Pearson Product Moment Correlation (PPMC) and Principal Component Analysis (PCA) for objective comparison and source determination of unbranded black ballpoint pen inks

The aim of this work was to evaluate the feasibility of combining Raman Spectroscopy (RS) and Fourier Transform Infrared (FTIR) spectroscopy with Pearson Product Moment Correlation (PPMC) and Principal Component Analysis (PCA) for objective comparisons of unbranded black ballpoint pen inks; more specifically, to determine the original source of an ink treated as unknown. Eleven unbranded black ballpoint pens obtained during an education fair in Malaysia in May 2014 were prepared and analysed using RS and FTIR, where one of the pens was used to write a simulated threatening note. The spectra of the ballpoint pen inks obtained from the RS and FTIR analysis, including the ink on the simulated threatening note were then subjected to PPMC and PCA. The linear correlations of r=0.756 and r=0.999 and the similarities in terms of PC1 and PC2 scores of one of the inks to the ink on the simulated threatening note, which indicated a strong relationship between the two inks, substantiate the feasibility of combining RS and FTIR with the statistical and mathematical techniques of PPMC and PCA for objective comparison and source determination of ballpoint pen inks.