Liquid Cathode Glow Discharge Atomic Emission Spectroscopy Is Highly Sensitive To Detect Metal Elements In Solution

The real-time,on-line,highly sensitive and rapid detection of metal elements is a very important research topic in many fields.Traditional analytical methods such as atomic absorption spectroscopy(AAS).inductively coupled plasma emission spectrometry(ICP-AES).and inductively coupled plasma mass spectrometry(ICP/MS)are the most effective methods for detecting these metal elements.However,because of the large size,high cost,complicated operation,high energy consumption,and large gas consumption of the instrumentation equipment used in these methods,these instrumentation can only be used in the laboratory,and therefore cannot be used for continuous on-line detection.In recent years,the electrolyte cathode glow discharge atomic emission spectrometry(ELCAD-AES)technology has provided new ideas for the development of low-cost,on-line metal detectors.Compared with other techniques,ELCAD-AES eliminates the need for flammable or expensive gases,without vacuum environment and atomizer sample parts,and power is less than 100 W.It also has the advantages of a portable device,simple operation,and low cost.However,the originally designed ELCAD device was bulky,excessive sample consumption,poor stability of plasma,high detection limit.In order to solve these problems,in the past 20 years,researchers have made a lot of improvements for ELCAD.The most representative ones are the solution cathode glow discharge technology,dc atmospheric pressure glow discharge technology,liquid injection-atmospheric pressure glow discharge technology,ac electrolyte atmospheric pressure discharge technology,etc.In this thesis,based on the characteristics of the ELCAD,a new liquid cathode glow discharge-atomic emission spectrometry(LCGD-AES)was developed.It was used for the determination of some metal elements.The concrete research content is as follows:(1)A novel liquid cathode glow discharge(LCGD)was developed as a micro-plasma excitation source of the atomic emission spectrometry(AES)for the simultaneous detection of trace Cu,Co and Ni in aqueous solution.In order to evaluate the analytical performance,operating parameters,such as discharge voltage,supporting electrolyte,solution pH and solution flow rate were thoroughly investigated.The results showed that the optimum conditions are 640 V applied voltage,pH = 1 HNO3 as supporting electrolyte and 4.5 mL min-1 flow rate.The R2 of Cu,Co and Ni are 0.9977.0.9991 and 0.9977.respectively.The RSD(n=10)are 1.4%for Cu,3.2%for Co and 0.8%for Ni.Under this condition,the power of LCGD is below 55 W and the discharge is quite stable.The limits of detections(LODs)of Cu.Co and Ni are 0,380,0.080 and 0.740 mg L-1,respectively,which are in good agreement with the closed-type ELCAD-AES.The LCGD-AES technique offers the advantages of small size,low power consumption,reduced/no inert gas requirement and low cost in set-up compared to ICP-AES and may be developed as a portable detector for in site and real-time monitoring of metal elements in solution samples.(2)A novel flowing liquid cathode glow discharge(LCGD)was developed as an excitation source of the atomic emission spectrometry(AES)for the determination of Ca and Zn in digested calcium and zinc gluconates oral solution and blood samples.The electron temperature and electron density of LCGD were calculated at different discharge voltages.The discharge stability and parameters affecting the LCGD were investigated in detail.In addition,the measured results of real samples using LCGD-AES were verified by ICP-AES.The results showed that the optimized analytical conditions are pH = 1 HNO3 as supporting electrolyte,4.5 mL min-1 solution flow rate.The power consumption of LCGD is 43.5-66.0 W.The R2 and the RSD ranged from 620 to 680 V are 0.9942-0.9995 and 0.49%-2.43%,respectively.The limits of detections(LODs)for Zn and Ca are 0.014-0.033 and 0.011-0.097 mg L-1,respectively,which are in good agreement with the closed-type electrolyte cathode atmospheric glow discharge(ELCAD).The obtained results of Ca and Zn in real samples by LCGD-AES are basically consistent with the ICP-AES and reference value.The results suggested that LCGD-AES can provide an alternative analytical method for the detection of metal elements in biological and medical samples.(3)A novel liquid cathode glow discharge(LCGD)was developed as a low-power and portable excitation source of atomic emission spectrometry(AES)for direct analysis of metal elements in water samples from rivers and lakes.The electron temperature and electron density of LCGD were calculated at different discharge voltages.The discharge stability and parameters affecting the LCGD-AES were investigated in detail.Moreover,the measurement results of samples using LCGD-AES were evaluated by ion chromatography.The results showed the optimized operating parameters are 660 V discharge voltage,pH=1 HNO3 as supporting electrolyte and 4.0 mL min-1 solution flow rate.High concentration of some metals may interfere with the detection of K,Na,Ca,and Mg.Low molecular weight organic compounds do not have a remarkable enhancement on emission intensity.With addition of 0.5%cetyltrimethylammonium chloride,the emission intensity of each element can increase significantly.The power of LCGD is below 52 W.The limits of detection were 0.195 mg L-1 for K,0.017 mg L-1 for Na.0.012 mg L-1 for Ca and 0.013 mg L-1 for Mg.The measurement results of this method are basically in aggrement with the comparative values of ion chromatography,indicating that LCGD-AES can be used as an alternative miniaturized analytical instrument for the direct detection of metal elements in water samples.