Forensic Identification of Dyes in Ballpoint Pen Inks Using LC–ESI–MS

Abstract

The aim of this work was to develop a new technique using flow injection analysis combined with LC–ESI–MS which allows identification of dyes in ballpoint pen inks. A sample preparation procedure for the extraction of dyes from ballpoint pen strokes has been developed. The characteristic group of ions for each sample of 21 studied ballpoint pen inks corresponding to the present dyes has been determined using flow injection method. LC separation conditions for identified dyes have been optimized on reversed-phase sorbent based on silica gel. The best composition of the mobile phase for the dyes mixture LC separation was 0.1% aqueous formic acid and acetonitrile. Detection of dyes was carried out using mass spectrometry with electrospray ionization in positive and negative modes after reversed-phase liquid chromatography separation. Dye composition of ink was additionally confirmed comparing the data obtained from the literature. Flow injection analysis allows obtaining intensive ions of unknown strokes. It is difficult to get this information using only chromatographic methods, because dyes peak intensity can be low and noise of basic line high. Flow injection method allows distinguishing the analyzed 21 ballpoint pens by determining a characteristic set of dyes. The developed flow injection technique is very simple and quick. As a result, a novel approach for the identification of dyes in the ballpoint pen inks by flow injection analysis with LC–ESI–MS and UV detection without using standard dye samples has been established. It can be an effective alternative to the existing LC–DAD–MS and IR spectroscopy methods.