Recent developments in the field of mass spectrometry taking place at the Caltech Jet Propulsion Laboratory are highlighted. The pertinent research and development is aimed at producing an ultrahigh sensitivity mass spectrograph for both spaceflight and terrestrial applications. The unique aspect of the JPL developed technology is an integrating focal plane ion detector that obviates the need for spectral scanning since all ions over a wide mass range are monitored simultaneously. The ion detector utilizes electro-optical technology and is therefore referred to as an Electro-Optical Ion Detector (EOID). A technical description of the JPL MS/EOID, some of the current applications, and its potential benefits for internal contamination analysis are discussed

Giffin, C. E.

English

NASA Technical Reports Server

]85-295 52
2128184 J
Mass SpectrometryTechnologyat the Jet PropulsionLaboratory (JPL)
by
Charles E. Giffin
INTRODUCTION
I
The purpose of this presentationis to inform the members of the NASA
Human ProductivityWorking Group about recent developmentsin the field of
mass spectrometery taking place at the Caltech Jet Propulsion Laboratory. {
The pertinent research and development is aimed at producing an ultra-
high sensitivity mass spectrograph for both spaceflight and terrestrial
applications. The unique aspect of the JPL developed technology is an
integratingfocal plane ion detector that obviates the need for spectral
scanningsince all ions over a wide mass rangeare monitored simultaneously.
The ion detectorutilizeselectro-opticaltechnologyand is thereforereferred
to as an Electro-OpticalIon Detector (EOID). A technical description of }
the JPL MS/EOID, some of the current applications, and its potential
benefitsfor internalcontaminationanalysisare discussedbelow.
MS/EOIDTECHNOLOGY
Figure 1 illustratesthe comparisonbetweena scanning mass spectrometer
and a non-scanningmass spectrograph. Simplyput, the spectrometercan moni-
tor only one ion speciesat a time while the spectrographmonitors simultan-
eously all ion species illuminatingthe focal plane. For high sensitivity,
the spectrometerutilizes an electron multiplier for an ion detector which
can achieve the ability to detect single ions passing through the image
slit. Classically,the mass spectrographhas used a photoplateto simultan-
eouslymonitor all the ion speciesalong the focal plane but requiredapprox-
imately10,000 ions to generate a detectableimage in the photographicemul-
sion. The duty cycle (i.e.,the fraction of time spent measuringindividual
i 3-16
" ,x
-- ' ......... " _1, !;
1985021227-282
https://ntrs.nasa.gov/search.jsp?R=19850021240 2020-03-22T19:31:44+00:00Z
ion currentsduring a spectral scan period) of a scanning mass spectrometer
can be as low as 0.01% per mass peak over a mass range of 20:1. The mass
spectrographhas a 100% duty cycle. Hence several orders of magnitude in-
creasein spectral sensitivitycan be achieved with a spectrographfitted
with an ion detector capable of detecting single ions. The EOID achieves
w
this requirement.
Figure2 illustratesthe EOID concept. Ionsexitingthe magnetic field
i of a mass spectrographimpinge on a two dimensionsalmicrochannelelectron
_Jltiplierarray (MCA). For each ion entering a microchannel104 electrons
exit the channel and are acceleratedto the phosphored surface of a fiber
optic vacuum window. Approximately100 photons are generated for each im-
pingingelectron giving an overall ion-to-photongain of 106. The photons
are guided fiber opticallyto a self-scannedlinear photodiode array (PDA)
where signals are integrated,co_erted hack to electrons and sent to a
computer. Figure 3 is a photographof "ion" images appearing on the exit
face of the fiber optic windowarisingfrom a sample of perfluoro-iso-octane
(MW = 438 amu).
Figure4 is a schematicrepresentationof the MS/EOID hardware implemen- i
tation. The focal plane is 12.7 cm long and is viewed by five 1024element !
PDAs interdigitatedfiber-opticallyfor mechanicalreasons. Hence theMS/EOID !
has 5120 individualdetector ele_nts (photodiodes)continuously observing
the mass spectralsignal. Each photodiodeis inactive for only 8.3j#wswhile
it is being readoutto the computer. Spectralintegrationtime can be varied
fromseveraltens of millisecondsto tens of seconds. Figure 5 is a summary
of the existing "miniaturized"MS/EOID specificationsand Figure 6 is a
photographof the instrument.
3-17
_I _ _._
1985021227-283
'i
APPLICATIONS
Inherentin the MS/EOIDconceptis the potentialfor both highsensitivity
!
as well as rapid transientresponse. Differentapplicationsmay stress one
over the other and in some cases both are required. In general,however,the
preservationof complete spectral informationwhile detecting ion currents
with singleion sensitivityhas openedup some interestingfieldsof research.
An applicationstressing sensitivityis that of amino acid analysis
; from proteinn_lecules sequencedby the Edman degradationchemical process.
, Determinationof the protein structureis accomplishedby successivelyclip-
_ ping amino acids, one by one off the proteinmolecule in the sequenator,and
analyzingeach sample for the prominentamino acid in that residue. Liquid
chromotographycoupledwith UV detectionis typicallyused. Thls is both time
consumingand not very sensitive(30 minutes for an LC run and ~1 ng detecta- i
I
bility). An automatedMS/EOIDis currentlyunder developmentat JPL that has
an analysistime of one minute and a detectabilityapproaching1 pg. Figure
7 is a block diagramof the systemand Figures8 and g are representativedata. I
Efficientsampleacquisitionand transporttogetherwith samplecontamination
are areas of concernbeing presentlyworked.
An MS/EOIDinstrumentsystemis currentlyunder developmentthat requires '_
both fast transientresponsean__ddand high sensitivity. This system will be
utilizedfor the real-timeanalysisof ambientaerosolsand biologicalparti-
cles in air. This systemconcept is shown schematicallyin Figure 10. Am-
bientaerosolparticlesare extractedfrom the air and formedinto a beam by
a differentiallypumped capillary/skimmersystem. As the particlesstrike a
hot rhenium filament,they are volatilizedand the plume of vapor is sub-
sequentlyionized by an electron beam. The burst of ions thus genrated
(in a time span of ~100-200i_) is acceleratedinto the mass analyzer,separ-
ated accordingto mass, and integratedby the EOID. Complete mass spectra
from each volatilized/ionizedparticle can be read out at intervals as
3-18 "
1985021227-284
closelyspaced as 4U ins. Figures 11 and 12 are data gathered from 1.7 pm
diameterpotassiumbiphthalateparticlesand three differentbacterial
particleswithout the benefit of MS/EOID. In these cases approximately
1UUU particlesper peak were requiredto generate the statistics necessary
to quantitatethe ion intensitymeasurementsusing a quadrupolemass filter I
in the manual scan mode. The MS/EOID for the particle analysis research is
currentlybeing assembledand will be operationalby early spring. A laser
ionizationmethod is also under developmentand will be studied in detail
z
after the MS/EOIDis interfacedto the particlebeam inlet system.
I
! APPLICATIONTO SPACE STATION INTERNALCONTAMINATION
i It is the author's opinion that the potential role MS/EOID could play
in the area of internal contaminationwould be as a quantitiativeanalysis
i tool for the elucidationof atmosphericc_ntaminantsaboard Space Station.
With the hundredsof contaminantsfound over the years in spacecraftenviron-
ments, it would appear that combined gas chromotography-massspectrometery
offersthe best chance for accuratelyassessingpotentiallyhazardouscondi-
tions in the environment.
The existing MS/EOID at JPL covers a much broader mass range than is
required(a maximum mass limit of 300 amu should be adequate). A small
MS/EOID at the University of Minnesota (built for upper atmosphere ba!lon
borne measurements)is too small with a maximum mass limit of 50 amu. Pre-
liminarycalculations show that if one limits the focal plane length
to b.4 cm a medium size MS/EOID could be constructedcovering a mass range
from 15 amu to 30U amu while taking advantage of the latest sta.e-of-the-
art high resolution microchannelelectron multiplier array and photodiode
array devicesavailableon the market.
3-19 |
1985021227-285
iI
• 'i
4
I
t '
,| The rational for using an MS/EOID over a more conventional mass spec-
trometer is speed of response coupled with high sensitivity. _sere a micro
GC column (silicon wafer _ype) developed that could effect the required
!
separation of contaminant species then the MS/EOID would likely be the only
mass spectrometer that could measure the spectra of the very narrow (frac-
tional second) peaks eluting from the GC. Because of its small size, the
i silicon wafer GC also utilizes very small sample aliquots thus requiring
a high sensitivity detector for the quantitiatve measurement of trace species.
L
!
|
,?
t
t
f
,(
3-20 I
i
t
q
1985021227-286
f
i
3-21
L .... i....
1985021227-287
'i
I /
_e _i°
3-22
1985021227-288
OF. POOR QUALITY, -_
D
|
o i
i
i,
t
3-23
1985021227-289

3-25
l
I. "
• . • _-., ,_I"'_,: _ - -,
1985021227-291

J'27
1985021227-293
OF POOR QUALITY
m
• o . •
t -
M*
.I J Jill _ i
(o)
|
lJ._., _1l
N ,
Flgure8 Representative Line Spectra;
(a) GlycIne-PTH, (b) Prollne-PTH, ,_
(c) Leucine-P'lli
, 3-28
1985021227-294
o,%,.,.r,.4. PD.Q2";t_
OF.POOR QUALIT'_
! m211_ iw
,llu _,_ _ IiL,r° _ t:tl_-pTt_ ,411111,i_Clml llll6 6Ly*._Ii F!llo-m'rt4. li:li_IL, q,
T I 100mdl;leconds I T I = _lOm,llllecor_ll
2
" ii -
@
, I
1
,_- 11,52 K _,lr
(o) (',:>) i
i
Milll,lllm_ I_IMII(i-_, li'Ji3 ,_ItI:)+F_TH
Y
l I ,e_ond
I
F ; i '
7,= <_ •
7 • •
7 _ 30--
2 • 8
1 -
>-
"" 20_ •
- \ 10 -- --
i "
i /
- _ I I I I 1 .... L --L_J-- 1 I 1 I
a " 0.05 0.1 0.5 1.0 5 10
I ICll _UIlll _AS _ OF PROLINE Ina_I
t 11,_< {t Ill:
i (4 (a)
Figure 9 Glycine/Proline-PTH E1utlon Characteristics and Sensitivity
• Curve #i: m/e = 192, Curve 02: m/e = 232,
1 TI : Spectral Integration Tlme
3-29
1985021227-295
,w
• ,' q;'l
i
3-30
1985021227-296
" 't
T.
J
t
OE POOR OU,._LITY
3-31
1985021227-297
O.RIC._I_.ALP,_,O,£IS
OF POOR QUALITY J
100- a) Pseudomonasputida 150
>-
P 0
Z 56l,&,l
l--
Z 50-
- 164
I I I
100-- b) Bacillus cereus 149
150
>-
56 !
u_ 70Z
" 169 i50- -_Z
-- 61 83
1?']41iI; I
I I i ':
c) Bacillus subtilis 150
100-
56 14_u_
z I
Z 50- 67
114
83 96 164 282
I 1 I
80 160 240
M/E
Figure 12 MASSSPECTRAFROMBACTERIALPARTICLES
3-32 _
_l "_"
1985021227-298


Mass spectrometry technology at the Jet Propulsion Laboratory (JPL)

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server