Stylus pen-based ambient ionization mass spectrometry for the analysis of volatiles and semivolatiles from liquid, viscous, and solid samples

Background

Ambient ionization mass spectrometry (MS) has attracted significant attention due to its simplicity and ease of operation. Contactless, or field-induced, ionization is one of the ambient ionization techniques. In this approach, no direct electrical contact or additional voltage is required on the ionization-assisted substrate. Instead, the electric field is induced by the high voltage applied to the orifice of the mass spectrometer. However, there remains a demand for exploring compact and readily available ionization substrates for use in field-induced ionization techniques. Results: A stylus pen, typically used for touch screens, is used as an ion source for analyzing volatile and semivolatile organic compounds. Vapors originating from volatile and semivolatile compounds placed underneath the inlet of the mass spectrometer were ionized when the stylus pen was positioned near the inlet, which is applied with a high voltage. The limits of detection for semivolatiles and volatiles were in the range of mM to a few hundred nM, depending on the vapor pressure and chemical structures of these analytes. Additionally, semivolatile compounds found in real samples could be directly detected using our method. Moreover, we also demonstrated the feasibility of using the stylus pen as the sampling probe to pick up samples from the surface of a glass slide, followed by bringing the pen close to the inlet of the mass spectrometer for direct MS analysis using our approach. Significance: The developed method provides a straightforward approach for analyzing volatiles and semi-volatiles under ambient conditions. Ionization of the analyte vapor near the mass spectrometer inlet can readily occur by placing a stylus pen close to the inlet, highlighting simplicity as the main advantage of the developed method. Consequently, this method can be easily coupled with a mass spectrometer that has a high voltage applied to its orifice.