Samples (solid, liquid, or semi-solid) are directly loaded onto the probe tip (e.g., by dipping, coating, or spotting) without dissolution, derivatization, or chromatographic separation. Upon heating, target compounds are volatilized from the matrix into the gas phase. Volatile molecules then undergo proton transfer or charge exchange with reagent ions (e.g., H₃O⁺, O₂⁻, etc.) in a high-voltage corona discharge zone near the probe (under ambient pressure), generating sample ions (e.g., [M+H]⁺ or [M-H]⁻).