Application Of Matrix-assisted Laser Desorption/ionization Time-of-flight Mass Spectrometry In The Inspection Of Red Inkpad

Research background and objectiveRecently,as economy development grow rapidly,forgeries of printed text for civil infringement and even criminal cases also show an increasing trend year by year.The printing ink component analysis is involved in various aspects including the contract dispute,the private loaning dispute,the property damage compensation,the inheritance,the labor dispute,etc.By analyzing the composition of the inkpad,we can obtain the important information such as the composition of the mud,the manufacturer and the batch,which can assist the judicial experts to judge when the seal is printed,and also play an auxiliary role in the settlement of civil cases and the detection of criminal cases.StructureThis thesis is mainly divided into 11 chapters,the introduction chapter includes the background,difficulties and methods.Chapter 1 discusses the target plate and target mode of Matrix-Assisted Laser Desorption/Ionization Time-Of-Flight Mass Spectrometry(MALDI-TOF-MS)in the analysis of inkpad from experimental point of view.Chapter 2 determines the suitable matrix and its concentration ratio of red inkpad samples and imprinted samples by experiments.Chapter 3 uses the MALDI-TOF-MS to test 7 kinds of inkpad samples,analyzes and compares the sample inkpad separately,and verifies MALDI-TOF-MS feasibility of testing printing oil and inkpad.Chapter 4is the summary part,elaborated the inkpad and its development history,the commonly used analysis method and its superiority and inferiority of inkpad,the basic principle of MALDI-TOF-MS,and the application of MALDI-TOF-MS in the document inspection.MethodsEstablishment of target method for inkpad: Three common point-target methods,thin-layer method,dry-point method and sandwich method,were selected to detect the same sample using three point-target methods,three groups of mass spectrometry data were collected,the data obtained from statistical analysis were selected,and the most suitable point-target method for inkpad analysis was selected from the three dimensions of peak number,signal intensity and repeatability.Matrix screening: Two kinds of MALDI common matrix SA and DHB,are arranged into two different concentrations of SA matrix solution,four different concentrations of DHB solution.Six kinds of matrix solution are used to detect the same sample,six groups of mass spectrometry data are collected,the data obtained from statistical analysis are selected,and the most suitable matrix and its concentration are selected from the three dimensions of peak number,signal intensity and repeatability.Inkpad analysis: the MALDI-TOF-MS detection of 7 different types of commercially available inkpad were carried out,and 7 groups of mass spectrometry data were collected.The mass spectra were smoothed,baseline corrected and marked peaks by software Flex Analysis3.3.The data clustering was analyzed and generated quasi-glue map by software Clin Protools2.2.ResultsTest results of target method for inkpad: The three methods could observe obvious clusters,the crystallization effect of dry point method was better than that of sandwich method than that of thin-layer method.The number of ion peaks measured by thin-layer method was less,and the strength was obviously weaker than that of drypoint method and sandwich method.The reproducibility of sandwich method is decent,that of dry-point method is ordinary,and that of thin-layer method is very poor.Matrix screening results: Samples 1 and 3 may contain polyethylene glycols,samples 2 and 4 may contain polypropylene alcohols.Clustering analysis of the data shows the results by two-dimensional scatter plot.Five kinds of inkpad are accumulated into three groups.7 samples can be accurately distinguished using the mass spectrometry quasi-gel map.ConclusionThe sandwich target method is more suitable for the analysis of inkpad by MALDI-TOF-MS,and the DHB solution with 20 g/L concentration has better effect in the analysis of printing oil and mud.Experiments show that MALDI-TOF-MS can be used as a new method for the analysis of inkpad,with the advantages of fast and high efficiency,low consumption of inspection materials,etc.