вход по аккаунту


Collision Activation Mass Spectrometry with Novel Analysis Technique.

код для вставкиСкачать
above mentioned drawbacks of the DADI method. If the
collision gas is admitted to or just behind the ion source,
the products formed by collisional processes in the first field
free region can be analyzed by the newly established “linked
scan t e ~ h n i q u e ” ~The
~ ] . operating principle of this method
consists essentially of giving daughter ions m i , m i ... arising
from a freely selectable parent ion m: so much additional
kinetic energy (velocity)that they acquire the same momentum
as their precursor m:. Having the same momentum they
are recorded at the same place as m: at the collector site
without altering the magnetic field. The required additional
kinetic energy is imparted by increasing the accelerating voltage I.: Thereby the ion trajectory in the electric sector is
stretched and in order to focus the beam on to the intermediate
slit the electric sector voltage E mus*
changed simultaneously (“linked)in such a way that VEIVremains constant.
A continuous linked scan of this sort produces a daughter
ion spectrum of m: much like a DADI scan, save that now
the principle of double focusing is operative. The signals are
sharp and d o not overlap. The measurement takes place earlier
with respect to formation of the investigated ions than in
the DADI configuration, reducing the probability of their
isomerization before collision.
We tested the method by examining the ion C12HloO+
(m/e 170)formed from diphenyl carbonate by decarboxylation
under electron impact. McLafferty et aLC4]have determined
Collision Activation Mass Spectrometry with Novel
Analysis Technique
By Richard Robbiani, Thomas Kuster, and Joseph Seibl“]
The analysis of collision induced degradation reactions of
ions in the gas phase (CA-mass spectrometry[’]) has acquired
increasing importance recently as a means for investigating
ion structures. Ion cyclotron resonance (ICR) is preferably
employed for such measurements, especially if ions of long
lifetimes are the subject of interest. Otherwise double focusing
mass spectrometers of Nier Johnson geometry are used in
the so called DADI mode of operation[’], whereby the collision
gas is admitted to the field free region between magnetic
and electric sector. This mode of operation requires reversal
of the instrument’s conventional configuration, as the magnetic
sector must precede the electric sector and therefore is not
easily applicable to existing instrumentation. In addition under
these conditions the principle of double focusing (mutual compensation of energy dispersion of electric and magnetic field)
is not operative for ions generated in this region. The peaks
appear broadened by collisional scattering and tend to overlap,
often in a quite disturbing manner.
We would like to point out that collision induced degradations can be investigated with double focusing mass spectrometers in their usual configuration (the electric sector preceding the magnetic sector) while simultaneously avoiding the
2 50
mie +
Id’ O-H
Fig. I . Collision activation spectra of m / e = 170 from diphenyl carbonate (a), diphenyl
ether (b), o-phenylphenol (c), and p-phenylphenol (d). Pure CA spectra, monomolecular
components have been eliminated by substraction.
[*] Prof. Dr. J . Seibl, Dr. R. Robbiani, Dr. T. Kuster
Laboratorium fur Organische Chemie der Eidgenossischen Technischen
Universitatstrasse 16, CH-8092 Zurich (Switzerland)
the DADI-CA spectrum of this product and compared it
with the spectra of diphenyl ether and the isomeric phenylphenols which were determined under identical conditions.
Ati<qew. Chem. I n t .
Ed. Euyl. 16 ( 1 9 7 7 ) N o . 2
The authors found that the decarboxylation product gave
a spectrum similar to that of the diphenyl ether but different
from those obtained from the phenylphenols and concluded,
that a diphenyl ether structure must be attributed to the
fragment of diphenyl carbonate. The conclusion is of course
somewhat relativized by the statement that the spectra of
the isomeric phenylphenols are mutually identical. Our LS-CA
spectra of the diphenyl carbonate fragment, of diphenyl ether,
and of two of the isomeric phenylphenols are shown in Figure
1. Corroborating the results reported in L4] the spectra of
fragment (a) and diphenyl ether (b) are virtually identical
and are taken to indicate identical structures. In accordance
with expectation, it appears that differences in internal energy
of the decomposing ions of different origin d o not influence
their behavior under CA conditions to any significant extent,
at least not in this case. The spectra of the isomeric pheaylphenols (c) and (d) are again different from (a) and (b), in
line with the finding in [51, but in contrast to the DAD1
results they are by no means identical. The differences are
absolutely sufficient for structural identification of the respective isomer. These opposing results of DADI-CA versus LS-CA
suggests that the molecular ions of phenylphenols can isomerize completely to a common structure within the short period
of time required to travel from the first to the second field-free
region of the instrument. To move the observational window
closer in time to the ion production process seems to be
a suitable way for analyzing ion processes preceding the collisional activation step.
The described method is applicable to other modes of operation like linked scan of sector- and magnet field as well,
and is suited for a further shift of the observational window
to even shorter time lags between ion formation and collision
process, as for example in combination with field-desorption
Received: November 4, 1976 [Z 615 IE]
German version: Angew. Chem. 89, 115 (1977)
CAS Registry numbers:
Diphenyl carbonate, 109-09-0; diphenyl ether, 101-84-8; o-phenylphenol, 9043-7; p-phenylphenol, 92-69-3
[l] K. Levsen, H. Schw,arz, Angew. Chem. 88, 589 (1976); Angew. Chem.
Int. Ed. Engl. 15, 509 (1976).
[2] U. P. Schfunegyer, Angew. Chem. 87, 731 (1975); Angew. Chem. Int.
Ed. Engl. 14, 679 (197s).
[3] A. F . Wesion, K . R. Jennings, S. Ecans, R. M. Elliott, Int. J. Mass
Spectrom. Ion Phys. 20, 317 (1976).
[4] F . W McLafferry, K. Lersen, Org. Mass Spectrom. 8, 355 (1974).
to give reactive nitrite ylides ( 2 u ) and/or ( Z b ) , which react,
for example, with dipolarophiles to form live-membered
Stabilized vinyl cations are reviewed in article by M. Hanack.
Classically stabilized cations of this type are a-arylvinyl ( 1 ),
dienyl (Z), and allenyl cations (3); the nonclassically stabilized
vinyl cations include cyclopropylvinyl ( 4 ) and cyclopropylidenemethyl cations ( 5 ) . Vinyl cations can be readily generated
heterocyclic compounds (3). Further possible reactions of ( I )
include photochemical dimerization and intramolecular reactions, when R'=vinyl or allyl. [Azirine Photochemistry. Acc.
Chem. Res. 9, 371-378 (1976); 61 references]
[Rd 916 IE-L]
by solvolysis, particularly if the "super leaving groups" F3CSOY and F9C4-S07 are employed. The more stable the
intermediary vinyl cation the less the rearrangement that takes
place in the solvolysis. [Stabilized Vinyl Cations. Acc. Chem.
Res. 9, 364-371 (1 976); 44 references]
[Rd 915 IE-L]
The photochemistry of 2H-azirines ( 1 ) is dealt with in an
article by A . Pudwu. 2 H-Azirines-cyclic amines-are versatile substrates which can serve as precursors for other heterocycles. They react both with electrophiles as well as with
nucleophiles and can participate as dienophiles or dipolarophiles in thermally allowed [4n, + z7[,] cycloadditions. O n electronic excitation 2H-azirines undergo irreversible ring opening
Ailyr11'. Chon.
16 ( 1 9 7 7 ) No. 2
The biological activity of sesquiterpenelactones forms the theme
of an article by E. Rodriguez, G . H. N . Towers, and J . C.
Mitchell. These compounds are characteristic components of
most Compositae, but are also occasionally found in other
angiosperms and even in liverworts. The bitter substances
often contain an a#-unsaturated y-lactone ring, which according to recent findings could be responsible for their activity
towards tumors and microorganisms as well as their cytoand phytotoxicity. Sesquiterpene lactones poison cattle, protect plants from being eaten by insects and in the case of
man give rise to allergic dermatitis on contact. [Biological
Activities of Sesquiterpene Lactones. Phytochemistry 15,
1573-1 580 (1976); 75 references]
[Rd 920 IE-R]
Без категории
Размер файла
201 Кб
mass, collision, activation, analysis, novem, spectrometry, techniques
Пожаловаться на содержимое документа