AUTOMATED ASSIGNMENT OF CHARGE STATES FROM RESOLVED ISOTOPIC PEAKS FOR MULTIPLY-CHARGED IONS

The recent proliferation of electrospray as an ionization method has g reatly increased the ability to perform analyses of large biomolecules by using mass spectrometry. The major advantage of electrospray is th e ability to produce multiply charged ions, which brings large molecul es down to a mass-to-charge ratio range amenable to most instruments. Multiple charging is also a disadvantage because mass (m) becomes ambi guous unless charge (z) can be assigned. This is typically performed w ith simple algorithms that use multiple peaks of the same m and differ ent z, but these methods are difficult to apply to complex mixtures an d not applicable when only one z appears for each m. The use of mass a nalyzers with higher resolving powers, like the Fourier transform mass spectrometer, allows resolution of isotopic peaks, providing an inter nal 1-Da mass scale that can be used for unambiguous charge assignment . Manual assignment of charge state from the isotopic peaks is time co nsuming and becomes inaccurate when either the signal level or resolvi ng power are low. For these cases, computer algorithms based on patter n recognition techniques have been developed to assist in assignment o f charge states to isotopic clusters. These routines provide for more rapid analysis with higher accuracy than available manually.