Spectral Characteristics And High-sensitivity Determination Of Metal Elements By Miniaturized Liquid Cathode Glow Discharge

Recently,electrolyte cathode glow discharge-atomic emission spectroscopy（ELCAD-AES）has attracted much attention in the academic field because of the advantages of small portable,low price,low energy consumption and no auxiliary gas.However,the originally designed ELCAD system has some flaws,such as large sample consumption,unstable plasma and low sensitivity.To solve the above problems,many improvements have been implemented,including discharge configuration,electrode materials and injection system.After that,the micro plasma excitation sources such as liquid injection-atmospheric pressure glow discharge（APGD）,solution cathode glow discharge system（SCGD）and atmospheric pressure dielectric barrier discharge（DBD）were proposed.At present,application of these technologies has been extended to industrial wastewater treatment,food safety and biomedical fields.But researchers generally focus on the improvement,practical application of devices,and often ignore the study of plasma characteristic.In thesis,a liquid cathode glow discharge（LCGD）system by using the platinum wire as the discharge anode,and using the liquid level of capillary overflow liquid as the discharge cathode was constructed.The distribution and discharge mode of glow in the plasma region were studied through the glow discharge image and the current-voltage curve,and the plasma parameters were diagnosed under different operating conditions Moreover,the metal elements were determined by LCGD-AES system.The analytical performance of this method was improved by adding organic sensitizer to electrolyte.The thesis is arranged as follow:1.On the basis of the constructed LCGD-AES,the plasma parameters were measured by atomic emission spectroscopy,and the K,Mg,Ag and Tl in aqueous solution were determined.Excitation temperature,rotation temperature,vibration temperature and electron density of plasma under different experimental conditions were calculated.The results showed that adding 5%formic acid can enhance the signal intensity of Ag and Tl about 7.9 and 1.8 times.Meanwhile,adding 5%formic acid can eliminate the interference of K⁺,Tl³⁺and CO₃^2-for Ag,Ag⁺and I^-for Tl.Under optimal experimental conditions,the detection limits（LOD）of K,Mg,Ag and Tl are 0.11,0.010,0.030 and 0.018 mg L^-1.After adding formic acid,the LOD of Ag and Tl is decreased by 10.7 and 2.6 times,and the sensitivity is enhanced by 13 and 1.8 times,respectively.Through the quantitative analysis of the K,Mg and Tl in the reference material,it is found that the measured value is highly consistent with the standard value.Hence,the LCGD-AES system can be used as a portable instrument for the determination of metal elements in aqueous solutions.2.Gallium（Ga）and indium（In）in water samples were determined by LCGD-AES.The results showed that the limits of detection（LOD）for Ga and In are 0.10 and 0.016mg L^-1,respectively.The relative standard deviations（RSD）are 2.9%for Ga and 3.9%for In,and the power is below 55 W.The linear correlation coefficient（R²）is better than0.99 with a range of 1-40 mg L^-1 for Ga and 0.1-30 mg L^-1 for In.To validate the utility and accuracy of the proposed system,two water samples spiked with various concentration of Ga and In are directly determined,and the results are only in good agreement with spiked values of In.After diluted 10 times for water samples,the spiked values of Ga agree well with the measured value,suggesting that the matrix can interfere with the determination of Ga.Therefore,LCGD-AES system can directly determine the In,however,Ga must be diluted,but it is only suitable for samples with high Ga content.3.On the basis of LCGD-AES system,Bi in natural water samples and drugs was successfully determined with formic acid as a matrix modifier.It was found that adding formic acid（3%,V/V）could enhance the emission intensity of Bi over 23-fold,and could effectively eliminate the interferences from Cl^-,Br^-and I^-ions.After adding 3%formic acid,the sensitivity of Bi was improved above 51-fold,limit of detection（LOD）was arrived at 0.092 mg L^-1 which decreased by 9.0-fold,and the energy consumption was as low as 40 W.The relative standard deviation（RSD,n=11）of 2 mg L^-1 Bi was reduced from 7.2%without formic acid to 1.8%with adding formic acid.The measured results of Bi in natural water samples by the proposed method were in agreement well with the spiked values,and the satisfactory recoveries between 106%and 113%were obtained.In order to further explore the applicability of this method,three samples containing Bi drugs were analyzed.Under 95%confidence level,the t test results show that there is no significant difference between the results of this method and the ICP-AES values.All results suggested that determination of Bi by LCGD with formic acid possesses merits of low LOD and power consumption,high sensitivity and stability,and good precision and accuracy.