Development Of On-line Monitoring System For Heavy Metals In Water With Microwave Plasma Atomic Emission Spectrometer

With the rapid development of economy,a lot of sewage or waste water has been discharged into the environment without treatment.The polluted water has been recycled into the human body and seriously endangers people's health.Heavy metals are highly toxic substances,which can cause serious damage to the body for a long time.The harm caused by water environment to human body is not only huge,but also long-lasting.Because of the outbreak of heavy metal poisoning every year,heavy metals contents are often considered as important indicators to judge the quality of water.Currently,most devices for online detection of heavy metals in water are complex,time-consuming,and can't test multiple elements at the same time.So,a simple,fast,accurate and multi-element detection system is urgently needed for real-time monitoring heavy metals in water.This dissertation developed an on-line monitoring system for heavy metals in water based on microwave plasma emission spectrometer?MP–AES?.The system includes desolvating high sensitivity sample introduction module,concentration standard introduction module,peristaltic pump and filtration module and MP–AES.The function and principle of each module were introduced.The flow path and the standard addition process in the whole system were discussed in detail after assembly of each module.The problem of matrix interference in MP-AES was discussed and provided several solutions.Meanwhile,the standard addition method was selected.The characteristic wavelength of each element was also selected to avoid the interference of the wavelength of other elements as well as the intensity.The reading time of each element was set according to the difficulty degree of element analysis and peak.Because the detection limit didn't meet the surface water environmental quality standard?GB3838-2002?,we further optimized the system to decrease the detection limit.Firstly,we tested the effect of gas?N₂?purity on the detection limit,and 99.95%N₂ was selected as the optimum plasma gas.Then a desolvating high sensitivity sample introduction module was added to decrease the detection limit.The results showed that the desolvating high sensitivity sample introduction module was very effective.The whole system was set up and applied for monitoring the environmental water samples.The detection limits of 19 elements in surface water environment quality standard?GB3838-2002?were determined,the detection limits of 15 elements meet the requirements of national standard and the detection limit of Sb,Se,Be,Tl slightly higher than the national standard limit.Hg has a complex form,low content and couldn't use the system for analysis.The recoveries for each element and long-term stability of the proposed system were carefully evaluated.The results showed that the recoveries and long-term stability of most elements were satisfied.In general,the proposed multi-element on-line monitoring system was feasible,sensitive and accurate,which can be commercially used for daily monitoring the heavy metals in aquatic environment in future.