A Hard-to-Soft Tunable Glow Discharge (HSTGD) Ion Source for Broad-Spectrum Analytical Applications.

The performance of conventional mass spectrometry ionization sources is fundamentally limited by their operating principles, restricting their universality across diverse analytes. To address this, we developed a versatile ion source based on a low-pressure glow discharge mechanism that effectively overcomes the biased ionization efficiency between polar and nonpolar compounds. Our source demonstrates exceptional broad-spectrum capability, efficiently ionizing species from polar molecules (e.g., water, alcohols) to nonpolar compounds (e.g., benzene derivatives, alkanes). It achieves excellent sensitivity and stability, evidenced by a linear response for ethanol from 1 to 100 ppm (R2 = 0.99) with a detection limit of 1 ppb. Notably, it generates significantly enhanced quasi-molecular ion peaks [M - H]+ for nonpolar alkanes like n-hexane while suppressing fragmentation, indicating a superior soft ionization environment. Complementing this soft ionization mode, the discharge parameters can be readily adjusted to switch to a tunable ionization mode rich in fragment information. This inherent tunability renders the source a powerful and versatile platform for comprehensive compositional analysis and structural elucidation in complex samples.