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A simple modification of mass spectrometer for the study of collision-induced fragmentations
Infernationaf Jaw-nal of Mass Specrromefv ad Ion Physics Ekevier PublishingCon;pany, Amsterdam. Printedin the Netherlands
SHORT
CO&lWLMCATIONS
A simple m&cation fragmentations
of a mass
spectrometer
for the study of colkion-induced
‘Xletastable peaks” are widely used in the identification of unknown organic compounds. hIany of the dittuse peaks which are attributed to the unimoiecular decomposition of metastabIe ions are, in fact, due to the coIIisioc-induced decomposition of ions with background g-as moIecr:%s. The effective cross-section for collisions between ions and neutral moIecuIes is in general much Iarger than for collisions between neutral moIecules. In the glancing collisions, very little momentum transfer occurs (a necessary condition fer the relationship m* = n~,~/rn~ to hofd) and it is Iikely that these collisions IargeIy increase the internal ener_q of the ion’ in the same way as energy is transferred from an electron beam. Thus the subsequent fragmentation shouId paraVel those observed by unimoIecuIar decomposition foIIowing electron bombardment. Previous work. notably by Jennings’, has shown the importance of collisioninduced decompositions. Jennings was able to show that the loss of large neutral fragments in coI:ision-induced processes prooably occurs fairiy rapidly in the lield-free region in much the same way that a normal fragment ion is formed by a series of unimolecuiar processes within the ion source. The resulting “metastable peaks” arc thus of pGrrticuIar importance in identifying the reactions by which normal fragment ions are formed. Studies in ion kinetic energy spectroscc_>y3 have also emphasized the very high sensitivity of detection of suchprocesses which can be reaIized_ These studies have also shown that collision-induced processes can be distinguished from unimolecular decompositions of metastable ions by the shape of the resuhant “metastabIe peak” as ~211 as by the pressure dependence of the “metastable peak” abundance_ Jennings varied his background pressure either by gently baking the mazs spectrometer or by deIiberateIy introducing small leaks into the vacuum sysrem. It is the purpose of this short communication to show that a controlled background pressure of any desired gas can be introduced very simply without detriment to the normal operation of the mass spectrometer. The note aIso ihustrates the variety of reactions which can be induced, by showing part of a simple mass spectrum. Construction details The compiete auxiIiary introduction system is shown schematica!Iy in Fig. 1. -4 flat about 1 inch square was Bed by hand on the flight tube between tne electric and magnetic sectors and a hole f/16- inch diameter whs driiled through the centre of this flat area A brass clamp was constructed as shown in the figure. It was Inr. J. Mass Spectrom.Ion Phys., 7 (1971) 88-92
SHORT
COMMUNICATIONS
89
Fig. 1. Schematic d i a g r a m o( the system used for i n t r o d u c i n g collision ~ts.
fitted with a seat for a 2a-inch d i a m e t e r O-ring a n d a brass t u b e t h r o u g h which gas c o u l d be fed t o the hole in the flight t u b e was h a r d soldered to the f r a m e o f the clamp. A c o m m e r c i a l E d w a r d s * high v a c u u m needle valve M o d e l L B 2 B was h a r d soldered to this brass tube. zhe other side o f the needle valve being c o n n e c t e d via a K o v a r - g l a s s seal to a t w o - t a p system ( s h o w n schematically in Fig. 1) b y m e a n s o f which s a m p l e at the desired pressure c o u l d be introduced.
Experimental T h e field-free region b e t w e e n the sectors o f the R M H - 2 m a s s s p e c t r o m e t e r ¢ u s e d in this w o r k is 590 m m long a n d it was f o u n d typically that as the pressure o f collision gas, indicated o n the gauge supplied w i t h the instrument, reached the o r d e r 10-5 t o r r there was n o further increase in the size o f the "'metastable p e a k s " a n d the n o r m a l m a s s p e a k s were a t t e n u a t e d , in general, b y a p p r o x i m a t e l y 30 ,%. This was n o t t r u e o f all n o r m a l m a s s peaks, however, a n d s o m e ( n o t a b l y m a s s 2 a n d mass 1) increased in size as *-he collision gas was introduced. M o s t o f the "'me'.astable p e a k s " so far o b s e r v e d increase in p e a k height b y a f a c t o r o f a b o u t 100 w h e n collision gas is introduced. In s o m e cases, however, the increase is m u c h smaller t h a n this; s o m e " m e t a s t a b l e p e a k s " a p p e a r to be f o r m e d b y truly unimolecular processes a n d d o n o t increase in height. It was f o u n d easily possible to c o n t r o l the pressure rise within the m a s s s p e c t r o m e t e r t o better t h a n I0 - 7 t o r r even w h e n gas was i n t r o d u c e d f r o m a t m o s p h e r i c pressure. Tlae RMI-I-2 m a s s s p e c t r o m e t e r is particularly suited t o m o d i f i c a t i o n in this w a y because it is divided into five differentially p u m p e d sections a n d the collision gas c a n b e confined within the field-free region. H o w e v e r , the modifications f o r i n t r o d u c i n g collision gas at a c o n t r o l l e d pressure c a n be readily carried o u t o n a n y single o r d o u b l e - f o c u s s i n g instrument. * Edw-ards High V a c u u m Ltd., M a n o r Royal, Crawley, Sussex, E n g l a n d .
Int. J. Mass Spectrom. Ion Phys., 7 (1971) 88-92.
SHORT
90
COMMUNICATIONS
Figs. 2,3 and 4 show part of the mass spectrum of pyrazine, with and without a prssure of 6x 10W6 torr of pyrazioe as collision gas. The sensitivity Lsed for
1
b
b
:
:
:
:
Fig. 2. Partial mass spectrum of pyrazine in the absence of coIlision gas.
Fig. 3. Partial mss spectrum of pyrazine WIIC~ collision gas at 6 x 10e6 tort E introduced to the field-free region in front of the magnetic sector- flhe spectrum is plotted at the same sensitivity as Fig. 2.) Inr_ J. _&fas.sSpecrrom. Ion Phys., 7 (1971) 88-92
SHORT
COMMUNICA-fIONS
9i
-.
c.4
*
-1c
a
-e
ht. 1. Mars Spemmn. Zon P&s-, 7 (1971) 88-92
92
SHORT
COMMUNICbLTIOMS
pIotting the spectrum in the absence of collision gas is near the maximum usable sensitivity. It can be seen that several new “metastable peaks” can be identified with certainty in the spectrum which includes collision gas. Although these peaks are not in the region of the mass spectrum most useful in structural diaguosis, it can be seen that most of the processes identified arise from fragmentations involving the parent mass of pyrazine (m/e 89) and of ions of masses 79,53 and 26, the major fragment ions in the normal s_pectrum.I&y thus provide valuable evidence of the routes by which these ions decompose. J. H. BEYNON R. M. CAPRIOLI
Department of Chemistry, Purdue Lkcersity, West Lofayette, Ind. 47907 (U.S.A.) 1 H. IV. ROSEXSIUCR
A>C
C. E.
MELTOK,
T. /. Chem. Pii_bs_, 26 (1957)
&ST
314.
2 K. R. JES?*'IXGS. ht. J_ Mass Spectrom. Ior? Ph~s , 1 (1968) 227. 3 J. I-i_ BEYXOX, R. M_ CAPRIOLI, W_ E. BXIXSGEE~ ~413 J. W. hw, Org. hfax Spectrom.. 3 (1970) 479. 4 J. H. BEYXOX, W. E. BMTIXGER, J. W. A.~TY XXD T. KOX&TS~, ht. J. Muss Specrrum. Zon P&s-,
3 (1969) 47_
First received January 22nd, 1971; in final form lMarch 18th, 1971. ht.
J. Mass Spectrum. Ion P&s.., 7 (1971) 88-92
A quadruple monopole mass spectrometer IMagnetic field mass spectrometers with multiple ion detectors or photoplates are best qualified to measure simultaneously and continuously several ion species with different masses. With mass spectrometers free of magnetic fields such as quadrupoles for instance, oniy ion s_mies of one single mass can be measured continuously. Even the well known time-of-flight spectrometers as well as the gated quadrupoIes aIs0 work discontinuously. For the study of dissociation phenomena in a short pulse of a hypervelocity gas flow, we sought a mass analyser with which we could measure four ion species simultaneously and continuously within a mass range from 1 u to 50 u. A 1 u mass resolution is sufIicient but multipliers for fast recording are necessary_ The shape of the spectrometer housing has to be that of a rocket of small diameter as the gas flow in the expansion chamber must be kept undisturbed_ On the other hand such an instrument should also be coupled to the end flange of a shock tube for measuring the time-current trac& of several ion species after shock wave reflection. For this purpose a high time resoIution of less than 10 psec is desirabIe in order to study ionization phenomenaWe did not find an appropriated commercial instrument for these investigations, so we constructed a simple mass spectrometer with the above properties. It ht. 3. Mass Spectrom. Ion Pfzys., 7 (1971) 92-95
SHORT
CO&lWLMCATIONS
A simple m&cation fragmentations
of a mass
spectrometer
for the study of colkion-induced
‘Xletastable peaks” are widely used in the identification of unknown organic compounds. hIany of the dittuse peaks which are attributed to the unimoiecular decomposition of metastabIe ions are, in fact, due to the coIIisioc-induced decomposition of ions with background g-as moIecr:%s. The effective cross-section for collisions between ions and neutral moIecuIes is in general much Iarger than for collisions between neutral moIecules. In the glancing collisions, very little momentum transfer occurs (a necessary condition fer the relationship m* = n~,~/rn~ to hofd) and it is Iikely that these collisions IargeIy increase the internal ener_q of the ion’ in the same way as energy is transferred from an electron beam. Thus the subsequent fragmentation shouId paraVel those observed by unimoIecuIar decomposition foIIowing electron bombardment. Previous work. notably by Jennings’, has shown the importance of collisioninduced decompositions. Jennings was able to show that the loss of large neutral fragments in coI:ision-induced processes prooably occurs fairiy rapidly in the lield-free region in much the same way that a normal fragment ion is formed by a series of unimolecuiar processes within the ion source. The resulting “metastable peaks” arc thus of pGrrticuIar importance in identifying the reactions by which normal fragment ions are formed. Studies in ion kinetic energy spectroscc_>y3 have also emphasized the very high sensitivity of detection of suchprocesses which can be reaIized_ These studies have also shown that collision-induced processes can be distinguished from unimolecular decompositions of metastable ions by the shape of the resuhant “metastabIe peak” as ~211 as by the pressure dependence of the “metastable peak” abundance_ Jennings varied his background pressure either by gently baking the mazs spectrometer or by deIiberateIy introducing small leaks into the vacuum sysrem. It is the purpose of this short communication to show that a controlled background pressure of any desired gas can be introduced very simply without detriment to the normal operation of the mass spectrometer. The note aIso ihustrates the variety of reactions which can be induced, by showing part of a simple mass spectrum. Construction details The compiete auxiIiary introduction system is shown schematica!Iy in Fig. 1. -4 flat about 1 inch square was Bed by hand on the flight tube between tne electric and magnetic sectors and a hole f/16- inch diameter whs driiled through the centre of this flat area A brass clamp was constructed as shown in the figure. It was Inr. J. Mass Spectrom.Ion Phys., 7 (1971) 88-92
SHORT
COMMUNICATIONS
89
Fig. 1. Schematic d i a g r a m o( the system used for i n t r o d u c i n g collision ~ts.
fitted with a seat for a 2a-inch d i a m e t e r O-ring a n d a brass t u b e t h r o u g h which gas c o u l d be fed t o the hole in the flight t u b e was h a r d soldered to the f r a m e o f the clamp. A c o m m e r c i a l E d w a r d s * high v a c u u m needle valve M o d e l L B 2 B was h a r d soldered to this brass tube. zhe other side o f the needle valve being c o n n e c t e d via a K o v a r - g l a s s seal to a t w o - t a p system ( s h o w n schematically in Fig. 1) b y m e a n s o f which s a m p l e at the desired pressure c o u l d be introduced.
Experimental T h e field-free region b e t w e e n the sectors o f the R M H - 2 m a s s s p e c t r o m e t e r ¢ u s e d in this w o r k is 590 m m long a n d it was f o u n d typically that as the pressure o f collision gas, indicated o n the gauge supplied w i t h the instrument, reached the o r d e r 10-5 t o r r there was n o further increase in the size o f the "'metastable p e a k s " a n d the n o r m a l m a s s p e a k s were a t t e n u a t e d , in general, b y a p p r o x i m a t e l y 30 ,%. This was n o t t r u e o f all n o r m a l m a s s peaks, however, a n d s o m e ( n o t a b l y m a s s 2 a n d mass 1) increased in size as *-he collision gas was introduced. M o s t o f the "'me'.astable p e a k s " so far o b s e r v e d increase in p e a k height b y a f a c t o r o f a b o u t 100 w h e n collision gas is introduced. In s o m e cases, however, the increase is m u c h smaller t h a n this; s o m e " m e t a s t a b l e p e a k s " a p p e a r to be f o r m e d b y truly unimolecular processes a n d d o n o t increase in height. It was f o u n d easily possible to c o n t r o l the pressure rise within the m a s s s p e c t r o m e t e r t o better t h a n I0 - 7 t o r r even w h e n gas was i n t r o d u c e d f r o m a t m o s p h e r i c pressure. Tlae RMI-I-2 m a s s s p e c t r o m e t e r is particularly suited t o m o d i f i c a t i o n in this w a y because it is divided into five differentially p u m p e d sections a n d the collision gas c a n b e confined within the field-free region. H o w e v e r , the modifications f o r i n t r o d u c i n g collision gas at a c o n t r o l l e d pressure c a n be readily carried o u t o n a n y single o r d o u b l e - f o c u s s i n g instrument. * Edw-ards High V a c u u m Ltd., M a n o r Royal, Crawley, Sussex, E n g l a n d .
Int. J. Mass Spectrom. Ion Phys., 7 (1971) 88-92.
SHORT
90
COMMUNICATIONS
Figs. 2,3 and 4 show part of the mass spectrum of pyrazine, with and without a prssure of 6x 10W6 torr of pyrazioe as collision gas. The sensitivity Lsed for
1
b
b
:
:
:
:
Fig. 2. Partial mass spectrum of pyrazine in the absence of coIlision gas.
Fig. 3. Partial mss spectrum of pyrazine WIIC~ collision gas at 6 x 10e6 tort E introduced to the field-free region in front of the magnetic sector- flhe spectrum is plotted at the same sensitivity as Fig. 2.) Inr_ J. _&fas.sSpecrrom. Ion Phys., 7 (1971) 88-92
SHORT
COMMUNICA-fIONS
9i
-.
c.4
*
-1c
a
-e
ht. 1. Mars Spemmn. Zon P&s-, 7 (1971) 88-92
92
SHORT
COMMUNICbLTIOMS
pIotting the spectrum in the absence of collision gas is near the maximum usable sensitivity. It can be seen that several new “metastable peaks” can be identified with certainty in the spectrum which includes collision gas. Although these peaks are not in the region of the mass spectrum most useful in structural diaguosis, it can be seen that most of the processes identified arise from fragmentations involving the parent mass of pyrazine (m/e 89) and of ions of masses 79,53 and 26, the major fragment ions in the normal s_pectrum.I&y thus provide valuable evidence of the routes by which these ions decompose. J. H. BEYNON R. M. CAPRIOLI
Department of Chemistry, Purdue Lkcersity, West Lofayette, Ind. 47907 (U.S.A.) 1 H. IV. ROSEXSIUCR
A>C
C. E.
MELTOK,
T. /. Chem. Pii_bs_, 26 (1957)
&ST
314.
2 K. R. JES?*'IXGS. ht. J_ Mass Spectrom. Ior? Ph~s , 1 (1968) 227. 3 J. I-i_ BEYXOX, R. M_ CAPRIOLI, W_ E. BXIXSGEE~ ~413 J. W. hw, Org. hfax Spectrom.. 3 (1970) 479. 4 J. H. BEYXOX, W. E. BMTIXGER, J. W. A.~TY XXD T. KOX&TS~, ht. J. Muss Specrrum. Zon P&s-,
3 (1969) 47_
First received January 22nd, 1971; in final form lMarch 18th, 1971. ht.
J. Mass Spectrum. Ion P&s.., 7 (1971) 88-92
A quadruple monopole mass spectrometer IMagnetic field mass spectrometers with multiple ion detectors or photoplates are best qualified to measure simultaneously and continuously several ion species with different masses. With mass spectrometers free of magnetic fields such as quadrupoles for instance, oniy ion s_mies of one single mass can be measured continuously. Even the well known time-of-flight spectrometers as well as the gated quadrupoIes aIs0 work discontinuously. For the study of dissociation phenomena in a short pulse of a hypervelocity gas flow, we sought a mass analyser with which we could measure four ion species simultaneously and continuously within a mass range from 1 u to 50 u. A 1 u mass resolution is sufIicient but multipliers for fast recording are necessary_ The shape of the spectrometer housing has to be that of a rocket of small diameter as the gas flow in the expansion chamber must be kept undisturbed_ On the other hand such an instrument should also be coupled to the end flange of a shock tube for measuring the time-current trac& of several ion species after shock wave reflection. For this purpose a high time resoIution of less than 10 psec is desirabIe in order to study ionization phenomenaWe did not find an appropriated commercial instrument for these investigations, so we constructed a simple mass spectrometer with the above properties. It ht. 3. Mass Spectrom. Ion Pfzys., 7 (1971) 92-95