2.5 µL of peptide standards leucine-enkephalin and bradykinin (Merck, 1 mg/mL in 30:70 water:methanol v/v) were applied to microscope slides and allowed to dry. Stainless steel 120 mesh was optionally placed over the dry standards before exposure to the plasma. The standards were exposed to the RFargon plasma for up to 1 minute before analysis by MALDI, or dissolved in 3x20 µL aliquots of 30:70 methanol:water and analysed by direct infusion.