Size Effect on Fragmentation in Tandem Mass Spectrometry

Abstract

The collision energy or collision voltage necessary to obtain 50% fragmentation (characteristic collision energy/voltage, CCE or CCV) has been systematically determined for different types of molecules [poly(ethylene glycols) (PEG), poly(tetrahydrofuran) (PTHF), and peptides] over a wide mass (degrees of freedom) range. In the case of lithium-cationized PEGs a clear linear correlation (R(2) > 0.996) has been found between CCE and precursor ion mass on various instrument types up to 4.5 kDa. A similar linear correlation was observed between CCV and the mass-to-charge ratio. For singly and multiply charged polymers studied under a variety of experimental conditions and on several instruments, all data were plotted together and showed correlation coefficient R(2) = 0.991. A prerequisite to observe such a good linear correlation is that the energy and entropy of activation in a class of polymers is likely to remain constant. When compounds of different structure are compared, the CCV will depend not only on the molecular mass but the activation energy and entropy as well. This finding has both theoretical and practical importance. From a theoretical point of view it suggests fast energy randomization up to at least 4.5 kDa so that statistical rate theories are applicable in this range. These results also suggest an easy method for instrument tuning for high-throughput structural characterization through tandem MS: after a standard compound is measured, the optimum excitation voltage is in a simple proportion with the mass of any structurally similar analyte at constant experimental conditions.

A Comparison of Energy-Resolved Vibrational Activation/Dissociation Characteristics of Protonated and Sodiated High Mannose N-Glycopeptides

“…Among the precursor ion doubly protonated precursor ions, the order of precursor ion depletion with increasing vibrational energy deposition was consistent with general predictions based on proton mobility [29,30] as well as predictions for vibrational energy deposition requirement based on the number of vibrational degrees of freedom ( Figure 1a) [38,39]. For instance, the [NLTK + GlcNAc 2 Man 5 + 2H] 2+ underwent dissociation at lower collision energies than the other protonated precursor ions.…”

“…The value of E k50 alone is of limited use for comparing precursor ion stabilities, as the amount of vibrational energy required to bring about unimolecular dissociation also depends on the number of available vibrational degrees of freedom, f v [38,39]. The value of f v is calculated as:…”

Quantitative Comparison of Tandem Mass Spectra Obtained on Various Instruments

“…The similarity index in this range is better than 0.99, comparable to that observed among the quadrupole type instruments. This collision energy range corresponds to the beginning of fragmentation; the survival yield [10,11,14] is 50% or higher (i.e., the sum of fragment ion intensities is less than the intensity of the protonated molecule). This energy range may be useful for identifying low energy fragments (e.g., for identifying glycoforms).…”

“…Various tuning parameters, ion-molecule reactions (mainly in ion traps), and contaminations in the ion source or ion optics may also influence relative ion intensities, although these have usually minor effect compared with the effect of collision energy. Studying energydependent (or energy resolved) mass spectra it is typical to keep all instrument parameters constant, and vary the collision energy only [9][10][11]. Note that in single stage mass spectra using electrospray ionization, similar changes may be induced varying the skimmer/cone voltage [12].…”

“…It is known that ion trap instruments often yield different tandem mass spectra from quadrupole type instruments, but quantitative comparisons are relatively rare. A recent study on leucine enkephalin (YGGFL [13]) has shown that setting the collision energy to a value producing 50% survival yield [10,11,14] (when the total abundance of fragments is equal to that of the protonated molecule), tandem mass spectra obtained on various instrument types are qualitatively similar [13], although Bsimilarity^was not defined in a quantitative manner.…”