The Development Of Automatic Spectrum Analysis Program Of Laser-based Mass Spectrometry And Its Theoretical Study

With the development of science and technology,the demand for elemental analysis of solid sample is mounting,especially in domains like metallurgy,environtology,geology,material production control,semiconductor industry,space exploration,and so on.Solid sample has a great variety,and its matrix is very complex,which make it the most difficult sample to analyze compared to gas and liquid samples.The traditional solution analysis method is time consuming,easy to get contaminated and has potential danger due to the usage of strong acid and alkali.Laser-based mass spectrometry can well address this problem,it has fast analysis speed,simple spectrum,high resolution,low detection limit and hardly needs sample preparation,which make it widely used in all kinds of areas.Compared with organic matter analysis,elemental analysis is relatively simple,for it doesn't need ms/ms analysis.Yet it is not an easy task and commonly requires experienced person who works on mass spectrometer,which limits the spread of this technique.If it is possible to transform the experience of data processing and spectrum analysis into executable programs in the computer,the performance of the technique would be greatly improved,and it would save a lot of time for the people who use these programs.Although laser-based mass spectrometry has such merits,it is characterized by severe non-chemometrics effect,which deteriorates its analysis accuracy largely.Under such circumstances,we need to understand its happening mechanism and explore the parameters that influence them,which lays the foundations for improving experimental results.Based on our previous experience on laser-based mass spectrometry study,we combined it with the technique of aperture-less tip near-field enhancement and successfully developed a brand new technique that is able to perform high-resolution nano-scale analysis,which stands pn the very front of the research trend.Nevertheless,its underlying mechanism has barely studied,which is badly needed to be done,for it is very important for the further mature and development of this technique.According to the background above,the following paragraphs briefly introduce the research contents and results of this thesis.Based on the great semi-quantitative analysis performance of our laser ablation/ionization mass spectrometer made in house,the first part illustrates the development of an automatic data processing and spectrum analysis program aimed at elemental analysis.This program can be divided into data processing system,calibration system,spectrum analysis system and information display system,and the data processing system further includes signal data generation and overlying,signal smoothing,baseline subtraction and peak detection.The program successfully analyzes four different kinds of samples,including metal(standard SRM 1263a),pressed powder disc(including Al,Fe,Mn,Cr and Ni),ceramics(from Yaozhou Kiln)and ore(Nantan iron meteorite),extracts nearly all the information carried by the spectrum,realizes automatic qualitative and semi-quantitative analysis,and largely improves analysis efficiency.As to the phenomenon of minimizing matrix effect in laser ablation/ionization mass spectrometry by the femtosecond pulsed laser,the second part develops a set of theoretical model to reproduce the processes giving rise to this phenomenon.Theoretical relative sensitivity coefficients of certain elements meet well with those of experimental values,which proves the model to be valid.Moreover,we utilize the chemometrics method of orthogonal partial least squares to analyze experimental results,and confirm that the key reason of femtosecond laser minimizing matrix effect is the reduction of thermal effect.The third part combines the theories of aperture-less tip near-field enhancement and laser direct ablation/ionization,and for the first time establishes a set of theoretical model to support the technique of tip enhanced ablation/ionization mass spectrometry,which is utilized to analyze Ti coating layer sample and inorganic salt mixed residue sample.Theoretical nano-scale ablation pit morphologies of Ti sample and ablation volumes under both lasers are in great accordance with corresponding experimental results,as well as the theoretical spectra of the nine inorganic salts.In spite of it,the model is able to give values such as the three-dimensional distribution of sample temperature,plasma temperature,total particle/ion number density,ionization efficiency,ion kinetic energy distribution and angular distribution,which sheds light into the inner properties of this technique.Similarly,the chemometrics tool is also utilized in this part to investigate the factors influencing experimental results.Via cluster analysis of partial least squres,we discover that the action of inorganic salt ions in the experiment is greatly correlated with their natural valence state;via loading analysis,we know that the thermal properties affect nanosecond laser model to a greater extent compared with femtosecond laser model,and the first ionization potential plays a vital role in both the models.These results meet well with model and experimental outcomes,which proves our research to be reasonable and lays the foundation for the further optimization of this technique.