ThP416 Exploring dendrimers as calibrants for ion mobility-mass spectrometry (IM-MS)
SCOTT M. GRAYSON, Michael Malkoch, Jamie Godfrey, Surinthra Mongkhontreerat, Nick Tomczyk, Jakub Ujma, Kevin Giles
Tulane University, New Orleans, LA
KTH Royal Institute of Technology, Stockholm, SE-100 28, Sweden
Polymer Factory Sweden AB, Stockholm, SE-114 28, Sweden
Waters Corp., Wilmslow, SK9 4AX, United Kingdom
Introduction
The field of ion mobility – mass spectrometry (IM-MS) has matured rapidly in the last decade to provide a powerful tool for measuring aspects of molecular size and structure (specifically collision cross section, or CCS) while simultaneously providing accurate measurements of molecular mass (specifically m/z). However, as with any new means of characterization, reliable standards must be identified that provide precision in these measurements. Because dendrimers represent one of the rare synthetic macromolecules that can be prepared as truly monodisperse polymers while also exhibiting a relatively discrete, immutable size, they are logical materials to investigate as potential calibrants for IM-MS.
Methods
Dendrimers based on the 2,2-bis-(hydroxymethyl)propionic acid monomer (bis-MPA) were prepared using a benzylidene protecting group on both alcohols. After coupling the activated ester onto the desired oligo-alcohol core, removal of the benzylidene group revealed as second tier of alcohols that could be subjected to further iterations of dendrimer growth. Ion-mobility data were acquired on a standard SYNAPT G2-Si HDMS and a cyclic IMS enabled research platform that provides high-resolution IM-MS (HR-IM-MS) separations. This research platform comprises a modified SYNAPT HDMS system fitted with a prototype cyclic IMS device, dual gain ADC and modified TOF optics. Data were investigated using MassLynx, Driftscope and UNIFI software.
Preliminary Data or Plenary Speakers Abstract
Polyester dendrimers based on bis-MPA have already been explored as MALDI-TOF MS calibrants, and show advantages over traditional peptide/protein calibrants in regards to regularly spaced peaks from m/z = 750-30,000, an uncommon breadth in solubility, and extended shelf-lives. For ion mobility applications, initial evaluation focused on the lower molecular weight samples (755-1717), as these dendrimers were expected to generate single charged ions when mixed with alkali cations. Preliminary comparison against existing calibration standards such as polyalanine and Ultramark confirmed that the dendrimers provided strong ESI signal in a similar mass range (755-1717). While the ratio of CCS(N2) relative to m/z followed a trend similar to oligomeric polyaniline, the mass range and CCS(N2) continued beyond what was observed for the particular polyalanine sample (up to the 16-mer at m/z =1155.6). Ultramark, on the other hand, exhibited a higher mass range (1022-1922), but exhibited smaller CCS(N2) values up to 372.6 Å2. One of the distinct advantages then is the dendrimer calibrants provided CCS(N2) values as high as 431.9 Å2 . Another appealing feature of the dendritic calibrants is their relatively fixed size. Unlike linear polymers, which are well-known to exhibit significant changes in macromolecular size (e.g. from an extended rod-like conformations to more compact coils) depending upon the quality of the solvent when in solution, the highly branched dendrimers exhibit much less conformational flexibility. This more defined shape was confirmed by preliminary comparisons of mobility peak widths between a dendrimer (m/z = 975) and a poly(ethylene glycol) oligomer of similar molecular mass (m/z = 975). The observed peak width for the dendrimer were consistently more resolved than the linear polymer, with a ~ 20% reduction in FWHM values. These observation, combined with the inherent synthetic modularity of dendritic polymers, makes them attractive candidates for further investigation as ion mobility mass spectrometry calibrants.
Novel Aspect
Compact, monodisperse dendrimers shows promise as a general ion mobility, mass and collision cross section calibrant.
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