A radiofrequency (RF) current was initially envisioned as a method for achieving similar digestion results without the need for electrically conductive ITO slides, allowing for greater flexibility of sample analysis. Using a standard of the peptide leucine enkephalin, the digestion products generated included 'classical' abc-xyz peptide fragments (particularly c-and z-type fragments), as well as neutral loss products such as [M-COOH+H] + . The presence of c-and z-type fragments suggests a mechanism more heavily reliant on free electron-or radicalmediated reactions than the DC setup, as in-spec fragmentation methods such as Electron Transfer Dissociation (ETD) and Electron Capture Dissociation (ECD) often produce these fragments through charge remote fragmentation characteristic of odd-electron reactions . To further elucidate the mechanism of action of the digestionspecifically, to ascertain the contribution between free electrons and metastables -a steel mesh was placed between the electrode and standards to be analysed. As seen previously when the argon plasma was applied to leucine-enkephalin, a drop in intensity of comparable peaks was observed in mesh-covered samples -however, there were no peaks unique to either mesh-covered or control samples generated (Supplementary 9). These results suggest that the mechanism is primarily driven by metastable ions and/or Reactive Oxygen or Nitrogen Species (RONS), with potentially little effect from free electrons. RONS, incorporating OH, NO, O, and H radicals (among others), are known to generate by low temperature plasmas, as described previously . Increased exposure to the RF-AP tended to reduce the intensity of higher m/z (>500) peaks, while increasing the intensity of lower m/z (<150) peaks -for example, increased exposure time leads to a lower intensity of the peak at 464.19 (annotated as [c4 + 2H + Na] + ), but a higher intensity of the peak at 120.08 (annotated as [Phe-COOH-H2+H] + ). Several notable peaks and their respective annotations from the digestion of leucineenkephalin are enumerated in Table ; peptide abc-xyz fragments are described with 'all-explicit' nomenclature . The peaks generated included c-type fragments, as well as derivatives of a-, c-, z-, and y-type fragments, in addition to neutral losses from the parent ion. Subsequent experiments on a range of standards, including bradykinin (Supplementary 1), mNeonGreen (Supplementary 2), ubiquitin, L-phenylalanine, DL-beta-phenylalanine, and creatinine also demonstrated the production of peaks unique to those compounds after exposure to the RF-AP source -these were generally annotated as products of polymerisation, digestion, or both. For macromolecules -like mNeonGreen -several products were generated after exposure of the standard to the plasma (figure ), although it was not consistent between products whether the peak intensity would increase or decrease after 5 seconds of exposure.