Trapping of wide range mass-to-charge ions and dependence on matrix amount in internal source MALDI-FTMS

Internal ionization source MALDI-FTMS shows clear variation of number average molecular weight (M-n) for an equimolar mixture of four PEG polymers (PEG 2000, PEG 4000, PEG 6000, PEG 8000) when the 2,5-dihydroxy benzoic acid (DHB) matrix to PEG ratio is varied or the laser power is changed. As the matrix to analyte ratio is increased, the analyte signal of higher molecular mass ions increases and the signal of lower mass ions decreases. Laser power dependence studies show a similar trend. Possible explanations for these observations are discussed. (c) 2005 American Society for Mass Spectrometry.