Determination Of Metal Elements In Aqueous Solution By Liquid Cathode Glow Discharge With Chemical Sensitizer

The development of industry and agriculture has promoted economic prosperity,meanwhile,brought a series of environmental pollution problems.Detection of heavy metals in pollutants,especially the on-line and real-time determination of heavy metal in water is of great importance and necessary for environmental warning.Currently,electrolyte cathode glow discharge atomic emission spectroscopy?ELCAD-AES?is one of the most promising methods for on-line detection of metal elements.The early ELCAD-AES has some advantages for the analysis and detection of some elements,such as small and portable devices,low operating costs,low energy consumption,no extra gas consumption,and operation in atmospheric air.However,there are still some deficiencies,such as large solution consumption,high detection limit,and poor stability.To solve these problems,on the basis of establishing a new liquid cathode glow discharge atomic emission spectroscopy?LCGD-AES?,the effect of sensitization and analytical performance was investigated on LCGD-AES by adding organic sensitizer in the electrolyte solution.Meanwhile,the possible enhancement mechanism of organic sensitizer was also discussed.The main contents are as follows:1.Based on the LCGD-AES that has been constructed,organic compounds are added to the electrolyte solution for elemental signal sensitization and used to determine Ni in sample water.The operating parameters of LCGD-AES and the effects of organic substances on signal intensity of Ni were studied in detail.The results showed that the optimal operating conditions were:discharge voltage of 660 V,solution flow rate of 2.4mL min^-1,and pH=1.0 HNO₃ as the supporting electrolyte.Adding 5%formic acid and1 CMC Triton X-405 in electrolyte solution could most obviously enhance the signal intensity of Ni about 1.23 and 7.56 times,respectively.The interference of coexisting ions on Ni was also studied.The results found that most of foreign ions didn't interfere with Ni,but Cu²⁺and SO₄^2-suppressed the signal intensity of Ni.Add 5%formic acid and 1 CMC Triton X-405 to eliminate the interference,respectively.It was found that adding formic acid could eliminate the interference of Cu²⁺and SO₄^2-,and Triton X-405could eliminate the interference of SO₄^2-.The LODs,R² and RSD of Ni in pH=1.0HNO₃,adding formic acid and Triton X-405 were 0.47,0.25,0.49 mg L^-1;0.9980,0.9980,0.9942 and 3.22%,2.09%,5.01%,respectively.On this basis,the real samples were determined by the method of spiked recovery,and the recoveries were 156-178%,107-115%,and 155-258%,respectively.The results show that 5%formic acid can eliminate the interference of coexisting matrix in the sample.Therefore,the determination of Ni by LCGD-AES with formic acid is accurate and reliable and can be used to analyze and measure Ni in water samples.2.The addition of cetyltrimethylammonium bromide?CTAB?,cetyltrimethylammonium chloride?CTAC?and Triton X-405 on Ag,Cd,Cu,Mn,Pb and Zn emission intensities in LCGD-AES was investigated.The results show that 7CMC Triton X-405 can increase the emission intensity of Ag by 4.60 times,0.15%CTAB can increase the intensity of Cd by 2.45 times,0.1%CTAB can increase the intensity of Cu by 1.42 times,0.05%CTAC can increase the intensity of Mn and Zn by1.73 and 2.41 times,0.1%CTAC can increase the intensity of Pb by 1.76 times,respectively.The optimal LODs of Ag,Cd,Cu,Mn,Pb and Zn can reached 0.013,0.027,0.021,0.018,0.15 and 0.049 mg L^-1,respectively.The recovery of the elements is90-111%except for Ag and Mn after adding surfactants.However,without adding surfactants,the recovery is only 10-111%.The results suggested that adding surfactants can significantly eliminate the interference of the coexisting matrix in the real samples.By studying the changes of the emission intensity of NO,NH,N₂ and OH,the physical properties of the electrolyte solution,the electron temperature and density of plasma before and after adding the surfactant,the possible mechanism of the surfactant to enhance the element signal was preliminarily discussed.3.Low molecular weight organic compounds?LMWOC?,such as formic acid,acetic acid,methanol,and ethanol,were added into the electrolyte solution to create an LMWOC-sensitized LCGD-AES system.The results show that formic acid not only enhanced the signals of Ag,Cd,Cu,Mn,Pb and Zn by 3.3,3.7,1.2,1.5,15.6 and 1.3times,respectively,but also made the LODs reduce from 0.017,0.042,0.040,0.20,0.20and 0.044 mg L^-1 to 0.00057,0.014,0.020,0.11,0.025 and 0.035 mg L^-1,respectively.In real water sample detection,formic acid eliminated the interference of coexisting substances on Cu,Mn and Zn.In addition,the possible mechanism of the signal enhancement of the LMWOC was studied from three aspects of spectral properties,plasma parameters and the physical properties of the electrolyte solution.It was found that LMWOC changed the spectrum of OH,N₂,NO,and new spectra of CO were produced after adding methanol and ethanol.There were no clear relationship between plasma properties,physical properties and the enhancement of elemental signals.The possible mechanism for LMWOC to enhance the signal intensity of metal elements is that the LMWOC was oxidized by active particles HO·in LCGD to generate carbon radicals?·CO₂H,·CH₂OH?.Therefore,a large amount of HO·were consumed,which is beneficial to the production of a large amount of greatly reductive·H and e^-.They could react with metal ions in plasma region,which results in improving transport efficiency and atomization efficiency of metal ions,and accordingly increasing atomic signal intensity.