Forensic discrimination of black printed materials with dye inks

The printed materials used in cases of stalking, intimidation, etc. is assumed to be black texts printed by inkjet printers. We examined discrimination of black printed materials by dye inks in an analysis of dye components using TLC and HPLC-PDA, analysis of solvents components using GC/MS, and analysis of trace elements using ICP-MS. We also attempted to classify the samples using multivariate analysis based on the analysis results, and to identify the manufacturer. In this study, a total of 17 samples were analyzed, including inks manufactured by Canon, EPSON, Brother, and their compatible inks. One hundred twenty five of the 136 pairs of samples were distinguished by TLC, and One hundred twenty nine of the 136 pairs of samples were distinguished by HPLC-PDA. HPLC-PDA can perform separation analysis for all samples and therefore seemed a better method. GC/MS detected components such as 2,2-sulfonyl diethanol, triethanolamine, and tetraethyleneglycol. Samples were distinguished by 109/136 patterns by mainly using these components as indicators. The quantitative analysis of Li and Cu was performed by ICP-MS, and the concentration ratio of those two elements (Li/Cu) was calculated. Samples were distinguished by 120/136 patterns by this ratio. Samples were distinguished by 133/136 patterns by combining all analyses. In many cases, it is possible to distinguish inks by dye components, but inks with different model numbers may show similar results. Thus a combination of GC/MS and ICP-MS should be used for judgment. In addition, by conducting principal component analysis and cluster analysis based on the area values of each detected component by GC/MS and the detected intensities of Li and Cu by ICP-MS, it is possible to estimate the manufacturer.