Electrolytic eluent generator with stabilized operating voltage

Abstract

To provide an electrolytic eluent generator having stable operating voltage.SOLUTION: An electrolytic eluent generator includes an electrolyte reservoir, an eluent generation chamber, and an ion exchange membrane stack. The electrolyte reservoir includes: a chamber housing an aqueous electrolyte solution including an electrolyte and a surfactant; and a first electrode. The eluent generation chamber includes a second electrode. The ion exchange connector includes an ion exchange membrane stack, and a compression block.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates generally to the field of ion chromatography, including electrolytic eluent generators having stable operating voltages.

[0002] Introduction Ion chromatography (IC) is a widely used analytical technique for the measurement of anionic and cationic analytes in a variety of sample matrices. Typical separation columns for IC have internal diameters ranging from about 2 to 4 millimeters and are operated at flow rates ranging from 0.2 to 3 mL / min. To improve the performance of IC, research is being conducted to develop smaller diameter separation columns. Such small columns, with internal diameters of about 1 mm or less, are typically referred to as capillary separation columns.

[0003] In ion chromatography, dilute solutions of acids, bases, or salts are commonly used as chromatographic eluents. Traditionally, these eluents are prepared offline by dilution with reagent-grade chemicals. Offline preparation of chromatographic eluents is tedious, prone to operator error, and often can lead to contamination. For example, dilute NaOH solutions, which are widely used as eluents in ion chromatographic separations of anions, are easily contaminated by carbonates. Preparation of carbonate-free NaOH eluents is difficult because carbonates can be introduced as impurities from reagents or by adsorption of carbon dioxide from the air. The presence of carbonates in NaOH eluents can impair the performance of ion chromatographic methods and can also result in undesirable chromatographic baseline shifts during the hydroxide gradient and even irreproducible retention times of target analytes. In recent years, several approaches utilizing electrolysis of water and charge-selective electromigration of ions through ion exchange media have been investigated by researchers to purify or generate high purity ion chromatography eluents. U.S. Patent Nos. 6,036,921, 6,225,129, 6,316,271, 6,316,270, 6,315,954, and 6,682,701 describe electrolytic devices that can be used to generate high purity acid and base solutions using water as a carrier. Using these devices, high purity, contaminant-free acid or base solutions are automatically generated on-line for use as eluents in chromatographic separations. Summary of the Invention

[0004] In a first embodiment, the electrolytic eluent generator can include an electrolyte reservoir, an eluent generation chamber, and an ion exchange connector. The electrolyte reservoir can include a chamber that contains an aqueous electrolyte solution including an electrolyte and a surfactant, and a first electrode. The eluent generation chamber can include a second electrode. The ion exchange connector can include an ion exchange membrane stack and a compression block.

[0005] In various embodiments of the first aspect, the eluent generation chamber can be configured to operate at a pressure of up to about 15000 psi.

[0006] In various embodiments of the first aspect, the second electrode can be a perforated cathode.

[0007] In various embodiments of the first aspect, a compression block can be disposed between the electrolyte reservoir and the ion exchange membrane stack, and the compression block can include a plurality of channels.

[0008] In various embodiments of the first aspect, the surfactant may be (a) an anionic surfactant and the ion exchange membrane stack may have a net negative charge and may be configured to allow cations to pass through and block anions and bulk liquid flow, or (b) a cationic surfactant and the ion exchange membrane stack may have a net positive charge and may be configured to allow anions to pass through and block cations and bulk liquid flow.

[0009] In various embodiments of the first aspect, the surfactant may be a non-ionic surfactant.

[0010] In various embodiments of the first aspect, the surfactant may be a caustic and acid stable surfactant.

[0011] In a second aspect, the method can include providing an aqueous electrolyte solution to an electrolyte reservoir, the aqueous electrolyte solution including an electrolyte and a surfactant, the electrolyte reservoir being coupled to an eluent generation chamber by an ion exchange connector. The ion exchange connector can include an ion exchange membrane stack and a compression block. The method can further include applying a voltage or current across a first electrode in the eluent generation chamber and a second electrode in the electrolyte reservoir, electrolytically splitting water at the first electrode to form hydroxide anions or hydronium ions in the eluent generation chamber, and transferring the ions from the electrolyte reservoir through the ion exchange membrane stack to the eluent generation chamber, where they combine with the hydroxide anions to form a cationic hydroxide solution or combine with the hydronium ions to form an anionic acidic solution for ion chromatography.

[0012] In various embodiments of the second aspect, the electrolyte can include a potassium electrolyte.

[0013] In various embodiments of the second aspect, the electrolyte can include a methanesulfonic acid electrolyte.

[0014] In various embodiments of the second aspect, the surfactant may be (a) an anionic surfactant and the ion exchange membrane stack may have a net negative charge and may be configured to allow cations to pass through and block anions and bulk liquid flow, or (b) a cationic surfactant and the ion exchange membrane stack may have a net positive charge and may be configured to allow anions to pass through and block cations and bulk liquid flow.

[0015] In various embodiments of the second aspect, the surfactant can be a non-ionic surfactant.

[0016] In various embodiments of the second aspect, the surfactant can be a caustic and acid stable surfactant.

[0017] In various embodiments of the second aspect, the surfactant may be at a concentration of about 1 ppm to 100 ppm.

[0018] In various embodiments of the second aspect, the eluent generation chamber can be at a pressure of up to about 15000 psi.

[0019] In various embodiments of the second aspect, the current across the anode and cathode can produce a voltage that remains within about + / - 2.0 V or less for at least seven days.

[0020] In various embodiments of the second aspect, the current across the anode and cathode can produce a voltage that varies by no more than 10% of the starting voltage for a period of at least seven days.

[0021] In various embodiments of the second aspect, the compression block can include a plurality of channels, and the method can further include generating an air bubble in the electrolyte reservoir, wherein the air bubble does not attach to the plurality of channels.

[0022] In a third embodiment, the electrolytic eluent generator can include an electrolyte reservoir, an eluent generation chamber, and an ion exchange connector. The electrolyte reservoir can include a chamber housing an aqueous electrolyte solution and a first electrode. The eluent generation chamber can include a second electrode. The ion exchange connector can include an ion exchange membrane stack and a compression block including a surface-modified polymer having a hydrophilic surface.

[0023] In various embodiments of the third aspect, the aqueous electrolyte solution can include potassium electrolyte.

[0024] In various embodiments of the third aspect, the aqueous electrolyte solution can include a methanesulfonic acid electrolyte.

[0025] In various embodiments of the third aspect, the surface-modified polymer is a chemically modified polymer. In certain embodiments, the chemically modified polymer can be chemically modified using sodium borohydride. In certain embodiments, the chemically modified polymer can be modified by converting a ketone functional group to an alcohol functional group. In certain embodiments, the chemically modified polymer can include an alcohol-functionalized polyetheretherketone (PEEK-OH).

[0026] In various embodiments of the third aspect, the surface-modified polymer can be an oxygen plasma treated polymer. In certain embodiments, the oxygen plasma treated polymer can include alcohol and carbonyl functional groups.

[0027] In various embodiments of the third aspect, the eluent generation chamber is configured to operate at a pressure of up to about 15000 psi.

[0028] In various embodiments of the third aspect, the second electrode can be a perforated cathode.

[0029] In various embodiments of the third aspect, a compression block can be disposed between the electrolyte reservoir and the ion exchange membrane stack, and the compression block can include a plurality of channels.

[0030] In a fourth aspect, the method can include providing an aqueous electrolyte solution to an electrolyte reservoir, the electrolyte reservoir being coupled to an eluent generation chamber by an ion exchange connector. The ion exchange connector can include an ion exchange membrane stack and a compression block. The compression block can include a surface-modified polymer having a hydrophilic surface. The method can further include applying a current or voltage across a first electrode in the eluent generation chamber and a second electrode in the electrolyte reservoir, electrolytically splitting water at the cathode to form hydroxide anions or hydronium ions in the eluent generation chamber, and transferring the ions from the electrolyte reservoir through the ion exchange membrane stack to the eluent generation chamber, where they combine with hydroxide anions to form a cationic hydroxide solution or combine with hydronium ions to form an anionic acidic solution for ion chromatography.

[0031] In various embodiments of the fourth aspect, the aqueous electrolyte solution can include potassium electrolyte.

[0032] In various embodiments of the fourth aspect, the aqueous electrolyte solution can include a methanesulfonic acid electrolyte.

[0033] In various embodiments of the fourth aspect, the surface-modified polymer can be a chemically modified polymer. In certain embodiments, the chemically modified polymer can be chemically modified using sodium borohydride. In certain embodiments, the chemically modified polymer can be modified by converting a ketone functional group to an alcohol functional group. In certain embodiments, the chemically modified polymer can include an alcohol-functionalized polyetheretherketone (PEEK-OH).

[0034] In various embodiments of the fourth aspect, the surface-modified polymer can be an oxygen plasma treated polymer. In certain embodiments, the oxygen plasma treated polymer can include alcohol and carbonyl functional groups.

[0035] In various embodiments of the fourth aspect, the eluent generation chamber is at a pressure of up to about 15000 psi.

[0036] In various embodiments of the fourth aspect, the current across the anode and cathode can produce a voltage that remains within about + / - 2.0 V or less for at least seven days.

[0037] In various embodiments of the fourth aspect, the current across the anode and cathode can produce a voltage that varies by no more than 10% of the starting voltage for a period of at least seven days.

[0038] In various embodiments of the fourth aspect, the compression block can include a plurality of channels, and the method can further include generating an air bubble in the electrolyte reservoir, wherein the air bubble does not attach to the plurality of channels.

[0039] For a more complete understanding of the principles disclosed herein, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: [Brief description of the drawings]

[0040] [Figure 1] 1 illustrates a chromatography system including an eluent generator according to various embodiments. [Figure 2A] 1 illustrates an eluent generator according to various embodiments. [Figure 2B] 1 illustrates an eluent generator according to various embodiments. [Diagram 3] 1 illustrates chemical modification of PEEK according to various embodiments. [Figure 4] 1 illustrates a method for chemically modifying a membrane compression block of an eluent generator, according to various embodiments. [Diagram 5] 1 illustrates a method for chemically modifying a membrane compression block of an eluent generator, according to various embodiments. [Figure 6]1 illustrates a method of operation of a chemically modified eluent generator according to various embodiments. [Figure 7] 1 illustrates a method of operating a surfactant-based eluent generator, according to various embodiments. [Figure 8] 1 shows the operating voltage profile of an unmodified electrolytic KOH generator. [Figure 9] FIG. 1 shows the operating voltage profile of an electrolytic KOH generator with a PEEK membrane compression block component modified using sodium borohydride in dimethyl sulfoxide (DMSO). [Figure 10] 1 shows the operating voltage profile of an electrolytic KOH generator with a PEEK membrane compression block component modified using oxygen plasma. [Figure 11] Separation of seven common anions is shown and results obtained using an unmodified electrolytic KOH generator are compared to results using an electrolytic KOH generator equipped with a PEEK membrane compression block component modified using oxygen plasma. [Figure 12] We demonstrate the reproducibility of fluoride and phosphate separation using an electrolytic KOH generator equipped with a PEEK membrane compression block component modified using oxygen plasma. [Figure 13] 1 shows the operating voltage profile of an electrolytic KOH generator with a PEEK membrane compressed block component treated with TERGITOL MIN foam. [Figure 14] 1 shows the operating voltage profile of an electrolytic KOH generator with TRITON H55 treated PEEK membrane compression block components.

[0041] It should be understood that the figures are not necessarily drawn to scale, and that objects within the figures are not necessarily drawn to scale in relationship to each other. The figures are representations intended to provide clarity and understanding to various embodiments of the devices, systems, and methods disclosed herein. Wherever possible, the same reference numbers are used throughout the drawings to refer to the same or similar parts. Furthermore, it should be understood that the drawings are not intended to limit the scope of the present teachings in any way. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0042] SUMMARY OF THE DISCLOSURE Described herein are embodiments of systems and methods for ion separation.

[0043] The section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described in any way.

[0044] In this detailed description of various embodiments, for purposes of explanation, numerous specific details are set forth to provide a thorough understanding of the disclosed embodiments. However, those skilled in the art will appreciate that these various embodiments may be practiced without or with these specific details. In other instances, structures and devices are shown in block diagram form. Furthermore, those skilled in the art will readily appreciate that the specific order in which the methods are presented and performed is illustrative, and it is contemplated that the order may be altered and still remain within the spirit and scope of the various embodiments disclosed herein.

[0045] All literature and similar materials cited in this application, including but not limited to patents, patent applications, articles, books, papers, and Internet web pages, are expressly incorporated by reference in their entirety for any purpose. Unless otherwise stated, all technical and scientific terms used herein have the meaning commonly understood by one of ordinary skill in the art to which the various embodiments described herein belong.

[0046] It will be understood that there is an implicit "about" before temperatures, concentrations, times, pressures, flow rates, cross-sectional areas, etc. discussed in the present teachings, so that very small insignificant deviations are within the scope of the present teachings. In this application, the use of the singular includes the plural unless specifically stated otherwise. Also, the use of "comprise," "comprises," "comprising," "contain," "contains," "containing," "include," "includes," and "including" is not intended to be limiting. It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present teachings.

[0047] As used herein, "a" or "an" can refer to "at least one" or "one or more." Also, the use of "or" is inclusive, so that a phrase "A or B" is true when "A" is true, then "B" is true, or when both "A" and "B" are true. Further, unless otherwise required by context, singular terms shall include plurals and plural terms shall include the singular.

[0048] A "system" refers to a set of components, real or abstract, including a whole in which each component interacts with or is related to at least one other component within the whole.

[0049] Chromatography Systems FIG. 1 illustrates an embodiment of a chromatography system 100. The chromatography system 100 may include a pump 102, an electrolytic eluent generator 104, a continuously regenerated trap column 106, a degasser 108, a sample injector 110, a chromatographic separation device 112, an electrolytic suppressor 114, a detector 116, and a microprocessor 118. The chromatographic separation device 112 may be in the form of a capillary column or an analytical column. A recycle line 120 may be used to transfer liquid from the output of the detector 116 to the inlet of the electrolytic suppressor 114, a recycle line 122 may be used to transfer liquid from the outlet of the electrolytic suppressor 114 to the inlet of the degasser 108, and a recycle line 124 may be used to transfer liquid from the outlet of the degasser 108 to the inlet of the continuously regenerated trap column 106.

[0050] The pump 102 can be configured to pump liquid from a liquid source 124 and be fluidly connected to the electrolytic eluent generator 104. In one embodiment, the liquid can be deionized water, an aqueous solution containing electrolyte(s), or a mixture of an organic solvent and deionized water or an aqueous solution of electrolyte(s). Some examples of electrolytes are sodium acetate and acetic acid. The eluent mixture containing an organic solvent can include a water-miscible organic solvent, such as, for example, methanol. The pump 102 can be configured to transport liquid at pressures ranging from about 20 PSI to about 15,000 PSI. Under certain circumstances, pressures in excess of 15,000 PSI may be implemented. It should be noted that the pressures shown herein are listed relative to ambient pressure (13.7 PSI to 15.2 PSI). The pump 102 can be in the form of a high pressure liquid chromatography (HPLC) pump. Additionally, the pump 102 can be configured such that the liquid only contacts the inert portions of the pump 102, thereby preventing significant amounts of impurities from leaching out. In this context, significant means an amount of impurities that interferes with the intended measurement. For example, the inert portion can be made of polyetheretherketone (PEEK), or at least coated with a PEEK lining that does not leach significant amounts of ions when exposed to liquids.

[0051] An eluent is a liquid that includes an acid, a base, a salt, or a mixture thereof, and can be used to elute analytes through a chromatography column. Additionally, an eluent can include a mixture of a liquid and a water-miscible organic solvent, where the liquid may include an acid, a base, a salt, or a combination thereof. The electrolytic eluent generator 104 is configured to generate a generant. A generant refers to a particular type of acid, base, or salt that can be added to the eluent. In one embodiment, the generant can be a base, such as a cationic hydroxide, or the generant can be an acid, such as carbonic acid, phosphoric acid, acetic acid, methanesulfonic acid, or a combination thereof.

[0052] 1, the eluent generator 104 can be configured to receive liquid from the pump 102 and then add a generant to the liquid. The liquid containing the generant can be delivered from the eluent generator 104 to the inlet of a continuously regenerated trap column 106.

[0053] The continuously regenerative trap column 106 is configured to remove cationic or anionic contaminants from the eluent. The continuously regenerative trap column 106 can include an ion exchange bed with an electrode at the eluent outlet. An ion exchange membrane interface can separate the eluent from a second electrode, and the contaminant ions can be swept toward the second electrode by the ion exchange membrane. In various embodiments, anion removal can utilize an anion exchange bed with a cathode at the eluent outlet separated from the anode by an anion exchange membrane. Alternatively, cation removal can utilize a cation exchange bed with an anode at the eluent outlet separated from the cathode by a cation exchange membrane. The contaminant ions can be swept from the regenerative trap column 106 using recycled liquid via a recycle line 124 downstream of the degassing assembly 108.

[0054] The degasser 108 may be used to remove residual gases. In one embodiment, the residual gases may be hydrogen and oxygen. The degasser 108 may include a tubing section that is gas permeable and liquid impermeable, such as, for example, an amorphous fluoropolymer or, more specifically, Teflon AF. The flowing liquid may be delivered from the degasser 108 to the sample injector 110 with a significant portion of the gas removed. The gas may be purged from the degasser 108 using recycled liquid via a recycle line 122 downstream of the electrolytic suppressor 114. The recycled liquid containing the residual gas may also be delivered from the degasser 108 and directed to the continuously regenerated trap column 106.

[0055] The sample injector 110 can be used to inject a bolus of a liquid sample into the eluent stream. The liquid sample can include multiple chemical components (i.e., matrix components) and one or more analytes of interest.

[0056] The chromatographic separation device 112 can be used to separate various matrix components present in a liquid sample from the analyte(s) of interest. Typically, the chromatographic separation device 112 may be in the form of a hollow cylinder that contains a packed stationary phase. As the liquid sample flows through the chromatographic separation device 112, the matrix components and the target analytes can have different retention times to elute from the chromatographic separation device 112. Depending on the properties of the target analytes and the matrix components, they can have different affinities for the stationary phase of the chromatographic separation device 112. The output of the chromatographic separation device 112 can be fluidly connected to an electrolytic suppressor 114.

[0057] The electrolytic suppressor 114 can be used to reduce the eluent conductivity background and improve the analyte response by efficient exchange of eluent counterions for regenerant ions. The electrolytic suppressor 114 can include an anode chamber, a cathode chamber, and an eluent suppression bed chamber separated by an ion exchange membrane. The anode chamber and / or the cathode chamber can generate the regenerant ions. The eluent suppression bed chamber can include a flow path of the eluent separated from the regenerant by an ion exchange barrier, and the eluent counterions can exchange with the regenerant ions across the ion exchange barrier. The cathode chamber or the anode chamber can be supplied with recycled liquid via a recycle line 120 downstream of the conductivity detector 116. The output of the electrolytic suppressor 114 can be fluidly connected to the detector 116 to measure the presence of the separated chemical components of the liquid sample.

[0058] As shown in FIG. 1, the eluent output from detector 116 is recycled to electrolytic suppressor 114 via recycle line 120, the output of electrolytic suppressor 114 is recycled to degasser 108 via recycle line 122, the output of degasser 108 is recycled to continuously regenerative trap column 106 via recycle line 124, and the output of continuously regenerative trap column 106 flows to waste.

[0059] The detector 116 may be in the form of a UV-Vis spectrometer, a fluorescence spectrometer, an electrochemical detector, a conductivity detector, a charge detector, or a combination thereof. Details regarding charge barriers and charge detectors based on two electrodes can be found in U.S. Pre-Grant Publication No. 20090218238, which is fully incorporated herein by reference. In situations where a recycle line 120 is not required, the detector 116 may also be in the form of a mass spectrometer or a charged particle detector. Charged particle detectors atomize the effluent stream and generate charged particles that can be measured as a current proportional to the concentration of the analyte. Details regarding charged particle detectors can be found in U.S. Patent Nos. 6,544,484 and 6,568,245, which are fully incorporated herein by reference.

[0060] The electronic circuitry may include a microprocessor 118, a timer, and a memory portion. Additionally, the electronic circuitry may include a power supply configured to apply the control signal, respectively. The microprocessor 118 may be used to control the operation of the chromatography system 100. The microprocessor 118 may be integrated into the chromatography system 100 or may be part of a personal computer that communicates with the chromatography system 100. The microprocessor 118 may be configured to communicate with and control one or more components of the chromatography system, such as the pump 102, the eluent generator 104, the sample injector 110, and the detector 116. The memory portion may be used to store instructions for setting the magnitude and timing of the current waveform with respect to switching of the sample injector 110 to inject the sample.

[0061] 2A illustrates the principle of operation of an electrolytic generator cartridge 200. The cartridge can include a high pressure eluent generation chamber 202 and a low pressure electrolyte reservoir 204. In various embodiments, the high pressure generation chamber 202 can operate at pressures up to about 15,000 psi, such as, for example, from about 2,000 psi to about 10,000 psi.

[0062] The eluent generation chamber 202 can include a perforated platinum (Pt) electrode 206. The electrolyte reservoir 204 can house a Pt electrode 208 and an electrolyte solution. In various embodiments, the electrolytic generator cartridge 200 can generate a base, such as KOH, and the electrode 206 can be a cathode capable of forming hydroxide ions, and the electrode 208 can be an anode. In other embodiments, the electrolytic generator cartridge 200 can generate an acid, such as carbonic acid, phosphoric acid, acetic acid, methanesulfonic acid, and the electrode 206 can be an anode capable of forming hydronium ions, and the electrode 208 can be a cathode. The eluent generation chamber 202 can be connected to the electrolyte reservoir 204 by an exchange connector 210, which can allow the passage of ions of only one charge from the electrolyte reservoir 204 to the high pressure generation chamber 202. The exchange connector 210 can also play an important role of a high pressure physical barrier between the low pressure electrolyte reservoir 204 and the high pressure generation chamber 202. In various embodiments in which the electrolysis generator cartridge 200 is a base generator, the replacement connector 210 can allow the passage of cations while substantially preventing the passage of anions from the electrolyte reservoir 204 to the production chamber 202. In alternative embodiments in which the electrolysis generator cartridge 200 is an acid generator, the replacement connector 210 can allow the passage of anions while substantially preventing the passage of cations from the electrolyte reservoir 204 to the production chamber 202.

[0063] To generate a KOH eluent, deionized water can be pumped through the eluent generation chamber 202 and a DC current can be applied between the electrodes 208 and 206. Under an applied electric field, electrolysis of water can occur at both the electrodes 208 and 206 of the device 200. Water can be oxidized to form H+ ions and oxygen gas at the electrode 208 of the electrolyte reservoir 204: H2O→2H++1 / 2O2↑+2e-. Water can be reduced to form OH- ions and hydrogen gas at the electrode 206 of the KOH generation chamber 202: 2H2O+2e-→2OH-+ H2↑. The H+ ions generated at the anode 206 are converted to KOH in the electrolyte reservoir 204. + To displace the ions, the displaced ions can migrate across the cation exchange connector 210 to the eluent generation chamber 202. + The ions can combine with the hydroxide ions generated at the cathode 206 to generate a KOH solution, which can be used as an eluent for anion exchange chromatography. The concentration of the generated KOH can be determined by the current applied to the generator cartridge 200 and the flow rate of water as a carrier through the generator chamber 202.

[0064] To produce a metasulfonic acid eluent, deionized water can be pumped through the eluent generation chamber 202 and a DC current can be applied between the electrodes 208 and 206. Under the applied field, electrolysis of water can occur at both the electrodes 208 and 206 of the device 200. Water can be oxidized to form H+ ions and oxygen gas at the electrode 206 of the KOH generation chamber 202: H2O→2H++1 / 2O2↑+2e-. Water can be reduced to form OH- ions and hydrogen gas at the electrode 208 of the electrolyte chamber 204: 2H2O+2e-→2OH-+ H2↑. The OH generated at the electrode 206 is then oxidized to form H+ ions and oxygen gas: H2O→2H++1 / 2O2↑+2e-. -As the ions displace the metasulfonate ions in the electrolyte reservoir 204, the displaced ions can migrate across the anion exchange connector 210 to the eluent generation chamber 202. These metasulfonate ions can combine with the hydronium ions generated at the electrode 206 to generate a metasulfonic acid solution that can be used as an eluent for cation exchange chromatography. The concentration of the generated metasulfonic acid can be determined by the current applied to the generator cartridge 200 and the flow rate of water as a carrier through the generation chamber 202.

[0065] 2B shows a cross-sectional view of the electrolysis generator 200. The stack of ion exchange membranes 212 is supported by a PEEK compression block 214 so that the generation chamber 202 can withstand high pressure. In various embodiments, the PEEK compression block 214 may be perforated with an open vertical channel, which may typically be cylindrical. The electrolyte solution in the low pressure electrolyte reservoir 204 is in direct contact with the ion exchange membrane stack 212 via the open vertical channel 216 of the PEEK membrane compression block 214.

[0066] During operation of the electrolysis generator 202, oxygen gas may be generated at the anode located in the electrolyte reservoir 204. Most of the oxygen gas rises and is released through a vent port in the low-pressure electrolyte reservoir 204. However, some oxygen gas may dissolve in the alkaline solution and coalesce to form gas bubbles. These oxygen bubbles may adhere to the hydrophobic surfaces of the low-pressure electrolyte reservoir 204 and the PEEK membrane compression block 214, and some of the gas bubbles may settle and block the open vertical channels 216 of the PEEK membrane compression block 214.

[0067] When the open vertical channels of the PEEK membrane compression block 214 are blocked by oxygen bubbles, the contact between the electrolyte solution in the low pressure electrolyte reservoir 204 and the ion exchange membrane stack 212 may be reduced or lost. Thus, the movement of ions in the electrolyte reservoir 204 across the cation exchange membrane stack 212 into the eluent generation chamber 202 may be restricted as a result, resulting in an increase in the operating voltage of the electrolyte generator 200. A higher operating voltage may lead to a higher operating wattage and, in some cases, an excessive amount of heat generated during the operation of the electrolyte generator 202. The excessive amount of heat may lead to damage to the ion exchange membrane 212 and may be detrimental to the reliable operation of the electrolytic eluent generator 202. There is a need to develop new embodiments of the electrolytic eluent generator that can avoid the effects of air bubbles that may adhere to the hydrophobic surfaces of the low pressure electrolyte reservoir 204 and the open vertical channels 216 of the PEEK membrane compression block 214.

[0068] Air bubbles in aqueous solutions tend to adhere to solid surfaces, such as the surfaces of the low pressure electrolyte reservoir 204 and the PEEK membrane compression block 214. The contact angle of the air bubbles on the solid surface depends on the hydrophobicity of the solid surface. The contact angle of the air bubbles can typically be less than 90° on a hydrophilic surface, and the contact angle of the air bubbles can typically be greater than 90° on a hydrophobic surface. The amount and size of air bubbles that adhere to a hydrophilic surface in an aqueous solution can be significantly reduced when compared to a hydrophobic surface in an aqueous solution.

[0069] chemical modification An embodiment of an electrolytic eluent generator is described that is constructed using high strength polymer components that are surface modified to be hydrophilic to reduce and minimize the amount and size of oxygen bubbles that attach to the surfaces of the low pressure electrolyte reservoir and the PEEK membrane compression block. The surface modified electrolytic eluent generator can eliminate the blockage of the open vertical channels of the PEEK membrane compression block and can maintain continuous fluid contact between the electrolyte solution in the low pressure electrolyte reservoir and the ion exchange membrane stack, thus providing stabilization of the operating voltage and improved operational reliability of the electrolytic KOH generator.

[0070] The hydrophobic surface of the PEEK membrane compressed block can be chemically modified to a hydrophilic surface by converting the PEEK ketone functional groups to alcohol functional groups (PEEK-OH) using sodium borohydride in dimethyl sulfoxide (DMSO), as shown in Figure 3.

[0071] FIG. 4 illustrates a method 400 for chemically modifying a PEEK membrane compressed block. At 402, a modification solution can be prepared. For example, sodium borohydride and dimethyl sulfoxide can be added to a flask while stirring with a magnetic bar, and an atmosphere of argon blanket is applied. The flask can be heated in an oil bath, such as at 120° C. After the sodium borohydride is completely dissolved, the PEEK membrane compressed block can be processed, as shown at 404. For example, a part can be added to the flask. In various embodiments, reacting the part with the modification solution can continue for four hours or more. At 406, the part can be removed from the modification solution, and at 408, the part can be washed. For example, after cooling to room temperature, the DMSO solution can be discarded, and the PEEK part can be washed twice with isopropyl alcohol and three times with acetone, respectively. After washing the part, an electrolytic KOH eluent generator cartridge can be assembled, as shown at 410.

[0072] 5 illustrates a method 500 for modifying the hydrophobic surface of a PEEK membrane compression block using oxygen plasma treatment to form a hydrophilic surface containing alcohol and carbonyl functional groups on the PEEK surface. The PEEK membrane compression block part can be cleaned at 502. For example, the PEEK membrane compression block part can be cleaned using DI H 2 After thorough rinsing with O, the parts can be dried in an oven overnight. At 504, the parts can be processed. For example, the parts can be placed in the plasma chamber of a plasma cleaner / sterilizer for oxygen plasma treatment. In various embodiments, the oxygen plasma treatment can be performed with high levels of oxygen plasma for 60 minutes at a time, and the plasma treatment is repeated three times. At 506, the oxygen plasma treated parts can be used to assemble an electrolytic KOH eluent generator cartridge.

[0073] 6 illustrates a method 600 of operating a chemically modified electrolytic eluent generator. At 602, the electrolytic eluent generator is + The electrolytic eluent can be prepared with an electrolyte solution, such as an ionic electrolyte solution. At 604, a voltage can be applied to the electrolytic eluent generator, which can generate the electrolytic eluent at 606. In various embodiments, the current through the anode and cathode produces a voltage that remains within about + / - 2.0V, such as within about + / - 1.0V, or even within about + / - 0.5V, for at least seven days. In various embodiments, the current through the anode and cathode produces a voltage that varies by no more than about 10% of the starting voltage for at least seven days. At 608, the electrolytic eluent can be used to perform a chromatographic separation.

[0074] Surfactants In another preferred embodiment of the electrolytic eluent generator, a surfactant containing ionic or hydrophilic functional groups can be used to coat the PEEK surface to reduce and minimize the amount and size of oxygen bubbles that attach to the surface of the low pressure electrolyte reservoir and the PEEK membrane compression block. In this embodiment, a small amount of surfactant can be added to the electrolyte solution. The surfactant should be chemically stable in the electrolyte solution and cannot migrate across the ion exchange membrane stack under the applied electric field.

[0075] In various embodiments, the surfactant may be an ionic surfactant or a non-ionic surfactant. In certain embodiments, the ionic surfactant may be an anionic surfactant when used in a base generator, such as for the generation of KOH. Alternatively, the cationic surfactant may be a suitable ionic surfactant for use in an acid generator, such as for the generation of methanesulfonic acid. Additionally, the surfactant may be stable in caustic or acidic solutions.

[0076] In various embodiments, the surfactant can be at a concentration between about 1 ppm and about 100 ppm.

[0077] 7 illustrates a method 700 of operating an electrolytic eluent generator using a surfactant. At 702, a surfactant can be added to an electrolyte solution, and at 704, the electrolytic eluent generator is operated to add a surfactant to the electrolyte solution. +The electrolyte solution may be prepared with an electrolyte solution, such as an ionic electrolyte solution. For example, a non-ionic surfactant, such as TERGITOL MIN foam, may be added to the electrolyte solution. In another example, if the eluent is a base, an anionic surfactant, such as TRITON H55, may be added to the electrolyte solution, and the ion exchange membrane stack may have a net negative charge and be configured to allow cations to pass and block anions and bulk liquid flow. In yet another example, if the eluent is an acid, a cationic surfactant may be added to the electrolyte solution, and the ion exchange membrane stack may have a net positive charge and be configured to allow anions to pass and block cations and bulk liquid flow. Advantageously, the ion exchange membrane stack may prevent the surfactant from contaminating the eluent. At 706, a voltage may be applied to the electrolytic eluent generator, and at 708, the electrolytic eluent generator may generate the electrolytic eluent. In various embodiments, the current through the anode and cathode produces a voltage that remains in a range of about + / - 2.0 V, for example, in a range of about + / - 1.0 V, for at least 7 days. In various embodiments, the current through the anode and cathode produces a voltage that fluctuates by no more than about 10% of the starting voltage for at least 7 days. At 710, the electrolytic eluent can be used to perform a chromatographic separation.

[0078] While the present teachings will be described in conjunction with various embodiments, it is not intended to limit the present teachings to such embodiments. Rather, the present teachings encompass various alternatives, modifications, and equivalents, as will be appreciated by those skilled in the art.

[0079] Furthermore, in describing various embodiments, the specification may present the method and / or process as a specific order of steps. However, to the extent that the method or process does not rely on the specific order of steps described herein, the method or process should not be limited to the specific order of steps described. As one skilled in the art will appreciate, other orders of steps may be possible. Thus, the specific order of steps described herein should not be interpreted as a limitation in the claims. In addition, one skilled in the art can readily appreciate that claims directed to the method and / or process should not be limited to performing those steps in the order written, and that the order may be changed and still remain within the spirit and scope of the various embodiments.

[0080] result Figure 8 shows an example of the operating voltage profile of an unmodified electrolytic KOH generator under conditions of 1.5 mL / min, 60 mM KOH and 4150 psi. The operating voltage of the cartridge remains relatively stable over a day of continuous operation. However, after that, the operating voltage of the cartridge starts to rise from about 12 V to over 35 V, leading to the generation of excessive amounts of heat during operation of the electrolytic KOH eluent generator.

[0081] Figure 9 shows a typical operating voltage profile obtained with an electrolytic KOH eluent generator using a PEEK membrane compression block component modified by converting the PEEK ketone functional groups to alcohol functional groups using sodium borohydride in dimethyl sulfoxide (DMSO). Under conditions of 1.5 mL / min, 60 mM KOH, and 3550 psi, the device operating voltage is stable in the range of 15.7 V to 16.5 V during 7 days of continuous operation. That is, the voltage varies within a range of approximately + / - 0.5 V and less than 10% of the starting voltage.

[0082] Figure 10 shows a typical operating voltage profile obtained for an electrolytic KOH eluent generator using oxygen plasma modified PEEK membrane compression block components at 1.5 mL / min, 60 mM KOH, 3995 psi, where the device operating voltage is stable in the range of 14.5 V to 15.5 V during 10 days of continuous operation, i.e., the voltage remains within about + / - 0.5 V and less than 10% of the starting voltage.

[0083] Figure 11 shows the separation of seven common anions on a DIONEX IONPAC AS11-HC 4 μm column (see Table 1 for anion concentrations). The results show that identical separations were obtained using a standard DIONEX EGC 500 KOH cartridge and a modified DIONEX EGC-500 KOH cartridge assembled using a PEEK membrane compression block treated with oxygen plasma. Test conditions were 1.5 mL / min, 30 mM KOH, 4200 psi, 15 min / run and 10 μL injection. The baseline has been shifted on the y-axis to provide a comparison between retention time and peak shape. The results show that surface modification by oxygen plasma treatment does not affect the performance of the DIONEX EGC-500 KOH cartridge.

[0084] Table 1: Analytes for comparison of modified and unmodified KOH generators TIFF2025037906000002.tif51153

[0085] Figure 12 shows the separation of fluoride (2 mg / L) and phosphate (20 mg / L) on a DIONEX IONPAC AS11-HC 4 μm column obtained using a DIONEX EGC 500 KOH cartridge assembled with an oxygen plasma treated PEEK membrane compression block. Test conditions were 1.5 mL / min, 60 mM KOH, 4350 psi, 60 min / run, and 10 μL injection. The baseline has been shifted on the y-axis to provide a comparison of retention time and peak shape. The results show excellent retention time reproducibility of the target analytes over 400 consecutive runs.

[0086] Figure 13 shows an overlay of operating voltages obtained with a DIONEX EGC 500 KOH cartridge assembled using a PEEK membrane compression block treated with TERGITOL MIN foam. Under conditions of 1.5 mL / min, 60 mM KOH, and 4150 psi, the device operating voltage remained stable in the range of 11.5 V to 13.5 V over 12 days of continuous operation, i.e., the voltage remained within a range of approximately + / - 1.0 V and less than 10% of the starting voltage.

[0087] Figure 14 shows an overlay of operating voltages obtained with a DIONEX EGC 500 KOH cartridge assembled using a PEEK membrane compression block treated with TRITON H55 (anionic surfactant). Under conditions of 1.5 mL / min, 60 mM KOH, and 3950 psi, the device operating voltage remained stable in the range of 12 V to 13.4 V over 7 days of continuous operation; that is, the voltage remained within a range of approximately + / - 1.0 V and less than 10% of the starting voltage.

Claims

1. 1. An electrolytic eluent generator comprising: an electrolyte reservoir including a chamber containing an aqueous electrolyte solution including an electrolyte and a surfactant, and a first electrode; an eluent generation chamber including a second electrode; an ion exchange connector including an ion exchange membrane stack and a compression block.

2. 10. The electrolytic eluent generator of claim 1, wherein the eluent generation chamber is configured to operate at a pressure of up to about 15,000 psi.

3. The electrolytic eluent generator of claim 1 , wherein the second electrode is a perforated electrode.

4. 2. The electrolytic eluent generator of claim 1, wherein the compression block is disposed between the electrolyte reservoir and the ion exchange membrane stack, the compression block including a plurality of channels.

5. the surfactant is an anionic surfactant and the ion exchange membrane stack has a net negative charge and is configured to allow cations to flow and block anions and bulk liquid flow; or 2. The electrolytic eluent generator of claim 1, wherein the surfactant is a cationic surfactant and the ion exchange membrane stack has a net positive charge and is configured to allow anions to flow and block cations and bulk liquid flow.

6. 2. The electrolytic eluent generator of claim 1, wherein the surfactant is a non-ionic surfactant.

7. 2. The electrolytic eluent generator of claim 1, wherein the surfactant is a caustic and acid stable surfactant.

8. providing an aqueous electrolyte solution to an electrolyte reservoir, the aqueous electrolyte solution comprising an electrolyte and a surfactant, the electrolyte reservoir being coupled to an eluent generation chamber by an ion exchange connector, the ion exchange connector comprising an ion exchange membrane stack and a compression block; applying a voltage or current between a first electrode in the eluent generation chamber and a second electrode in the electrolyte reservoir; electrolytically splitting water at the first electrode to form hydroxide anions or hydronium ions in the eluent generation chamber; and transferring ions from the electrolyte reservoir through the ion exchange membrane stack to the eluent generation chamber where they combine with the hydroxide anions to form a cationic hydroxide solution or combine with the hydronium ions to form an anionic acid solution for ion chromatography.

9. The method of claim 8 , wherein the electrolyte comprises a potassium electrolyte.

10. The method of claim 8 , wherein the electrolyte comprises a methanesulfonic acid electrolyte.

11. the surfactant is an anionic surfactant and the ion exchange membrane stack has a net negative charge and is configured to allow cations to flow and block anions and bulk liquid flow; or 9. The method of claim 8, wherein the surfactant is a cationic surfactant and the ion exchange membrane stack has a net positive charge and is configured to allow anions to flow and block cations and bulk liquid flow.

12. The method of claim 8 , wherein the surfactant is a non-ionic surfactant.

13. The method of claim 8, wherein the surfactant is a caustic and acid stable surfactant.

14. The method of claim 8, wherein the surfactant is at a concentration of about 1 ppm to 100 ppm.

15. The method of claim 8 , wherein the eluent generation chamber is at a pressure of up to about 15,000 psi.

16. 9. The method of claim 8, wherein the current across the anode and the cathode produces a voltage that remains within about + / - 2.0 V or less for at least seven days.

17. 9. The method of claim 8, wherein the current across the anode and the cathode produces a voltage that varies by no more than 10% of a starting voltage over a period of at least seven days.

18. the compressed block includes a plurality of channels; The method of claim 8 , wherein the method includes generating an air bubble in the electrolyte reservoir, the air bubble not attaching to the plurality of channels.

19. 1. An electrolytic eluent generator comprising: an electrolyte reservoir including a chamber containing an aqueous electrolyte solution and a first electrode; an eluent generation chamber including a second electrode; An electrolytic eluent generator comprising an ion exchange connector, the ion exchange connector comprising an ion exchange membrane stack and a compressed block comprising a surface modified polymer having a hydrophilic surface.

20. 20. The electrolytic eluent generator of claim 19, wherein the surface-modified polymer is a chemically modified polymer.

21. 21. The electrolytic eluent generator of claim 20, wherein the chemically modified polymer is chemically modified using sodium borohydride.

22. 21. The electrolytic eluent generator of claim 20, wherein the chemically modified polymer is modified by converting a ketone functional group to an alcohol functional group.

23. 23. The electrolytic eluent generator of claim 22, wherein the chemically modified polymer comprises alcohol-functionalized polyetheretherketone (PEEK-OH).

24. 20. The electrolytic eluent generator of claim 19, wherein the surface modified polymer is an oxygen plasma treated polymer.

25. 25. The electrolytic eluent generator of claim 24, wherein the oxygen plasma treated polymer comprises alcohol and carbonyl functional groups.

26. 20. The electrolytic eluent generator of claim 19, wherein the eluent generation chamber is configured to operate at a pressure of up to about 15,000 psi.

27. 20. The electrolytic eluent generator of claim 19, wherein the second electrode is a perforated cathode.

28. 20. The electrolytic eluent generator of claim 19, wherein the compression block is disposed between the electrolyte reservoir and the ion exchange membrane stack, the compression block including a plurality of channels.

29. providing an aqueous electrolyte solution to an electrolyte reservoir, the electrolyte reservoir being coupled to an eluent generation chamber by an ion exchange connector, the ion exchange connector including an ion exchange membrane stack and a compression block, the compression block including a surface-modified polymer having a hydrophilic surface; applying a current or voltage between a first electrode in the eluent generation chamber and a second electrode in the electrolyte reservoir; electrolytically splitting water at the first electrode to form hydroxide anions or hydronium ions in the eluent generation chamber; and transferring ions from the electrolyte reservoir through an ion exchange membrane stack of the ion exchange connector to the eluent generation chamber to combine with hydroxide anions to form a cationic hydroxide solution or combine with the hydronium ions to form an anionic acid for ion chromatography.

30. 30. The method of claim 29, wherein the aqueous electrolyte solution comprises a potassium electrolyte.

31. 30. The method of claim 29, wherein the aqueous electrolyte solution comprises a methanesulfonate electrolyte.

32. 30. The method of claim 29, wherein the surface-modified polymer is a chemically modified polymer.

33. 33. The method of claim 32, wherein the chemically modified polymer is chemically modified using sodium borohydride.

34. 33. The method of claim 32, wherein the chemically modified polymer is modified by converting a ketone functional group to an alcohol functional group.

35. The method of claim 34, wherein the chemically modified polymer comprises an alcohol-functionalized polyetheretherketone (PEEK-OH).

36. 30. The method of claim 29, wherein the surface modified polymer is an oxygen plasma treated polymer.

37. 37. The method of claim 36, wherein the oxygen plasma treated polymer contains alcohol and carbonyl functional groups.

38. 30. The method of claim 29, wherein the eluent generation chamber is at a pressure of up to about 15,000 psi.

39. 30. The method of claim 29, wherein the current between the anode and cathode results in a voltage that remains within about + / - 2.0 V or less for at least 7 days.

40. 30. The method of claim 29, wherein the current between the anode and cathode results in a voltage that fluctuates by no more than 10% of the starting voltage for at least 7 days.

41. the compressed block includes a plurality of channels; 30. The method of claim 29, wherein the method further comprises generating an air bubble in the electrolyte reservoir, the air bubble not attaching to the plurality of channels.

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