U.S. patent application number 12/398095 was filed with the patent office on 2009-07-02 for chemical suppressors and method of use.
This patent application is currently assigned to Dionex Corporation. Invention is credited to Christopher A. Pohl, Kannan Srinivasan.
Application Number | 20090166293 12/398095 |
Document ID | / |
Family ID | 32770777 |
Filed Date | 2009-07-02 |
United States Patent
Application |
20090166293 |
Kind Code |
A1 |
Srinivasan; Kannan ; et
al. |
July 2, 2009 |
CHEMICAL SUPPRESSORS AND METHOD OF USE
Abstract
A non-electrolytic method and apparatus for treating an aqueous
sample stream including analyte ions and matrix ions of opposite
charge, for pretreatment or suppression. The apparatus includes an
ion exchange membrane capable of passing only ions of opposite
charge to the analyte ions, a sample stream flow channel, a first
aqueous stream ion receiving flow channel adjacent one side of the
sample stream flow channel and separated therefrom by the first ion
exchange membrane, and stationary flow-through ion exchange packing
disposed in the sample stream flow channel. The ion receiving
channel has an ion exchange capacity for the matrix ions less than
about 25% of the ion exchange capacity for the matrix ions.
Inventors: |
Srinivasan; Kannan; (Tracy,
CA) ; Pohl; Christopher A.; (Union City, CA) |
Correspondence
Address: |
MORGAN, LEWIS & BOCKIUS, LLP
ONE MARKET SPEAR STREET TOWER
SAN FRANCISCO
CA
94105
US
|
Assignee: |
Dionex Corporation
Sunnyvale
CA
|
Family ID: |
32770777 |
Appl. No.: |
12/398095 |
Filed: |
March 4, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10356345 |
Jan 30, 2003 |
7517696 |
|
|
12398095 |
|
|
|
|
Current U.S.
Class: |
210/656 ;
210/198.1; 210/198.2; 210/200 |
Current CPC
Class: |
B01D 15/367 20130101;
G01N 30/96 20130101; B01D 61/48 20130101; Y10T 436/25 20150115 |
Class at
Publication: |
210/656 ;
210/198.1; 210/198.2; 210/200 |
International
Class: |
B01D 15/08 20060101
B01D015/08; B01D 15/10 20060101 B01D015/10; G01N 30/96 20060101
G01N030/96 |
Claims
1. A non-electrolytic apparatus for treating an aqueous sample
stream including analyte ions and matrix ions of opposite charge,
said apparatus comprising a first ion exchange membrane capable of
passing only ions of opposite charge to said analyte ions, a sample
stream flow channel, a first aqueous stream ion receiving flow
channel adjacent one side of said sample stream flow channel and
separated therefrom by said first ion exchange membrane, stationary
flow-through first packing of ion exchange material disposed in the
sample stream flow channel of the same charge as said first
membrane and having a first ion exchange capacity for said matrix
ions, said first ion receiving channel having an ion exchange
capacity for said matrix ions less than about 25% of said first ion
exchange capacity for said matrix ions, said apparatus not
including electrodes disposed to apply an electric field between
said sample stream flow channel and said first ion receiving flow
channel.
2. The apparatus of claim 1 further comprising a second ion
exchange membrane of the same charge as said first ion exchange
membrane, and a second aqueous stream ion receiving flow channel
disposed adjacent the other side of said sample stream flow and
separated therefrom by said second ion exchange membrane.
3. The apparatus of claim 1 in which said first ion receiving flow
channel is substantially free of ion exchange capacity for said
matrix ions.
4. The apparatus of claim 1 further comprising neutral flow-through
packing in said first ion receiving flow channel.
5. The apparatus of claim 2 in which the second aqueous stream ion
receiving flow channel has an ion exchange capacity for said matrix
ions less than about 25% of said first ion exchange capacity for
said matrix ions.
6. The apparatus of claim 1 in ion chromatography apparatus,
further comprising a chromatography separator in fluid
communication with the inlet of said sample stream flow channel and
a detector for said analyte ions in fluid communication with the
outlet of said sample flow channel.
7. The apparatus of claim 1 for treatment of a sample stream in
combination with a chromatography apparatus, said apparatus further
comprising a chromatography separator having an inlet and an
outlet, said inlet being in fluid communication with said sample
stream, and a detector in fluid communication with said
chromatography separator.
8. The apparatus of claim 1 in which said first packing comprises a
screen.
9. A non-electrolytic apparatus for treating an aqueous sample
stream including analyte ions and matrix ions of opposite charge,
said apparatus comprising a first ion exchange membrane capable of
passing only ions of opposite charge to said analyte ions, a sample
stream flow channel, a first aqueous stream ion receiving flow
channel adjacent one side of said sample stream flow channel and
separated therefrom by said first ion exchange membrane, stationary
flow-through first packing of ion exchange material disposed in the
sample stream flow channel of the same charge as said first
membrane and having a first ion exchange capacity for said matrix
ions, said first ion receiving channel having second flow-through
ion exchange packing of opposite charge to said first ion exchange
packing disposed in said first ion receiving flow channel, said
apparatus not including electrodes disposed to apply an electric
field between said sample stream flow channel and said first ion
receiving flow channel.
10. A chromatography apparatus including apparatus for treating an
aqueous sample stream including analyte ions and matrix ions of
opposite charge, said apparatus comprising a chromatography
separator having an inlet and an outlet, said inlet being in fluid
communication with said sample stream, said treating apparatus
being disposed upstream or downstream from said chromatography
separator and comprising a first ion exchange membrane capable of
passing only ions of opposite charge to said analyte ions, a sample
stream flow channel, a first aqueous stream ion receiving flow
channel adjacent one side of said sample stream flow channel and
separated therefrom by said first ion exchange membrane, stationary
flow-through first packing of ion exchange material disposed in the
sample stream flow channel of the same charge as said first
membrane and having a first ion exchange capacity for said matrix
ions, said first ion receiving channel having an ion exchange
capacity for said matrix ions less than about 25% of said first ion
exchange capacity for said matrix ions.
11. The chromatography apparatus of claim 10 in which said treating
apparatus further comprises a second ion exchange membrane of the
same charge as said first ion exchange membrane, and a second
aqueous stream ion receiving flow channel disposed adjacent the
other side of said sample stream flow and separated therefrom by
said second ion exchange membrane.
12. The apparatus of claim 10 in which said first ion receiving
flow channel is substantially free of ion exchange capacity for
said matrix ions.
13. The apparatus of claim 10 further comprising neutral
flow-through packing in said first ion receiving flow channel.
14. The apparatus of claim 11 further comprising second
flow-through ion exchange packing of opposite charge to said first
ion exchange packing disposed in said first ion receiving flow
channel.
15. The apparatus of claim 10 in ion chromatography apparatus, in
which said chromatography separator is in fluid communication with
the inlet of said sample stream flow channel.
16. The apparatus of claim 10 further comprising a detector in
fluid communication with said chromatography suppressor.
17. The apparatus of claim 10 without electrodes for applying an
electric field between said sample stream flow channel and first
ion receiving flow channel.
18. A chromatography method comprising flowing an aqueous sample
stream including analyte ions of one charge and matrix ions of
opposite charge to said analyte ions through a chromatography
separator to separate the analyte ions, flowing the sample stream
including the separated analyte ions through a sample stream flow
channel, and simultaneously flowing an aqueous stream through an
ion receiving flow channel separated therefrom by a first ion
exchange membrane capable of passing only ions of opposite charge
to said analyte ions and of blocking bulk liquid flow to reduce the
concentration of said matrix ions in an effluent from said sample
stream flow channel, said sample stream flow channel having
stationary flow-through first packing of ion exchange material
disposed in the sample stream flow channel of the same charge as
said first membrane and having a first ion exchange capacity for
said matrix ions, said ion receiving channel having an ion exchange
capacity for said matrix ions less than about 25% of said first ion
exchange capacity for said matrix ion.
19. The method of claim 18 in which said first ion receiving flow
channel is substantially free of ion exchange capacity for said
matrix ions.
20. The method of claim 18 in which second flow-through ion
exchange packing of opposite charge to said first ion exchange
packing is disposed in said first ion receiving flow channel.
21. The method of claim 18 further comprising detecting said
separated analyte ions in the sample stream exiting from said
sample stream flow channel.
22. The method of claim 18 in which an electric field is not
applied between said sample stream flow channel and said first ion
receiving flow channel.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a divisional application of U.S.
application Ser. No. 10/356,345, filed on Jan. 30, 2003.
BACKGROUND OF THE INVENTION
[0002] The present application relates to a chemical suppression
device and method for reducing the concentration of matrix ions of
opposite charge to ions to be analyzed, and specifically for use of
an ion chromatography suppressor or to a pretreatment device.
[0003] Ion chromatography is a known technique for the analysis of
ions which typically includes a chromatographic separation stage
using an eluent containing an electrolyte, and an eluent
suppression stage, followed by detection, typically by an
electrical conductivity detector. In the chromatographic separation
stage, ions of an injected sample are eluted through a separation
column using an electrolyte as the eluent. In the suppression
stage, electrical conductivity of the electrolyte is suppressed but
not that of the separated ions so that the latter may be determined
by a conductivity cell. This technique is described in detail in
U.S. Pat. Nos. 3,897,213; 3,920,397; 3,925,019; and 3,926,559.
[0004] Suppression or stripping of the electrolyte is described in
the above prior art references by an ion exchange resin bed. A
different form of suppressor column is described and published in
U.S. Pat. No. 4,474,664, in which a charged ion exchange membrane
in the form of a fiber or sheet is used in place of the resin
bed.
[0005] The sample and eluent are passed on one side of the membrane
with a flowing regenerant on the other side, the membrane
partitioning the regenerant from the effluent of chromatographic
separation. The membrane passes ions of the same charge as the
exchangeable ions of the membrane to convert the electrolyte of the
eluent to weakly ionized form, followed by detection of the
ions.
[0006] Another membrane suppressor device is disclosed in U.S. Pat.
No. 4,751,004. There, a hollow fiber suppressor is packed with
polymer beads to reduce band spreading. There is a suggestion that
such packing may be used with other membrane forms. Furthermore,
there is a suggestion that the function of the fiber suppressor is
improved by using ion exchange packing beads. No theory is set
forth as to why such particles would function in an improved
manner.
[0007] Another suppression system is disclosed in U.S. Pat. No.
4,459,357. There, the effluent from a chromatographic column is
passed through an open flow channel defined by flat membranes on
both sides of the channel. On the opposite sides of both membranes
are open channels through which regenerant solution is passed. As
with the fiber suppressor, the flat membranes pass ions of the same
charge as the exchangeable ions of the membrane. An electric field
is passed between electrodes on opposite sides of the effluent
channel to increase the mobility of the ion exchange. One problem
with this electrodialytic membrane suppressor system is that very
high voltages (50-500 volts DC) are required. As the liquid stream
becomes deionized, electrical resistance increases, resulting in
substantial heat production. Such heat is detrimental to effective
detection because it greatly increases noise and decreases
sensitivity.
[0008] In U.S. Pat. No. 4,403,039, another form of electrodialytic
suppressor is disclosed in which the ion exchange membranes are in
the form of concentric tubes. One of the electrodes is at the
center of the innermost tube. One problem with this form of
suppressor is limited exchange capacity. Although the electrical
field enhances ion mobility, the device is still dependent on
diffusion of ions in the bulk solution to the membrane.
[0009] Another form of suppressor is described in U.S. Pat. No.
4,999,098. In this apparatus, the suppressor includes at least one
regenerant compartment and one chromatographic effluent compartment
separated by an ion exchange membrane sheet. The sheet allows
transmembrane passage of ions of the same charge as its
exchangeable ions. Ion exchange screens are used in the regenerant
and effluent compartments. Flow from the effluent compartment is
directed to a detector, such as an electrical conductivity
detector, for detecting the resolved ionic species. The screens
provide ion exchange sites and serve to provide site-to-site
transfer paths across the effluent flow channel so that suppression
capacity is no longer limited by diffusion of ions in the bulk
solution to the membrane. A sandwich suppressor is also disclosed
including a second membrane sheet opposite to the first membrane
sheet and defining a second regenerant compartment. Spaced
electrodes are disclosed in communication with both regenerant
chambers along the length of the suppressor. By applying an
electrical potential across the electrodes, there is an increase in
the suppression capacity of the device. The patent discloses a
typical regenerant solution (acid or base) flowing in the
regenerant flow channels and supplied from a regenerant delivery
source. In a typical anion analysis system, sodium hydroxide is the
electrolyte developing reagent and sulfuric acid is the regenerant.
The patent also discloses the possibility of using water to replace
the regenerant solution in the electrodialytic mode.
[0010] In one form of sandwich suppressor of the foregoing type
sold by Dionex Corporation for more than one year, for cation
analysis, sulfonated and aminated screens of capacity similar to
that of the eluent channel were disposed in the regenerant channel.
The purpose of the sulfonated screen was to allow improved lifetime
under solvent conditions.
[0011] U.S. Pat. No. 5,045,204 discloses an electrodialytic device
using an ion exchange membrane separating two flowing solutions in
flow-through channels for generating a high purity chromatography
eluent (e.g., NaOH). Water is electrolyzed in a product channel to
provide the source of hydroxide ion for sodium which diffuses
across the membrane. The patent discloses a mode of eliminating
hydrogen gas generated in the product channel.
[0012] U.S. Pat. No. 5,248,426 discloses a suppressor of the
general type described in U.S. Pat. No. 4,999,098 in an ion
chromatography system in which the effluent from the detector is
recycled to the flow channel(s) in the suppressor adjacent the
sample stream flow channel.
[0013] U.S. Pat. No. 5,597,481 disclosed a suppressor-type device
of the foregoing type used in sample pretreatment to reduce or
suppress matrix ions in the eluent of opposite charge to the
analyte ions and then to analyze the analytes in their conductive
forms. Using existing suppressor devices, ion exchange interactions
and hydrophobic interaction of the analytic, particularly in the
eluent flow channel, affects recovery of certain analytes such as
oligonucleotides and oligosaccharides. In order to improve
recovery, high concentrations of eluents coupled with solvents are
generally used. Similarly, in order to elute certain highly charged
multifunctional analytes from the chromatographic column, high
concentrations of eluents are normally used. High concentrations of
eluents, however, are not easily suppressed.
[0014] U.S. Pat. No. 6,077,434 discloses, methods and apparatus are
provided of improved current efficiency. In one embodiment, an
aqueous sample stream including analyte ions of one charge and
matrix ions of opposite charge flows through a sample stream flow
channel, while flowing an aqueous stream through an ion receiving
flow channel separated therefrom by a first ion exchange membrane,
and passing a current between the channels to reduce the
concentration of the matrix ions. The sample stream flow channel
has an upstream sample stream portion containing the matrix ions
and an adjacent downstream portion in which the matrix ions have
been suppressed. The upstream portion has an electrical resistance
no greater than about 0.9 times that of the downstream portion. The
ion receiving flow channel includes stationary flow-through first
packing of ion exchange material. Neutral or low capacity packing
may be disposed in the sample stream flow channel. In another
embodiment, a second ion exchange membrane adjacent to the sample
stream flow channel is used defining an ion source flow channel
through which another aqueous stream flows. The first membrane has
a net charge of no greater than about 0.9 times the net charge of
the second membrane. In another embodiment, the downstream portion
has a net charge of no greater than about 0.9 times the net charge
of the upstream portion. In a further embodiment, current is passed
at a first amperage between the upstream sample stream portion and
an adjacent upstream ion receiving stream portion using first and
second electrodes, and a second current is passed at a second lower
amperage between the downstream sample stream portion and an
adjacent downstream ion receiving stream portion using third and
fourth electrodes.
[0015] There is a need to provide other ways to increase the
capacity of suppressors and suppressor-like pretreatment devices to
permit suppression of a high concentration of eluent. Similarly, in
sample preparation applications it would be useful to have a
suppressor with improved recovery of analytes and suppress high
concentrations of eluent or mobile phase.
SUMMARY OF THE INVENTION
[0016] In one embodiment of the invention, a non-electrolytic
apparatus is provided for treating an aqueous sample stream
including analyte ions and matrix ions of opposite charge. The
apparatus comprises a first ion exchange membrane capable of
passing only ions of opposite charge to the analyte ions, a sample
stream flow channel, a first aqueous stream ion receiving flow
channel adjacent one side of the sample stream flow channel and
separated therefrom by the first ion exchange membrane, and
stationary flow-through first packing of ion exchange material
disposed in the sample stream flow channel of the same charge as
the first membrane and having a first ion exchange capacity for the
matrix ions. The first ion receiving channel has an ion exchange
capacity for the matrix ions less than about 25% of the first ion
exchange capacity for the matrix ions. The application does not
include electrodes disposed to apply an electric field between the
sample stream flow channel and the first ion receiving flow
channel.
[0017] In another embodiment, a chromatography apparatus including
apparatus is provided for treating an aqueous sample stream
including analyte ions and matrix ions of opposite charge, the
apparatus comprising a chromatography separator having an inlet and
an outlet, the inlet being in fluid communication with the sample
stream. The treating apparatus is disposed upstream or downstream
from the chromatography separator and comprises a first ion
exchange membrane capable of passing only ions of opposite charge
to the analyte ions, a sample stream flow channel, a first aqueous
stream ion receiving flow channel adjacent one side of the sample
stream flow channel and separated therefrom by the first ion
exchange membrane. Stationary flow-through first packing of ion
exchange material is disposed in the sample stream flow channel of
the same charge as the first membrane and having a first ion
exchange capacity for the matrix ions. The first ion receiving
channel has an ion exchange capacity for the matrix ions less than
about 25% of the first ion exchange capacity for the matrix
ions.
[0018] In another embodiment, a non-electrolytic method is provided
for treating an aqueous sample stream including analyte ions of one
charge and matrix ions of opposite charge to the analyte ions. The
method comprises flowing the sample stream through a sample stream
flow channel, simultaneously flowing an aqueous stream through an
ion receiving flow channel separated therefrom by a first ion
exchange membrane capable of passing only ions of opposite charge
to the analyte ions and of blocking bulk liquid flow to reduce the
concentration of the matrix ions in an effluent from the sample
stream flow channel, the sample stream flow channel having
stationary flow-through first packing of ion exchange material
disposed in the sample stream flow channel of the same charge as
the first membrane and having a first ion exchange capacity for the
matrix ions. The ion receiving channel has an ion exchange capacity
for the matrix ions less than about 25% of the first ion exchange
capacity for the matrix ion. No electric field is applied between
the sample stream flow channel and the first ion receiving flow
channel.
[0019] In another embodiment, a chromatography method is provided
comprising flowing an aqueous sample stream including analyte ions
of one charge and matrix ions of opposite charge to the analyte
ions through a chromatography separator to separate the analyte
ions. The sample stream including the separated analyte ions flows
through a sample stream flow channel, and simultaneously flowing an
aqueous stream through an ion receiving flow channel separated
therefrom by a first ion exchange membrane capable of passing only
ions of opposite charge to the analyte ions and of blocking bulk
liquid flow to reduce the concentration of the matrix ions in an
effluent from the sample stream flow channel, the sample stream
flow channel having stationary flow-through first packing of ion
exchange material disposed in the sample stream flow channel of the
same charge as the first membrane and having a first ion exchange
capacity for the matrix ions, the ion receiving channel having an
ion exchange capacity for the matrix ions less than about 25% of
the first ion exchange capacity for the matrix ion.
BRIEF DESCRIPTION OF THE DRAWING
[0020] FIG. 1 is a schematic view of a suppressor according to the
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0021] The system of the present invention is useful for
determining a large number of ionic analyte so long as the ions are
solely anions or solely cations. Suitable samples include surface
waters and other liquids such as industrial chemical waste, body
fluids, beverages such as fruits, wines and drinking water.
[0022] The present invention is directed to a method and apparatus
for treating an aqueous sample stream including analyte ions of one
charge and matrix ions of opposite charge. In one application, the
treatment is in a suppressor for ion chromatography and the matrix
ions are the electrolyte ions in the eluent of opposite charge to
the analyte ions. In another application, the method and apparatus
is used for pretreating an aqueous sample stream prior to analysis,
preferably including separation on a chromatography column. In this
instance, the matrix ions typically are compounds of high ionic
strength in the sample stream (e.g., commercial sodium hydroxide)
which can obscure the sample peaks by large interfering peaks of
the sample matrix ions. Such matrix ions can severely change
chromatography because the sample matrix ion is of such high
concentration it becomes the major eluting ion, temporarily
overriding the eluent. A typical minimum concentration to warrant
pretreatment is when the matrix ion is at least ten times the molar
ionic concentration of the chromatographic eluent. Such a system to
which the present improvement in suppression capacity is applicable
to devices set forth in Stillian, et al., U.S. Pat. No. 5,597,481,
incorporated herein by reference.
[0023] As used herein, the term "matrix ion" refers to either the
electrolyte in an eluent used for chromatography which is
suppressed or whose concentration is reduced to non-interfering
levels after separation and prior to detection, or to matrix ions
in a sample stream whose concentration is significantly reduced
prior to separation and/or detection. Since, in either case, the
matrix ions are suppressed in the device, the term "suppressor"
will be used generically to include a suppressor for ion
chromatography and a pre-treatment device including the
modifications of the present invention.
[0024] For the analysis of anions, the matrix ions typically are a
base (e.g., sodium hydroxide or other alkyl metal hydroxides).
Other matrix compounds include sodium carbonate, sodium
bicarbonate, ammonium hydroxide, or alkyl ammonium hydroxide. For
cation analysis, the matrix ions typically are an acid such as a
common mineral or organic acid (e.g., sulfuric acid, phosphoric
acid or methane sulfonic acid).
[0025] The term "packing" refers to stationary flow-through solid
material disposed in a flow channel of the suppressor. It can be a
screen or a porous monolithic matrix, a resin particle bed or other
form. It can be strongly charged, weakly charged or of neutral
charge, as will be explained. The term packing is alternatively
called "bridging means."
[0026] During suppression, the conductivity and noise caused by
matrix ions in an analysis stream is reduced. The present invention
serves to increase the capacity of the suppressors described above.
Various embodiments of such suppressors will be described
herein.
[0027] The specific purpose of the suppressor stage in ion
chromatography is to reduce the conductivity and noise of the
analysis stream background while enhancing the conductivity of the
analytes (i.e., increasing the signal/noise ratio), while
maintaining chromatographic efficiency. Thus, the following
parameters bear upon the performance of the suppressor: (1) dynamic
capacity of suppression, measured as .mu.Eq./min of eluent for each
device; and (2) background conductivity measured as .mu.S/cm per
device.
[0028] In one embodiment, a suppressor of increased capacity
according to the invention can be used in a chromatography system
using a chemical or electrochemical suppressor of the type
described in Pohl, et al., U.S. Pat. No. 4,999,098, incorporated
herein by reference. A chemical suppressor (i.e., one which relies
on chemical regenerant solution and in which an electric current is
not applied and so which does not require electrodes) is preferred
herein. In some instances, the invention may be applicable to
electrochemical suppressors. The invention will be described with
respect to an ion chromatography system in which a chemical
suppressor is disposed between the chromatography column and
detector.
[0029] FIG. 1 illustrates a chemical suppressor for performing the
present invention. As illustrated in FIG. 1 of the '098 patent, the
suppressor can be used in a system which includes a chromatographic
separator, typically in the form of a chromatographic column, which
is packed with a chromatographic separation medium. In one
embodiment referred to above, such medium is in the form of
ion-exchange resin. In another embodiment, the separation medium is
a porous hydrophobic chromatographic resin with essentially no
permanently attached ion-exchange sites. This other system is used
for mobile phase ion chromatography (MPIC) as described in U.S.
Pat. No. 4,265,634. An ion exchange site-forming compound,
including hydrophobic portion and an ion-exchange site, is passed
through the column and is reversibly adsorbed to the resin to
create ion-exchange sites.
[0030] Arranged in series with the chromatographic column is the
suppressor serving to suppress the conductivity of the electrolyte
of the eluent from the column but not the conductivity of the
separated ions. The conductivity of the separated ions is usually
enhanced in the suppression process.
[0031] As further illustrated in FIG. 1 of the '098 patent, the
effluent from the suppressor is directed to a detector, preferably
in the form of flow-through conductivity cell, for detecting all
the resolved ionic species therefrom. A suitable sample is supplied
through a sample injection valve and passed through the apparatus
in the solution of eluent from an eluent source or reservoir drawn
by a pump, and then through the sample injection valve. The
chromatography effluent solution leaving the column is directed to
the suppressor wherein the electrolyte is converted to a weakly
conducting form. The chromatography effluent with separated ionic
species is then treated by the suppressor and passed through the
conductivity cell.
In the conductivity cell, the presence of ionic species produces an
electrical signal proportional to the amount of ionic material.
Such signal is typically directed from the cell 12 to a
conductivity meter, not shown, thus permitting detection of the
concentration of separated ionic species.
[0032] Referring to FIG. 1 herein, a device is schematically
illustrated in the form of a sandwich membrane suppressor device
including a central sample stream flow channel defined on both
sides by ion-exchange membranes to the exterior of which are ion
receiving flow channels. The specific structure of a chemical
sandwich suppressor may be of the type illustrated in FIGS. 2 and 3
of the '098 patent but, preferably without the electrodes. In one
embodiment, the device includes means defining a sample stream flow
channel in the form of a sample stream compartment, partially
bounded by a sample stream gasket defining a central cavity. To
minimize dead space in the cavity, it is preferable to form both
ends of the flow channels in a peak or V-shape. Stationary
flow-through packing, preferably bridging means in the form of a
sample stream screen, may be disposed in the cavity. Ion exchange
membrane sheets are mounted to extend along opposite sides of the
sample stream screen and, together with a gasket, define the outer
perimeter of the sample stream flow channel. External support
blocks may be provided in the form of a rigid nonconductive
material, such as polymethylmethacrylate, or polyether-ether ketone
(PEEK) and serve to provide structural support for the remainder of
membrane the device.
[0033] The ion-exchange membrane sheets may be of a type such as
disclosed in the '098 patent. In particular, such sheets may be
cation-exchange or anion-exchange membranes with polyethylene,
polypropylene, polyethylene-vinylacetate-based substrates. Other
suitable substrates include poly-vinylchloride or
polyfluorocarbon-based materials. The substrate polymer is solvent
and acid or base resistant. Such substrates are first grafted with
suitable monomer for later functionalizing. Applicable monomers
include styrene and alkylstyrenes such as 4-methylstyrene,
vinylbenzylchloride or vinylsulfonates, vinylpyridine and
alkylvinylpyridines. As an example, to form a cation-exchange
membrane, the sheets grafted with styrene monomers are
functionalized suitably with chlorosulfonic acid, sulfuric acid, or
other SO.sub.2 or SO.sub.3 sources. To form an anion-exchange
membrane, the sheets grafted with vinylbenzylchloride monomers are
functionalized with alkyl tertiary amines such as trimethylamine or
tertiary alkanolamines, such as dimethylethanolamine. Particularly
effective membranes are no more than 10 mil thick, and preferably
no more than 2-5 mil when dry. Suitable polyethylene substrate
membranes of the foregoing type are provided by RAI Research Corp.,
Hauppauge, N.Y. (the cation exchange membrane provided under
designation RS010 (0.008 inch thick) and the anion-exchange
membrane under designation R4015 (0.004 inch thick)). Other cation
exchange membranes supplied by the same company which are
fluorocarbon based include R1010 (0.002 inch thick) and R4010
(0.004 inch thick).
[0034] For a flat sheet suppressor, one embodiment of the packing
includes continuous portions which extend substantially the entire
distance of the flow channels in which they are used and transverse
to flow. In an alternate embodiment illustrated in FIG. 6 of the
'098 patent, only one membrane is used which separates an ion
receiving flow channel from sample stream flow channel 31. The
packing, when used, preferably defines a continuous convoluted
flow-through passageway in the flow channel in which it is disposed
along substantially the entire length of the membrane. This creates
turbulence and thus increases the efficiency of mixing and transfer
of the ions across the membrane as described below. The physical
configuration of the packing is preferably a screen.
[0035] FIG. 1 herein is a schematic view of a suppressor used in
the chemical mode. The overall structure of the device can be the
same as a commercial AMMS.RTM. or CMMS.RTM. suppressor sold by
Dionex Corporation with the exception of the ion exchange capacity
of the packing in the regenerant flow channels. FIG. 1 will first
be described with respect to a commercial anion membrane
suppressor, such as one sold by Dionex Corporation under the
trademark AMMS.RTM.. In general terms, the device can be used for
treating an aqueous stream including analyte ions and matrix ions
of opposite charge. For the analysis of anions illustrated in FIG.
1 as A.sup.- in a Na.sup.+A.sup.- salt, the device 10 includes an
eluent flow channel 12 bounded on both sides along the flow path by
cation exchange membranes 14 and 16 capable of passing only ions of
opposite charge to the analyte ions, e.g., capable of passing the
sodium ions, assuming a sodium hydroxide eluent. Eluent flow
channel 12, also termed a sample flow channel, includes stationary
flow-through first packing 18 of ion exchange material having the
same charge as membranes 14 and 16, i.e., a positive charge for the
analysis of anions. The function of that flow-through packing is as
described above. Regenerant or ion receiving flow channels 20 and
22, respectively, are disposed on the opposite side of membranes 14
and 16, respectively, from flow channel 12. The low ion exchange
capacity or absence of capacity in flow channels 20 and 22 provide
for increased current capacity for the suppressors of the present
invention as will be described below. Packing 24 and 26, in the
embodiments in which packing are present, is disposed in flow
channels 20 and 22, respectively.
[0036] As set forth above, the system of the present invention is
applicable to the use of the apparatus for pretreating an aqueous
stream prior to separation by chromatography or for use as a
suppressor in ion exchange chromatography downstream from the
chromatography column. Thus, the present description will be
referred to in general terms with the eluent flow channel 12 of
device 10 being referred to interchangeably as an eluent flow
channel or a sample flow channel and the regenerant flow channels
20 and 22 will also be referred to as ion receiving flow channels.
This is because, whether the device 10 is used as a pretreatment
device or a suppressor, the matrix ion of opposite charge to the
analyte ion flow into the ion receiving flow channels 20 and
22.
[0037] Referring again to FIG. 1, the flow pattern and
configuration for the Dionex AMMS.RTM. device and that of the
present invention are the same. Thus, in one form, the device has a
high capacity cation exchange packing 18, such as cation screens,
in the eluent flow channel, such as described in U.S. Pat. No.
4,998,098. In operation as a suppressor, the cations from the
eluent in the sample are driven across membranes 14 and 16 and
exchanged for hydronium ions supplied from an external chemical
reservoir. FIG. 1 illustrates device 10 as a suppressor. There,
NaOH is used as an eluent and so the analyte ions A.sup.- in the
sample stream flow channel are in the sodium ion salt form
(Na.sup.+ A.sup.-). The illustrated chemical regenerant is a strong
acid, as sulfuric acid, flowing in the ion receiving channels 22
and 24 countercurrently to the eluent stream. The sodium ions flow
into an ion receiving channel to form a salt, e.g., of NaHSO.sub.4.
The analyte ions A.sup.- exit the device 10 in acid form
H.sup.+A.sup.- and flow to a detector, not shown, typically an ion
conductivity detector. Except for the ion exchange capacity of the
packing in the ion receiving channels, such a chemical regenerant
system is described in the prior art such as in U.S. Pat. No.
4,999,098.
[0038] As set forth above, device 10 can be used for treating an
aqueous stream including analytes of one charge and matrix ions of
opposite charge to the analyte ions. The samples stream flows
through the sample stream flow channel while an aqueous stream
flows through at least one ion receiving flow channel separated
therefrom by the ion exchange membrane capable of passing of ions
of opposite charge to the analyte ions and the blocking of bulk
liquid flow. As illustrated, the device is in a flat sandwich form.
However, the invention is also applicable to a device using a
single membrane in a single ion receiving channel or in a tubular
form. Also, the device is illustrated using countercurrent flow
between the sample stream flow channel and ion receiving flow
channel. Alternatively, flow can be concurrent.
[0039] Device 10 of the present invention has a substantially lower
ion exchange capacity for the matrix ion in the ion receiving
channels 20 and 22 than in the sample stream flow channel 12. Thus,
according to the invention, the ion exchange capacity for the
matrix ions in the ion receiving channel(s) is less than about 25%
of that in the sample stream flow channel, preferably less than
20%, 15%, 10%, 5% or less, and may have essentially no capacity.
The term "ion exchange capacity" in the ion receiving flow
channel(s) refers to the capacity of packing for the removed ions,
if present in such channel(s). Thus, in one embodiment, there is no
ion exchange capacity for the matrix ions in the ion receiving flow
channel(s). This could be accomplished by having no packing in the
ion receiving channel(s) or by the use of a neutral screen or a
neutral packed particle bead or by use of an ion exchange screen or
resin with opposite functionality only to the removed ions in the
ion receiving flow channel(s). There, the ion receiving flow
channel(s) are substantially free of ion exchange capacity for the
matrix ions.
[0040] The ion exchange capacity for the matrix ions in the sample
stream flow channel is typically as used for the eluent flow
channel of a membrane suppressor of the type sold by Dionex
Corporation under the AMMS.RTM. mark and as described in U.S. Pat.
No. 4,999,098. Suitable ranges of ion exchange capacity in the
sample stream flow channel are from 0.01 to 5 meqv/gm, preferably
0.05 to 1 meqv/gm, and more preferably from 0.1 to 0.3 meqv/gm. The
ion exchange capacity in the sample stream flow channel is
beneficial particularly when the regenerant is consumed. It permits
the device to have significant static capacity so that the process
of suppression can continue uninterrupted for some time.
[0041] In the above embodiment using packing of very low capacity
or no capacity for the matrix ions (cations for anion analysis) in
the ion receiving flow channel(s), the removed cations, e.g.,
Na.sup.+, are substantially unretained by the regenerant screen in
such flow channels. An advantage of this lack of retention capacity
is that the removed cations are quickly equilibrated, the cations
are quickly removed from the suppressor devices and suppression
capacity is improved. Also, the cost of the device is reduced
because the neutral function screens are cheaper to manufacture.
Further, unfunctionalized neutral materials are less likely to
swell in the presence of a solvent and are more compatible with
solvents. This reduces back pressure in the presence of a solvent,
thus reducing the amount of pressure required to dispense the
regenerant solution into the regenerant flow channels.
[0042] As an alternative to the neutral screens, packing lightly
functionalized for low ion exchange capacity for the matrix ions
may be used, preferably less than the aforementioned percentages of
the capacity of the ion exchange packing in the sample stream flow
channel.
[0043] In another embodiment, the matrix ion receiving channel
includes packing of opposite charge to the matrix ion. Thus, for
anion analysis wherein the eluent is NaOH, an aminated regenerant
screen can be used in the matrix ion receiving channel. The
capacity of such packing is preferably relatively low for the
removed cations, e.g., from 0.01 to 0.1 meqv/gm, preferably from
0.0 to 0.02 meqv/gm. This results in no substantial retention of
the removed cation and can result in increased suppressor capacity
because the ions are removed faster from the regenerant channel and
the suppressor device.
[0044] Although the above system has been described with respect to
anion analysis, it is also applicable to cation analysis with a
reversal of polarities of the membranes and reagents.
[0045] The above system illustrates an ion exchange screen as the
preferred flow-through ion exchange packing. However, it should be
understood that other ion exchange packing may also be employed for
the sandwich suppressor or other relatively flat suppressor. For
example, ion exchange or neutral particles may be packed in the
regenerant flow channels for this purpose. Here, it would be
preferable to include some mode to keep the ion exchange particles
in the device by using a porous polymeric support that has smaller
pores than the resin being used, such as sintered polyethylene
available from General Polymeric.
[0046] A tubular form of suppressor of the present invention may
also be used as illustrated in U.S. Pat. No. 4,999,098, but
preferably in the chemical mode.
[0047] In order to illustrate the present invention, the following
examples of its practice in the chemical mode are provided.
Example 1
[0048] The performance in terms of dynamic capacity of a standard
AMMS III suppressor from Dionex Corporation was compared to a
device of the present invention. The device of the present
invention was assembled by fitting neutral regenerant screens in
place of the functionalized cation exchange regenerant screens and
using standard AMMS III suppressor components. A Dionex DX500 ion
chromatography system was used for this testing. The dynamic
suppression capacity was determined by pumping at 1 ml/min various
concentrations of NaOH by conventional proportioning. The
regenerant was 100 mN sulfuric acid pumped at 10 ml/min
(conventional chemical suppression mode).
[0049] Results: The dynamic capacity of the standard AMMS III
suppressor was measured as 170 ueqv/min. The device of the present
invention showed a dynamic capacity of 210 ueqv/min which was an
increase of 23% in capacity. Thus, removing the retention of the
eluent cation in the regenerant chamber as per the current
invention resulted in improved operational capacity.
Example 2
[0050] The experimental setup was similar to Example 1 except the
regenerant was 150 mN sulfuric acid and was dispensed using the
displacement chemical regeneration approach of U.S. Pat. No.
6,436,719.
[0051] Results: The dynamic capacity under these conditions for a
standard suppressor was 70 ueqv/min. The device of the present
invention on the other hand showed a capacity of 90 ueqv/min. A 29%
increase in capacity was observed as per the present invention.
Example 3
[0052] The performance in terms of dynamic capacity of a standard
CMMS III suppressor from Dionex Corporation was compared to a
device of the present invention. The device of the present
invention was assembled by fitting neutral regenerant screens in
place of the functionalized regenerant screens using standard CMMS
III suppressor components. A DX500 ion chromatography system was
used for this testing. The dynamic suppression capacity was
determined by pumping at 1 ml/min various concentrations of MSA by
conventional proportioning. The regenerant was 100 mN
tetrabutylammonium hydroxide base pumped at 10 mil/min
(conventional chemical suppression mode). The dynamic capacity of
the standard CMMS III suppressor was measured as 65 ueqv/min.
[0053] Results: The device of the present invention showed a
dynamic capacity of 100 ueqv/min which was an increase of 53% in
capacity. Thus, removing the retention of the anion in the
regenerant chamber as per the present invention resulted in
improved operational capacity.
Example 4
[0054] The experimental setup was similar to Example 3 except the
regenerant was dispensed using the displacement chemical
regeneration approach of U.S. Pat. No. 6,436,719.
[0055] Results: The dynamic capacity under these conditions for a
standard suppressor was 35 ueqv/min. The device of the present
invention on the other hand showed a capacity of 55 ueqv/min. A 57%
increase in capacity was observed as per the present invention.
Example 5
[0056] An AMMS III suppressor was assembled with cation exchange
based lightly functionalized regenerant screens with a cation
exchange capacity of 0.01 meqv/gm by replacing the standard
regenerant screens that had a capacity of 0.3 meqv/gm. This device
when tested for dynamic capacity under conditions outlined in
Example 1 showed performance similar to the device of Example
1.
Example 6
[0057] An AMMS III suppressor was assembled with anion exchange
based aminated regenerant screen in place of the standard cation
exchange based sulfonated screen in the two regenerant chambers.
The suppressor was tested following the conditions outlined in
Example 1. This unit also showed performance comparable to the
suppressor of Example 1.
* * * * *