Capillary Electrophoresis of Ballpoint Pen Inks

Two capillary electrophoretic (CE) methods have been designed to differentiate and identify organic and inorganic dyes present in black and blue ballpoint pen inks. CE was chosen because the technique provides chemical information that can provide better discrimination between ink formulations than thin-layer chromatography (TLC) when comparing ink samples during document analysis. One CE buffer was designed to separate and analyze 10 blue ballpoint pen ink formulations. An alternative buffer was designed to separate and analyze 15 black ballpoint pen inks and 2 different inkjet cartridge products from the same manufacturer. The capillary detection method using a photo-diode array (PDA) to acquire absorbance data (190-600 nm) provides lambda max ((λmax) and characteristic UV-Vis spectra for analytes. Simultaneous spectral data collection avoids the necessity for densitometry measurements.Mobility values (μep) calculated from a migration time replace hand-measured TLC Rf values. The sample electropherograms are reproducible with 2 μg/mL concentration limits of detection, which is superior when compared to TLC separations. Specific chemical identification can be determined based on spectral and mobility value match to reference dye standards. All inks were differentiated from one another in the respective category (blue, black, or inkjet formulation). When possible, chemical compounds were identified in a particular ink to aid characterization. CE offers additional advantages over TLC, including lower reagent consumption, smaller sample requirements, lower detection limits, quantitative analysis, method automation, direct reference comparison, electronic data storage, and searchable spectral libraries. Other complimentary techniques (TLC, positive- and negativeion
mode electrospray-ionization mass spectrometry) can be performed because little sample (20 nL) is consumed for CE analysis. The same CE buffers formulated for ballpoint pen inks have been applied to color inkjet printer formulations, food dyes, gel pen inks, and textile dyes.