A non-invasive and rapid method for discrimination of inkjet printouts by ion mobility spectrometry combined with chemometrics

The identification and differentiation of inkjet printouts can be important to establish the authenticity of questioned documents during judicial processes. In this work, we developed an analytical method based on ion mobility spectrometry (IMS) combined with chemometrics to identify inkjet printouts for rapid on-site detection. The characteristic peaks in IMS spectra were first identified by HS-GC-MS which showed the chemical differences between inkjet printouts. To achieve further differentiation of the inkjet printouts, principal component analysis (PCA) was performed. The results demonstrated that they can grouped based on the types of inks used, regardless of the printer type and the aging time of the document. For accurate discrimination of inkjet printed documents, a supervised model based on orthogonal partial least square discriminant analysis (OPLS-DA) was developed, which provided good quality (R2Y = 0.954, Q2 = 0.953). The model gave excellent accuracy by correctly classifying 99.37% of the validation set (159 samples). Furthermore, the partial least squares (PLS) models were applied to predict the formation time of documents. A combination of Orthogonal signal correction (OCS) combined and discrete wavelet transform (DWT) was used for data processing showing the best performance for the PLS model. It provided satisfactory predictions for inkjet printouts over 7-1446 days aging time. IMS combined with chemometrics was confirmed to be feasible and accurate for questioned documents identification and can be further applied in solving actual cases.