MOLECULAR-WEIGHT DETERMINATION OF PLASMID DNA USING ELECTROSPRAY-IONIZATION MASS-SPECTROMETRY

lonization and molecular weight (MW) determination of megadalton size plasmid DNA has been achieved using electrospray ionization (ESI) with Fourier transform ion cyclotron resonance (FTICR) mass spectrometry, DNA molecules were shown to remain intact through electrospray ionizat ion by collection on a specially prepared surface, followed by agarose gel electrophoresis. Individual highly charged ions of plasmid DNA pr oduced by ESI were trapped in an FTICR cell for up to several hours an d reacted with acetic acid to induce charge state shifts, Measurements of mass-to-charge ratios for these multiple peaks arising from charge state shifting give MW measurements of individual ions with an averag e accuracy of 0.2%, The MW distribution was obtained by measurements f or a number of individual ions from the same sample [plasmid DNA: pGEM -5S MW(cal) = 1.946 MDa], yielding a MW(obs) of 1.95 +/- 0.07 MDa for ions clustered in the vicinity of the expected MW.