Are Derrick shifts real? An investigation by tandem mass spectrometry

Abstract

The phenomenon of collision-induced dissociation (CID) of fast ions, prompted by collisions with thermal gas molecules, has been known since the earliest days of mass spectrometry.' It has since become well established2 that the overall CID process can be meaningfully separated into two consecutive steps occurring on well-separated timescales. The first is a fast (-10-'s-10-'4s) collisional activation (CA) step in which some portion of the initial translational energy To of the fast ion is converted into internal energy of both projectile and target, as well as into translational energy of the latter. The second step is the dissociation of the now energized (and isolated) projectile ion, and is often considered in terms of statistical theories of unimolecular reaction rates:The energized projectile ions M+" which emerge from the CA step (i) have lost translational energy AT, given by: A T G ( T ( ) -T ) = A E & + A E~+ TG (2)where T and TG are the post-collision translational energies of Mf and of the (formerly thermal) target G, respectively. AE" represents a change in internal energy resulting from the collision. Study of CID processes of fast ions (keV energy range) has been conducted in mass spectrometers using techniques such as mass analysed ion kinetic energy spectroscopy (MIKES) .3 Such translational energy spectra are commonly transformed to mass spectra (masses of fragment ions F' ) via the simple relationship:where m denotes mass and TF is the translational energy of fragment F' . Equation (3) is a simple consequence of conservation of mass, momentum and translational energy under the restrictive assumptions that AT, (2), is zero, and that there is zero conversion of the internal energy of M f " to translational energy of the fragments in step (ii), (1). The latter assumption may be shown' to introduce negligible error to the assignment of fragment ion mass mF from measured values of TF, although this effect does result in the ' NRCC No. 28467i Author to whom correspondence should be addressed well-known broadening of the peaks in translational energy spectra. The first assumption ( A T = ( ) ) is almost always made in work of this kind, although it is clear that it cannot, in principle, be exactly valid for CID reactions. Early examples of appreciable translational energy shifts (defined as shifts from peaks arising from unimolecular reaction ( A T = 0 by definition) to peaks due to the corresponding CID reaction) have been published (e.g. Fig. 80 of Ref. 3). Nonetheless, interpretation of translational energy spectra of fragment ions formed by CID reactions has almost invariably employed (3). In the case of small organic ions, such mass assignments are unlikely to be in serious error since (3) can be corrected and then differentiated to give:For the typical values T,, = 8000 eV and mM = 100 Da, AT, (for AmF=lDa) is about 80eV. Such a large translational energy loss is impossible4 if the resulting trajectory is to fall within the acceptance aperture of the analysing sector, even if the mass of the t...

Unimolecular and collision‐induced dissociation reactions of peracetylated methyl glucopyranoside

“…For simplicity in the description of the acetylated hexose species, the code 'Ac246' will refer to a species with acetates located at C(2), C(4) and C (6). Similarly, Ac23 represents a species which retains acetates at C(2) and C(3).…”

“…Peracetylated methyl glucopyranoside was prepared with deuterium-labelled (d3) acetates at C(2), C(3), C (4) and C(6), and doubly labelled on C(4) and C (6), and on C(2) and C(3) starting from methyl-a-~-4,6-benzylidene glucopyranoside. This was protected with one tertbutyldimethylsilyl group at the 2and 3-OH groups (separated by column chromatography on silica gel) followed by acetylation with acetic anhydride-d, and deprotection followed by acetylation and purification by column chromatography on silica gel giving rise to 2a and 2b.…”

Fast‐atom bombardment mass spectrometric study of some N‐ and S‐glycosides of acetylated hexose isomers

“…3). The 2-deoxy derivative (7) affords nearly the same peak-ratio as compound 4, indicating that the absence of the C-2 acetyl group does not affect the extent of acetic acid loss. In the case of the 3-OMe derivative (8) the situation is completely different.…”

Critical Moments in Time: Reflections on the Development of Orthogonal Acceleration Time-of-Flight Mass Spectrometry

“…Bateman provided a copy of the paper to Guilhaus prior to publication in case he had some objection or wished to claim coauthorship, neither of which he did. The magnetic sector-oa-TOF provided an elegant solution to the difficulties that had plagued other configurations, including four-sectors and sectorquadrupole instruments [32][33][34]. VG went on to successfully commercialize this technology, receiving orders for the first magnetic sector oa-time-of-flight instruments late in 1992 [35].…”