Quantitative Analysis Of Trace Heavy Metals In Seawater By Hydride Generation Coupled With Solution-cathode Glow Discharge-atomic Emission Spectrometry

With the rapid development of industrial and agricultural productionand technology,various heavy metals are becoming more and more widely used,and the demand is increasing.At the same time,the pollution of these heavy metals to the ocean is becoming more and more serious.The complexity of the seawater matrix and the low content of the polluted elements in seawater have brought serious challenges to the detection of heavy metals in the seawater.Therefore,simple,rapid and sensitive technology of trace heavy metal analysis is of great significance for protecting marine environment.Solution cathode glow discharge-atomic emission spectroscopy（SCGD-AES）is a fast-developing micro-plasma atomic spectroscopy,which does not need atomized gas.SCGD is low-power and energy consumption,which can be operated under atmospheric pressure.This paper is aimed at some elements with poor sensitivity and selectivity in the analysis and high detection limit such as lead,selenium,arsenic and mercury,and high salinity and complexity of seawater matrix.The sampling system of the instrument was improved and combined with hydride generator.The analytical performance of the instrument was improved.And a new quantitative analysis method for lead and simultaneous quantitative analysis of selenium,arsenic and mercury in seawater were established.The following works have been carried out in this paper:The detection system of SCGD-AES was simplified by using miniaturized spectrograph instead of traditional monochromator.And the parameter conditions in quantitative analysis of lead were optimized.The analytical performance of the instrument for Pb was evaluated,and the detection limit of Pb was reduced.The results have shown that the beat performance of miniaturized SCGD-AES was obtained when1060 V as the voltage,HCl with pH=1 as electrolyte whose flow rate was 2.2mL·min^-1,the detection limit of Pb by miniaturized SCGD-AES was 33μg·L^-1.Besides,with 3%formic acid as the sensitizer,and the detection limit of Pb was reduced to 7μg·L^-1.On the basis of the miniaturized SCGD,a hollow titanium tube was used instead of the solid tungsten rod as the discharge anode as well as the sample introduction system,by which gas sampling was realized.The improved miniaturized SCGD-AES was then combined with hydride generator.The volatile hydrides converted from aqueous solution was delivered to the glow discharge region of SCGD-AES and stimulated efficiently on the premise of the stability of the micro-plasma.This paper focuses on the best conditions in quantitative analysis of trace lead in seawater by hydride generation coupled with miniaturization SCGD-AES.The influence of operating parameters of hydride generation（the kind and the concentration of the carrier acid,the concentration of reductant,oxidant,sensitizer and masking agent）and the miniaturized SCGD-AES（the kind,concentration and flow rate of the electrolyte,and the voltage）to the analytical performance of the couplet instrument were considered.The results have shown that the best performance of HG-SCGD-AES was obtained when 2%HCl as the carrier acid of the hydride generation,adding 1.5%K₃Fe（CN）₆,1%oxalic acid and 3%formic acid in the sample,2.5%NaBH₄ as the reductant,SCGD with the voltage of1100 V,HNO₃ with pH=1 as the electrolyte,whose flow rate was 2.2 mL·min^-1.Compared with the previous liquid injection,the efficiency of injection and atomization were greatly improved.The detection limit for Pb in seawater was improved to 0.17μg·L^-1,which was reduced by 194 times.And the linear range was from 0 to 100μg·L^-1,whose correlation coefficient was 0.9996,the RSD of the signal was 2.1%.Then the method was applied to the quantitative analysis of Pb in standard seawater.The result of this measurement coincides with the reference value.Besides,the method was applied to quantitative analysis of Pb in surface seawater in coastal Yellow Sea.The results were in well agreement with ICP-MS（Inductively coupled plasma mass spectrometry）,with the recoveries between 96.0%to 103.0%.Subsequently,the coupled instrument was used in simultaneous quantitative analysis of selenium,arsenic and mercury in seawater.The operating parameters of hydride generation（the concentration of carrier acid and reductant）and miniaturized SCGD-AES（the voltage,the concentration and the flow rate of electrolyte）were optimized.The results have shown that the best performance of HG-SCGD-AES was obtained when 5%HCl as the carrier acid of the hydride generation,1.5%NaBH₄ as the reductant,SCGD with the voltage of 1060 V,HCl with pH=1 as the electrolyte,whose flow rate was 2.2 mL·min^-1.The detection limits of Se,As,Hg were 0.54μg·L^-1,0.92μg·L^-1,1.91μg·L^-1,respectively.And the linear range was from 0 to 100μg·L^-1,whose correlation coefficient was 0.9992,0.9994,0.9985,and the RSD of the signal was 2.1%,1.9%,2.7%,respectively.The results have shown that the method has good precision and stability.Finally,the method was applied to quantitative analysis of Se,As,Hg in surface seawater in coastal Yellow Sea.The results of the method were in well agreement with ICP-MS,with the recoveries between 94.9%to 105.3%.