Zero volt paper spray ionization mass spectrometry for direct analysis of samples on filter paper substrate

Zero volt paper spray ionization (zvPSI) is a newly developed sample introduction/ionization technique for mass spectrometry (MS), which combines favorable features of paper spray ionization (PSI) and solvent-assisted inlet ionization (SAII). With a simple platform similar to PSI, zvPSI allows direct MS analysis of a broad type of samples (liquid, (semi-)solid, and imprint) without applying voltage.

In zvPSI-MS, a rectangular paper slip was used as a sample loader, extraction medium, and droplet emitter to introduce sample extract into the inlet of a mass spectrometer. For (semi-)solid and imprint samples, analyte(s) was directly extracted with solvent and instantaneously introduced into a mass spectrometer by aspiration. Solution samples were analyzed after being dried-up or by dispensing directly onto paper. Ionization was achieved by SAII and ionized molecules were detected by an ion-trap mass spectrometer.

The developed method allowed direct voltage-free MS analysis of samples on filter paper substrate. Favorable features of PSI and SAII were successfully combined, such as fast data acquisition, flexible sample handlings, and direct extraction capability from solid samples (PSI), with no need for external high-voltage, laser, or nebulizing gas to convert analytes into gas-phase ions (SAII). Comparable to PSI and SAII, a wide variety of compounds such as amino acids, peptides, lipids and synthetic polymers were shown to be analyzed.

The developed method (zvPSI-MS) expanded the analytical utility of PSI and SAII to voltage-free direct MS analysis of a broad type of samples (liquid, (semi-)solid, and imprint).