Comparison of the internal energy distributions of ions produced by different electrospray sources

Abstract. The similarity between two tandem mass spectra, which were measured on different instruments, was compared quantitatively using the similarity index (SI), defined as the dot product of the square root of peak intensities in the respective spectra. This function was found to be useful for comparing energy-dependent tandem mass spectra obtained on various instruments. Spectral comparisons show the similarity index in a 2D Bheat map^, indicating which collision energy combinations result in similar spectra, and how good this agreement is. The results and methodology can be used in the pharma industry to design experiments and equipment well suited for good reproducibility. We suggest that to get good long-term reproducibility, it is best to adjust the collision energy to yield a spectrum very similar to a reference spectrum. It is likely to yield better results than using the same tuning file, which, for example, does not take into account that contamination of the ion source due to extended use may influence instrument tuning. The methodology may be used to characterize energy dependence on various instrument types, to optimize instrumentation, and to study the influence or correlation between various experimental parameters.

Section: Resultsmentioning

confidence: 99%

Section: Spectral Comparisonsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Quantitative Comparison of Tandem Mass Spectra Obtained on Various Instruments

Bazsó

Ozohanics

Schlosser

et al. 2016

“…Studies involving the effect of various instrumental parameters on the energetics of the ESI source have also been conducted, and they aimed at gaining a better understanding of the ionization mechanism and of the possibility of efficiently tuning the internal energy of the ions generated [49,[52][53][54]. It has been demonstrated that in ESI the shape of the P(E) curve corresponds approximately to a thermal energy distribution [53].…”

Section: Esorption Electrospray Ionization (Desi) Is An Ambient Ionmentioning

confidence: 99%

Internal energy distributions in desorption electrospray ionization (DESI)

Nefliu

Smith

Venter

et al. 2008

108

The internal energy distributions of typical ions generated by desorption electrospray ionization (DESI) were measured using the "survival yield" method, and compared with corresponding data for electrospray ionization (ESI) and electrosonic spray ionization (ESSI). The results show that the three ionization methods produce populations of ions having internal energy distributions of similar shapes and mean values (1.7-1.9 eV) suggesting similar phenomena, at least in the later stages of the process leading from solvated droplets to gas-phase ions. These data on energetics are consistent with the view that DESI involves "droplet pick-up" (liquid-liquid extraction) followed by ESI-like desolvation and gas-phase ion formation. The effects of various experimental parameters on the degree of fragmentation of p-methoxy-benzylpyridinium ions were compared between DESI and ESSI. The results show similar trends in the survival yields as a function of the nebulizing gas pressure, solvent flow rate, and distance from the sprayer tip to the MS inlet. These observations are consistent with the mechanism noted above and they also enable the user to exercise control over the energetics of the DESI ionization process, through manipulation of external and internal ion source parameters. [1, 24, 29 -32], and explosives detection [4,8,[33][34][35][36][37]. Investigations into the fundamentals of the droplet dynamics and ionization mechanism have also been conducted through systematic measurements of the droplet size and velocity [38], computer simulations [39], surface charging effects [40], or more simply, by evaluating the mass spectra of various types of analytes in conjunction with variations in the experimental parameters [41]. These investigations suggested that the primary ionization mechanism in DESI is "droplet pick-up", i.e., extraction of the analyte into the droplet, followed by electrospray ionization (ESI)-like mechanism in which the progeny droplets are desolvated yielding ionized molecules. One of the arguments supporting this conclusion, the similarity between the ESI and DESI mass spectra, also implies that the two ion sources should generate populations of ions with similar internal energy distributions, P(E). It should be noted though, that the initial events in the two experiments are quite different, and recent simulations show that the process of formation of progeny droplets from the initial ϳ4 m droplets in DESI is not dependent on charge build-up as it is in ESI. These dissimilarities need not result in differences in the final internal energy (E) since the later processes occurring in the atmospheric pressure interface are probably the same for these two processes and, as we will show later, dominate the energetics of the process.Here we use the "survival yield" (SY) method [42] applied to a set of thermometer ions (benzylpyridinium cations) to judge internal energy deposition associated with soft ionization techniques [43] to measure and compare the internal energy distributions of the ions generated b...

“…These observations are in keeping with the suggestion that initially an ion's kinetic energy is quenched through collisions with the helium buffer gas and that much of this quenched kinetic energy is redistributed as internal energy within the ion, thus the internal energy of the ion rises initially [11].°Quenching°of°the°internal°energy°(mainly°vibra-tional) is much less efficient and therefore occurs over longer°time-scales°(a°factor°of°ϳ10 2°l onger)° [11].°How- ever, these time-scales for the collisional cooling of ion internal energy do not agree with those observed by Danell°and°Glish° [1],°who°observed°that°the°boundary activated decomposition onsets of leucine-enkephalin ions formed by nanoflow electrospray did not vary with the collisional cooling period prior to dissociation, and therefore concluded that the ions are collisionally cooled within a few milliseconds. This apparent discrepancy in collisional cooling time-scales is likely to be attributable in part to the different ionization techniques used (resulting in ion populations of different internal and kinetic energies as discussed above), and partly because of the different instruments used (source geometry and transfer lens voltages have both been shown°to°effect°internal°energy° [19]). °It°is°also°possible that the discrepancy may be due in part to the different techniques used to gauge internal energy.…”

Section: Effect Of Ion "Cool Times" On Internal Energymentioning

confidence: 99%

Comparison of the effects of ionization mechanism, analyte concentration, and ion “cool-times” on the internal energies of peptide ions produced by electrospray and atmospheric pressure matrix-assisted laser desorption ionization

Konn

Murrell

Despeyroux

et al. 2005

The propensities of a series of peptide ions produced by both electrospray and atmospheric pressure matrix assisted laser desorption ionization (AP-MALDI) to fragment in an ion trap mass spectrometer under various conditions were studied in detail by measuring the extent of fragmentation of precursor ions by collision induced dissociation (CID) as a function of applied resonance excitation RF voltage. For the most basic peptides, the energy required to fragment MH ϩ ions generated by electrospray exceeded that required to fragment equivalent AP-MALDI ions under identical instrumental conditions; the reverse was observed for a peptide incorporating no basic residues, while peptides of intermediate basicity showed little difference between the ionization methods. This correlation between peptide basicity and the difference in the energy required to induce fragmentation of MH ϩ ions generated by AP-MALDI and electrospray is attributed primarily to a trend in the internal energies of the ions generated by AP-MALDI (the greater the difference in gas-phase basicities between the matrix and the analyte the greater the internal energy of the analyte ions produced). Furthermore the internal energies of ions produced by AP-MALDI, but not the equivalent ions formed by electrospray, were observed to decrease with decreasing analyte concentration. We attribute this finding to the cooling effect of endothermic dissociation of analyte ion/matrix molecule clusters following the matrix assisted laser desorption step. Time-resolved analyses (measurement of extent of fragmentation of precursor ions by CID as a function of pre-CID "cool times") revealed that cooling periods in excess of 250 ms were required to achieve internal energy equilibrium through cooling collisions with the helium buffer gas. Furthermore, these analyses demonstrated that, even after these extended cooling times, equivalent ions formed by the two ionization techniques showed different propensities to fragment. We conclude that the two different ionization techniques produce ion populations that may differ in their three-dimensional structure. T he initial internal energy of an ion is determined by the internal energy of the analyte molecule before ionization and the energy deposited during ionization. The additional internal energy that must be acquired during ion activation in order for dissociation to occur is defined by the initial internal energy of the ion. Thus, for a fixed activation energy the extent of ion decomposition is a measure of the initial internal energy of that ion. Therefore, in order to compare the initial internal energies of peptide ions produced by electrospray and AP-MALDI, a series of energyresolved tandem mass spectrometry experiments were performed, in which the extent of decomposition of precursor ions by CID was measured as a function of applied resonance excitation RF voltage.Danell and Glish [1] and Wysocki and coworkers [2] investigated the differences between the internal ener-