Laser desorption mass spectrometry: Mechanisms and applications

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

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4 5

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