Preservation of a Labile Post-Translational Modification

In this work, the issue of preserving labile post-translational modifications (PTMs) for mass spectrometric analysis is studied. Electrospray ionization (ESI) and matrix assisted laser desorption ionization (MALDI) mass spectrometry (MS) are currently the methods of choice for the analysis of PTMs. However, even for softer ionization methods such as ESI and MALDI, several PTMs are labile and the modification can be lost upon ionization prior to MS detection. A new ionization method called alternating current (AC) ESI has been conjectured to be a 'softer' ionization technique, and, as such, is a candidate for preserving labile PTMs for high sensitivity and more efficient mass spectrometry. In this work, AC ESI and DC ESI are compared over a series of experimental studies using a model peptide. The impact of various parameters, including operating voltage, temperature, pH, and solvent, have been explored and the results analyzed within the context of potential PTM loss mechanisms. The results of this work demonstrate that AC ESI has significant potential to outperform DC ESI for pH-sensitive labile PTMs.