool was selected to hold the chromogenic reagents.The performance of the analyzer was evaluated in the laboratory.The relationships between grayscale values and concentrations of target analytes were established,and the kinetic characteristics and temperature effects on the chromogenic reactions were studied.The experimental results show that the measurement relative standard deviations within group(n=4)and among groups(n=5)were both less than 6%.The determination ranges for nitrite,phosphate,ferrous,ferric and silicate were 0.20-15.0,1.00-15.0,1.00-20.0,1.00-15.0 and 25.0-125 ?mol/L,respectively.In addition,the analyzer was successfully applied in waters of different environment,including a creek,a river dock,a reservoir and a wastewater treatment facility,and the nutrient concentrations obtained with the analyzer had good comparability with those obtained with laboratory standard methods.The analyzer is proved capable for rapid in-situ screening of nutrients in most water bodies.In conclusion,this research has made effective exploration on developing and applying in-situ water analyzers innovated in pump-and-valve free and low-cost.The developed in-situ analyzers and reagent preservation method are of good practicability.Based on the established methods,application scope of the developed analyzers can be broadened by adopting suitable chromogenic reagents. |
PDF Full Text Request