Study on the factors affecting the ionization efficiency of paper spray ionization

Abstract

Ambient ionization mass spectrometry is an emerging technique enabling high-throughput analysis with minimal sample preparation. Among them, paper spray ionization (PSI) mass spectrometry is one of the most popular techniques due to the advantages of the minimized amount of sample, reduced analysis time and cost. It is well known that PSI shares several common properties with electrospray ionization (ESI). However, its exact ionization mechanism has not been fully understood in previous researches.Here, the behavior of paper spray and its ionization efficiency were investigated by comparing them with the conventional electrospray theory. The key factors affecting the ionization efficiency were examined: paper position, thickness, surface property, flow rate of solvent supply and applied voltage. Paper spray modes, which mostly depend on the electric field and droplet charge density, were systematically scrutinized. These modes were recognized and classified by the number of visible spray jets and ionization efficiency. A hydrophobic paper was synthesized to assess the effect of paper surface property on the ionization efficiency. This resulted in an enhancement of sensitivity under a specific condition compared to unmodified paper. Finally, an optimized method was developed for residual antibiotic analysis using hydrophobic paper spray ionization-mass spectrometry. This systematic study proposes a plausible mechanism on PSI with its contributing factors, which provides a fundamental understanding for the development of new PSI applications.