Detection Of Trace Heavy Metal Pollutants Using Atmospheric Pressure Discharge In Air

Heavy metal pollution is becoming more and more serious,which has had a serious impact on human health and ecological balance.Therefore,how to quickly and effectively detect heavy metals online and strictly control the content of heavy metals in the environment and food is of great significance to human health and sustainable development of the environment.Because of low cost and no requirement for vacuum system,atmospheric pressure discharge is gradually becoming an ideal method for detecting trace heavy metal pollutants.In this paper,atmospheric pressure DC and AC discharges in air are used to on-line detect trace heavy metals in solid samples.The electrical characteristics of atmospheric discharge plasma,such as discharge images,the waveforms of voltage and discharge current,optical emission spectrum and the mechanism of detecting trace heavy metals in solid samples are studied.The effects of applied voltage and discharge gap on emission intensity of Cu I and plasma gas temperature in atmospheric pressure AC discharge in air are discussed to acquire the optimal experimental conditions,and the limits of detections of heavy metals Cu and Cd are calculated under the optimum experimental conditions.The main results are as follows:1.The discharge images,the waveforms of voltage and discharge current of atmospheric DC discharge in air are studied,and the mechanism of detecting heavy metal elements is discussed.At the same time,the rotational temperature and vibrational temperature are obtained by fitting the band of N₂?C³?_u?B³?_g,?35??=-2?with Specair software.When the applied voltage is 1.0 kV and discharge gap is 3.5 mm,the rotational temperature and vibrational temperatures of N₂?C³?_u?B³?_g,?35??=-2?are 2355 K and 4750 K,respectively.And the plasma gas temperature is 2355 K.The emission intensity of Cu I increases with the increase of concentration under this condition,but the correlation coefficient R² of the analytical curve is small.2.The discharge images,waveforms of voltage and discharge current of atmospheric pressure AC discharge in air under different applied voltages are studied,it is found that when the applied voltage is less than 3.8 kV and the discharge gap is less than 5.0 mm,the discharge is in glow mode and has remarkable stability.However,when the applied voltage is greater than 3.8 kV and the discharge gap is greater than 5.0 mm,the discharge is an unstable arc discharge.And the effects of applied voltage on transport charge during discharge and discharge power are discussed.The result shows that the emission spectrum intensity of Cu I reaches its maximum when applied voltage and discharge gap are 3.8 kV and 3.5 mm respectively.3.The optimal experimental conditions for the detection of trace heavy metals in solids by atmospheric pressure AC discharge in air are:3.8 kV applied voltage,3.5 mm discharge gap and 10 kHz driving frequency.Under the optimal experimental conditions,the limits of detections of Cu I and Cd I calculated are 0.0241 ug/g and 0.0318 ug/g,respectively.Compared with atmospheric pressure DC discharge,atmospheric pressure AC discharge for detection of heavy metals has a better correlation coefficient of analytical curve in air,which is more suitable for analysis of trace heavy metal pollutants.Moreover,the limits of detections of Cu I and Cd I by atmospheric pressure AC discharge is less than or equivalent to other heavy metal analysis techniques.