title: Identification and differentiation of the red ink entries of seals on document by laser desorption ionization mass spectrometry.
abstract: The establishment of approaches for the differentiation of the ink entries of seals on paper can provide evidence to authenticate the related documents and can play a key role in judicial expertise. The identification and discrimination method for 38 red ink entries of seals on paper has been investigated using laser desorption ionization mass spectrometry (LDI-MS). Six dye components for the ink pastes of seals, Scarlet powder (SP), Bronze Red C (BR), Fast Red R (FR), Basic Violet 3 (BV3), Pigment Red 22 (PR22) and Pigment Red 112 (PR112), have been identified by their LDI-MS spectra, and the results have been confirmed by electrospray ionization quadruple-time of flight mass spectrometry (QTOF-ESI-MS/MS) and inductively coupled plasma atomic emission spectrometry (ICP-AES). The 38 ink entries were classified into six groups based on the presence or the absence of the pigments in their positive and negative LDI-MS spectra, and the discrimination power (DP) was calculated to be about 82%. The ink entries within each group were further differentiated from the relative peak areas (RPA) of the fragments for the pigments and the profile of their LDI-MS spectra, and thus the DP was increased to 98%. All the 38 ink entries could be discriminated (the DP was 100%), if including the contribution of unknown peaks. Compared with the results obtained by the FTIR and Raman methods, the established LDI-MS approach could provide more information of the dye components in the ink entries. The results showed that the developed LDI-MS method is powerful, sensitive and rapid and can directly differentiate the red ink entries of seals from paper substrates, thus offering a novel approach to judge the authenticity of documents.
authors: Analytical & Testing Center of Beijing Normal University, Beijing 100875, China.
authors: Xiang-Feng
authors: XF
authors: Wang
authors: Institute of Beijing Criminal Science and Technology, Beijing 100054, China.
authors: Yun
authors: Y
authors: Zhang
authors: Analytical & Testing Center of Beijing Normal University, Beijing 100875, China.
authors: Yao
authors: Y
authors: Wu
authors: Institute of Beijing Criminal Science and Technology, Beijing 100054, China.
authors: Jing
authors: J
authors: Yu
authors: Analytical & Testing Center of Beijing Normal University, Beijing 100875, China. Electronic address: xiemx@bnu.edu.cn.
authors: Meng-Xia
authors: MX
authors: Xie
keywords: Differentiation; Identification; LDI-MS; Pigment; Red ink entries of seals