High-Precision Determination Of Metal Elements By Using Miniaturized Liquid Cathode Glow Discharge-atomic Emission Spectrometry

With the development of modern industry and agriculture,the problem of metal pollution has become prominent increasingly.Therefore,real time,on-line,and rapid detection of metal elements is very important.Traditional analytical techniques are the effective methods for detecting these metal elements.However,because of the large size,high cost,high energy consumption,and high operating environment requirements,they cannot be used for continuous on-line monitoring analysis.In recent years,electrolyte cathode atmospheric glow discharge（ELCAD）has received great interest due to its more compact and portable instrument,lower power consumption（75 W）,no inert gas requirement and operation in atmospheric pressure.It is considered as one of the most promising alternative miniaturized excitation that employed for an important tool in atomic spectrum analysis.In this thesis,based on the principle of ELCAD,a new miniaturized liquid cathode glow discharge-atomic emission spectroscopy（LCGD-AES）technique was established by improving the sample introduction system and excitation source system and applied for the determination of some metal elements.The specific research contents are as follows:1.A novel liquid cathode glow discharge（LCGD）was designed as a microplasma excitation source for atomic emission spectrometry（AES）and used for the determination of Pb,Cu,and Cd in digested ore samples.The operating parameters and stability of LCGD-AES were investigated in detail.The statistical analysis（t-test）was used for comparing the results of ore samples using LCGD-AES and inductively coupled plasma atomic emission spectrometry（ICP-AES）.The results showed that the optimized analytical conditions are 650 V discharge voltage,4.5 mL min^-1 solution flow rate,and pH=1.0 HNO₃ as the supporting electrolyte.The limits of detection for Pb,Cu and Cd were 0.019,0.47 and 0.37 mg L^-1,respectively.The correlation coefficients（R²）and relative standard deviations（RSD）were 0.9985 and 1.19%for Pb,0.9868 and2.37%for Cu,and 0.9960 and 3.98%for Cd.The power consumption was below 65 W.The recoveries were in the range from 79.1¹15.1%.Moreover,the measurement results of ore samples by LCGD-AES are comparable to the values obtained by ICP-AES.Therefore,the LCGD-AES may be developed as a portable analytical instrument for the direct determination of trace heavy metals.2.In order to increase the stability of the instrument and reduce the sample solution,the sample introduction system was modified based on the original LCGD device.The parameters,surfactants and organic compounds affecting the modified LCGD were investigated in detail.The electron temperature and electron density of LCGD were calculated at different discharge voltages.In addition,the measured results of real samples using modified LCGD-AES were verified by ICP-AES.The results showed that the optimized analytical conditions are 650 V discharge voltage,2.5 mL min^–1solution flow rate and pH=1.0 HNO₃ as supporting electrolyte.The limits of detections for Cd,Ni,and Fe were 0.17,226,and 203μg L^-1,respectively.The R² and RSD of Cd,Ni and Fe were 0.9883⁰.9963 and 2.5%¹3.9%,respectively.The recoveries of Cd and Ni in soil samples ranged from 97.69⁰6.53%,while the Fe recoveries ranged from32.61⁶5.82%.Moreover,the measurement results of soil samples by modified LCGD-AES are well consistent with the value obtained by ICP-AES.3.In this paper,modified liquid cathode glow discharge-atomic emission spectrometry（LCGD-AES）was employed for the determination of Pb,Zn,Cu,Ni,Co and Mn in digested vegetables and soil samples.The discharge stability and parameters affecting the LCGD-AES were investigated in detail.Moreover,the measurement results of samples using modified LCGD-AES were evaluated by ICP-AES.The results showed the optimized operating parameters are 650 V discharge voltage,pH=1.0HNO₃ as supporting electrolyte and 2.4 mL min^–1 solution flow rate.High concentration of some ions may interfere with the detection of metal elements.Low molecular weight organic compounds have influence on emission intensity.With addition of 4%（V/V）formic acid,the emission intensity of each element can increase significantly.The measurement results of LCGD are basically in aggrement with the comparative values of ICP-AES,and the sample recovery rate is 85.2¹25.4%.The t-test results showed that there was no significant difference between the LCGD-AES and ICP-AES.All results indicate that LCGD-AES can be used as a promising technique for continuous monitoring of metal elements under field conditions with improved in future.