Rapid Determination Of Metal Elements By Liquid Cathode Glow Discharge-atomic Emission Spectrometry

In the field of inorganic analytical chemistry,plasma is greatly promoted the development of the atomic spectrometry.The miniaturization of analytical systems has become an important direction for analytical chemistry.The common structure of emission spectrometer is consisted of the following four parts:sample introduction,excitation source,spectral system and data collection.The miniaturization of spectral system and data collection has been developed by microfiber spectrometers of AvaSpec 2048 and Ocean Optics USB4000.Therefore,the direction of the small-scale emission spectrometer is changed into sample introduction and excitation source.Since the plasma has high excitation temperature,it can excite lots of atoms or molecules with low cost.So it is promising to develop portable instruments using the plasma as excitation source for atomic emission spectrometry?AES?.In this paper,we established two different sampling types?static and flowing?of liquid cathode glow discharge-atomic emission spectrometry and further investigated the application in the determination of metal elements by plasma induced high voltage.Based on this,the main research contents of this thesis are as follows:1.A novel static liquid cathode glow discharge-atomic emission spectrometry was designed for the direct determination of Cu in aqueous solutions.The two electrodes are simultaneously immersed into the measured solution,in which the glow discharge plasma was produced in the solution between the needle-like Pt cathode and the electrolyte around it.The effects of discharge voltage,solution pH,and the ionic surfactant cetyltrimethylammonium chloride?CTAC?on emission intensities were investigated.The results showed that the optimal operation conditions are discharge voltage of 135 V,pH of 1,and addition of 0.15%CTAC.CTAC can enhance the emission intensity and lower the LOD of Cu I.The net intensity of atomic emission lines of Cu I at 324.8 nm with 0.15%CTAC is improved by 1.5 fold,and the LODs of the Cu at 135 V with 0.15%CTAC and without CTAC are 0.019 and 0.234 mg L^-1,respectively.2.A novel flowing liquid cathode glow discharge-atomic emission spectrometry?LCGD-AES?was constructed for simultaneously determination of K,Na,Ca,Mg and Zn in water samples?tap water,mineral water,Yellow River water and waste water?.The test solution is driven by a peristaltic pump into the capillary,in which the glow discharge plasma was produced between the needle-like Pt anode and electrolyte around a quartz capillary cathode.The effects of the supporting electrolyte,discharge voltage and organic additives on emission intensity were investigated in detail.The limits of detections?LODs?of metals were compared with those measured by the closed-typeelectrolyte-cathodedischarge-atomicemissionspectrometry?ELCAD-AES?.In addition,the measured results of water samples using LCGD were verified by ICP.The results showed that the optimal operation conditions are pH=1HNO₃ as supporting electrolyte,addition of 0.15%formic acid and 650 V discharge voltage.The R² and the RSD are ranged from 0.9887 to 0.9990 and 1.10%to 2.19%,respectively.LODs of K,Na,Ca,Mg and Zn are 0.02,0.04,0.19,0.04 and 0.05 mg L^-1,which are satisfied the recommended levels of the China standards for drinking water quality.3.A flowing liquid cathode glow discharge-atomic emission spectrometry?LCGD-AES?was introduced for simultaneously determination of Cu and Pb in digested ores samples.The stability of LCGD and the effects of discharge voltage,capillary diameter and flow rate on emission intensity were systematically investigated.The results showed that the optimization analytical conditions were 675 V discharge voltage,1.0 mm capillary diameter and 5.5 mL min^-1 flow rate.The analytical response curves had good linearity in the range of 1–10 mg L^-1.The RSD was 2.05%for Cu and1.27%for Pb.The LODs of Cu and Pb were 0.36 and 0.20 mg L^-1,respectively,which are in agreement with the closed-type ELCAD.The recovery of samples is ranged from85.2–105.6%,suggesting that the determinated results have high accuracy.