Abstract:
Electrolytic eluent recycle systems for ion chromatography using a multi-channel electrolytic ion exchange device which integrates suppression, eluent generation, and eluent recycle. The systems recycle the eluent into the analytical system without passing the eluent through the electrode chambers. Also, such systems with a channel for electrolytic removal of ions from the suppression effluent before recycle.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/062,747 filed on Jan. 28, 2008. 
    
    
     BACKGROUND OF THE INVENTION 
     Trovion, a company now located in Campbell, Calif., has developed, manufactured and marketed electrolytic ion exchange devices for analytical scale water purification. The Trovion CIRA products are designed to integrate into analytical instrumentation with the product water flow rate being compatible with instrumentation. 
     In the Trovion electrolytic ion exchange devices, the product water, or analytical stream, never passes through the electrode chambers. As a result, the product water or sample stream is not contaminated with electrolysis by-products such as oxygen, hydrogen, ozone and hydrogen peroxide. Since ozone and hydrogen peroxide can damage ion exchange materials, minimizing contact of critical ion exchange components with these oxidizers is advantageous. 
     In US Patent Application US20060231404, an electrolytic suppressor and eluent purifier is disclosed in which the electrode chambers are isolated from the analytical or waste stream (resulting from the feed). For the suppression of hydrochloric acid, no damage to the ion exchange materials was observed since chloride is not received into the anode compartment, but instead is received into a non-electrolytic central mixed bed waste chamber. 
     In US Patent Application US20060186046, an ion chromatography system using catalytic gas elimination combined with eluent recycle is described. In this system, electrolytic suppressors are used and the recycled eluent is recovered in the electrode chambers. Since the electrode chambers produce hydrogen and oxygen, catalytic elimination of the hydrogen and oxygen gases is used. The catalytic recombination of oxygen and hydrogen to water eliminates problems associated with dissolved gases in the eluent stream and aids in reducing electrolytic by products such as ozone and hydrogen peroxide. 
     SUMMARY OF THE INVENTION 
     One embodiment of the invention is an integrated suppressor and eluent generator apparatus for ion chromatography comprising a suppressor chamber comprising ion exchange material and including an inlet and an outlet, a first electrode chamber comprising a first electrode and including an inlet and an outlet, a second electrode chamber comprising a second electrode and including an inlet and an outlet, an eluent generator chamber comprising flow-through ion exchange material and including an inlet and an outlet, a first barrier preventing significant liquid flow, but permitting transport of ions of only one charge, positive or negative, disposed between the eluent generator chamber and the second electrode chamber, a second barrier preventing significant liquid flow, but permitting transport of ions of only one charge, positive or negative, disposed between the suppressor chamber and the eluent generator chamber, an eluent recycle conduit providing fluid communication, directly or indirectly, between the suppressor chamber and the eluent generator chamber, and an electrode rinse conduit disposed between first and second electrode chambers isolated from said eluent recycle conduit. 
     Another embodiment is an integrated suppressor and eluent generator apparatus for ion chromatography comprising a suppressor chamber comprising ion exchange material and including an inlet and an outlet, a first electrode chamber comprising a first electrode and including an inlet and an outlet, a second electrode chamber comprising a second electrode and including an inlet and an outlet, an eluent generator chamber comprising flow-through ion exchange material and including an inlet and an outlet, a first barrier preventing significant liquid flow, but permitting transport of ions of only one charge, positive or negative, disposed between the eluent generator chamber and the second electrode chamber, a second barrier preventing significant liquid flow, but permitting transport of ions of only one charge, positive or negative, disposed between the suppressor chamber and the eluent generator chamber, a third barrier preventing significant liquid flow, but permitting transport of ions of only one charge, positive or negative, disposed between the first electrode chamber and the suppressor chamber, an ion removal chamber comprising ion exchange material, a fourth barrier preventing significant liquid flow, but permitting transport of ions of only one charge, positive or negative, disposed between the first electrode chamber and the ion removal chamber, and an eluent recycle conduit providing fluid communication between the suppressor chamber and the eluent generator chamber and comprising the ion removal chamber and an eluent recycle conduit portion disposed between the ion removal chamber and the eluent generator chamber. 
     A further embodiment is an ion chromatography method using an integrated suppressor and eluent generator chamber apparatus for ion chromatography comprising a suppressor chamber comprising ion exchange material and including an inlet and an outlet, a first electrode chamber comprising a first electrode and including an inlet and an outlet, a second electrode chamber comprising a second electrode and including an inlet and an outlet, an eluent generator chamber comprising flow-through ion exchange material and including an inlet and an outlet, a first barrier preventing significant liquid flow, but permitting transport of ions of only one charge, positive or negative, disposed between the eluent generator chamber and the second electrode chamber, and a second barrier preventing significant liquid flow, but permitting transport of ions of only one charge, positive or negative, disposed between the suppressor chamber and the eluent generator chamber. The method comprises flowing an eluent stream comprising separated ionic species of one charge, positive or negative, through the suppression chamber to suppress the eluent, recycling the suppressed eluent from the suppressor chamber, directly or indirectly, to the eluent generator chamber, passing a current between the first and second electrodes through the suppressor chamber and eluent generator chamber, during suppression, for suppression and eluent generation, and flowing an aqueous rinse solution through the first and second electrode chambers and between them. 
     Another embodiment comprises an ion chromatography method using an integrated suppressor and eluent generator apparatus for ion chromatography comprising a suppressor chamber comprising ion exchange material and including an inlet and an outlet, a first electrode chamber comprising a first electrode and including an inlet and an outlet, a second electrode chamber comprising a second electrode and including an inlet and an outlet, an eluent generator chamber comprising flow-through ion exchange material and including an inlet and an outlet, a first barrier preventing significant liquid flow, but permitting transport of ions of only one charge, positive or negative, disposed between the eluent generator chamber and the second electrode chamber, a second barrier preventing significant liquid flow, but permitting transport of ions of only one charge, positive or negative, disposed between the suppressor chamber and the eluent generator chamber, a third barrier preventing significant liquid flow, but permitting transport of ions of only one charge, positive or negative, disposed between the first electrode chamber and the suppressor chamber, an ion removal chamber comprising ion exchange material, and a fourth barrier preventing significant liquid flow, but permitting transport of ions of only one charge, positive or negative, disposed between the first electrode chamber and the ion removal chamber. The method comprises flowing an eluent stream comprising separated ionic species of one charge, positive or negative, through the suppression chamber to suppress the eluent, flowing the suppressed eluent from the suppressor chamber, directly or indirectly to the ion removal chamber and then to the eluent generator chamber, and passing a current between the first and second electrodes through the suppressor chamber, ion removal chamber, and eluent generator chamber, during suppression, for suppression, removal of ions in the ion removal chamber, and for eluent generation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1-12  are schematic representations of different integrated devices according to the invention. 
         FIGS. 13-17  depict experimental results using selected integrated devices of one of  FIGS. 1-12 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Electrolytic devices are disclosed in which the analytical stream (sample-containing eluent) does not pass through the electrode chambers. In all embodiments, a separate liquid flow is used for the electrode chambers. Some details of the construction, materials, operation and ion movement in the electrolytic device disclosed herein can be found in US patent application US20060231404. 
     The invention relates to improvements in integrated devices for eluent suppression and generation of eluents which can be used as the eluent (e.g. an acid or a base) for sample ions of one charge, positive or negative, to be chromatographically separated in an ion chromatograph (IC) system. Integrated devices which combine suppression with other operations are disclosed in U.S. Pat. Nos. 6,027,643 and 6,508,985; and in US Patent Applications US20060231404 and US20060186046, collectively “the prior art integrated device publications,” and incorporated by reference for their disclosures of operation and construction, including details of suitable barrier and ion exchange materials. 
     The term “ion exchange materials” refers to ion exchange resins, e.g. ion exchange particles in an ion exchange particle bed, ion exchange fibers, ion exchange screens, or ion exchange monoliths. Typically, one of two types of ion exchange materials are used, anion exchange materials and cation exchange materials (i.e. ones with anion and/or cation exchangeable ions) such as disclosed in the prior art integrated device publications. Anion and cation exchange materials may be mixed to produce a mixed ion exchange material, e.g. in a mixed packed bed of anion and cation particles. Typically, the cation exchange material is a strong acid ion exchanger, i.e., a material containing sulfonic acid groups, and the anion exchange material is a strong base ion exchange containing quaternary amine groups. Preferably, the ion exchange materials are conductive so that ions may migrate through the ion exchange material towards the respective electrodes. 
     The invention uses a number of barriers which prevent significant liquid flow but which permit the transport of ions of only one charge, positive or negative, preferably through exchangeable ions on the barriers. Suitably such barriers are ion exchange membranes of one of two types, anion or cation exchange (i.e. ones with exchangeable anions or cations as disclosed in the prior art integrated device publications). These ion exchange membranes typically have strong basic or strongly acidic functional groups. An anion exchange membrane will transport only anions through the membrane, while the membrane prevents the bulk flow of liquid from one side of the membrane to the other. A cation exchange membrane will transport only cations through the membrane, while the membrane prevents the bulk flow of liquid from one side of the membrane to the other. Thus, preferably the membranes are conductive so that ions may migrate through the ion exchange membrane towards their respective electrodes. The invention will be described using ion exchange membranes as such barriers. 
     Anion Analysis Using the Device of  FIG. 1 . 
       FIG. 1  shows one embodiment of a device to be used for anion analysis. The integrated suppressor and eluent generator device  20  has four discrete chambers. It includes a first electrode chamber in the form of an anode chamber  22  containing an anode electrode  24 , defined on one side by a cation exchange membrane  26  or connector (CM), separating the anode chamber  22  from suppression chamber  28 . Suppression chamber  28  may be filled with a strong cation exchange material (e.g. Dowex 50WX8 cation exchange resin in a packed bed  30 ). A cation exchange membrane  32  or connector (CM) (of the same charge, positive or negative, as membrane  26 ) separates suppression chamber  28  from an eluent generator chamber  34 . (The eluent generator generates a base, KOH as illustrated, to replenish part or all of the KOH eluent to be supplied to a chromatographic separator.) Chamber  34  is also referred to as a receiving chamber since it “receives” the eluent. 
     As shown in  FIG. 1  for anion analysis, suppressor chamber  28 , suitably containing high capacity cation exchange in a packed bed, is used to electrolytically suppress the eluent, illustrated as KOH, fed to chamber  28  from a chromatography separator (not shown) in line  38 . The suppressed eluent ions (illustrated as K + ) are transmitted across cation exchange membrane  32  and received into chamber  34  in which eluent, e.g. KOH, is generated suitably for use as the eluent feed in line  38  to suppressor chamber  28 . The chamber may contain ion exchange material having exchangeable cations or anions, or a mixture, (e.g. cation, anion or a mixture of anion and cation ion exchange resin particles in a bed). In this configuration, the device could be used for integrated suppression and eluent generation. 
     More specifically, as illustrated for anion analysis in  FIG. 1 , the eluent (an aqueous solution of KOH) flows in line  38  from a chromatographic separator (e.g. a chromatography column in which ions of one charge, positive or negative, are separated) to the inlet of suppressor chamber  28 . Solution flowing through the suppressor chamber  28  flows in line  40  to the inlet of chamber  34  in which eluent is electrolytically generated. Between the outlet of suppressor chamber  28  and the inlet of chamber  34 , the separated ions in line  40  are detected, e.g. in conductivity cell  42  in line  40 . 
     An electrode chamber  44  contains an electrode  46  which is connected with electrode  24  to a power supply so that electrodes  24  and  46  are of opposite charge and a current is passed between the electrodes through all barriers and chambers of the device. As illustrated, electrode  46  is a cathode. Electrodes  24  and  46  may be flow-through electrodes or may be disposed in chambers  22  and  44 , preferably parallel to liquid flow, with clearance for liquid flow. Electrode  46  is separated from chamber  34  by barrier  48  illustrated as an anion exchange membrane of opposite charge to cation exchange membrane  26  adjacent to electrode chamber  24 . 
     An aqueous rinse water solution flows in line  50  into chamber  24  and out recycle line  52  to electrode chamber  44  and may flow in line  54  to waste. In an alternative, not shown, the rinse water may flow in the opposite direction between chambers  34  and  44 . The rinse water is isolated from eluent flow. An advantage of a single recycle stream flowing sequentially between the electrode chambers versus flowing in parallel, is that the flow rate is equal in both electrode chambers. 
     Eluent solution (e.g. KOH) generated in chamber  34  is recycled in line  56  to an eluent reservoir (not shown) for use as all or part of the eluent to be supplied with the sample analytes to a chromatography column, not shown, for analyte separation and subsequent flow in line  38  to suppressor chamber  28 . 
     Eluent generation in chamber  34  is performed by the electrolytic reactions illustrated in the prior art integrated device publications except that the electrodes are isolated from eluent flow, e.g. by membrane  48  which isolates electrode  46  from the chamber  34  in which eluent, e.g. KOH, is generated. Thus, the H 2  and O 2  gases generated at the electrodes are substantially isolated from chamber  34   
     Since the analytical stream (suppressed eluent) flowing in line  40 , chamber  34 , and line  56  never passes through the electrode chambers, the recycled generated eluent in line  56  will not contain oxygen, hydrogen and should not have appreciable concentrations of electrochemical by-products. A separate liquid flow is passed through the electrode chambers and in recycle line  52  which is isolated from the eluent stream. The electrode wash liquid typically is deionized water and serves as a source of water for electrolysis to produce hydronium at the anode and hydroxide at the cathode. The electrode rinse solution could be recycled. 
     In the device of  FIG. 1 , analyte anions will be present in the recycled eluent, but no hydrogen, oxygen, ozone or hydrogen peroxide. Over time, the analyte anions will accumulate in the recycled eluent in line  58  which can compromise performance. 
     For anion analysis, an anion trap column (not shown) placed in line  40  between the conductivity cell  42  and the eluent generation chamber  34  would remove the trace anions. This anion trap column could contain high capacity anion exchange resin material, e.g. in a packed bed, so that the lifetime of the trap could be very long. In addition to removing analytes form the recycled eluent, the trap column could also be designed to trap anionic oligomers leaching from the sulfonated cation exchange materials of the suppression chamber  28  and chamber  34 . 
     For cation analysis, the polarity of all elements, e.g. the membranes and ion exchange materials, are reversed. 
     In  FIG. 2 , a device similar to that of  FIG. 1  is illustrated with like parts designated with like numbers. The cation exchange material of the eluent chamber  34  is replaced with a composite (mixture) of anion and cation exchange materials (i.e. ones with anion and cation exchangeable ions). In this configuration, the anion exchange material of eluent chamber  34  can retain the analyte anions as well as anionic oligomer leach from the suppression chamber. Fully sulfonated cation exchange materials are known to leach anionically charged (typically sulfonated) material which are oligomers that result form sulfonation or incomplete polymerization. These anionic oligomers will bind substantially irreversibly to anion exchange materials. Thus, the anion exchange material in eluent generation chamber  34  will prevent contamination of the analytical anion separator column by the anionic leach from the suppression chamber  28 . The anion exchange capacity in the eluent chamber  34  should be high enough so that the recycled eluent, water splitting or electrophoretic displacement will not result in a significant concentration of the analyte in the recycled eluent. The anion exchange capacity in eluent generation chamber  34  will also act to trap the analytes (sample anions). The anion capacity and selectivity will be sufficient so that the eluent formed in the chamber can not displace the anions into the eluent. Water splitting will occur in the eluent chamber as a result of the intimate contact of anion and cation exchange material and the applied electric field. Water splitting can displace retained analytes from the anion resin of eluent generation chamber  34 . If the anion capacity is sufficient, water splitting will not be able to displace a significant amount of the trapped analyte anions. In principle, this should eliminate the need for an external anion trap column. 
     In  FIG. 3 , like parts with  FIG. 1  will be designated with like numbers. The eluent chamber  34  contains only anion exchange material. In this configuration, water splitting occurs only at the cation membrane  32 -anion exchange interface  34  and retention of analyte anion and anionic oligomers leach should be complete as a result of the high capacity anion exchange material. 
     A potential complication of the devices in  FIGS. 2 and 3  with carbonate eluent may result from the fact that the anion exchange material of the eluent chamber  34  will affect the ratio of carbonate/bicarbonate and hydroxide in the solution and anion exchange phase. When polarized, there will be a continuous flux of hydroxide from the cathode chamber into the eluent chamber. Thus, some time will be required for the recycled eluent to fully equilibrate with the anion exchange resin and the continuous flux of hydroxide. 
     Other configurations for anion analysis are shown in  FIGS. 4 ,  5  and  6 . Like parts with  FIG. 1  will be designed with like numbers. The devices of  FIGS. 4 ,  5  and  6  incorporate an integrated anion removal chamber  60  independent of chamber  34  on the anode side of the device for anion analysis. These devices are compatible with hydroxide, but not carbonate eluent, since the carbonate would be removed into the anode chamber along with the analyte. 
     In the devices of  FIGS. 4-6 , analyte anions are removed into the electrode rinse in anode chamber  22  and would flow in line  52  to cathode chamber  44  which could be drawn into chamber  34  across anion exchange membrane  48 . Since the anionic analyte concentration will be low, this should not be a major issue. An anion trap column (not shown) external to the integrated device  20  upstream in the electrode rinse streams  50  and  52  would trap such analyte anions. 
     In the device of  FIG. 4 , an anion removal chamber  60  is integrated into the device, containing mixed bed material. Chamber  60  is disposed between anode chamber  22  and suppressor chamber  28 . Here, suppressed eluent/analytes flows in line  40  from suppressor chamber  28  through conductivity cell  42  to ion removal chamber  60  which is bounded on the anode chamber  22  side by anionic membrane barrier  26 . Cation exchange membrane barrier  62  separates ion removal chamber  60  from suppressor chamber  28 . As illustrated, the analyte anions are transmitted across anion exchange membrane  26  toward anode  24 . Thus, the solution exiting chamber  60  in line  64  has been purified of the analyte anions and is a pure water source for generation of eluent (KOH) in chamber  34 . 
     As in the device of  FIG. 1 , a possible problem with the device of  FIG. 4  is the potential for anionic oligomer from the cationic eluent chamber. A solution to this is shown in  FIG. 5 , where the eluent chamber  34  contains a mixed anion and cation exchange material. As in  FIG. 2 , the anion exchange material of the mixed exchange material in the eluent chamber will minimize anionic leach. Anionic oligomers, which are strongly retained by the anion exchangers, accumulate in the eluent chamber since anions are not removed in this chamber. 
     The device of  FIG. 6  contains only anion exchange material in the eluent chamber  34 . This configuration further minimizes the risk of anionic oligomers in the recycled eluent. 
     Most anion samples will contain alkali and alkaline-earth metals. These cations will accumulate in the recycled eluent causing adverse chromatographic effects such as poor peak symmetry, reduced peak response and poor recovery. In addition, retention times may be affected since the carbonate-bicarbonate ratio will be changed as the cations accumulate in the recycled eluent. 
     For samples high in cations such as sodium, potassium, ammonium, calcium and magnesium, the sample cations may need to be removed prior to injection of sample in the eluent for chromatographic analysis in the separator which flows in line  38  to suppressor chamber  28 . For manual sample injection, this could be accomplished using a cation exchange column in the hydronium form for sample pretreatment prior to separation. When using an autosampler, a cation trap column (hydronium form) could be placed between the autosampler and an injection valve. The cation trap column capacity could be designed to last as long as the recycled eluent, and would be replaced with the eluent. 
     Electrode Rinse in Anion Analysis 
     The electrode rinse solution provides aqueous flow through the electrode chambers and when electrolyzed, provides hydronium and hydroxide for regeneration of the ion exchange materials. The electrode rinse could be delivered to the electrode chambers via a peristaltic pump and the electrode rinse could be recycled. 
     The electrolysis reaction produces oxygen and hydrogen gases. These gases must either be vented so they do not accumulate in the rinse container or recombined (using a platinum or palladium catalyst) to water. The simplest approach uses an open electrode rinse container which provides the required venting. It is also possible to separate the cathode and anode streams. 
     At the anode, ozone is produced and at the cathode, hydrogen peroxide. Both are these compounds are strong oxidizers and can attack not only the ion exchange materials, but can react with other ions forming anionic oxidizers such as hypochlorite and percarbonate. 
     By minimizing the production of hydrogen peroxide or by consuming it after production, the adverse effects of hydrogen peroxide can be minimized. Since hydrogen peroxide is not stable in base, the electrode rinse solution for anion analysis could be dilute sodium hydroxide. This should prevent the build-up of hydrogen peroxide in the recycled electrode rinse solution for anions 
     For cation analysis in ion chromatography, an acid eluent such as sulfuric, nitric or methanesulfonic acid can be used and recycled using the devices shown in  FIGS. 7-12 . For  FIGS. 7-12 , like parts will be designated with like numbers as in  FIGS. 1-6 . In general, the cation analysis devices of  FIGS. 7-12  have the same components as the anion analysis devices of  FIGS. 1-6  except for a change of polarity of the analytes, reagents and charged components of the devices. Referring to  FIGS. 7-9 , for cation analysis, the suppression chamber  28  contains anion exchange resin and eluent generation chamber  34  contains anion, cation or a mixture of ion exchange materials. An external cation trap column, not shown, is preferably disposed in line  40  between the outlet of conductivity cell and eluent generation chamber  34  An advantage of the devices of  FIGS. 7-12 , is their compatibility with electrochemically active eluents such as nitric and hydrochloric acids. In a conventional electrolytic suppressor used in cation analysis, the eluent anion is removed into the anode chamber  44  (previously the cathode chamber). If the eluent anion is electroactive such as chloride, oxidation of the chloride to hypochlorite occurs. The hypochlorite will concentrate in the anion exchange material of the anode chamber causing degradation of the ion exchange material and subsequent failure of the suppressor. In the devices below, the eluent anion is not removed into the electrode chamber, but instead into the non-electroactive receiving chamber (eluent generation chamber). 
     As illustrated, sulfuric acid is used as an eluent. Chamber  34  in  FIG. 7  contains only anion exchange material. The anion resin will be in the sulfate/bisulfate and hydroxide forms depending on the resin and applied current. To the extent that the anion resin is in the hydroxide form, degradation of the anion resin could occur resulting in trace amines and ammonia being added to the recycled eluent. This may cause an increase in background conductivity of the suppressed eluent. A solution to this problem is to replace the anion exchange resin of eluent generation chamber  34  with mixed bed resin, as shown in  FIG. 8 . Trace cations from the anion resin degradation as well as analyte cations, will be trapped for some period in the cation resin of the mixed bed. 
     The device of  FIG. 9  replaces the mixed bed of eluent generation chamber  34  in  FIG. 8  with cation resin. This eliminates the cationic degradation products of chamber  34  and may also trap any degradation products from suppression chamber  28  and will retain analyte cations for some period. Sulfonated anionic leach from the cation resin of the chamber (see  FIG. 9 ) would be present in the eluent but then trapped by the anion resin of the suppression chamber. 
     In  FIGS. 10 ,  11  and  12 , a cation removal chamber  60  is added adjacent to the cathode  24  for continuous removal of cation analytes. Since the cation removal chamber  60  is continuously regenerated, an external trap cartridge may be eliminated. Any cationic degradation from the suppression chamber (amines and ammonia) should also be removed in the analyte removal chamber. Analyte cations are removed into cathode chamber  22  and the water exiting the analyte removal chamber  60  is deionized before entering eluent generation chamber  34 . The analyte cations in the electrode rinse can be drawn into eluent generation chamber  34  from anode chamber  44 . Since the analyte concentration will be low, this is not considered to be a major issue. 
     In  FIGS. 10 ,  11  and  12 , the eluent generation chambers contain anion resin, mixed bed resin and cation resin, respectively. 
     Counter Ion Effects in Cation Analysis 
     Each injection of a sample for cations analysis will introduce sample anion contaminants (counter-ions) into the system. One approach to the counter-ion problem is to restrict the use of the recycle approach to samples with low TDS (below 10 ppm). In this case, the sample anion contaminants may not present a problem during the lifetime of the recycled eluent. 
     In most samples, the sample anion contaminants will be the anions such as chloride and sulfate. These anions will accumulate in the recycled eluent in the acid from and will increase the acid eluent concentration causing a decrease in retention times. This could offset the decrease in the eluent concentration from dilution of the eluent by sample injection. 
     For samples high in anion contaminants such chloride or sulfate, it may be necessary to remove the sample anions prior to injection. For manual sample injection, this could be accomplished via an anion trap column in the hydroxide form. When using an autosampler, an anion trap column could be placed between the autosampler and an injection valve. The anion trap column capacity could be designed to last as long as the recycled eluent, and would be replaced with the eluent. 
     An alternative approach uses an electrolytic cation exchange device as the trap column. This could be a CIRA device (CIRA 10A) or a Dionex CR-ATC. With these devices, regeneration is continuous and the trap would not have to be replaced periodically. 
     Electrode Rinse for Cations 
     The electrode rinse for cations can not contain base since the cation of the base will be electrophoretically drawn into the eluent chamber. One proposed solution is to use water as the electrode rinse with an anion exchange cartridge in the hydroxide form. This should help degrade the hydrogen peroxide, but degradation of the hydroxide form resin will result in ammonia and amines. 
     In order to illustrate the present invention, the following non-limiting examples of its practice are set forth. 
     Example 1 
     Anion IC Using an Integrated Suppressor and Eluent Generator 
     An integrated suppressor and eluent generator device for anion IC ( FIG. 1 ) was constructed using machined high density polyethylene hardware to retain the electrodes, membranes and resin. The internal flow dimensions of the suppression chamber were 0.40 cm in diameter and 3.81 cm in length. The internal flow dimensions of the eluent generation chamber were 0.40 cm in diameter and 1.27 cm in length. 
     The anode chamber contained a platinum gauze electrode (Unique Wire Weaving Inc, Hillside, N.J.). In contact with the anode and separating the anode chamber from the suppression chamber was a cation membrane (Electropure Excellion I-100 cation membrane, a product of Electropure Inc, Laguna Hills, Calif.). The suppression chamber was filled with cation exchange resin (DOWEX™ 50×4 (200 mesh), a product of the Dow Chemical Company, Midland, Mich.) in the hydronium form. A cation membrane (Electropure Excellion I-100 cation membrane, a product of Electropure Inc, Laguna Hills, Calif.) separated the suppression chamber from the eluent generation chamber. 
     The eluent generation chamber was filled with cation exchange resin (DOWEX™ 50×4 (200 mesh), a product of the Dow Chemical Company, Midland, Mich.) in the hydronium form. Separating the eluent generation chamber from the cathode chamber is anion membrane (Electropure Excellion I-200 anion membrane, a product of Electropure Inc, Laguna Hills, Calif.) The cathode chamber contained platinum gauze electrodes (Unique Wire Weaving Inc, Hillside, N.J.). The cathode is in direct contact with the cation membrane and cathode chamber. A Dionex ATC3 anion trap column (not shown in  FIG. 1 ) was placed between the conductivity cell outlet and the eluent generator chamber inlet chamber to trap the analyte anions from the suppressed eluent. 
     The device of  FIG. 1  was tested using a Dionex DX500 Ion Chromatography system (a product of Dionex Corp, Sunnyvale, Calif.) consisting of a GP50 pump, CD25 conductivity detector and a LC30 chromatography oven. An eluent of 4.5 mM sodium carbonate and 1.4 mM sodium bicarbonate was pumped at a flow of 1.2 mL/min to a analytical anion exchange column (AG22/AS22 a product of Dionex Corp., Sunnyvale, Calif.) for separation of the sample anions. An Agilent E3611A DC power supply (Agilent Corp., Santa Clara, Calif.) was used to power the device of  FIG. 1  at a constant current of 35 mA (approximately 30V). A peristaltic pump (MASTERFLEX LS, a product of the Cole-Parmer company, Vernon Hills, Ill.) was used to recycle deionized water at a flow rate of 2.0 mL/min to the anode chamber and then to the cathode chamber and then back to the deionized water container. 
     From the outlet of the analytical column, the eluent was directed to the inlet of the suppression chamber, out of the suppression chamber and to the conductivity cell, out of the conductivity cell and to the trap column and then to the eluent generation chamber. From the outlet of the generation chamber the eluent can be directed to waste (non-recycle mode) or back to the eluent container (recycle mode).  FIG. 13  shows a chromatogram obtained with the system described above. 
     Table I shows retention times and chromatographic efficiencies for the common anions using the device of  FIG. 1 . The chromatographic efficiencies are comparable to those obtained with commercially available electrolytic suppressors. 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE I 
               
             
             
               
                   
               
               
                 Chromatographic Efficiency for Anion ER 
               
             
          
           
               
                   
                   
                   
                 Plates 
               
               
                 Peak 
                 Name 
                 RT min 
                 (ER) 
               
               
                   
               
             
          
           
               
                 1 
                 fluoride. 
                 3.083 
                 4986 
               
               
                 2 
                 chloride 
                 4.457 
                 11107 
               
               
                 3 
                 nitrite 
                 5.353 
                 8488 
               
               
                 4 
                 bromide 
                 6.387 
                 12149 
               
               
                 5 
                 nitrate. 
                 7.137 
                 12151 
               
               
                 6 
                 phosphate 
                 9.577 
                 9415 
               
               
                 7 
                 sulfate. 
                 11.13 
                 11081 
               
               
                   
               
             
          
         
       
     
     Recycling an eluent volume of 500 mL, the retention time trend data in  FIG. 14  was obtained. The data represents 26 complete recycle (regeneration) of the 500 mL of eluent. This number of cycles is equivalent to operating the system continuously for 30 days with a 2 L container of eluent being recycled. 
       FIG. 15  shows the retention time standard deviation for the nine cycles using a 500 mL volume of eluent. This corresponds to continuously operating for 11 days (24 hours/day) with 2 L of eluent. The retention time standard deviation is less than 1.22% for all analytes. 
     Example 2 
     Cation IC Using an Integrated Suppressor and Eluent Generator 
     An integrated suppressor and eluent generator apparatus for cation IC ( FIG. 7 ) was constructed using machined high density polyethylene hardware to retain the electrodes, membranes and resin. The internal flow dimensions of the suppression chamber were 0.40 cm in diameter and 3.81 cm in length. The internal flow dimensions of the eluent generation were 0.40 cm in diameter and 1.27 cm in length. 
     The cathode chamber contained a platinum gauze electrode (Unique Wire Weaving Inc, Hillside, N.J.). In contact with the cathode and separating the cathode chamber from the suppression chamber was an anion membrane (Electropure Excellion I-200 anion membrane, a product of Electropure Inc, Laguna Hills, Calif.). The suppression chamber was filled with anion exchange resin (DOWEX™ 1×4 (200 mesh), a product of The Dow Chemical Company, Midland, Mich.) in the hydroxide form. An anion membrane (Electropure Excellion I-200 anion membrane, a product of Electropure Inc, Laguna Hills, Calif.) separated the suppression chamber from the eluent generation chamber. The eluent generation chamber was filled with anion exchange resin (DOWEX™ 1×4 (200 mesh), a product of The Dow Chemical Company, Midland, Mich.) in the hydroxide form. Separating the eluent generation chamber from the anode chamber is cation membrane (Electropure Excellion I-100 cation membrane, a product of Electropure Inc, Laguna Hills, Calif.). The anode chamber contained platinum gauze electrodes (Unique Wire Weaving Inc, Hillside, N.J.). The anode is in direct contact with the cation membrane and anode chamber. A Dionex CTC3 cation trap column (not shown in  FIG. 1 ) was placed between the conductivity cell outlet and the eluent generator chamber inlet chamber to trap the analyte cations from the suppressed eluent. 
     The device of  FIG. 7  was tested using a Dionex DX500 Ion Chromatography system (a product of Dionex Corp, Sunnyvale, Calif.) consisting of a GP50 pump, CD25 conductivity detector and a LC30 chromatography oven. An eluent of 20 mN sulfuric acid was pumped at a flow of 1.0 mL/min to a analytical cation exchange column (CG12A/CS12A a product of Dionex Corp., Sunnyvale, Calif.) for separation of the sample cations. An Agilent E3611A DC power supply (Agilent Corp., Santa Clara, Calif.) was used to power the device of  FIG. 7  at a constant current of 50 mA (approximately 25V). A peristaltic pump (MASTERFLEX LS, a product of the Cole-Parmer Company, Vernon Hills, Ill.) was used to recycle deionized water at a flow rate of 2.0 mL/min to the anode chamber and then to the cathode chamber and then back to the deionized water container. From the outlet of the analytical column, the eluent was directed to the inlet of the suppression chamber, out of the suppression chamber and to the conductivity cell, out of the conductivity cell and to the trap column and then to the eluent generation chamber. From the outlet of the generation chamber the eluent can be directed to waste (non-recycle mode) or back to the eluent container (recycle mode).  FIG. 16  shows a chromatography obtained with the system described above. 
     Recycling an eluent volume of 120 mL, the retention time trend data in  FIG. 17  was obtained. This number of cycles is equivalent to operating the system continuously for 30 days with a 2 L container of eluent being recycled. 
     Table II show the % RSD of retention times for the analyte cations over the 22 cycles of the sulfuric acid eluent. 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE II 
               
             
             
               
                   
               
               
                 % RSD for Retention Times, Cation Chromatography with Integrated 
               
               
                 Suppression and Eluent Generation (22 cycles) 
               
             
          
           
               
                   
                   
                 Average 
                   
               
               
                 Peak 
                 Name 
                 RT min 
                 % RSD 
               
               
                   
               
             
          
           
               
                 1 
                 lithium 
                 3.91 
                 0.908 
               
               
                 2 
                 sodium 
                 4.75 
                 1.00 
               
               
                 3 
                 ammonium 
                 5.48 
                 1.06 
               
               
                 4 
                 potassium 
                 6.90 
                 1.12 
               
               
                 5 
                 magnesium. 
                 11.5 
                 2.99 
               
               
                 6 
                 calcium 
                 13.8 
                 3.07