Analysis Of Major Components In Imprints Of Water Based Stamp-Pad Inks And Stability Research

In recent years, the economic cases about forging and tampering related imprint of the file have been increasing. The study on imprint of water based stamp-pad ink which is a new environmental stamp-pad ink is almost blank space on forensic science. This thesis play a significant role for analyzing the major components and stability on 5 red water based stamp-pad inks on the market by rapid resolution liquid chromatography (RRLC), rapid resolution liquid chromatography tandem mass spectrometry (RRLC/MS) and gas chromatography tandem mass spectrometry (GC/MS).The pretreatment method and RRLC analysis condition for imprint of water based stamp-pad ink were established in this thesis. Separation was achieved by Agilent Zorbax Eclipse Plus Phenyl-Hexyl(4.6x50mm,1.8μm) column and gradient elution solvents of 15mmol/L ammonium acetate in water and acetonitrile. Kept the column temperature at 30℃and multi-wavelength monitored at 254nm,410nm,486nm and 515nm with diode array detector(DAD). The precision and accuracy of pretreatment method and RRLC analysis condition were verified by colorant standards. The linear correlation coefficient were greater than 0.9999, while the relative standard deviation of retention time and peak area were lesser than 3%, and the average recovery of standard addition was in the range of 98.9%-104.6%. The established method is simple, rapid and reliable, and it can meet the requirements for imprint determination in material evidence identification.The colorants were qualitatively detected by RRLC/MS full scan negative mode, while the volatile components were qualitatively detected by GC/MS full scan mode. The result showed that the main colorants of water based stamp-pad ink were Acid Red R, Eosin Y and Pigment Red 112; the main solvents were 1,2-Propandiol, Glycerol and Polyethylene Glycol Compounds; the main plasticizer was Dibutyl Phthalate. There was the complementary relationship of the experiment results within the two instrument analysis methods. This study made a basic research on water based stamp-pad ink and imprint, and it provided the basis for the subsequent projects by other various kinds of method for the future.The preliminary research about the stability rule of the natural aging, sealing process and artificial illumination aging has been made by RRLC and GC/MS. Variation trend of main colorants and primary volatile components have been analyzed by relative peak area method. The result showed that the relative ratio of acid red R was increased and pigment red 112 was declined with natural aging time and sealing number increasing of Trodat and Noris brand, while the relative ratio of Eosin Y and pigment red 112 were mainly stable of Shiny brand. The relative ratio of volatile components was increased with their molecular weight and boiling point increasing by the infrared aging time extending. The relative ratio of acid red R and Eosin Y were declined, even disappeared, and pigment red 112 was raised by the ultraviolet aging time extending.