Determination Of Metal Elements Based On Liquid Anode Glow Discharge

In recent years,the rapid development of industry,agriculture and science and technology has brought huge economic benefits,however,it also caused serious pollution to the environment,especially the pollution caused by metal,which not only destroys the ecosystem,but also poses a threat to human life and health.Therefore,it is very important to establish an in-situ,real time and on-line analysis method.Although traditional commercial analytical techniques,such as atomic absorption spectroscopy,atomic fluorescence spectroscopy,inductively coupled plasma atomic emission spectroscopy/mass spectrometry,can accurately and quickly realize the analysis and detection of metal elements,they are difficult to carry on real-time field analysis due to their disadvantages such as expensive equipment,large volume,high energy consumption and complex operating conditions.Recently,liquid electrode glow discharge micro-plasma excitation sources have attracted widely attention because of portable device,simple operation and low energy consumption.Among them,electrolyte cathode glow discharge（ELCAD）has been extensively studied.However,the detection limits,sensitivity and stability need to be further improved.In this paper,a new liquid anode glow discharge-atomic emission spectroscopy（LAGD-AES）system was established,in which a DC power supply was used as the driver,a conical platinum rod was used as the cathode,and an overflowing solution from the top of the capillary surrounded by platinum wire was used as the anode.By using the characteristics of a resistance to stabilize the discharge current,a buffer bottle to eliminate the pulsation of the peristaltic pump and the switching function of the flow injection sampler,and it was used for the analysis and detection of metal elements.The specific research contents are as follows:1.The LAGD-AES system was used for the determination of Ag and Pb in solution,and the experimental parameters,analytical performance and stability were compared with liquid cathode glow discharge（LCGD）.The results showed that LAGD has the advantages of low solution acidity,high sensitivity and low energy consumption（<10W）.The optimal operating parameters are discharge voltage 490 V（Ag）/580 V（Pb）,pH=1.6 HNO₃ as supporting electrolyte,and solution flow rate 2.8（Ag）/2.0 m L min^-1（Pb）.The detection limits（LODs）of Ag and Pb are 0.0024 and 0.0890 mg L^-1,respectively,which is lower than one order of magnitude of LCGD(Ag:0.0212 mg L^-1;Pb:0.3048 mg L^-1).In addition,the stability and precision are significantly improved.Therefore,the LAGD-AES system can be used as a portable instrument for the highly sensitive detection of trace metal elements.2.The contents of Li,Na,K,Rb and Cs were analyzed in brine and mineral water by LAGD-AES technique.The results showed that the optimal working parameters are630 V discharge voltage,2.0 m L min^-1 flow rate,pH=1.7 HNO₃ as supporting electrolyte and 0.5 mm discharge gap.Some alkaline-earth metal ions(Ca²⁺,Mg²⁺and Sr²⁺)and transition metal Cr³⁺interfere the determination of alkali metals.In addition,In³⁺and Cd²⁺have different degrees of interference with Li,Rb and Cs.The limit of detections（LODs）of Li,Na,K,Rb and Cs are 3.15,7.57,6.21,31.1 and 135μg L^-1.The relative standard deviations（RSD,n=11）are below 5%,and the power consumption is about 12 W.The analysis result for Li certified reference material（GSB07-1378-2001）agrees well with the certified standard value,and the relative error was-2.3%.The results of Na and K in actual samples were basically consistent with those of ICP-AES,and the results of water samples after labeling were basically consistent with those of labeling,and the recovery of labeling was 86-112%.All results demonstrated that the LAGD-AES can be used as an outstanding technique for highly sensitive detection of alkali metals due to its compact and portable instrument,no inert gas requirement,and low energy consumption.3.Cu and Mg elements were successfully detected in solution by using LAGD-AES technique,and the effects of chemical modifiers on the signal strength and the matrix interference were investigated.The results showed that the best experimental conditions are 570 V（Cu）and 540 V（Mg）discharge voltage,pH=1.6 HNO₃ as supporting electrolyte,and 2.6 m L min^-1 solution flow rate.In this case,the LOD of Cu and Mg are 0.0483 and 0.0 053 mg L^-1,respectively.After adding 1%acetic acid and 0.5%methanol,the signal of Cu and Mg can be increased by 1.16 and 1.20 times,respectively.The study of matrix effect found that Mg has strong anti-interference ability for foreign ions.When the concentration of foreign ions（32 kinds）is 20 mg L^-1,only Li⁺,Be²⁺and Cr³⁺can interfere with the determination of Mg.But they can interfere greatly with the determination of Cu.After adding 1%acetic acid and 0.5%methanol,the interference of Cu and Mg can be eliminated/weakened to some extent.Through analysis of Cu and Mg standard samples,it is found that the measured values are basically consistent with the standard values,with the relative errors were 2.5%and1.0%,respectively.Therefore,LAGD-AES system has good stability,high sensitivity and low detection limit,and can be used for the detection of Cu and Mg with high sensitivity.