Study On Surface-Enhanced Laser-Induced Breakdown Spectroscopy For Elemental Detection Of Aqueous Solution

Laser-induced breakdown spectroscopy(LIBS),a laser-excited atomic emission spectroscopy technique,is a powerful and rapid analytical technique which is widely applied for soil detection,industrial production,space exploration and environmental monitoring.In the case of liquid samples,the fluidity of liquid causes poor reproducibility of direct measurement due to water splashing and quenching of intensity.The surface-enhanced LIBS(SENLIBS)that transforms the liquid sample to solid sample is a simple method for effectively improving stability and sensitivity in aqueous analysis.However,low detection sensitivity,low detection accuracy and spectral interferences restrict the development of SENLIBS.To drive these problems,this thesis makes a systematic study on SEBLIBS.The detailed contents are as follows:A method of resonant exciting element in substrate of SENLIBS was proposed,by which,the limits of detection(Lo D)of several analytic element could be improved simultaneously.This method takes the advantage of that the major element in SENLIBS plasma was the particles from substrate.An enhancement factor of about 5 for Cu in aluminum alloys verified the feasibility of the proposed method.A Lo D of 0.074 mg/L and an enhancement factor of about 5 were achieved in the quantitative analysis of Pb by SENLIBS.The consistency of exciting wavelength in this method provids ideas in further study on instrument simplification and increases the detecting efficiency.A method of resonant exciting analytic element of SENLIBS was proposed,by which,the Lo D of analytic element could be improved significantly.The excitation mechanism and characteristics of LIBS assisted with laser-induced fluorescence(LIBS-LIF)and resonant LIBS(RLIBS)were studied.The results indicated that RLIBS was more suitable for samples of SENLIBS due to stratified structure of samples in SENLIBS and smaller ablation volume in RLIBS.Pb in aqueous solution was detected by RLIBS.The Lo D and Lo Q were0.0021 mg/L and 0.0069 mg/L with a linear range of 0.01～0.2 mg/L.It met the drinking water sanitation standard of China.A recovery rate between 90%and 110%was obtained in spiked and recovery trials of real tap water.The recoveries were quite acceptable.Meanwhile,the RLIBS spectrum was not subject to the interferences which were in LIBS and LIBS-LIF.These results indicated the proposed method has applicative value and great potential application.A method combining laser ablation molecular isotopic spectrometry enhanced by molecular laser-induced fluorescence(LAMIS-MLIF)and isotopic dilution has been developed.The mechanism of determination of isotopic abundance ratio by isotopic fluorescence ratio in LAMIS-MLIF was discussed.Comparing to previous study on isotopic abundance analysis by LIBS,the proposed method was not affected by uneven distribution of analytic element.Meanwhile,the R~2of calibration curve for isotopic abundance of B reached to 0.999.On the basis of that,isotopic dilution method was used to quantitate analysis in LIBS.For B in aqueous solution,the ARSD of signal was reduced from 20%to5%after data process.Combined with least square algorithm,the ARE of B in aqueous solution was 3.76%,which was better to other method in LIBS.An algorithm based on Richardson–Lucy deconvolution has been developed to reduce the impact of spectral interference in SENLIBS.The proposed algorithm had higher practicability due to its parameters depend on LIBS instrument.The proposed algorithm was used to detect Pb in water whose analytic line PbI 405.78 nm was interfered by the line of Mn I 405.89 nm.the R~2 increased from 0.965 to 0.996.The average relative error and the root mean square error of cross-validation decreased from 15.2%to 4.92%and 0.55 mg/L to 0.14 mg/L,respectively.The quantitative accuracy was improved significantly.This algorithm was also effective for iron alloys and aluminum alloys in which the broadening of the spectral line was compressed by a factor of 4.The proposed algorithm has good generalization capability.In summary,the SENLIBS technique was systemically investigated in this thesis.The method of resonant excitation,isotopic dilution and deconvolution could improve detection sensitivity and accuracy and weaken spectra interference,respectively.This thesis provides a theoretical and experimental guide for the development and application of SENLIBS.