Analysis of black writing ink by electrospray ionization mass spectrometry

Abstract

A method for the analysis of dyes and vehicles within writing inks was developed. The method was tested on a set of 18 black ink pens comprised of 6 ballpoint, 6 gel, and 6 rollerball pens. The sampling procedure utilized a small number of ink-coated paper fibers collected surreptitiously from the document, causing minimal damage and providing a sufficient quantity of ink for analysis. Methanol proved suitable for the extraction of ink components from ballpoint, gel and rollerball pens. Three separate electrospray ionisation-mass spectrometry (ESI-MS) methods were required to detect the dyes and vehicles from the inks. The ions present in the ESI-MS spectra at a signal-to-noise ratio of greater than 3:1 provided sufficient information to allow differentiation between the inks of each type. A tentative identification of the ink components was made based on a comparison of the ions present in the ink extract ESI-MS spectra with the ions present in a series of standards. The limits of detection for the standards were generally in the 2.5–10 ppm range. The method reported here extends the ESI-MS method of ink analysis to include gel and rollerball pens, includes the analysis of vehicles as well as dyes in the inks and demonstrates a minimally destructive sampling method that does not require a “biopsy” of the document.