One aspect of the disclosure provides a method of mass spectrometric analysis that includes producing either glow discharge within a noble gas between 3-100 mBar pressure, sampling and conditioning glow discharge products within a gas flow through a conductive channel (55), removing charged particles while transferring excited Ridberg atoms, and mixing conditioned discharge products with analyte flow within an enclosed chamber at elevated temperatures above 150 DEG Celsius for producing a Penning reaction between analyte molecules and Ridberg atoms. The method further includes sampling, by a gas flow, said analyte ions for mass spectrometric analysis, and at least one of the following steps: (i) removing charge within said conditioning channel (55); (ii) coaxially mixing of analyte flow with the flow of conditioned plasma; and (iii) cooling of the mixed flow within a sonic or supersonic jet for reducing the region of Penning ionization to cold jet.