U.S. patent application number 10/190854 was filed with the patent office on 2002-12-19 for suppressor for continuous electrochemically suppressed ion chromatography and method.
This patent application is currently assigned to Alltech Associates, Inc.. Invention is credited to Anderson, James M. JR., Benedict, Bart C., Gurner, Yuri, Pham, Hung Anthony, Saari-Hordhaus, Raaidah, Sims, Carl.
Application Number | 20020192832 10/190854 |
Document ID | / |
Family ID | 23439134 |
Filed Date | 2002-12-19 |
United States Patent
Application |
20020192832 |
Kind Code |
A1 |
Anderson, James M. JR. ; et
al. |
December 19, 2002 |
Suppressor for continuous electrochemically suppressed ion
chromatography and method
Abstract
Methods and devices for continuous electrochemically suppressed
ion chromatography are disclosed. In preferred aspect of the
invention, a chromatography effluent comprising analyte ions and
electrolyte is split into a first chromatography effluent flow
stream and a second chromatography effluent flow stream.
Electrolysis ions selected from the group consisting of hydronium
ions and hydroxide ions are generated by the electrolysis of water.
Electrolysis ions of the same charge as the electrolyte and the
second chromatography effluent stream are flowed through a
stationary phase thereby suppressing the electrolyte in the second
chromatography effluent flow stream. The analyte ions are
subsequently detected in the suppressed second chromatography
effluent flow stream.
Inventors: |
Anderson, James M. JR.;
(Arlington Hts, IL) ; Saari-Hordhaus, Raaidah;
(Mundelein, IL) ; Benedict, Bart C.; (Arlington
Hts, IL) ; Sims, Carl; (St. Paul, MN) ;
Gurner, Yuri; (Mendota Hts, MN) ; Pham, Hung
Anthony; (Waukyan, IL) |
Correspondence
Address: |
Ralph J. Gabric
BRINKS HOFER GILSON & LIONE
P.O. BOX 10395
CHICAGO
IL
60610
US
|
Assignee: |
Alltech Associates, Inc.
|
Family ID: |
23439134 |
Appl. No.: |
10/190854 |
Filed: |
July 8, 2002 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10190854 |
Jul 8, 2002 |
|
|
|
09365496 |
Aug 2, 1999 |
|
|
|
Current U.S.
Class: |
436/161 ;
204/542 |
Current CPC
Class: |
G01N 30/34 20130101;
G01N 30/96 20130101; G01N 2030/965 20130101 |
Class at
Publication: |
436/161 ;
204/542 |
International
Class: |
G01N 030/02 |
Claims
We claim:
1. A method of continuous electrochemically suppressed ion
chromatography comprising: (a) chromatographically separating
analyte ions in an aqueous mobile phase comprising electrolyte to
form an aqueous chromatography effluent comprising separated
analyte ions and electrolyte; (b) splitting the chromatography
effluent into a first chromatography effluent flow stream and a
second chromatography effluent flow stream; (c) generating
electrolysis ions selected from the group consisting of hydronium
ions and hydroxide ions by performing electrolysis of water; (d)
flowing the second chromatography effluent stream through a
stationary phase comprising ion-exchange resin during step (c); and
(e) detecting the separated analyte anions in the suppressed second
chromatography effluent stream.
2. The method of claim 1 wherein the analyte ions comprise anions,
the electrolyte comprises cations and the electrolysis ions
comprise hydronium ions.
3. The method of claim 1 wherein the analyte ions comprise cations,
the electrolyte comprises anions and the electrolysis ions comprise
hydroxide ions.
4. The method of claim 1 wherein the stationary phase remains
substantially in its unexhausted form during step (d).
5. The method of claim 4 wherein the stationary phase comprises
cation exchange resin in the hydronium form.
6. The method of claim 4 wherein the stationary phase comprises
anion exchange resin in the hydroxide form.
7. The method of claim 1 wherein steps (d) and (e) are performed
substantially simultaneously.
8. A method of continuous electrochemically suppressed ion
chromatography comprising: (a) chromatographically separating
analyte ions in a mobile phase comprising electrolyte to form a
chromatography effluent comprising separated analyte ions and
electrolyte; (b) splitting the chromatography effluent into a first
chromatography effluent stream and a second chromatography effluent
stream; (c) flowing the first chromatography effluent stream
through a first stationary phase comprising ion exchange resin and
flowing the second chromatography effluent stream through a second
stationary phase comprising ion exchange resin; (d) generating
electrolysis ions selected from the group consisting of hydronium
ions and hydroxide ions during step (c) by performing electrolysis
on water; (e) simultaneously flowing the second chromatography
effluent stream and the electrolysis ions that are of the same
charge as the electrolyte through the second stationary phase
during step (d) thereby driving the electrolyte away from the
second chromatography effluent stream and into the first
chromatography effluent stream; and (f) detecting the separated
analyte ions in the second chromatography effluent stream.
9. The method of claim 8 wherein the analyte comprise anions, and
in step (e) the electrolyte comprises cations and the electrolysis
ions comprise hydronium ions.
10. The method of claim 8 wherein the analyte ions comprise
cations, and in step (e) the electrolyte comprises anions and the
electrolysis ions comprise hydroxide ions.
11. The method of claim 8 wherein the second stationary phase
remains substantially in its unexhausted form during step (e).
12. The method of claim 11 wherein the second stationary phase
comprises cation exchange resin in its hydronium form.
13. The method of claim 11 wherein the second stationary phase
comprises anion exchange resin in its hydroxide form.
14. The method of claim 8 wherein gas by-products of the
electrolysis are removed from the second chromatography effluent
stream prior to detecting the analyte ions in step (f).
15. The method of claim 8 wherein the electrolyte in the first
chromatography effluent stream is removed and the first
chromatography effluent stream is reused as a mobile phase for
carrying analyte ions in a subsequent analysis run.
16. The method of claim 8 wherein steps (e) and (f) are performed
substantially simultaneously.
17. The method of claim 8 wherein the source of water for the
electrolysis is the chromatography effluent.
18. A suppressor adapted for use in a method of continuous
electrochemically suppressed ion chromatography, the suppressor
comprising: (a) an inlet, a first outlet, a second outlet and a
third outlet; (b) a first stationary phase comprising ion exchange
resin positioned in the path of fluid flow through the suppressor
from the inlet to the third outlet; (c) a second stationary phase
comprising ion exchange resin positioned in the path of fluid flow
through the housing from the inlet to the first outlet; and (d) a
first regeneration electrode positioned at the third outlet and a
second regeneration electrode positioned at the second outlet.
19. The suppressor of claim 18 wherein the first and second
stationary phases comprise free ion exchange resin.
20. The suppressor of claim 18 wherein the first and second
stationary phases comprise ion exchange resin encapsulated in a
membrane.
21. The suppressor of claim 18 further comprising sensor electrodes
positioned in the second stationary phase.
22. A system for continuous electrochemically suppressed ion
chromatography, the system comprising: (a) a mobile phase source;
(b) a pump; (c) a sample injector; (d) a chromatography column in
liquid communication with the mobile phase source and sample
injector; (e) a suppressor in liquid communication with the
chromatography column, the suppressor comprising an inlet for
receiving chromatography effluent, a first outlet, a second outlet,
and a third outlet, a first regeneration electrode positioned at
the third outlet and a second regeneration electrode positioned at
the second outlet, a first stationary phase comprising ion exchange
resin located in the path of fluid flow from the inlet to the third
outlet, a second stationary phase comprising ion exchange resin
located in the path of fluid flow from the inlet to the first
outlet; (f) a power source in electrical communication with the
first and second regeneration electrodes; and (g) a detector in
liquid communication with the first outlet of the suppressor.
23. The system of claim 22 wherein the first and second stationary
phase comprise free ion exchange resin.
24. The system of claim 22 wherein the first and second stationary
phases comprise ion exchange resin encapsulated in a membrane.
25. The system of claim 22 further comprising a gas permeable
membrane in liquid communication with, and positioned between in
the direction of liquid flow, the suppressor and the detector.
26. The system of claim 22 wherein the suppressor further comprises
sensor electrodes positioned in the second stationary phase.
27. A method of continuous electrochemically suppressed ion
chromatography comprising: (a) chromatographically separating
analyte ions in an aqueous mobile phase comprising electrolyte to
form an aqueous chromatography effluent comprising separated
analyte ions and electrolyte; (b) conducting electrolysis of water
to generate the electrolysis ions selected from the group
consisting of hydroxide ions and hydronium ions and flowing the
electrolysis ions through a stationary phase positioned in the
suppressor. (c) during step (b) suppressing the electrolyte in the
chromatography effluent by flowing the chromatography effluent
through a first inlet of the suppressor and across at least a
portion of the stationary phase; (d) flowing the suppressed
chromatography effluent through a first outlet of the suppressor to
a detector and detecting the analyte ions in the suppressed
chromatography effluent; (e) flowing detector effluent to the
suppressor through a second inlet; and (f) flowing the detector
effluent to waste through a second outlet in the suppressor.
28. The method of claim 27 wherein the stationary phase comprises
free ion exchange resin.
29. The method of claim 27 wherein the stationary phase comprises
ion exchange resin encapsulated in a membrane.
30. A suppressor for use in continuous electrochemically suppressed
ion chromatography, the suppressor comprising; a first inlet, a
first outlet and a second outlet; a first stationary phase located
in the path of fluid flow through the suppressor from the first
inlet to the first outlet; a second stationary phase located in the
path of fluid flow through the suppressor from the first inlet to
the second outlet; a pair of regenerator electrodes wherein the
first and second stationary phases are located between the
electrodes such that an electrical potential may be applied across
the first and second stationary phases; wherein the first
stationary phase and the second stationary phase comprise
oppositely charged ion exchange resin.
31. The suppressor claim 30 wherein the first stationary phase
comprises hydroxide ions and the second stationary phase comprises
hydronium ions.
32. The suppressor of claim 31 wherein the stationary phase
comprises free ion exchange resin.
33. The suppressor of claim 31 wherein the stationary phase
comprises ion exchange resin encapsulated in a membrane.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to the field of ion
chromatography (IC), and, in particular, to a suppressor for
continuous electrochemically suppressed ion chromatography and
method.
BACKGROUND OF THE INVENTION
[0002] Suppressed ion chromatography (SIC) is a commonly practiced
method of ion chromatography which generally uses two ion-exchange
columns in series followed by a flow through conductivity detector
for detecting sample ions. The first column, called the analytical,
chromatography or separation column, separates the analyte ions
(e.g., the sample ions) in a sample by elution of the analyte ions
through the column. The analyte ions are flowed through the
analytical column via a mobile phase comprising electrolyte.
Generally, a dilute acid or base in deionized water is used as the
mobile phase. From the analytical column, the separated analyte
ions and mobile phase are then flowed to the second column, which
is called the suppressor or stripper. The suppressor serves two
primary purposes: (1) it lowers the background conductance of the
mobile phase by retaining (e.g., suppressing) the electrolyte of
the mobile phase, and (2) it enhances the conductance of the
analyte ions by converting the analyte ions to their relatively
more conductive acid (in anion analysis) or base (in cation
analysis). The combination of these two functions enhances the
signal to noise ratio, and, thus, improves the detection of the
analyte ions in the detector. Accordingly, upon exiting the
suppressor, the analyte ions and suppressed mobile phase are then
flowed to the detector for detection of the analyte ions. A variety
of different types of suppressor devices and methods are discussed
in U.S. Pat. Nos. 3,897,213; 3,920,397; 3,925,019; 3,926,559; and
U.S. Ser. No. 08/911,847. Applicants hereby incorporate by
reference the entire disclosure of these patent applications and
patents.
[0003] As those skilled in the art will appreciate, both the mobile
phase and the sample contain counterions of the analyte ions. A
suppressor operates by ion exchange of suppressor ions, which are
located in the suppressor, with both (1) the mobile phase
electrolyte counterions and (2) the sample counterions. In anion
analysis, for example, the suppressor ions normally comprise
hydronium ions and the mobile phase comprises electrolyte such as
sodium hydroxide or mixtures of sodium carbonate and sodium
bicarbonate. In cation analysis, the suppressor ions normally
comprise hydroxide ions, and the mobile phase may comprise
electrolytes such as hydrochloric acid or methanesulfonic acid. The
suppressor ions are located on a stationary phase, which may be an
ion exchange membrane or resin. As the mobile phase and sample
(which contains both analyte ions and counterions of the analyte
ions) are flowed through the stationary phase of the suppressor,
the electrolyte counterions in the mobile phase and the sample
counterions are retained on the stationary phase by ion exchange
with the suppressor ions. When the suppressor ions are either
hydronium or hydroxide, ion exchange of the electrolyte counterions
with suppressor ions converts the mobile phase to water or carbonic
acid, which are relatively non-conductive. On the other hand, the
ion exchange of sample counterions with suppressor ions (i.e.,
hydronium or hydroxide ions) converts the analyte ions to their
relatively more conductive acid (in anion analysis) or base (in
cation analysis). Thus, the analyte ions, which are now in their
relatively more conductive acid or base form, are more sensitive to
detection against the less conductive background of the mobile
phase.
[0004] However, unless the suppressor ions are continuously
replenished during the suppression process, the concentration of
suppressor ions on the stationary phase is reduced. Eventually the
suppressor will become exhausted and its suppression capacity is
either lost completely or significantly reduced. Thus, the
suppressor must be either replaced or regenerated. The need to
replace or regenerate the suppressor is inconvenient, may require
an interruption in sample analysis, or require complex valving or
regeneration techniques known in the art. Methods of
electrochemically regenerating an at least partially exhausted
suppressor are known in the art. See, for example, U.S. Pat. Nos.
5,633,171 and 5,773,615, which are directed to intermittent
electrolytic packed bed suppressors. The assignee of this
application also discloses, among other things, similar methods of
intermittent electrochemical regenerating of a suppressor in U.S.
Pat. No. 5,759,405. A method of an intermittent, but "frequent,"
chemical regeneration of a suppressor is disclosed in U.S. Pat. No.
5,597,734. One problem associated with such "intermittent" methods
of electrochemically regenerating a suppressor is that the
suppressor being regenerated must be taken "off-line", that is,
while being regenerated the suppressor is not used in a sample or
analysis run. An example of a known technique for continuously
regenerating a suppressor by continuously replenishing suppressor
ions is disclosed in U.S. Pat. No. 5,352,360.
[0005] Another problem associated with SIC is that a separate
suppressor unit is usually required, and, therefore, the number of
components in the system is increased over traditional IC systems.
Traditional IC systems usually contain a mobile phase source, a
pump, a sample injector, an analytical column and a detector for
detecting the sample ions. In SIC, a separate suppressor unit is
added to the system. This, in turn, increases the complexity of the
system and also increases extra-column volume which may decrease
chromatographic resolution and sensitivity. Therefore, it would be
advantageous to have a system of ion suppression chromatography
which reduced the number of system components in traditional SIC
systems.
[0006] Another problem associated with prior art SIC systems is
that the mobile phase is converted to a weakly ionized form, which
renders the mobile phase unsuitable for reuse. Thus, it would be
advantageous if a system of SIC were developed in which the mobile
phase is converted back to its strongly ionized form after
suppression and, thus, may be reused.
SUMMARY OF THE INVENTION
[0007] In its various aspects, the present invention addresses one
or more of the foregoing problems associated with SIC.
[0008] In one aspect of the invention, a method of continuous
electrochemically suppressed ion chromatography is provided.
Analyte ions in a mobile phase comprising electrolyte are separated
in a chromatography column resulting in a chromatography effluent
comprising electrolyte and separated analyte ions. The
chromatography effluent is then split into a first chromatography
effluent stream and a second chromatography effluent stream.
Electrolysis ions selected from the group consisting of hydronium
ions and hydroxide ions are generated by the electrolysis of water.
The electrolysis ions having the same charge as the electrolyte and
the second chromatography effluent stream, which contains
electrolyte and analyte ions, are simultaneously flowed through a
stationary phase thereby suppressing the electrolyte in the second
chromatography effluent stream. In a preferred aspect of the
invention, the electrolysis ions force the electrolyte away from
the second chromatography effluent stream and into the first
chromatography effluent stream thereby effectively suppressing the
second chromatography effluent stream. The analyte ions in the
suppressed second chromatography effluent stream are then
detected.
[0009] In another aspect of the invention, a suppressor adapted for
use in a method of continuous electrochemically suppressed ion
chromatography is provided. The suppressor comprises an inlet, a
first outlet, a second outlet and a third outlet. A first
stationary phase comprising ion exchange resin is positioned in the
path of fluid flow through the suppressor from the inlet to the
third outlet. A second stationary phase comprising ion exchange
resin is positioned in the path of fluid flow through the
suppressor from the inlet to the first outlet. A first regeneration
electrode is positioned at the third outlet and a second
regeneration electrode is positioned at the second outlet.
[0010] In yet another aspect of the invention, the suppressor
further comprises sensor electrodes positioned in the second
stationary phase for detecting the analyte ions in the
suppressor.
[0011] In yet another aspect of the invention, a method of
suppressed ion chromatography is provided wherein the suppressed
chromatography effluent is converted back to its strongly ionized
state after suppression. Thus, the mobile phase is recycled and may
be reused in a subsequent sample run.
[0012] In a further aspect of the invention, a method of continuous
electrochemically suppressed ion chromatography is provided where
analytical column effluent, which contains separated analyte ions
and electrolyte, is flowed to a first inlet of a suppressor. The
suppressor comprises a stationary phase. The chromatography
effluent is flowed through at least a portion of the stationary
phase to suppress the chromatography effluent. The suppressed
chromatography effluent is flowed to a detector where the analyte
ions are detected. The detector effluent is then flowed back to the
suppressor through a second inlet and out a second outlet to
waste.
[0013] In another aspect of the invention, a suppressor is provided
wherein the same suppressor may be used in both anion and cation
analysis. The suppressor has a first inlet, a first outlet and a
second outlet. A first stationary phase is located in the path of
fluid flow through the suppressor from the first inlet to the first
outlet. A second stationary phase is located in the path of fluid
flow through the suppressor from the first inlet to the second
outlet. A pair of regeneration electrodes are further provided
wherein the first and second stationary phases are located between
the electrodes such that an electrical potential may be applied
across the first and second stationary phases. The first and second
stationary phases further comprise oppositely-charged ion exchange
resin.
DESCRIPTION OF THE DRAWINGS
[0014] FIGS. 1 and 2 are schematic views of two systems according
to the present invention using a suppressor adapted for use in a
method of continuous electrochemically suppressed ion
chromatography.
[0015] FIG. 3 is a schematic view illustrating the method of
operation of a suppressor adapted for use in a method of continuous
electrochemically suppressed ion chromatography of the present
invention.
[0016] FIG. 4 is an exploded perspective view of a suppressor
adapted for use in a method of continuous electrochemically
suppressed ion chromatography according to one aspect of the
invention.
[0017] FIG. 4a is a cross-section view of the suppressor
illustrated in FIG. 4 along line A-A.
[0018] FIG. 5 is an illustration of the method of operation of a
suppressor adapted for use in a method of continuous
electrochemically suppressed ion chromatography according to one
aspect of the invention wherein the suppressor includes sensor
electrodes for detecting analyte ions.
[0019] FIG. 6 is an exploded view of an integrated suppressor and
detector that may be used according to another aspect of the
invention.
[0020] FIG. 7 is an illustration of the operation of a suppressor
according to another aspect of the present invention.
[0021] FIG. 8 is an illustration of another suppressor
configuration according to the present invention.
[0022] FIG. 9 is a chromatogram generated by the sample run
discussed in Example 1.
[0023] FIG. 10 is a chromatogram generated by the sample run
discussed in Example 2.
[0024] FIG. 11 is a chromatogram generated by the sample run
discussed in Example 3.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE
INVENTION
[0025] FIG. 1 illustrates a system of continuous electrochemically
suppressed ion chromatography according to one aspect of the
invention. The system comprises a mobile phase source 10 comprising
electrolyte, a pump 11, a sample injector 12 and a chromatography
column 14, all in fluid communication. The pump 11, sample injector
12 and chromatography column 14 may be selected from the variety of
types known by those skilled in the art. For example, preferred
pumps include the ALLTECH 526 pump available from ALLTECH
ASSOCIATES, INC. (Deerfield, Ill.). Preferred chromatography
columns include the ALLTECH ALLSEP or UNIVERSAL CATION COLUMNS.
Preferred sample injectors include the RHEODYNE 7725 injection
valve.
[0026] A suppressor 15 in fluid communication with the
chromatography column 14 is further provided. The suppressor 15,
which contains electrodes (not shown), is discussed in further
detail below. The suppressor 15 is connected to a power source 18.
Preferred power sources include the KENWOOD PR36-1.2A. The system
also preferably includes a gas permeable tubing or membrane 17 in
liquid communication with the suppressor 15 and a detector 21. The
gas permeable tubing is preferably TEFLON AF tubing available from
BIOGENERAL of San Diego, Calif. A preferred detector for use in the
invention is the ALLTECH MODEL 550 CONDUCTIVITY DETECTOR. Other
suitable detectors for use with the present invention are
electrochemical detectors. The detector 21 measures or records the
analyte ions detected by the detector. Finally, back pressure
sources 21a, 21b and 21c are preferably included to control
operating pressure in the system. By manipulating the operating
pressure, gas bubbles from the electrolysis may be controlled.
[0027] In operation, the direction of fluid flow is as follows. The
mobile phase is flowed from mobile phase source 10 by pump 11
through injection valve 12 to chromatography column 14 to
suppressor 15 and then to detector 21. Upon exiting the detector
21, the mobile phase is flowed through a cross 21b through back
pressure regulator 21a and then to recycling valve 19, which
directs fluid flow either to waste or back to mobile phase source
10 as discussed below. The recycling valve 19 is preferably a
three-way valve.
[0028] FIG. 2 illustrates another system for use in the method of
continuous electrochemically suppressed ion chromatography
according to the present invention. This system differs from the
system of FIG. 1 in that the suppressor and detector are integrated
to give an integrated suppressor and detector 16. The integrated
suppressor and detector 16 has sensor electrodes (not shown) for
detecting analyte ions and is discussed in further detail below.
Additionally, a measuring device 20 is in electrical communication
with the integrated suppressor and detector 16 for recording
analyte (or sample) ions. A preferred measuring device is the
OAKTON 1/4 DIN CONDUCTIVITY AND RESISTIVITY CONTROLLER (OAKTON 100
SERIES). Also in electrical communication with the integrated
suppressor and detector 16 is power source 18.
[0029] The path of fluid flow through the system of FIG. 2 is as
follows. Fluid flow is from mobile phase source 10 by pump 11
through injection valve 12 to chromatography column 14 to
integrated suppressor and detector 16. Upon exiting the integrated
suppressor and detector 16, the mobile phase is flowed through
recycling valve 19, which directs fluid flow either to waste or
back to mobile phase source 10 as discussed below. The recycling
valve 19 is preferably a three-way valve.
[0030] According to one aspect of the invention, and with reference
to FIG. 1, the mobile phase comprising electrolyte and analyte ions
(e.g., sample ions that are to be detected) are flowed to
chromatography column 14 where the analyte ions are separated. The
separated analyte ions and electrolyte exit the chromatography
column 14 as chromatography effluent and flowed to suppressor 15
where the electrolyte is suppressed. The operation of suppressor 15
is described with reference to FIG. 3 for anion analysis and a
mobile phase consisting of an aqueous solution of sodium hydroxide.
As those skilled in the art will quickly appreciate, the invention
may easily be adapted for cation analysis and/or different
electrolytes.
[0031] Referring to FIG. 3, the suppressor 15 comprises first
stationary phase 31 and second stationary phase 31a. By stationary
phase, it is meant chromatography packing material comprising ion
exchange resin in either free resin form or encapsulated in a
membrane matrix that permits liquid flow therethrough. The
stationary phase is preferably a strong cation exchanger, such as
sulfonic acid cation exchanges such as BIORAD AMINEX 50WX8. The
suppressor may also include end filters, 26a and 26b, comprising
strong cation exchange resin encapsulated in a TEFLON filter mesh
located at both ends of the suppressor 15. These end filters limit
the amount of gas, which is generated at the regeneration
electrodes during electrolysis, from entering the suppressor 15
during electrolysis. Preferred end filters are ALLTECH NOVO-CLEAN
IC-H Membranes. The suppressor 15 further comprises first
regeneration electrode 22 and second regeneration electrode 23. In
this embodiment, the first regeneration electrode 22 is the cathode
and the second regeneration electrode 23 is the anode. The first
and second regeneration electrodes are preferably flow-through
electrodes that are connected to power source 18 (not shown). The
preferred electrodes are made of a titanium housing with
flow-through titanium frits, 26c and 26d. The electrodes are
platinum plated to provide an inert, electrically-conductive
surface. The suppressor 15 further comprises an inlet 24 for
receiving the chromatography column effluent and a first outlet 25
for flowing suppressed chromatography effluent (which contains
analyte ions) to the detector 21. The suppressor also comprises
second and third outlets 28 and 30, respectively, through
regeneration electrodes 23 and 22, respectively.
[0032] During a sample run power is continuously applied to
activate regeneration electrodes 22 and 23 while providing water to
the suppressor 15. The water source may be the chromatography
effluent or a separate water source may be provided. In any event,
electrolysis of the water occurs at the regeneration electrodes
generating electrolysis ions selected from the group consisting of
hydronium ions and hydroxide ions. In the present embodiment,
hydronium ions are generated at the anode (second regeneration
electrode 23) and hydroxide ions are generated at the cathode
(first regeneration electrode 22). The hydronium ions are flowed
from the second regeneration electrode 23 across second stationary
phase 31a and first stationary phase 31 to first regeneration
electrode 22. The hydronium ions eventually combine with the
hydroxide ions generated at first regeneration electrode 22 to form
water, which may exit the suppressor at third outlet 30.
[0033] In operation, the chromatography effluent is introduced into
the suppressor 15 at inlet 24. In this embodiment, the
chromatography effluent comprises separated anions in an aqueous
sodium hydroxide eluant. Upon entering the suppressor at inlet 24,
the chromatography effluent is split into two chromatography
effluent flow streams; namely a first chromatography effluent flow
stream and a second chromatography effluent flow stream. The first
chromatography effluent flow stream flows in a first chromatography
effluent flow path from the inlet 24 through the first stationary
phase 31 positioned between the inlet 24 and the first regeneration
electrode 22. Thus, the first chromatography effluent flow path is
defined by the flow of the first chromatography effluent flow
stream from inlet 24 to first regeneration electrode 22. The first
chromatography effluent flow stream may exit the suppressor 15
through the first regeneration electrode 22 and third outlet 30.
The second chromatography effluent flow stream flows in a second
chromatography effluent flow path from the inlet 24 through second
stationary phase 31a, which is positioned between the inlet 24 and
the second regeneration electrode 23, to the second regeneration
electrode 23. Preferably, a portion of the second chromatography
effluent exits the suppressor 15 at first outlet 25 and another
portion at second outlet 28 through second electrode 23. The second
chromatography effluent stream exiting at first outlet 25 is flowed
to the detector where the analyte ions are detected.
[0034] In the suppressor, the sodium ion electrolyte in the
chromatography effluent preferably migrates from the second
chromatography effluent flow stream into the first chromatography
effluent flow stream by the combined action of the hydronium ion
flow from the second regeneration electrode 23 to the first
regeneration electrode 22 and the negative charge at the first
regeneration electrode 22. The second chromatography effluent flow
stream thus comprises separated anions which combine with the
hydronium electrolysis ions to create the highly conductive acids
of the analyte anions. The second chromatography effluent flow
stream further comprises water that is generated, at least in part,
by the hydroxide ions from the sodium hydroxide eluant combining
with the hydronium electrolysis ions.
[0035] A portion of the second chromatography effluent flow stream
exits the suppressor at second and first outlets 28 and 25,
respectively. The suppressed second chromatography effluent
comprises an aqueous solution of the separated analyte anions in
their acid form along with oxygen gas generated at the second
regeneration electrode from the hydrolysis of water. Because the
oxygen gas may interfere to some extent with the detection of the
analyte anions at the detector, the suppressed second
chromatography effluent exiting first outlet 25 is preferably
flowed through a gas permeable membrane such as gas permeable
tubing 17 where the oxygen gas is removed prior to detecting the
analyte ions. In this respect, a back pressure source 21a (see FIG.
1) may also be included in the system to create sufficient back
pressure to efficiently force oxygen gas through gas permeable
tubing 17 and out of first suppressor effluent. Similarly, back
pressure sources 21b and 21c are likewise provided (see FIG. 1) to
provide further pressure control in the system. As can be
ascertained from FIG. 3, increasing the backpressure in the
suppressed second chromatography effluent stream exiting at outlet
25 could disturb fluid flow through the suppressor 15. Therefore,
it is preferable to apply counterbalancing pressure in the second
chromatography effluent stream exiting at second outlet 28 and
first chromatography effluent stream exiting at third outlet 30.
The suppressed second chromatography effluent flow stream exiting
suppressor 15 at first outlet 25 is then flowed through the gas
permeable tubing 17 to the detector 21 where the analyte ions are
detected.
[0036] Because power is applied while analyte ions are flowed
through the suppressor 15, that is, the regeneration electrodes are
continuously activated and an electrical potential is continuously
applied across the first stationary phase 31 and second stationary
phase 31a, there is a continuous flow of hydronium ions from the
second regeneration electrode 23 to the first regeneration
electrode 22. It is believed that this continuous flow of hydronium
ions allows the second stationary phase 31a in the second
chromatography effluent flow path to continuously remain in its
substantially unexhausted form. Thus, in the present embodiment, a
hydronium form ion exchange resin will remain substantially in its
unexhausted or hydronium form in the second chromatography effluent
flow stream because sodium ions are substantially precluded from
entering the second chromatography effluent flow stream (and thus
they are unavailable to exhaust the second stationary phase 31a)
and are driven into the first chromatography effluent flow stream.
Additionally, although the first stationary phase 31 in the first
chromatography effluent flow path may become at least partially
exhausted by ion exchange of the sodium ions with hydronium ions, a
continuous supply of hydronium ions is available to continuously
regenerate the first stationary phase 31 by ion exchange with
retained sodium ions.
[0037] The first chromatography effluent flow stream will exit the
suppressor 15 at third outlet 30 as a third suppressor effluent and
will comprise hydroxides of the sample counteractions and an
aqueous sodium hydroxide solution which is formed from the
hydroxide ions generated at the first regeneration electrode 22
combining with, respectively, the sodium ion electrolyte and the
hydronium electrolysis ions generated at the second regeneration
electrode 23. The third suppressor effluent flow stream further
comprises hydrogen gas generated by the electrolysis of water at
the first regeneration electrode 22. The third suppressor effluent,
in this embodiment, also may contain a portion of the analyte
anions. By removing the hydrogen gas through known methods in the
art (as, for example, by gas permeable tubing) and removing the
analyte anions by known methods, the aqueous sodium hydroxide
solution may be reused by flowing it back to the eluant source 10
and using it as the mobile phase in a subsequent sample run.
Alternatively, the third suppressor effluent flow stream exiting
the suppressor at exit 30 may be flowed to waste.
[0038] As those skilled in the art will recognize, the suppressor
discussed above may be used in methods for continuous
electrochemically suppressed ion chromatography for both anion and
cation analysis. Moreover, various eluants may be used such as
hydrochloric acid or methanesulfonic acid for cation analysis and
sodium carbonate/bicarbonate, sodium hydroxide, or sodium phenolate
for anion analysis. The first stationary phase 31 and the second
stationary phase 31a may be different or the same. Moreover, within
either the first or second chromatography effluent flow paths, the
stationary phase may be the same or a combination of free ion
exchange resin or ion exchange resin encapsulated in a membrane
matrix. The stationary phase, however, must permit fluid flow
therethrough and the ion flow as discussed above. Examples of
suitable stationary phases for anion analysis include DOWEX 50WX8
and JORDIGEL SO.sub.3. Examples of suitable stationary phases for
cation analysis include AMINEX AG-X8 and ZIRCHROM RHINO PHASE
SAX.
[0039] As illustrated in FIG. 3, inlet 24 is preferably positioned
closer to first regeneration electrode 22 than to second
regeneration electrode 23 along a horizontal axis. Thus, the
distance that the first chromatography effluent streams travels
from inlet 24 to first regeneration electrode 22 is preferably
shorter than the distance traveled by the second chromatography
effluent stream from inlet 24 to second regeneration electrode 23.
Most preferably, the horizontal distance X" between the center of
inlet 24 and the second regeneration electrode 23 is about 0.930
inches to about 1.205 inches and the horizontal distance X' between
the center inlet 24 and the first regeneration electrode 22 is
about 0.466 inches to about 0.741 inches. Preferably, the distance
Y between the center axis of inlet 24 and first outlet is about
0.232 inches to about 0.464 inches. The distance Z between first
outlet and second electrode is about 0.466 inches to about 0.741
inches.
[0040] The distance Z' between first outlet and first electrode 22
is preferably about 0.930 inches to about 1.025 inches.
[0041] FIGS. 4 and 4a further illustrate suppressor 15 of the
system described with respect to FIG. 1. The suppressor comprises
end caps 302 and 310. The suppressor further comprises first
regeneration electrode 304 and second regeneration electrode 308.
Positioned within first regeneration electrode (not shown in FIG.
4) and second regeneration electrodes are frits 313 and 311,
respectively. Frits 313 and 311 are preferably constructed from
porous, non-conductive, non-electroactive materials such as
polyolefins, or PAT.TM. (peek alloyed with teflon), or
surface-oxidized titanium. Or the frits may preferably be
constructed from inert, electro-active materials such as platinum
coated titanium. The suppressor also includes O-rings 305 and 310a
for providing a fluid tight seal between suppressor housing 306 and
regeneration electrodes 304 and 308. The suppressor 15 further
comprises an inlet 307, a first outlet 309, a second outlet 323 and
a third outlet 321.
[0042] Preferably, it is desireable to flow the gas bubbles (oxygen
and hydrogen gas) formed by the electrolysis away from the
detector. Alternatively, it is desireable to remove the gas bubbles
from the system prior to the detector. This is desireable because
the gas bubbles could interfere with the detection of the analyte
ions at the detector. The gas bubbles can be flowed away from, or
removed prior to, the detector in a variety of ways. One method for
removing gas bubbles prior to the detector was previously
illustrated by using gas permeable tubing 17 prior to the detector.
By increasing the back pressure in the system using back pressure
source 21a, gas bubbles can be "forced" out of the system through
gas permeable tubing 17 prior to the detector 21. Of course, it is
desireable to balance the back pressure generated by back pressure
source 21a, otherwise sample analysis could be affected. Therefore,
back pressure sources 21b and 21c are preferably provided to
counter the back pressures generated by source 21a to permit
efficient operation of the system.
[0043] Back pressure sources 21a, 21b and 21c may preferably be
constructed from an in-line filter comprising a porous frit of
plastic or metal from about 2-10 microns.
[0044] Instead of two sources 21b and 21c, one such source could be
used where the fluid flow in tubing 17a and 17b is merged in a
T-configuration into one such source (not shown). Alternatively,
instead of back pressure sources 21b and 21c, the back pressures
created by source 21a can be balanced by altering the length of
tubing 17a and 17b. Increasing the tubing length increases the back
pressure created by the suppressed chromatography effluent flowing
therethrough.
[0045] In another aspect of the invention, sensor electrodes may be
placed in the suppressor 15 resulting in an integrated suppressor
and detector. A system for continuous electrochemically suppressed
ion chromatography using an integrated suppressor and detector is
illustrated in FIG. 2. In this embodiment, the suppressor described
with reference to FIGS. 1, 3, 4, and 4a may be adapted by placing
sensor electrodes in the second chromatography effluent flow path.
The sensor electrodes are connected to a recording device and the
separated analyte ions are detected while in the second
chromatography effluent flow path within the suppressor.
[0046] Another adaption of an integrated suppressor and detector is
illustrated in FIG. 5. The chromatography effluent is preferably
introduced into the integrated suppressor and detector 416 at inlet
417. Upon entering the integrated suppressor and detector, the
chromatography effluent is split into two flow paths; namely a
first chromatography effluent flow stream and a second
chromatography effluent flow stream much like previously described.
The first chromatography effluent flow stream is flowed towards a
first regeneration electrode 422 and the second chromatography
effluent flow stream is flowed to the second regeneration electrode
424. The first and second regeneration electrodes are preferably
flow-through electrodes as previously described. As those skilled
in the art will appreciate, by configuring the chromatography
effluent flow paths and the regeneration electrodes in this manner,
the oxygen and hydrogen gas bubbles formed by the electrolysis of
water are flowed away from the sensor electrodes 426 and 428, and,
therefore, will not interfere with the detection of the analyte
ions at the sensor electrodes 426 and 428.
[0047] In ion analysis, the integrated suppressor and detector
works as follows. The chromatography effluent comprising aqueous
sodium hydroxide and separated analyte anions is flowed from the
chromatography column to the integrated suppressor and detector
416. The chromatography effluent is introduced into the suppressor
and detector at inlet 417, where the flow path of the
chromatography effluent is split. A portion of the chromatography
effluent--the first chromatography effluent flow stream--is flowed
to the first regeneration electrode 422 and a second portion of the
chromatography effluent--the second chromatography effluent flow
stream--is flowed to the second regeneration electrode 424. The
flow of hydronium ions from the second regeneration electrode 424
to the first regeneration electrode 422 causes the sodium ions and
sample countercations to migrate towards the first regeneration
electrode 422 (the cathode) and away from the sensor electrodes 426
and 428, which are positioned in the second chromatography effluent
flow path. Additionally, the sodium ions, the sample
countercations, and the hydronium ions combine with the hydroxide
ions generated at the first regeneration electrode 422 to form an
aqueous sodium hydroxide and sample countercation hydroxide
solution that may be reused as the mobile phase.
[0048] Thus, because sodium ions migrate towards the first
regeneration electrode 422 and away from the sensor electrodes 426
and 428, the hydronium ion concentration in the area around the
sensor electrodes 426 and 428 far exceeds the sodium ion
concentration. The analyte anions combine with hydronium ions to
form the relatively more conductive acid of the analyte ion in the
areas around the sensor electrodes which increases the sensitivity
of the analyte ions to detection in the area around the sensor
electrodes. After detection, the acid of the analyte ions is flowed
through second regeneration electrode 424 and out of the integrated
suppressor and detector 416. Moreover, the electrolysis of water
provides a continuous supply of hydronium ions at regeneration
electrode 424 that are flowed across the stationary phase 420 to
first regeneration electrode 422. The source of the water for the
electrolysis may be from the aqueous chromatography effluent or
from a separate aqueous regenerant source.
[0049] The previously described embodiments offer certain
advantages. For example, gas bubbles formed by the electrolysis of
water are flowed away from the sensor electrodes, which reduces the
extent to which these bubbles interfere with the detection of the
analyte ions. Additionally, the analyte ions do not have to flow
through, or be in contact with, regeneration electrodes before
detection by the sensor electrodes. This reduces the possibility
that analyte ions will be chemically altered by contact with the
regeneration electrodes. The concentration of unwanted counterions
of the analyte ions in the area of the sensor electrodes is reduced
which increases sensitivity of the system. On this point, it has
unexpectedly been discovered that the above-described T-cell
embodiment produces greater sensitivity over conventional
suppressor systems. Without being restricted to theory; it is
presently believed that this increased sensitivity is due to the
preferential migration of incoming analyte ions toward the
oppositely charged regeneration electrode which concentrates the
analyte ions in the area of the sensor electrodes, provided of
course the sensor electrodes are positioned near the oppositely
charged regeneration electrode as illustrated in FIG. 5.
[0050] With further reference to FIG. 5, the horizontal distance A
between first regeneration electrode and inlet 417 is preferably
about 0.406 inches to about 0.509 inches. The horizontal distance B
between inlet 417 and sensor electrodes 426 and 428 is preferably
about 0.447 inches to about 0.522 inches. The horizontal distance C
between sensor electrodes 426 and 428 and second regeneration
electrode 424 is preferably about 0.391 inches to about 0.915
inches.
[0051] FIG. 6 is an exploded view of an integrated suppressor and
detector 500 according to one aspect of the invention. First and
second end caps 502 and 504 are provided. Positioned within first
end cap 502 and a first female cell 506 is first regeneration
electrode 507. Positioned within second end cap 504 and a male cell
508 is second regeneration electrode 509. The regeneration
electrodes are preferably as described above. Also included are
first and second sensor electrodes 521 and 513, respectively. The
sensor electrodes are preferably made of inert, conductive
materials, such as platinum, gold, or platinum or gold plated
stainless steel or titanium. The electrodes must allow liquid flow
from the suppressor inlet to regenerate electrode 509, and must
therefore either allow flow around or through them. O-rings 506a
and 509a are provided to provide a fluid tight seal between first
regeneration electrode 507 and female cell 506 and second
regeneration electrode 509 and male cell 508, respectively. Spacer
517 and seal gaskets 519 and 515 are positioned between sensor
electrodes 513 and 521. The spacer functions to reproducibly set
the distance between sensor electrodes 513 and 521 and the gaskets
are provided for a fluid tight seal. Seal gaskets 523 and 511 are
further provided to give a fluid tight seal between female cell 506
and sensor electrode 521 and male cell 508 and sensor electrode
513, respectively. An adapter 508a is provided for receiving
chromatography effluent at inlet 508b. Preferably, end caps 502 and
504, female cell 506, male cell 508 and adaptor 508a are
constructed from an electrically non-conductive material, such as
PEEK, polyolefin, acrylic, plysulfone, or glass.
[0052] FIG. 7 illustrates yet another aspect of the invention using
a suppressor without porous electrodes. In this embodiment, the
suppressor 600 comprises first and second regeneration electrodes
602 and 604, respectively. The first regeneration electrode 602 is
the anode where hydronium ions are generated by the electrolysis of
water. Hydroxide ions are generated at the cathode, second
regeneration electrode 604. The suppressor further comprises first
stationary phase 608 and second stationary phase 610 separated by
flow restrictor 120. For anion analysis, the first and second
stationary phase is cation exchange packing material as previously
described.
[0053] The chromatograpahy column effluent is flowed to the
suppressor 115 at first inlet 116. Power is applied during the
sample run thereby creating an electrical potential across the
first and second stationary phase. Using anion analysis in an
aqueous sodium hydroxide mobile phase, for example, the
chromatography effluent is flowed through the suppressor as
indicated by the arrows where suppression occurs as previously
described. Sodium ions are driven from the chromatography effluent
by the combined action of the hydronium ion flow from anode 602 to
cathode 604 and by the attraction of the negative charge at cathode
604. The sample anions are converted to their highly conductive
acids by combining with the hydronium ions. The suppressed sample
ions are then flowed from first outlet 116a through tubing 118 to
the detector (D) where the sample ions are detected. The tubing 118
is preferably gas permeable as previously described. Thus, the gas
generated from the electrolysis may be removed prior to the
detector through the gas permeable tubing 118 as previously
described. The detector effluent may then be flowed back through
the suppressor at second inlet 117 and out second outlet 117a and
then to waste.
[0054] FIG. 8 discloses yet another embodiment of the invention
where the same suppressor 215 is configured for use in both cation
analysis and anion analysis. In this embodiment, the suppressor
comprises a first stationary phase 216 comprising cation exchange
resin and a second stationary phase 217 comprising anion exchange
resin. Preferably, the first-and second stationary phase meet at
the longitudinal central axis of inlet 220. Chromatography column
effluent is flowed from the chromatography column to the suppressor
215 through inlet 220. Depending on whether the sample run
comprises anion or cation analyte ions, a detector will be
positioned downstream of either first outlet 222 or second outlet
224. Alternatively, detectors may be placed downstream of both
outlets 222 and 224. In cation analysis, a portion of the
chromatography effluent will flow from the inlet 220 to first
outlet 222. Conversely, in anion analysis, a portion of
chromatography effluent will flow from inlet 220 to second outlet
224. The same suppressor, therefore, may be used for both cation
and anion analysis.
[0055] In operation, power is continuously applied thereby creating
an electrical potential across the first and second stationary
phases during the sample run. Water is supplied to the system,
either from the chromatography effluent or from a separate water
reservoir, and electrolysis occurs at the first electrode 240 and
the second electrode 242. In this embodiment, the first electrode
240 is the anode and the second electrode 242 is the cathode.
Hydronium ions are generated at the anode 240 and flowed from the
anode towards cathode 242. Hydroxide ions are generated at cathode
242 and are flowed from the cathode towards anode 240.
[0056] Thus, in anion analysis, the chromatography effluent is
flowed from inlet 220 through first stationary phase 216 where the
mobile is suppressed and the sample anions are converted to their
conductive acids by ion exchange with hydronium ions. Sodium ions
from the mobile phase flow away from first stationary phase 216 and
into second stationary phase 217. The sodium ions then exit the
suppressor 215 as sodium hydroxide at outlet 222. The suppressed
mobile phase and sample anions exit suppressor 215 at outlet 224
and are flowed to the detector where the sample anions are
detected. Conversely, the electrolyte of the mobile phase (sodium)
migrates to second stationary phase 217 and exits at outlet 222
with the hydroxide ions generated by the electrolysis of water. The
stream exiting at outlet 222 may be treated and re-used as the
mobile phase in a subsequent sample run or flowed to waste.
EXAMPLE 1
[0057] In this example, a chromatogram was generated using a
suppressor illustrated in FIG. 3 and the system of FIG. 1 where,
instead of back pressure sources 21b and 21c, long length tubing
was connected to second and third outlets, 28 and 30, respectively,
of the suppressor 15. The following equipment and parameters were
used.
1 Analytical Column: ALLTECH ALLSEP column (Methacrylate-based
anion exchanger with quaternary amine functionalities), 100 .times.
4.6 mm; 7 .mu.m particle size Column Temp: Ambient Eluant: 0.85 mM
NaHCO.sub.3/0.90 mM Na.sub.2CO.sub.3 Flow rate: 1.0 ml/min.
Detector: Suppressed Conductivity Suppressor: Bed length = 35.5 mm
Distance X' = 11.85 mm (see Figure 3) Distance Y = 11.8 mm Distance
Z = 11.85 mm Distance X" = 23.6 mm Distance Z' = 23.6 mm
Electrodes: Ti frits, 40.mu. porosity and coated with Pt. Constant
Current: 75 mA with corresponding voltage 18 V.
[0058] Tubing exiting at third outlet 30 was 76 inches in length
with 0.063" OD and 0.007" ID. Tubing exiting at second outlet 28
was 50 inches in length with 0.063" OD and 0.007" ID. At first
outlet 25, and 10 .mu.pt frit was provided and tubing to the
detector was 0.031" ID and 0.250" OD. The chromatogram of FIG. 9
was obtained.
EXAMPLE 2
[0059] Similar equipment and parameters as Example 1, except
backflow sources (see FIG. 1, reference numerals 21b and 21c were
used in the tubing connected to the second outlet 23 and third
outlet 30 (see FIG. 3) of the suppressor 15. The backflow sources
were placed 5 inches from the anode and cathode. The tubing had
0.040" ID. The backpressure sources were in-line .mu.micron
filters, PEEK alloy TEFLON available from ALLTECH ASSOCIATES,
Deerfield, Ill. as part no. 68250. An additional 20 inches of
tubing was placed on the downstream side of the back pressure
sources. Also, in this example, a constant current of 100 mA was
applied creating a corresponding voltage of 24V. The chromatogram
of FIG. 10 was obtained.
* * * * *