Real-Time Formation of Nitrate and Nitrite Species in Plasma-Activated Liquids: From Distilled Water to Cell Culture Solutions

Abstract Plasma-activated liquids (PALs) provide a versatile route for delivering plasma-generated chemistry in fields ranging from biomedicine to agriculture. Their reactivity stems from gas-phase reactive oxygen and nitrogen species dissolving into the liquid, yet how the choice of solution governs this chemistry remains insufficiently investigated. Here, we systematically compare deionized water (DW), mineral water (MW), tap water (TW), phosphate‑buffered saline (PBS), and Dulbecco’s modified Eagle medium (DMEM) treated under identical conditions using a surface dielectric barrier discharge (sDBD) in a gas‑tight reactor. By coupling in situ optical absorption spectroscopy with liquid-phase analysis, we reveal a direct link between the gas-phase O₃–NOx transition and the formation of NO₂⁻, HNO₂, and NO₃⁻ in each solution. Among the tested media, PBS exhibited the fastest transition, driven by its high ionic strength and rapid O₃ consumption. While nitrate concentrations converged across solutions, nitrite and nitrous acid were strongly modulated by initial pH, buffering capacity, and ionic composition. Dilution of PBS delayed the transition and reduced buffering, favoring HNO₂ accumulation. These findings demonstrate that PAL chemistry emerges from the interplay between plasma conditions and solution properties. Recognizing this dual control enables predictive tailoring of PALs for specific targeted applications.