International Journal of Moss Spectrometry and Ion Physics, 53 (1983) 151-166 Elsevier Science Publishers B.V.. Amsterdam - Printed in The Netherlands
LASER DESORPTION
R.
J.
MASS SPECTROMETRY: MECHANISMS AND APPLICATIONS*
COTTER AND J.-C.
Department
of
University
School
151
TABET
Pharmacology of
and Experimental
Medicine,
725
Therapeutics,
North
Wolfe
Street,
The Johns Baltimore,
Hopkins
MD 21205
(U.S.A.)
ABSTRACT A conventional time-of-flight mass spectrometer has been adapted for pulsed This instrumental configuration enables investigation of 1 aser desorption. “time resolved” mass spectra, i.e. de1 ayed mass analysis following the 1 aser The energy spread of ions formed after the laser pul se is time pulse. To date this has enabled focussing of ions produced by 1 aser dependent. Mechanisms of laser desorption and applications of desorption up to 3628 amu. this instrumental configuration are discussed.
INTRODUCTION Five laser
years
ago,
desorption
by obtaining
for
mass
01 igopeptides. appl ications labile
of
there
for have
Ki stemaker,
et (m/z
magnetic
sector
V in
order
recorded
to
analysis of
laser
desorption
time,
(ref.2-11).
surprisingly al.
(ref.1)
few
cover
the
since required
molecul
ami n (m/z
ar
1345.5).
the
range.
Finally
to
Seydel
and
been
amu),
of
article ion,
et
Lindner
on the occasion honor at College
the which
by (M+Na)+,
al.
for
on their
was reduced
to
650
(ref.9)
dicyanocobalamin
0 1983 Elsevier Science Publishers B.V.
on
was obtained
voltage
and
(ref.l),
reports
us has
intensity
Hercules, for
of
molecular
signal
of
non-volatile/thermally
The original
(MH) +,
* Dedicated to Professor R. D, MacFarlane and presented at a symposirrm held in his - 18 May, 1983.
OOZO-7381/83/$03.00
for
accelerating
mass i ens,
glycosides
MW > 1,000
a cationized low
potential
biomolecules
a number
interest (i .e.
examples.
reported
been
spectrometry
particular
A relatively
instrument,
have
compounds
the
non-volatile
oligosaccharides,
mass
1 arge
demonstrated
large
there
Of
of
1251).
of
several
that
protonated
hydroxycobal
spectra
analysis
been
digitonin
mass
and coworkers
Since
compounds
potential
Ki stemaker
(ref.11)
of his Station,
(m/z
1041)
and
also
50th birthday TX, USA, 15
152 reported
the
laser and
instrument), lipid
interest
well
as the
phase
the
between
techniques.
Ki stemaker
ion
expl ained thermal
processes times
was
apparent
exists
that
times
lattice
from
in
energies are
when
desorption”
ion
These
ions”
results
are
.16),
report
of of
for
long in
ion
our
From this
own recent
latter
greater
abundance
can
be correlated R4N+ from
consistent
with
that
be bett.er
evidence
KCl,
this ions
who noted
and
the
support
molecular
might
rather
K+ from
gas
for
to
of
Strong
times
also
as
“soft
appear
(ref
(ref.18).
(i.e.
process,
species
solids
in
been
measurements
(ref.4,6,17)
desorption
has
desorption
ev)
and
demonstrated
formation
may be desorbed
“preformed
considered.
the
which
pulses
other
laser
their
aromatic
studies
the
(M+K)+
(0.26
(MW 1890)
there
{ ref .12)
the
a time-of-flight
desorption
and
process.
laser species
laser
by Heinen
laser
and that
technique
for
for
non-polar
those
ions,
> 2,000).
the
ions
model
short
neutral
than
desorbed
(mu1 ti-photon)
following
(m/z this
cationized
al so suggested
Mf,
compound
Furthermore,
laser
A thermal
on “time-resolved
longer
etc .)
(ref.13,14),
as an el ectronic
emission report
model
formation,
A-like
desorption
a thermal
of
(on
and co-workers
suggested
attachement
radical
laser
of
of
(ref.15).
by alkali
of
formation
spreads
interpretation
vanielli
reaction
compounds energy
digitonin
1 ipid
and mechanisms
relationship
non-volatile kinetic
a synthetic
of
on applications
nature
and have
spectrum
Rhodomicrobium
reports
ion-molecule
sucrose,
mass
from
from with
in
ionization”
is
spectra
A extracted Concurrent
an
desorption
work and
it
for
with R4NC1,
a thermal
model
(ref.18). Determination is
an important
spreads noted
range
the for
of
6 to for
suggested
desorption the
ion
25 ev the
that
kinetic
-19)
, while
of
ions
distinct
processes.
produced
by a 1 aser
thin
bulk
suggested
kinetic
spreads
as
large
dependent
measurements
pul se
indicated
that,
the
as
effects
of
have
the
threshold
total of
been and
spreads 50 ev
is are
these
ions
The thermal
Hardin
Hillenkamp
and that
Time
by
mechanism
thermal
(ref.21))
at
sms.
energy
(ref.20).
while
films,
desorbed
instrument)
non-equilibrium)
solids
laser
measurements
instruments
(i.e.
from of
sector
ight
energy
of
formation,mechani
a magnetic
have
microprobe
a non-thermal
ion
time-of-f1
instrument (ref
distributions
the
(on
However,
laser
evaporation
energy
elucidating
by Ki stemaker
( ref -15).
on a quadrupole
reported
in
key
measured above
Vestal
the
of
in
have
the been
has involved
in
predominant
represent
two
ion
current
ion
formation,
153 ions
are
produced
produced
additional
considered
to
resolved ions
promptly ions
for
be equilibrium
spectra
produced
following
(~60
for
laser
laser
microseconds effects.
ions
to
the
several
range
pulse,
while
thermal
potassium
by the
the
ns),
from
higher
laser
(ref.22).
indicate
very of
of
The
Recently
which
tenths
use
we have
that
high
the
values
an electron
latter
are
reported
energy
time-
spread
of
ev) , immediately
(lo-20
volt
power
several
microseconds
1 ater.
In this mass
paper
we report
spectrometry
detection
which
and
on and
pertain
discuss
both
to
several the
applications
of
the
technique
particular
we demonstrate
the
use
of
the
spread
recorded
in
sensitivity
for
mass
desorption
mass
energy
focussing
and
of
ions
high
the
to time
the
aspects
mechanisms
of
of
non-volatile delayed
mass
laser
ion
desorption
formation/
In
molecules.
technique
spectrum
and
for
for
reducing
improving
the
ions.
METHODS The
laser
viously
(ref
Model
2000
laser
is
40
the
at
signals
housing
the
sample
are
recorded
digitized 8100
and
via
in
the
2048
with
are
a maximum to
interface.
laser
CO2 laser The
1 aser
each
a Biomation
time
resolution II+
Generally
is
power
entire
an Apple
a pulse
beam
focussed
and
not
laser to
spatial of
While
density
1 aser
pulse, spectra
the
and
irradiation,
500 LIS
microprobe
instruments
(ref.21).
small is
a spot al so
ion
size
improved
region may
upon
application
( ref .18)
and
enables
is
the
particle
does
to
‘mass \\\
Secondly,
region of
is
a drawout the
study
time
which
loss
larger
the
\
laser
may
for the
beam _,
broader
(ref.23). of
resolution
total
period are
dependent
spectra
instruments
some
Ions
pulse, of
in
during
field-free.
pulsed
resembles
produce
be
micro-
beam methods
result
analog can
instruz&tal.Lconfi-
by it
the
CA) Model
time”
this
required
on
10 nS/channel.
The
Rather,
be expected
sensitivity. source
as
important. of
formation
configuration
the.ion only
between
characteristic
larger this
currents
as
differences
onto
of
(Cupertino,
“real
fundamental
resolution
irradiation
(ref.241,
source
the
focussed
which type
several
of
mounted
(Cupertino,iCA)
twenty
NY)
width
mass
of
pre-
The
GaAs lens,
estimated
which
of
with
length
Following
from
channels
transferred
desorption,
The
MW/cm2.
multiplier
a parallel
are
guration
to
is *rl the
CVC (Rochester,
focal
region.
detail
added. There
is
source
in
for
1 Hz.
a 10”
described
a standard
215A
of
using
at
recorder,
spectra-
computer
the
surface
stored
waveform
Digitized
were
of
rate
mm2)
been
modified
MA) Model
repetition (41
is
tube,
(Needham.
area
has
spectrometer
a 2m flight
a maximum
sample
vacuum
beam
The mass
a Tachisto
nS and
a broad
.18) _ TOF with
spectrometer
of
withdrawn be delayed phenomena.
ion laser from for
the up
154 On normal initiated
operation,
by the
selected
Ma+,
TABLE
1
sample 0.01 0.02 0.05 0.10 0.20
“sample
K+ and
resol
ution,
used
to
also
so that
the
record
only )
the
Kinetic
energy time
the
delay
emission
of
energy
This
.
ions is
high
and
kinetic
40
where
from
U
mass
energy
to 28
mass, be
the
ranges
mass
(TABLE
known
flight
range amu alllu amu amu arnu
result
in
itself
can
spectrum
of
two
the
spreads
K+ ion
are
by the
loss
at
pulse
of
also
time
be
maximum
model
the
source
region
been
shown
in
ions
which
of
at
a rate
The
at
decreasing
predicts
between
Fig.1.
by
continued
relaxation
microseconds
period
reported
pulse
First,
produces
several
has
drawout
effects.
during
following ion
formation
proportional
of the and
to
their
sampled
results
*“O
l/2
(1)
S
)
initial= distance = time to
more
kinetic energy in the source region travel the distance s
energetic
by the
was determined
spread
the
over
=
t
region
the
is
ions.
energy
a thermal
m _--
=
SO
of
the
sampled
nS laser
with
t
a given
range
energy:
t
For
using
Biomation
of
for ions
result
Secondly, drift
the
desorbed
temperatures
(ref.13).
d.rawout , ions
ion mass
the
consistent
instantaneous pulse
of
the
of
mass
kinetic
results
after
The mass
l50 l200 l1,250 l- 5,000 l-20,000
higher
laser
initial
the
is
is
recorder
mass
section
spread
times
spectrum
= kMl’*+b,
US cls US fiS &S
that
of
and
waveform
time
mass
of
energy
pulse.
microcomputer t
mass
ution.
distribution
(ref.25) in
increasing
high
the
laser
Biomation
by the
features
resol
dependence
recently
Odecrease
delay
time
AND DISCUSSION
The
obvious
of
the
equation,
20.48 40.96 102.40 204.80 409.60
RESULTS
laser
the
total
is
AS/channel
than
” on the
made
US/channel US/channel pS/channel US/channel US/channel
TABLE 1 it
the
are
Cs+ and
recording
rather
interval
interval
From
us
digitized
pulse
assignments
of
(0.01
drawout
by the
1) , and mass times
the
drawout
earlier
shown
in
ions field. (ref.25)
Fig.
I
cover
are
lost
However, as
more the
quickly
“ha1 f-life”
approximately
a period
of
from
1 US. time
much
the of
Since lbnger
ions the than
155
LASER
MSOAPTION K+
Fig.
that
needed
decrease
1. Peak width
to
in
clear
the
The average magnitude 774’K)
similar
istic
the
drawout
with
high
suggested instrunental
to
the
pulse
produced
of
consistent
of
the
formed
ions
order
there
energy
by Hillenkamp configuration
is are
source,
of
very
long
are
reflects
after
the
thermal
thermionic
emission
10 ev and greater
low
produced
(ref.21,22)
the data
an equilibrium of
time.
a real
by desorption,
some uncertainty
are
W,DM
temperatures.
of
KCL
vs. delay
produced
with
surface
promptly
kinetic
from the
mechanisms
equilibrium
ions
ions
is
energies
real
of potassium
of ions
energies
that
However,
the
energy
PEAI:
OF
in
the
while
the around
are
of
(i.e.
0.1
ev =
from
of
a hot
It
is
finite
highest
intensities to
2.0
t=o,
that
excitation
20 clS (1.0
into
width of
1 ikely
a
filament_
be translated
the
determination
by non-equilibrium
recorded
pulse
cannot
Because
intensity,
laser model
the as
for ev).
this
of and ions
156 Laser 1.
desorption
spectra.
Tr.imethylene Fig.
bis
2 shows
(pyri-diniun
the
laser
desorption
bromide).
The doubly-charged
consistent
with
desorption
{ ref .26).
other
bromide)
cation
desorption
spectrum (m/z
methods
Si ngly-charged
100) with
cations
of
trimethylene
is
not
the are
bis
observed,
exception
of
80
c
N+-CH3
m/z
94
C
N+-CH=CH2
m/z
106
0
0
which field
produced:
m/t
Na+
Li+
_I_
Fig. 2. Laser bis (pyridinium
desorption bromide).
mass
spectrum
of
(pyridinium
trimethylene
is
157
0 0
by decomposition addition
the
resolution
reactions unresolved
using
the
which peaks
fast
0
which
indicates is
that
Fl ufenamic
2.
The
laser
conjugate
of
cationized
acid
of
200,202
the
have
charge been
technique
120
centers.
In
investigated
at
m/z
200
N+-CH2-CH2-CH2-Br
m/z
200,202
of
one
of
leading
the to
high
(ref.26):
+-CH2-CH2-CH2-N
process
char’ges
by addition
singly-charged
of
an
cations.
gl ucuronide.
desorption
spectrtmi
flufenamic
intact
m/z
one
bombardment
reduction
a favorable
remove
at
atom
C electron
m/z
+-CH2-CH=CH2
acid
molecule
is and
of
the
shown the
in
enzyme Fig.
catalyzed
3.
glucuronic
Ions
acid
and
glucuronic
acid
corresponding aglycon
to
the
moieties
are
observed.
3.
Phosphatidyl
choline.
Phosphatidyl
choline
analyzed
by laser
easily Fig.
4.
4 corresponds
Cesium
iodide.
Cesium
iodide
met hods.
The
20
spectra
of
the
two
has
sodium
in
have Fig.
converted is
a quaternary
desorption.
the
clusters
spectrum
(each
spectrum
clusters
to
is
been
multiplied
(m/r
8-bit the X100.
such
molecular
“preformed species
ions”
are
reported
in
645).
observed
5 illustrates
to
and
The major salt
been
into
normalized
amine,
numbers) Cs+ ion,
using the
most
dynamic
are
added.
while
the
of
the
range The intensity
desorption available lower of
when
portion the
upper
168 CSC
USER
DESORPTION
FLUFENMIC
ACID
SPECTRUM GL”C”RONlDE
K+
\+NA+ 483.3
HA
542
676
535
1oas
1283
CHANNEL
Fig. acid
3. Laser glucuroni&.
desorption (sample
200
mass spectrum courtesy R.
phosphotidyl
of flufenamic Van Breemen).
choline
di-laurcyl
186 WH+N~)+ 645
Fig. 4. choline.
Laser
desorption
mass
spectrum
of
phosphotidyl
159
Cs&+ 653
cs4 13+
K+
Na+
Fig. 5. iodide. Face-to-face
5.
Figs.
In both
Time
Fig. different by
the
cases,
7 show
8 shows delay
the times.
electronic
of
mass
1
653
spectrum
of
cesium
dimers. the
M+K+ ions
focussing
same
desorption
porphyrin
6 and
delay
Laser
“*I;
laser are
high
mass
desorption
the
major
mass
spectra
In pulse
this
sample
of
two
porphyrin
dimers.
ions.
ions. of
case
which
spectra
cyclosporin the
triggers
A (MW 1201)
waveform the
recorder laser,
at has
so that
several been the
triggered laser
160
tH-N
I
Fig. 6. porphyrin et. al.,
\
--p-“yNH
N
\
1018.5
Laser desorption mass spectrum dimer. (compound synthesized ref. 30)
of the by J-P
H (FTF4) &lman,
161
Na+
I
cs+
Fig. 7. Laser desorption mass spectrum of the Co (FTF4) i;rph$-in dimer. (cornp ound synthesized by J.P.C87lmn, _ ., ref. 30)
162 “flash” of
and
the
the
mass
of
0.1
10 nS/channel)
Most In
noticeably,
of
are
this
desorption
technique a number
of that
following
flight
tube.
Analysis The been
the
laser
General
instrunent
(-2.7
used
to
obtained molecular
ion
@/channel) whether can
to
Mf or
be analyzed
the
portion
(time
resolution
of
the
record
MH+ ion
and
detected.
the
the
up.”
initial
peaks
due
laser
to
source
period
ions
ions
of
for
is
no longer mass
9-12
of
1202
low
energy The
It
l
MH+ ions
time
de1 ay
decomposition
described
may al so be
produced prior
at
JJS, continued
technique
(ref.24)
this
of
escape.
energy,
during
However,
of
fragmentation
techniques
desorption
promptly to
mass
occuring
analysis
in
the
instruments and
Cs’
voltages array
9.
ion
higher detectors
mass
the
peak.
spectrum
formed,
it
produces is
clear
that
Standing
of
our
to
our
3628
resolution
ions
of
instrumental was
produce
some uncertainty that
in
post-acceleration
phophazine
time
beam
by MacFarlane
used
of
generally
particle
than
was tuned the
of
by
As a test
delay While
used
has
beam used
and/or
spectrum
The time
base
some form
techniques
pulsed
and detection.
this is
occur.
“cleaned the
by the
on time-of-flight
desorption
as
been
of
life
sources
metastable
changes
mass- ions.
or
Fig_
has
1 ag focussing”
internal
ions
plasma
in
several
decreased.
in
the
“time
undergone
high mass
laser
species
used the
region
concentration
impact
transmission
shown
in
the
ly , accelerating
the is
a time
spectrum.
ha1 f
energetic
greatest
.28),
ions
and more to
also
the
building
coincidence
(ref
improve
and
Thus,
AIS.
from
of
in
6.6
kV) , mu1 tichannel
configuration,
(at
1 ing”
produced
the
have
high
as the
Field
(ref,29).
spectra
reflecting
“tai is
ions
of
electron
pulse
using
such
hand
US
ion,
tube
of
(1))
“tailing”
of
flight
time
the
and detection
and
left
spectrum
the
equation
similar for
the
molecular
improvements
of
with
the
complete
JJS ta
of
the
the
lighter
ago
accomplished
(ref.27)
are
about
is
analysis
desorption,
12.3
residence
effect
ions
the
reduces
9.5
from
energy
to
while
years
which
ion
Finally,
in
the
therefore
expected
molecular
portion
obvious
is
has
on the
and the
of
kinetic
size,
source,
signals
both
decreased.
in
energies
the
mass
widths
Referring
thermal
in
low
peak
produces
negligible.
as
figure,
changed
decomposition
period
masses
is
the the
The decrease time
the
appear
illustrated.
time
spreads,
both
AS/channel)
delay
metastablc
In
are
addition,
energy
pulse
spectrum.
resolution
As the
drawout
this
a
(0.2 as to magnitude
163
LASER PULSE
I
DELAY TIrE ~ul.4us LASER PULSE
K+
JEUY TIME 12.3 us LASER
Fig. 8. Laser desorption mass spectra of CYCLOSPORIN A (MW 1201) at 9.5, 10.4 and 12.3 US after the laser pulse. Spectra on the left cover the full mass range at a time resolution of 0.1 us/channel, Spectra on the right were delayed 100 us to cover the molecular ion region at a time resolution of 10 ns/channel. Molecular ion species include: MH+, MNa+, MK', (M-H+2Na)+, (M-H+Na+K)+ and (M-H+2K)+.
LASER DESORPT ION PHOSPHAZINE
C~~~~4O~~lza~4~4
I
M,W. 3628 (58
Fig.
(MW
9.
Laser
3628).
SCANS)
desorption
mass spectrum
of
phosphazine
166 CONCLUSIONS The
increase
in
high
evaporation/desorption note
for
point
, analysis
general can
the
future of
been weak.
ly
be desorbed
spread
in
and metastable
analytical
mass
sensitivity
and time analytical
ions
great
potential’
greater
The
delayed
than
results abundance
decomposition
m/z
resulting (energy) of
and that will
suggest
the
that to
an encouraging Up
been_ rare,
attention
improve
form
desorption.
have
here
sample
bulk
focussing
laser
1000
reported
from
and high
the
to this signals mass
effects
viability
of
of
have ions energy
this
technique.
ACKNOWLEDGEMENT This Science
work
was supported
by a grant,
CHE-80-16440,
from
the
National
Foundation.
REFERENCES 1
z
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