JP2005009878A - Electrical conductivity detector for ion chromatography, and ion chromatographic system using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a non-suppressor type high sensitivity ion chromatographic system which does not cause spreading of peaks caused by using the conventional suppressor and not requiring a complicated device, such as a regeneration mechanism or the like or a complicated operation. <P>SOLUTION: Analyte ions are detected by ion chromatography, including a process for introducing at least two kinds of analyte ions into an ion exchange column, a process of making eluent flow into the ion exchange column to separate and elute the analyte ions and a process for introducing the eluate into an electrical conductivity detector, wherein a fixed phase having surface charge opposite to that of the analyte ions is inserted in the space between at least two electrodes arranged mutually facing in a mutually separated state, to measure the current flowing across two electrodes. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to the field of separation of ions by liquid chromatography and subsequent detection of ions, ie ion chromatography. In particular, the present invention relates to an ion chromatography system that does not require a complicated operation and enables high-sensitivity detection by using a novel conductivity detector for ion chromatography.
[0002]
[Prior art]
In ion chromatography, the sample containing analyte ions is injected into the column while the eluent is sent to the ion exchange column, and the ion species eluted from the column with a difference in retention time and the amount thereof are detected by an electrical conductivity detector, etc. This ion chromatography has a “suppressor method” that uses a suppressor and a “non-suppressor method” that does not use a suppressor.
[0003]
The suppressor method includes two ion exchange columns in series, followed by a flow-through conductivity detector for detecting sample ions. The first column, referred to as the analytical column or separation column, separates the analyte ions in the sample by eluting with the eluent through the sample. Analyte ions flow through the analytical column with an eluent containing electrolyte. In general, dilute acid or alkaline solutions prepared with deionized water are used as eluents. The separated analyte ions and eluent are flowed from the analytical column to the next column called a suppressor. The suppressor reduces the background conductivity of the eluent by preserving the electrolyte of the eluent, while the analyte ion to be detected has a high conductivity component (conducting acid in anion analysis, or in cation analysis). Is replaced by a conductive base). In this way, the S / N ratio is improved to increase the sensitivity of the analyte ions by the detector.
[0004]
Conventionally, as an example of an electrical conductivity detector used in such an ion chromatographic system, there is a pentapolar electrical conductivity detector as shown in FIG. The pentode electrode is composed of five ring electrodes including two voltage application electrodes 20 a and 20 b, two measurement electrodes 21 a and 21 b, and one guard electrode 22. The applied voltage is controlled so that the voltage applied to the resistance R of the substance to be measured between the measurement electrodes is always constant to reduce the influence of the polarization phenomenon on the electrode surface and the noise caused by the pump pulsation.
[0005]
For example, in the case of anion analysis, a mixed solution of sodium carbonate and sodium bicarbonate, borate buffer, sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, etc. are flowed as the eluent, and the analyte ions are separated by a separation column. The ions are detected by an electrical conductivity detector through a suppressor. The electrical conductivity measured by the detector is grasped as a signal in which the contribution of the ion species in the sample is superimposed with the electrical conductivity of the eluent itself as the background. For example Na₂CO₃) Is converted to an acid or the like having a lower degree of dissociation (eg, carbonic acid), thereby reducing the background electrical conductivity and improving the measurement sensitivity of the signal due to the ionic species in the sample.
[0006]
Such a suppressor may be an ion exchange membrane in addition to the ion exchange resin. As an ion exchange membrane type suppressor, for example, in the case of anion analysis, a tube made of a sulfonic acid type cation exchange membrane is used. When sodium carbonate, the eluent, flows through this tube, sodium ions are cations, so they pass through the cation exchange membrane, while the protons in the sulfuric acid removal solution flowing outside the tube still Permeates the cation exchange membrane and enters the eluent, and then carbonic acid H₂CO₃Is formed in the tube. Since carbonic acid is a weak acid and dissociation hardly proceeds, the electric conductivity of the eluent decreases. On the other hand, the anion in the sample is repelled by the sulfonic acid groups present at a high concentration on the exchange membrane and cannot permeate the membrane, so it remains in the eluent and contributes to electrical conduction. Proportional to degrees.
[0007]
However, suppressor ions (ie, hydronium ions or hydroxide ions) must be continuously replenished and the suppressor needs to be replaced or regenerated. In addition to regeneration or replacement, the membrane-type ion suppressor has problems such as a broad peak, clogging of the membrane, and a resin-type ion suppressor that requires cleaning.
[0008]
In order to solve such a problem, an integrated suppressor and detector in which an ion exchange resin is filled in a cell have been reported (for example, see Patent Document 1). However, for example, when the eluent is NaOH, the cation exchange resin filled in the cell (counter ion is OH⁻Type) Na⁺Adsorbs and OH⁻Elutes. Therefore, the counter ion of the cation exchange resin is all Na⁺Since the effect of the suppressor is lost when it is converted to OH, the counter ion of the cation exchange resin in the cell is replaced with OH using the regenerative electrode.⁻It will be necessary to return to Such a reproduction electrode complicates the detection device and makes it difficult to handle.
[0009]
On the other hand, there is a non-suppressor type ion chromatography in which analysis can be performed without providing a suppressor by appropriately selecting a separation column, a mobile phase, and a detector. Non-suppressor type ion chromatography has a simple configuration and is easy to handle, so its application range is expanding, such as being used in continuous measurement equipment for field measurements. If the electrical conductivity of the battery is large, the noise of the baseline also becomes large and the sensitivity becomes poor. Therefore, development of an electrical conductivity measuring instrument having high sensitivity and stability is desired.
[0010]
[Patent Document 1]
JP-T-2002-513912
[0011]
[Problems to be solved by the invention]
An object of the present invention is to provide a non-suppressor type high-sensitivity ion chromatographic system that does not have a peak spread due to the use of a conventional suppressor and does not require a complicated device such as a regeneration mechanism or a complicated operation.
[0012]
[Means for Solving the Problems]
In view of the above problems, the present inventors have conducted intensive research, and as a result, by using a novel electrical conductivity detector, analyte ions can be easily detected with extremely high sensitivity by a method completely different from the ion suppressor method. The present invention has been completed.
[0013]
That is, in the first aspect of the present invention, a step of introducing at least two types of analyte ions into an ion exchange column, and a step of separating and eluting the analyte ions by flowing an eluent through the ion exchange column. And introducing the eluate into an electrical conductivity detector in which a stationary phase having a surface charge opposite to that of the analyte ions is interposed between at least two electrodes arranged opposite to each other. A method of detecting analyte ions by ion chromatography comprising measuring a current between the two electrodes.
[0014]
In a preferred embodiment of the present invention, the stationary phase is a cation exchanger or anion exchanger filled between the two electrodes or covering at least a part of the surface of the two electrodes. Also, in one embodiment of the present invention, the stationary phase interacts (contacts) with the analyte ions and electrolyte ions in the eluent, and the analyte ions are relative to the electrolyte ions in the eluent. It is an ion exchanger that improves the detection sensitivity of analyte ions flowing between the electrodes by improving mobility. In the present embodiment, when the eluate is a weak electrolyte solution, the stationary phase is preferably a strongly basic anion exchange resin. In another embodiment, the stationary phase is an ion exchanger that suppresses electrical conduction between the electrodes when in contact with the analyte ions. In this embodiment, the stationary phase is preferably a latex ion exchange resin, a coating ion exchange resin, or a phosphate ion exchange resin.
[0015]
In another aspect of the present invention, an electrical conductivity detector for detecting analyte ions in a liquid, wherein at least two electrodes are arranged opposite to each other, and a current between the two electrodes is measured. And a stationary phase interposed between the two electrodes and having a surface charge opposite to the analyte ions flowing between the two electrodes. Is done. In a preferred embodiment of the present invention, the stationary phase is a cation exchanger or anion exchanger filled between the two electrodes or coated on at least a part of the surface of the two electrodes.
[0016]
In a preferred embodiment, a stationary phase having a surface charge suitable for various conditions is inserted in the cell of the conductivity detector of the present invention. For example, when the analyte ion is an anion, the stationary phase is a basic anion exchange resin such as a quaternary ammonium salt, a latex type anion exchange resin, or a coating type anion exchange resin (both are analyte ions). Have the opposite charge). In another embodiment, for example, when the analyte ion is a cation, the stationary phase is an acidic cation exchange resin, a cation exchange resin formed by binding a phosphate group, or a latex cation exchange resin. Or a coating type cation exchange resin.
[0017]
In still another aspect of the present invention, an ion exchange column that separates analyte ions by eluting a sample containing analyte ions with an eluent, at least two electrodes that are spaced apart from each other, and the 2 Means for measuring the current between two electrodes, and a stationary phase interposed between the two electrodes and having a surface charge opposite to the analyte ions flowing between the two electrodes, An integrated ion exchange column and detector are provided.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
A preferred embodiment of the ion chromatography system of the present invention will be described with reference to FIG. The ion chromatography system of this embodiment includes an eluent 10 as a mobile phase, a pump 11 for feeding the eluent to a column, an injection valve 12 for introducing a sample, a separation column 13, and electric conductivity. It consists of a detector 14 and a measuring device 15 (data processor) connected to an electrical conductivity detector. The eluent 10 is preferably degassed by a degasser 16 before entering the pump 11. The pump 11, the injection valve 12, the degasser 16, and the separation column 13 can be appropriately selected from many models known to those skilled in the art. For example, a preferable pump may be a pump having extremely small pulsation and constant flow rate, and examples thereof include a multi-pump CCPM-II manufactured by Tosoh Corporation and a dual pump DP-8020. As the separation column, a column filled with various ion exchangers is used. From the structural aspect of the ion exchanger, there are a surface coating type, a surface thin film type, and an all porous fine particle type, and from the substrate surface, there are a polystyrene type, a polyacrylate type and a silica type. The cation exchanger has a sulfonic acid group on the surface, and the anion exchanger has an amino group on the surface. Specific examples include a filler in which a cation exchange group is introduced into a silica base material (such as Shodex YF-421 manufactured by Showa Denko), and a filler in which an anion or a cation exchange group is introduced into a polymer base material (manufactured by Tosoh Corporation). TSKgel PW or PWxl). Examples of the injection valve include a Leodyne 7725 injection valve.
[0019]
In the present invention, the electrical conductivity detector 14 is disposed in the flow path of the eluate eluted from the separation column 13. FIG. 3 schematically shows the measurement principle of the electrical conductivity detector according to one embodiment of the present invention. The electrical conductivity detector includes at least two electrodes 31a and 31b, a stationary phase 32, an AC voltage source 33, a resistor 34, and an ammeter 35. The stationary phase 32 may be filled between the electrodes, or is arranged so as to cover a part or all of the electrode surface. The two electrodes can use any conductive non-corrosive material such as carbon, platinum, titanium, stainless steel, or copper, and is preferably titanium. The AC voltage source 33 may be a DC voltage source. The eluate eluted from the separation column 13 flows in contact with the gap or surface of the stationary phase 32 disposed between the electrodes. This eluate contains, for example, chlorine ions Cl as analyte ions.⁻Sodium ion Na as its counter ion⁺, And electrolyte ions in the eluent.
[0020]
The electric conductivity of the eluate flowing between the two electrodes 31a and 31b is based on the anion and cation in the eluate and can be detected by measuring the current between the electrodes. The electrical conductivity is also called conductivity, and its unit is S / cm. S is called Siemens, the reciprocal of resistance (Ω^-1). The proportion of the total amount of electricity carried by an ion that is carried by a specific ion is called the transportation number. The ion mobility refers to the ion moving speed (cm / sec) when a unit electric field (1 V / cm) is applied, and the unit is cm.²It is expressed in / V · sec. It is considered that the mobility of ions between electrodes is influenced by the interaction with other ions and stationary phases, and greatly affects the detection of electrical conductivity.
[0021]
Examples of the stationary phase 32 include an ion exchanger. The ion exchanger is a general term for substances exhibiting an ion exchange phenomenon, and representative examples include an ion exchange resin, an ion exchange membrane, and an ion exchange cellulose. In addition, natural substances such as zeolites, acid clay, peat, lignite, synthetic zeolite, palm chit, zirconium tungstate, etc. are used for cation exchange, and basic dolomite, hydration is used for anion exchange. There are gels such as iron oxide and hydrated zirconium oxide. In this embodiment, when analyzing an anion, an anion exchanger is used as the stationary phase 32 inserted between the two electrodes (31a and 31b) of the electrical conductivity detector. A preferable anion exchanger is a strongly basic anion exchange resin, and examples thereof include a quaternary ammonium group.
[0022]
In one embodiment of the invention, when analyzing anions, an anion exchanger is used as the stationary phase. A preferred anion exchanger can be selected depending on the eluent conditions of ion chromatography. For example, when a weak electrolyte eluent (weak alkaline eluent or low conductivity solvent) such as borate buffer or carbonate buffer is used, it is a strongly basic anion exchange resin such as a quaternary ammonium group. That is, in the present embodiment, the mobility of analyte ions is increased by electrostatic interaction between ions in the eluent and analyte ions and a stationary phase (for example, ion exchange resin). Electrolyte ions inside are suppressed from dissociation by electrostatic interaction with the stationary phase surface, resulting in an increase in the conductivity difference (transport difference) between the analyte ion and the electrolyte ion (eluent component) between the electrodes. It is considered that the S / N ratio is improved. On the other hand, when using a strong electrolyte eluent (high conductivity solvent) such as sodium hydroxide, an analyte ion (nitrate ion, phosphate ion, The S / N ratio of sulfate ions, etc.) can be improved, and the detection sensitivity can be improved about 100 times. In this specification, “latex type anion exchange resin” refers to an ion exchange resin in which the surface of latex fine particles is coated with various anion groups or cation groups. Here, latex generally refers to colloidal fine particles dispersed in water, and is naturally known as rubber tree sap. Synthetic latex is produced by synthesizing this sap, and is obtained by dispersing fine particles of synthetic polymer having an average particle diameter of about 0.05 to 1.0 μm in water. Generally, it is synthesized by emulsion polymerization, and there are various synthetic latexes such as styrene-butadiene copolymer (SBR) and acrylonitrile-butadiene copolymer (NBR). Such latex fine particles can be applied as a carrier for chromatography. For example, latex fine particles having a copolymer of styrene and divinylbenzene as the core and covered with glycidyl methacrylate (GMA) are coated with epoxy on the surface. Various ion exchange groups can be attached through the group. In addition, the surface of an ethylene vinyl / divinylbenzene copolymer having a particle size of 10 to 25 μm is coated with a sulfonic acid group, and fine particles having a quaternary ammonium base having a particle size of several tens to several hundreds are dispersed around the sulfonic acid group. It is also possible to use a cured resin.
[0023]
Alternatively, it is also possible to use a coating type ion exchanger obtained by coating a treatment agent (modifier) on the surface of the base resin other than a covalent bond, for example, by an ionic bond, a hydrophobic bond, a hydrophilic bond, or a coordinate bond. it can. For example, an ODS resin is used as a base resin, and a cationic surfactant is dispersed on the resin surface to obtain a cationic surfactant-coated ion exchange resin. Therefore, in the method of the present invention, the type of stationary phase to be filled in the cell can be selected according to the eluent component, and can be optimized according to each measurement condition.
[0024]
In another embodiment of the present invention, when analyzing cations, a cation exchanger is used as the stationary phase. For example, a preferable cation exchanger when an eluent such as nitric acid is used is an ion exchange resin formed by bonding a phosphate group. When the electrical conductivity detector in the present embodiment is used, the S / N ratio of the divalent analyte ions can be particularly improved, compared with the case where the ion exchange resin is not filled between the electrodes. 10 times or more of sensitivity can be obtained. In this embodiment, when analyte ions flow into the cell, proton H, which is an eluent component, is used.⁺And the conductivity of the analyte ion (positive ion) increase in the negative direction. Therefore, when the analyte ion comes into contact with the stationary phase surface, a phase transition occurs on the stationary phase surface.²⁺Adsorbs (interacts) with the ion exchange resin to suppress the electrical conductivity between the electrodes (the ion exchange resin that showed conductivity in the eluent becomes insulating), thereby increasing the electrical conductivity. It seems that there was a big reaction in the direction of decreasing.
[0025]
The ion exchange resin used in the present invention preferably has a high ion exchange capacity. The ion exchange capacity refers to the amount of ions that can be exchanged by the ion exchange resin under a certain condition, and is expressed by, for example, milliequivalent (meq) / g-dry weight or milliequivalent (meq) / ml-swelled volume. Is done. A preferable ion exchange capacity is 0.1 to 1.0 meq / g. Here, the ion exchange capacity is considered to be related to the surface charge density of the ion exchange resin. That is, the larger the surface charge density of the ion exchanger, the more efficiently the analyte ions can be measured.
[0026]
The ion chromatography system of the present invention can be used to detect analyte ions, including anions and cations. In water quality inspection and food analysis, fluoride ions (F⁻), Chloride ion (Cl⁻), Nitrite ion (NO₂ ⁻), Bromide ions (Br⁻), Nitrate ion (NO₃ ⁻), Sulfate ion (SO₄ ^2-), Phosphate ion (PO₄ ^3-The analysis of seven types of ions is important, and these ions are said to be “seven types of standard inorganic ions”. For anion analysis, preferred eluents include aqueous sodium hydroxide or sodium carbonate / sodium bicarbonate. Since these eluents do not have a strong dissolution power, they must be used at a relatively high concentration, and a suppressor is required. Since sodium hydroxide has a low affinity for the separation resin, only weakly held anions are eluted, especially sulfate ions (SO₄ ^2-) And phosphate ions (PO₄ ^3-) And the like. According to the method of the present invention, even when sodium hydroxide is used as an eluent, not only a sufficient sensitivity can be obtained by the non-suppressor method, but particularly sulfate ion (SO₄ ^2-) And phosphate ions (PO₄ ^3-) And the like.
[0027]
Regarding the analysis of cations, ion chromatography is used for the analysis of monovalent cations, divalent cations, metal ions, and the like. As the eluent for monovalent cation separation, dilute nitric acid is usually used. For separation of divalent cations such as alkaline earth metal ions, a dilute nitric acid solution containing phenylene diammonium chloride is used as an eluent. In addition, preferred eluents are mainly composed of strong acids such as hydrochloric acid, methanesulfonic acid or sulfuric acid, and organic acids such as phthalic acid, gluconic acid, benzoic acid, hippuric acid, tartaric acid and citric acid as the main component. What to do is used.
[0028]
In a different embodiment of the present invention, an ion chromatography system is provided that uses the integrated ion exchange column and detector 43 shown in FIG. The integrated ion exchange column and detector 43 includes two electrodes (not shown) inside or at the end of a normal ion exchange column. Therefore, it is preferable that the same ion exchange resin as the separation column is filled between the two electrodes. Analyte ions in the eluent flowing between the two electrodes are separated by an ion exchange column and detected by two electrodes placed immediately thereafter.
[0029]
【Example】
The invention is more specifically described in the following examples. In the Examples, analysis results of anions and cations by ion chromatography under various conditions are shown.
[0030]
(Example 1) Anion chromatography using an electric conductivity detector filled with an ion exchange resin in the cell and changing the flow rate of the eluent.
In accordance with the embodiment shown in FIG. 1, an anion chromatography was carried out using an electric conductivity detector filled with an ion exchange resin in the cell and changing the flow rate of the pump to flow the eluent at various flow rates. The analytical column is TSKgel IC-anion-PWxl, 4.6 mm ID × 3.5 cm, the pump is Tosoh DP-8020, the injector is a rheodyne valve (20 μl), and the detector is between the electrodes of an electric conductivity meter manufactured by Nichi Kogyo Co., Ltd. A Yokogawa 3066 pen recorder was used as the data processor, which was filled with an ion exchange resin TSKgel IC-anion-SW (about 0.4 meq / g) having a quaternary ammonium group. As a control experiment, a similar experiment was performed using an electric conductivity detector in which no ion exchange resin was filled in the cell. The eluent was 6 mM ammonium tetraborate, and the sample was an anion mixed standard IV (manufactured by Kanto Chemical Co., Inc.). FIGS. 5A to 5C are chromatograms when no ion exchange resin is filled in the cell of the electrical conductivity detector. The pump flow rates are 0.8 ml / min, 0.4 ml / min, and 0.2 ml / min, respectively, in the order of (a) to (c). The detection cell conditions are an applied voltage of 1 V, a frequency of 10 kHz, and a measurement temperature of 30 ° C. The following peaks correspond to the following anions, respectively. 1: Fluoride ion F⁻(5 mg / l), 2: Chloride ion Cl⁻(10 mg / l), 3: nitrite ion NO₂ ⁻(15 mg / l), 4: bromide ion Br⁻(10 mg / l), 5: nitrate ion NO₃ ⁻(30 mg / l), 6: phosphate ion PO₄ ^3-(30 mg / l), 7: sulfate ion SO₄ ^2-(40 mg / l). From the results shown in FIGS. 5A to 5C, the peak width increases as the flow rate of the eluent decreases, and the height of peaks such as phosphate ions 6 and sulfate ions 7 whose elution time is slow decreases.
[0031]
On the other hand, FIGS. 6A to 6C show chromatograms when the ion exchange resin is filled in the cell of the electrical conductivity detector. The pump flow rates are 0.8 ml / min, 0.4 ml / min, and 0.2 ml / min, respectively, in the order of (a) to (c). From the results of FIGS. 6 (a) to 6 (c), the S / N ratio does not decrease even if the elution time of the sample is delayed by filling the cell with an ion exchange resin, and high sensitivity detection is possible. I understand. From these results, it was found that the analyte ion diffusion was suppressed by filling the cell of the electrical conductivity detector with the ion exchange resin, and the analyte ions having a slow elution time could be detected with high sensitivity.
[0032]
(Example 2) Anion chromatography using ammonium tetraborate as an eluent and filling various ion exchange resins in a cell
Using the same apparatus as in Example 1, anion chromatography was performed in which various ion exchange resins were filled in the cell. FIG. 7 is a chromatogram when the cell is not filled with an ion exchange resin as a control experiment (flow rate 0.8 ml / min, background 675 μS / cm). FIG. 8 shows a case where TSKgel IC-anin-SW (about 0.4 meq / ml) having a quaternary ammonium group is filled in the conductivity detector cell (flow rate 0.8 ml / min, background 495 μS / cm). FIG. 9 shows a case where TSKgel IC-anin-PWxl (about 0.03 meq / ml) is similarly filled (flow rate 0.8 ml / min, background 295 μS / cm). FIG. 10 shows quaternary alkylamine, latex particles (140 nm). Is loaded with Dionex AS12A (approximately 0.013 meq / ml) (flow rate 0.8 ml / min, background 270 μS / cm), FIG. 11 shows TSKgel IC-anin-PWxl120DM having quaternary ammonium groups (approximately 0.06 meq). / Ml) (flow rate 0.8ml / min, background FIG. 12 shows a case where TSKgelDEAE-AW03-02-13-1 having a tertiary amine group (about 0.1 meq / ml) is loaded (flow rate: 0.4 ml / min, background: 283 μS / cm). ). The eluent was 6 mM ammonium tetraborate, and the sample was an anion mixed standard IV (manufactured by Kanto Chemical Co., Inc.). The detection cell conditions are an applied voltage of 1 V, a frequency of 1 kHz, and a temperature of 30 ° C. From these results, when an ion exchange resin bonded with a quaternary ammonium group, which is a strongly basic ion exchange resin, is used, the conductivity peak increases as the ion exchange capacity increases, and the S / N ratio improves. I understand that When a weakly basic ion exchange resin such as a tertiary amine group was used, no improvement in sensitivity was observed. FIG. 13 is the result of plotting the relationship between the exchange capacity of the ion exchange resin filled in the cell and the amount of increase in peak height detected by electrical conductivity. The ion exchange resins filled in the cell were TSKgelIC-anion-SW (about 0.4 meq / g), TSKgelIC-anion-PWxl120DM (about 0.06 meq / ml), and TSKgelIC-anion-PWxl (about 0. 03 meq / ml) was used. Analyte ions are ◆ for Cl⁻, ■ is NO₂ ⁻, ▲ is Br⁻, X is NO₃ ⁻, * Is PO₄ ^3-, And ● are SO₄ ^2-It is. From the results shown in FIG. 13, it can be seen that although the rate of increase in peak height differs depending on the type of analyte ion, the increase in peak height is greater when an ion exchange resin having a large exchange capacity is used.
[0033]
On the other hand, as shown in FIG. 10, when latex type anion exchange resin is used in the cell of the conductivity detector, the peak of analyte ions (nitric acid, phosphoric acid, sulfate ion) having a long elution time is obtained. It was found that the direction of appearance (plus and minus) was reversed, and the S / N ratio was further improved. This is probably because the latex type anion exchange resin was filled in the cell and each analyte ion flowed into the cell caused a phase transition on the surface of the resin, which changed the surface state. . For example, when sulfate ions are adsorbed on a latex-type anion exchange resin, resins that have been electrically conductive until now have become insulating.
[0034]
(Example 3) Anion chromatography using sodium hydroxide as an eluent and filling various ion exchange resins in the cell
Anion chromatography was performed in the same manner as in Example 2 except that 5 mM sodium hydroxide was used as the eluent, using an electric conductivity detector filled with various ion exchange resins in the cell. The flow rate of the eluent is 0.8 ml / min, and the detection cell conditions are an applied voltage of 1 V, a frequency of 1 kHz, and a temperature of 30 ° C. FIG. 14 is a chromatogram when the cell is not filled with resin as a control experiment (background 800 μS / cm). FIG. 15 shows a case where quaternary alkylamine and latex particles (140 nm) Dionex AS12A (about 0.013 meq / ml) are filled in the cell of the conductivity detector (background 759 μS / cm), and FIG. It is a chromatogram when packed with TSKgel IC-anin-SW (about 0.4 meq / ml) having a quaternary ammonium group (background 513 μS / cm). From these results, depending on the type of ion exchange resin filled in the cell, different behavior appears when ammonium tetraborate is used as the eluent, but in either case the peak is in the negative direction (conductivity decreases). When the latex type anion exchange resin is filled in the cell, it can be seen that the S / N ratio of analyte ions (multivalent ions) having a slow elution time can be improved. As is clear from comparison between FIG. 14 and FIG. 15, the peaks of phosphate ions and sulfate ions with a slow elution time are very small in FIG. 14, but very large in FIG. It turns out that it is above. When 5 mM sodium hydroxide was used as the eluent, no improvement in sensitivity was observed even when an anion exchange resin bound with a quaternary ammonium group was filled. This is because the mobility of each analyte ion is increased by electrostatic adsorption on the resin surface, but the ion selective barrier of nitrate ions contained in the eluent due to electrostatic repulsion of the resin surface in the vicinity of the electrode. Is incomplete, the peak appears in the negative direction, and the S / N ratio is thought to have decreased.
[0035]
(Example 4) Cation chromatography packed with various ion exchange resins in a cell
According to the embodiment shown in FIG. 1, cation chromatography was performed using an electric conductivity detector in which various ion exchange resins were packed in the cell. The analytical column was TSKgelSuperIC-Cation, 4.6 mm ID × 15 cm, the eluent was 2 mM nitric acid, the flow rate was 0.8 ml / min, and the sample was a cation mixed standard II (manufactured by Kanto Chemical Co., Inc.). Other conditions are the same as in the first embodiment. FIG. 17 is a chromatogram when the cell is not filled with resin as a control (background 690 μS / cm). FIG. 18 shows a case where Dionex CS12A (about 0.7 meq / ml) having a carboxyl group and a phosphate group is filled in the cell of the conductivity detector (background 650 μS / cm), and FIG. 19 shows a quaternary ammonium group. When filled with TSKgel IC-anin-SW (about 0.4 meq / ml) (background 920 μS / cm) and FIG. 20 when filled with Dionex AS12A (about 0.013 meq / ml) (background 280 μS / cm) ). The following peaks correspond to the following cations, respectively. 1: Lithium ion Li⁺(0.5 mg / l), 2: sodium ion Na⁺(2 mg / l), 3: ammonium ion NH₄ ⁺(2 mg / l), 4: potassium ion K⁺(5 mg / l), 5: magnesium ion Mg²⁺(5 mg / l), 6: calcium ion Ca²⁺(5 mg / l). From these results, it is not possible to improve the S / N ratio by filling the cell with an ion exchange resin bonded with a quaternary ammonium group. However, an ion exchange resin bonded with a phosphoric acid group is placed in the cell. When filled, the S / N ratio of the divalent analyte ions can be improved and highly sensitive detection can be performed (see FIG. 18). In addition, this effect shows that the peak height is increased by about 10 times compared to when the cell is not filled with an ion exchange resin.
[0036]
(Example 5) Change in cell applied frequency and peak height
According to the embodiment shown in FIG. 1, the relationship between the case where the ion exchange resin is filled in the cell of the conductivity detector and the case where it is not filled is subjected to anion chromatography and the frequency of the applied voltage is changed. I investigated. The analytical column is TSKgelIC-anion-PWxl, 4.6 mm ID × 3.5 cm, the ion exchange resin packed in the cell is TSKgelIC-anion-SW (about 0.4 meq / g), the eluent is 6 mM ammonium tetraborate, and the flow rate is 0.00. The other conditions were the same as in Example 1 at 8 ml / min. The results are shown in FIGS. 21 (a) and (b). As a result, the peak height fluctuates at the same rate according to the cell application frequency change rate. By filling the cell with ion exchange resin within the range of 1 to 10 kHz, each ion component at a specific frequency is filled. Specificity was not observed.
[0037]
【The invention's effect】
The electrical conductivity detector of the present invention has a charge opposite to that of the stationary phase by a very simple method of filling a stationary phase made of an ion exchanger such as an ion exchange resin between two electrodes. Analyte ions can be measured with high sensitivity. The measurement sensitivity is remarkably improved when used in either the conventional suppressor method or the non-suppressor method, but especially when used in the non-suppressor method, the regeneration of the suppressor column or the suppressor tube is used. There is no need, and both anion ions and cation analyte ions can be efficiently detected by a very simple apparatus.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of an ion chromatography system according to one embodiment of the present invention.
FIG. 2 is a cross-sectional view of a conventional electrical conductivity detector.
FIG. 3 is a schematic diagram showing an electrical conductivity detector according to one embodiment of the present invention.
FIG. 4 is a schematic diagram of an ion chromatographic system using an integrated ion exchange column and detector according to one embodiment of the present invention.
FIG. 5 is an anion chromatogram when the flow rate of the pump is changed without filling the cell with ion exchange resin.
FIG. 6 is an anion chromatogram when an ion exchange resin is filled in a cell and the flow rate of the pump is changed.
FIG. 7 is an anion chromatogram performed without filling the cell with an ion exchange resin.
FIG. 8 is an anion chromatogram obtained by filling TSKgel IC-anin-SW (about 0.4 meq / ml) ion exchange resin having quaternary ammonium groups in the cell with ammonium tetraborate as an eluent. .
FIG. 9 is an anion chromatogram obtained by filling TSKgelIC-anin-PWxl (about 0.03 meq / ml) ion exchange resin having quaternary ammonium groups in the cell with ammonium tetraborate as an eluent. .
FIG. 10 Anion chromatography carried out by using ammonium tetraborate as an eluent and filling the cell with a quaternary alkylamine and latex ion (140 nm) Dionex AS12A (about 0.013 meq / ml) ion exchange resin. Gram.
FIG. 11 is an anion chromatogram obtained by filling TSKgelIC-anin-PWxl120DM (about 0.06 meq / ml) ion exchange resin having ammonium quaternary borate as an eluent and having a quaternary ammonium group in a cell. .
FIG. 12 Anion obtained by filling TSKgelDEAE-AW03-02-13-1 (about 0.1 meq / ml) ion exchange resin having ammonium tetraborate as an eluent and having a tertiary amine group in the cell. It is a chromatogram.
FIG. 13 is a graph showing a change in peak height with an increase in exchange capacity of an ion exchange resin filled in a cell in anion chromatography.
FIG. 14 is an anion chromatogram obtained by using sodium hydroxide as an eluent and without filling an ion exchange resin in a cell.
FIG. 15 shows an anion chromatogram obtained by filling a cell with sodium ion as an eluent and IONEX AS12A (about 0.013 meq / ml) ion exchange resin as a quaternary alkylamine and latex particles (140 nm). It is.
16 is an anion chromatogram obtained by filling TSKgel IC-anin-SW (about 0.4 meq / ml) ion exchange resin having quaternary ammonium groups in a cell with sodium hydroxide as an eluent. FIG.
FIG. 17 is a cation chromatogram performed without filling the cell with an ion exchange resin.
FIG. 18 is a cation chromatogram obtained by filling Dionex CS12A (about 0.7 meq / ml) ion exchange resin having a carboxyl group and a phosphate group in a cell.
FIG. 19 is a cation chromatogram obtained by filling a cell with TSKgel IC-anin-SW (about 0.4 meq / ml) ion exchange resin having a quaternary ammonium group.
FIG. 20 is a cation chromatogram obtained by filling a cell with Dionex AS12A (about 0.013 meq / ml) ion exchange resin.
FIG. 21 is a graph showing the relationship between the frequency of the voltage applied to the electrical conductivity detector and the peak height.
[Explanation of symbols]
10, 40 Eluent
11, 41 Pump
12, 42 Injection valve
13 Separation column
14 Electrical conductivity detector
15, 45 Data processor
16, 46 Degasser
17, 47 Temperature controller
20a, 20b Voltage application electrode
21a, 21b Measuring electrode
22 Guard electrode
23 AC voltage source
24, 34 resistance
25, 35 Ammeter
31a, 31b electrode
32 Stationary phase
33 AC voltage source
43 Integrated ion exchange column and detector

Claims (11)

Introducing at least two types of analyte ions into an ion exchange column;
Flowing an eluent through the ion exchange column to separate and elute the analyte ions;
The eluate is introduced into an electric conductivity detector in which a stationary phase having a surface charge opposite to that of the analyte ions is interposed between at least two electrodes arranged opposite to each other at a distance from each other. Measuring the current between the two electrodes;
To detect analyte ions by ion chromatography. 2. The cation exchanger or the anion exchanger according to claim 1, wherein the stationary phase is filled between the two electrodes, or is a cation exchanger or anion exchanger covering at least a part of the surface of the two electrodes. the method of. Analysis that flows between the electrodes by improving the relative mobility of the analyte ions relative to the electrolyte ions in the eluent when the stationary phase interacts with the analyte ions and the electrolyte ions in the eluent. The method according to claim 1 or 2, which is an ion exchanger that improves detection sensitivity of product ions. The method according to claim 3, wherein when the eluate is a weak electrolyte solution, the stationary phase is a strongly basic anion exchange resin. The method of claim 1 or 2, wherein the stationary phase is an ion exchanger that suppresses electrical conduction between the electrodes when in contact with the analyte ions. The method according to claim 5, wherein the stationary phase is a latex ion exchange resin, a coating ion exchange resin, or a phosphate ion exchange resin. An electrical conductivity detector for detecting analyte ions in a liquid,
At least two electrodes arranged oppositely and spaced apart from each other;
Means for measuring the current between the two electrodes, and a stationary phase interposed between the two electrodes and having a surface charge opposite to the analyte ions flowing between the two electrodes. Electrical conductivity detector. 8. The cation exchanger or the anion exchanger according to claim 7, wherein the stationary phase is filled between the two electrodes, or is a cation exchanger or anion exchanger covering at least a part of the surface of the two electrodes. Electric conductivity detector. The electrical conductivity detection according to claim 7 or 8, wherein when the analyte ion is an anion, the stationary phase is a basic anion exchange resin, a latex type anion exchange resin, or a coating type anion exchange resin. vessel. When the analyte ion is a cation, the stationary phase is an acidic cation exchange resin, a cation exchange resin formed by binding a phosphate group, a latex cation exchange resin, or a coating cation exchange resin. The electrical conductivity detector according to claim 7 or 8. An ion exchange column for separating analyte ions by eluting a sample containing analyte ions with an eluent;
At least two electrodes arranged oppositely and spaced apart from each other;
Means for measuring the current between the two electrodes, and a stationary phase interposed between the two electrodes and having a surface charge opposite to the analyte ions flowing between the two electrodes, An integrated ion exchange column and detector.

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