Plasma-based ambient ionization mass spectrometry: from reactive ion chemistry to fit-for-purpose analytical...

Ambient ionization mass spectrometry (AIMS) enables direct analysis of samples under open-air conditions with little or no pretreatment. Among AIMS techniques, plasma-based ionization has attracted particular attention because atmospheric-pressure plasmas can generate reagent ions, metastable species, radicals, photons, and gas streams that support rapid desorption and ionization of solid, liquid, gaseous, and heterogeneous surface samples. Representative sources include direct analysis in real time (DART), desorption atmospheric-pressure chemical ionization (DAPCI), flowing atmospheric-pressure afterglow (FAPA), plasma-assisted desorption/ionization (PADI), dielectric barrier discharge ionization (DBDI), and low-temperature plasma (LTP). This review critically examines plasma-based AIMS from the perspectives of discharge mechanism, ionization pathway, source architecture, and analytical performance. Rather than simply listing individual applications, we compare how different plasma-generation strategies influence reagent-ion chemistry, thermal effects, fragmentation, matrix tolerance, quantitative capability, and suitability for field deployment. Applications in environmental analysis, forensic analysis, explosive detection, pharmaceutical screening, food safety, biological analysis, and materials characterization are discussed with attention to both analytical value and remaining limitations. Plasma-based AIMS has strong potential for high-throughput screening and on-site testing, but routine implementation requires improved mechanistic understanding, source standardization, quantitative robustness, matrix-effect control, and integration with portable MS and validated data-analysis workflows. Future development should move beyond stand-alone application demonstrations toward fit-for-purpose, reproducible, and validated analytical platforms.