U.S. patent number 3,886,365 [Application Number 05/391,721] was granted by the patent office on 1975-05-27 for multiconfiguration ionization source.
This patent grant is currently assigned to Hewlett-Packard Company. Invention is credited to William P. Kruger, John A. Michnowicz.
United States Patent |
3,886,365 |
Kruger , et al. |
May 27, 1975 |
Multiconfiguration ionization source
Abstract
This is an ion-producing source having a distinct chemical
ionization configuration and a distinct electron impact
configuration. In this source, a hollow chamber including an ion
source and a source of sample molecules receives a hollow, slidable
cylindrical member having a chemical ionization chamber within it.
Orifices in the chamber and the cylindrical member connect the
chemical ionization source chamber to the electron source and to
the sample molecule source when the cylindrical member is pulled to
one position. When the cylindrical member is pulled to another
position, the slidable cylindrical member and the inside walls of
the chamber define the ionization region to which the electron
source and the sample molecule source are directly connected. By
moving the cylindrical member, the ionization source can be changed
from a chemical ionization source to an electron impact source.
Inventors: |
Kruger; William P. (Los Altos
Hills, CA), Michnowicz; John A. (Santa Clara, CA) |
Assignee: |
Hewlett-Packard Company (Palo
Alto, CA)
|
Family
ID: |
23547673 |
Appl.
No.: |
05/391,721 |
Filed: |
August 27, 1973 |
Current U.S.
Class: |
250/423R;
250/427 |
Current CPC
Class: |
H01J
49/145 (20130101); H01J 49/147 (20130101) |
Current International
Class: |
H01J
49/14 (20060101); H01J 49/10 (20060101); H01b
039/34 () |
Field of
Search: |
;250/424,423,427 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lawrence; James W.
Assistant Examiner: Anderson; B. C.
Attorney, Agent or Firm: Barrett; Patrick J.
Claims
We claim:
1. A multiconfiguration, multimode ionization source
comprising:
a vacuum tight envelope;
a chamber having walls surrounding an internal cavity and mounted
within the envelope, said chamber having a plurality of
openings;
an electron source disposed exterior to the chamber for supplying
electrons to the chamber through a first of said openings;
sample inlet means for supplying a gaseous sample through a second
of said openings for reaction with the electrons inside the chamber
to create ions, said ions exiting through a third of said
openings;
aperture control means for changing the size of the first and third
openings for changing the pressure of the sample in the chamber,
thereby changing the operating mode of the source from a first to a
second ionization mode; and
ion repelling means disposed inside the chamber for repelling ions
out of the chamber through the third opening.
2. A multiconfiguration ionization source as in claim 1
wherein:
the aperture control means comprises a movable member within the
chamber, said member having an electron opening smaller than said
first opening and also having an ion opening smaller than said
third opening;
said electrons from the source pass through the electron opening
and the first opening when said movable member is in a first
position;
said ions in the cavity pass through the ion opening and the third
opening when the movable member is in the first position; and
said electrons pass through only the first opening and said ions
pass through only the third opening when the movable member is in a
second position.
3. A multiconfiguration ionization source as in claim 2 wherein the
movable member comprises a hollow slidable cylinder having an ion
exit end and a handle end.
4. A multiconfiguration ionization source as in claim 3
including:
a bellows having a first end attached to the handle end of the
cylinder and by a second end to a wall of the vacuum tight
envelope; and
a handle surrounded by the bellows, one end of said handle attaches
to the cylinder while the other end of the the handle protrudes
through said vacuum tight envelope wall.
5. A multiconfiguration ionization source as in claim 4 wherein
there is an electron collector opposite the electron source, and
wherein there are magnets disposed adjacent the electron source and
the electron collector to direct the electrons from the electron
source.
6. A multiconfiguration ionization source as in claim 5 wherein an
ion lens assembly is attached to the electron source end of the
chamber for focusing ions into a utilization device.
7. A multiconfiguration ionization source as in claim 6 wherein a
vernier adjustment screw is attached to said handle for making fine
adjustments in the position of the cylinder for aligning the
electron opening with the electron source.
8. A multiconfiguration ionization source as in claim 3 wherein the
ion repelling means comprises:
a first and second repeller electrode mounted in and electrically
insulated from the hollow slidable cylinder; and
a connector connectable to a source of potential for making an
electrical connection with the first repeller electrode when the
slidable cylinder is in the first position and with the second
repeller electrode when the slidable cylinder is in the second
position.
9. A multiconfiguration ionization source as in claim 8 wherein
said ion opening is in the second repeller electrode.
10. A multiconfiguration ionization source as in claim 1 wherein
the first ionization mode is a chemical ionization mode and the
second ionization mode is an electron impact ionization mode.
Description
BACKGROUND OF THE INVENTION
Ion sources are employed with mass spectrometers in the analysis of
substances. Commonly used sources are the electron impact source
and the chemical ionization source. The first one has a large
electron entrance, a large ion exit, and an ionization region where
the incoming electrons fragment as well as ionize vapor molecules
thus providing a large quantity of information which does not
necessarily give clear indication of the identity of a substance.
The chemical ionization source has, on the other hand, a small
electron entrance, a small ion exit, and an ionization region where
the pressure can be maintained at such levels that ionmolecule
collisions are extremely likely to occur, such collisions leading
to ready identification of the molecular weight of a substance.
Operation of a mass spectrometer alternately with electron impact
and chemical ionization sources has required many hours of down
time during which the operation of the spectrometer stops. An
object of this invention is to permit changing between the electron
impact and the chemical ionization configurations with minimal
interruption of operation of the mass spectrometer.
BRIEF SUMMARY OF THE INVENTION
According to the preferred embodiment, this invention provides an
ionization source with two distinct ionization chambers, one which
operates as an electron impact ionization source and the other as a
chemical ionization source. The invention may be used with a mass
spectrometer and changes in configuration can be made easily and
quickly. The main elements of the invention include a hollow
chamber having a plurality of orifices transverse to the
longitudinal axis of the chamber. One of the orifices contains an
electron source, and another one is a gaseous sample inlet. A
hollow slidable cylindrical member having smaller transverse
orifices than those in the hollow chamber fits inside the hollow
chamber. At one of its ends, the cylindrical member has two
electrode inserts separated from each other along the longitudinal
axis and defining a first ionization region between them and the
inside walls of the hollow cylindrical member. This region is
connected to the sample inlet orifice and to the electron source
orifice when the hollow cylinder is in a first position. A second
ionization region is defined by the inside walls of the hollow
chamber, the outer electrode insert of the cylindrical member, and
the open end of the hollow chamber, when the cylindrical member is
in a second position. This second region is directly connected to
the electron source orifice and to the sample inlet. In this
manner, when the cylindrical member is in the first position, the
source operates as a chemical ionization source and when the
cylindrical member is in the second position, the source operates
as an electron impact source. The position of the cylindrical
member can be changed quickly and easily by simply pushing or
pulling a handle attached to the cylinder.
DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a cross-sectional view of the preferred embodiment of
the present invention in the chemical ionization configuration.
FIG. 2 shows the apparatus of FIG. 1 in the electron impact
configuration.
DESCRIPTION OF THE PREFERRED EMBODIMENT
FIGS. 1 and 2 show a vacuum envelope 14 which is connected to an
ordinary vacuum pump through a port 9 for evacuating air from the
envelope. An ion chamber 16, which may be a stainless steel tube,
is supported within envelope 14 by a support member 12 and has
orifices, 17, 17' and 23 transverse to its longitudinal axis.
Orifice 17 contains a filament 18 near the periphery of ion chamber
16 and near an end 19 of ion chamber 16. Orifice 23 is an inlet for
samples to be ionized. The ion chamber 16 has a preferably
cylindrical bore 24 along the longitudinal axis. Filament orifice
17 intersects bore 24 near end 19.
A hollow member 28 fits slidably inside bore 24, which member may
be made of stainless steel tubing. Electrode inserts 35 and 36 are
supported by and fastened to the inside of slide member 28 by
insulators preferably made of ceramic. Insert 35 is located at end
21 of member 28 and has a passage 34 through it. Insert 36 is
spaced apart fom insert 35 and has a passage 39 through it. A
connector 38 passes through passage 39 and engages passage 34 in
insert 35 when member 28 has been moved to the left as shown in
FIG. 2. A spring 40 attaches connector 38 to a base block 42, and
this block is in turn affixed to but electrically insulated from
chamber 16. Slide member 28 has a slot 44 through which base block
42 passes. The external surface of hollow member 28 is preferably
hardened to prevent galling or binding with chamber 16. A handle 48
attaches to end 53 of hollow member 28 and is used to displace this
member from the first position to the second position as shown in
FIGS. 1 and 2 respectively. A bellows 46 surrounds handle 48 and
connects the end 53 of hollow member 28 with a wall 55 of vacuum
envelope 14. A support member 12 surrounds the bellows 46 and
affixes the chamber 16 to wall 55. A pivot axle 75 between a
support member 71 and an arm 72 permits pulling or pushing arm 72,
which is connected to handle 48, for placing cylinder 28 in either
the chemical ionization configuration as shown in FIG. 1 or the
electron impact configuration as shown in FIG. 2. Arm 72 is
connected to handle 48 by a vernier screw arrangement 73 for making
fine alignment adjustments of electron passage 32 with filament
orifice 17.
As shown in FIG. 1, electrode inserts 35 and 36 and the inner
periphery of hollow member 28 define a first ionization region 30
when hollow member 28 is to the right, as in FIG. 1. A second
ionization region 30' is defined by the interior walls of chamber
body 16, the electrode insert 35 to the left, and the open end 19
of chamber 16 to the right. A passage 32 through the wall of hollow
member 28 permits entry of electrons into the ionization region 30
from orifice 17 when hollow member 28 is to the right. A sample
inlet 23 through the walls of ion chamber 16 permits entry of an
ionization sample into ionization region 30' when cylinder 28 is to
the left as shown in FIG. 2. Sample inlet 23, and sample inlet 20
passing through the walls of hollow member 28, permit entry of an
ionization sample into ionization region 30, when hollow member 28
is to the right as shown in FIG. 1. A passage 34 permits exit of
ions from the ionization region 30 to an ion lens assembly 26. Both
passages 32 and 34 may have a conical configuration to improve
entry of the electrons through the first passage and exit of the
ions through the second passage. Passages 32 and 34, the electron
entrance and ion exit passages respectively of the chemical
ionization chamber, are much smaller than the respective passages
17 and 21 of the electron impact chamber. The smaller size of
passages 32 and 34 permits maintaining a higher pressure in
ionization region 30 than in ionization region 30'.
Magnets 52 and 52' are located adjacent to filament 18 and to an
electron collector 50, respectively, which is disposed on the
periphery of chamber 16 diametrically opposed to filament 18. The
magnets direct an electron beam from the filament to the collector.
The ion lens assembly 26, adjacent to end 19, extends away from
chamber 16 and, when the appropriate potentials are applied,
focuses ions emerging from ionization regions 30 and 30' into a
mass filter for analysis (not shown).
A potential source 70 is connected to insert 35 by connector 38 to
maintain insert 35 at a potential for repelling ions when the
hollow member 28 is to the left, as shown in FIG. 2. When the
hollow member 28 is to the right, connector 38 engages only insert
36 to maintain a repelling potential on this insert, which insert
now becomes a repeller electrode.
When the hollow cylindrical member is to the left, the ionization
source is operating in the electron impact configuration where the
pressure inside ionization region 30' is about 10.sup..sup.-6 Torr;
the ionization electrons have energies of about 70 eV; and
mean-free-paths of about 2 .times. 10.sup.3 inches. The electrons
in this configuration fragment the sample molecules and produce
many ions whose mass-to-charge ratios do not necessarily correspond
to the molecular weight of the sample. When the hollow cylindrical
member is to the right, the ionization source is operating in the
chemical ionization configuration where the pressure in ionization
region 30 is up to 1.0 Torr; the ionization electrons have energies
of about 100 to 500 eV; and short mean-free-paths of about 2
.times. 10.sup..sup.-3 inches. The electrons in this configuration
do not fragment the sample molecules as much as in the electron
impact configuration, but produce an abundance of ions whose
mass-to-charge ratio corresponds more accurately to the molecular
weight of the sample.
* * * * *