Miniaturization Of Liquid Cathode Glow Discharge Atomic Emission Spectrometry And Its Application In The Detection Of Elements

The activities of human and the rapid development of industry,agriculture and technology have caused serious environmental pollution,among which metal elements pollution have become a relatively serious problem in today’s society.Since most metal elements exhibit varying degrees of toxicity to human health and ecological safety,in-situ,on-line and accurate analysis of trace metal elements in environmental samples is of great significance.At present,the commonly used methods for detecting metal elements are:atomic absorption spectrometry（AAS）,atomic fluorescence spectrometry（AFS）,inductively coupled plasma-atomic emission spectrometry（ICP-AES）and inductively coupled plasma-mass spectrometry（ICP-MS）,etc.However,these commercial instruments are not suitable for on-site,real-time and on-line analysis due to their large size,harsh operation conditions and high cost.In order to meet the demand of on-site determination,establishing a small,convenient,low-cost and efficient method for rapid determination of metal elements in various samples has attracted widespread attention.In this paper,based on the principle and characteristics of the electrolyte cathode atmospheric pressure glow discharge（ELCAD）,a liquid cathode glow discharge（LCGD）device is constructed,and then coupled with a fiber optic spectrometer and a flow injection sampler to obtain a miniaturized liquid cathod glow discharge-atomic emission spectroscopy（LCGD-AES）system,and used for the detection of metal elements in actual samples.The research contents of this thesis are as follows:1.The discharge principle,research progress and present situation of ELCAD were introduced and several typical ELCAD devices were listed.2.A series of improvements have been made to obtain the sampling system of the liquid cathode glow discharge device.The buffer bottle can eliminate the pulsation of the peristaltic pump and improve the stability of the discharge plasma,the six-way valve can achieve quantitative injection and continuous switching.On the other hand,the flow injection sampler can realize the continuous and rapid sample introduction,meanwhile,reduce the dead volume of the blank solution and the sample solution.The spectral detection system adopts micro optical fiber spectrometer,which can further realize the miniaturization of the instrument.All above reflect the concept of green and environmental protection.3.A simple sample introduction system has been successfully developed,and then integrated with liquid cathode glow discharge（LCGD）to form atomic emission spectrometry（AES）for the detection of rubidium（Rb）,cesium（Cs）and strontium（Sr）in water samples by using a fiber-optic spectrometer,in which a buffer bottle was employed to improve the stability of microplasma,and a six-port valve equipped with sample loop was used to reduce the sample consumption and enhance the analytical precision and speed.The effects of flow rate,discharge voltage,supporting electrolyte and solution p H on signal intensity of Rb,Cs and Sr were examined systemically.The matrix interferences of major cations and anions in aqueous solution were also evaluated.The results indicated that the optimal operating conditions are 2.4 mL min^-1flow rate,660 V discharge voltage and HNO₃（pH,1.0）as supporting electrolyte.Only Al³⁺ions interfere with the determination of Rb,Cs and Sr.The limits of detection（LODs）of Rb,Cs and Sr are 0.18,0.17 and 0.21 mg L^-1,respectively,which are basically inferior to those of the closed-type electrolyte cathode atmospheric discharge（ELCAD）.The relative standard deviations（RSD）is 2.7%for Rb,2.0%for Cs and2.5%for Sr,the correlation coefficients（R²）of Rb,Cs and Sr are over 0.99,and the power is below 50 W.The measured results of Rb,Cs and Sr are in agreement well with the spiked values,and the satisfactory recoveries of standard addition are obtained between 97 and 111%.The advantages of small size,low sample and power consumption and high stability suggested that the LCGD-AES is a promising technology for the detecting Rb,Cs,and Sr in water samples.4.A portable atomic emission spectrometry（AES）instrument was developed using liquid cathode glow discharge（LCGD）as an excitation source and fiber optic spectrometer as a detection system,and then employed for highly sensitive determination of lithium with the addition of surfactants.The effects of flow rate,discharge voltage,supporting electrolyte,solution p H and chemical modifier types on signal strength and discharge stability were systematically investigated.It was found that under the optimum conditions of 1.4 mL min^-1flow rate,640 V discharge voltage and HNO₃（pH,1.0）as supporting electrolyte,the addition of CTAB,CTAC and Triton X-405 enhances the lithium signal intensity about 3.7-,3.2-and 1.8-fold,respectively.The presence of Al³⁺and SO₄^2-interferes with the detection of lithium,but the interferences can be eliminated after adding CTAB,CTAC and Triton X-405.The sensitivity of lithium is improved with adding the surfactants by factors of 2.8 for0.15%CTAB,2.0 for 0.15%CTAC and 1.9 for 3 CMC Triton X-405,and the LOD with CTAB for lithium is reached to 0.47μg L^-1which improved about 6.5-time.Meanwhile,the energy consumption was below 60 W,and good precisions are obtained.The accuracy,reliability and repeatability of the methodology are verified by determination of real water samples,and the satisfactory recoveries of spiked solution are obtained between 90%and 115%.The results indicated the portable LCGD-AES with adding surfactants can be used for highly sensitive and field analysis of trace lithium in various types of complex samples due to its low cost,small size and low power consumption.5.Based on previous researchse,a simple and portable liquid cathode glow discharge-atomic emission spectrometry（LCGD-AES）system was constructed by combining a flow injection sampler（FI）with a miniaturized,low-power（<50 W）LCGD excitation source and a fiber-optic spectrometer,and then used for the detection of metal elements such as Zn,Fe,Pb,Mn,Mg,Cu and Ca in many samples.According to the signal intensity of metal elements,the parameters of the FI-LCGD-AES system were comprehensively evaluated.The optimal operating conditions are 2.2 mL min^-1flow rate,650 V discharge voltage,HNO₃（pH,1.0）as supporting electrolyte and 2.0mm discharge gap.Under these conditions,the stability test shows that the FI-LCGD-AES system has high stability and good reproducibility.In addition,the influence of coexisting ions was studied.Except for the high concentration(200 mg L^-1)of Al³⁺,Fe³⁺and Cl^-,most of the coexisting ions have no obvious interference,and the recoveries are in the range of 88-109%.The accuracy and reliability of the FI-LCGD-AES system is proved through the analysis of the certified reference materials and actual samples.It indicated that the system can efficiently and quickly detect metal elements such as Zn,Fe,Pb,Mn,Mg,Cu and Ca in a variety of samples.