Unlocking the Mysteries of the Desorption–Ionization Mechanism via Separate\nThermal and Charge Strategies

Herein, a new strategy is employed\nto build a controllable thermal-coupled\ncharge ionization (TCCI) device to elucidate the desorption–ionization\nmechanism of plasma ion sources. Efficient synergistic desorption\nand ionization are achieved within the TCCI device by independently\ncontrolling the desorption temperature and plasma charges. The TCCI\ndevice efficiently ionizes samples using abundant free electrons,\ncharges, and active species from arc plasma. The coexistence of free\nelectrons and hydroxide radicals confers redox capability to the TCCI\nsystem, implying the presence of a unified redox mechanism even when\nthe arc plasma is transmitted through a metal conductor over a distance.\nIn addition, molecular ions of the analytes facilitate the differentiation\nbetween primary and secondary amines during their analysis. Notably,\nthe TCCI device enables a switch between hard and soft ionization\nby adjusting the thermal desorption temperature. At high temperatures\n(>400 °C), the TCCI device exhibits hard ionization characteristics,\nproducing fragment ions beneficial for isomer discrimination. The\nTCCI mass spectrometry exhibits robust performance in terms of sensitivity\nand accuracy for detecting antibiotics and sterols in saline solutions,\nachieving linearity with correlation coefficients ≥0.99 and\nexcellent reproducibility. The successful analysis of seven pharmaceuticals\nand four sterols in complex matrices using the TCCI device demonstrates\nits excellent salt and matrix tolerance. Overall, the TCCI device,\nwith its independent control over thermal desorption and arc plasma,\nachieves efficient synergistic desorption and ionization, overcoming\nlimitations in existing ionization technologies and contributing to\nthe study of gas-phase ion dynamics and mechanisms.