JP6379593B2 - Ion conversion method and ion conversion apparatus for ionic compounds - Google Patents

Description

  The present invention relates to an ion conversion method and an ion conversion apparatus for an ionic compound.

  Ion chromatography is adopted in various official methods as a method for analyzing ion components, and in many cases, it is widely used as an analyzer based on a method of detecting electrical conductivity by a suppressor method.

  As a measure for the analysis of weak acid ions such as organic acids, the liquid eluted from the suppressor is introduced into the first electrical conductivity detector to detect strong acid ions, and then the effluent containing weak acid ions is alkali metal. Lead to salt converter containing cation exchange resin as ion and counter ion, convert counter ion from hydrogen ion to alkali metal ion, and then introduce into second conductivity detector to increase weakly acidic ion component A method for detecting sensitivity is disclosed (see Patent Document 1 and Patent Document 2).

  In the electrical conductivity detection method by the suppressor method, conversion of counter ions is usually performed in the suppression process. For example, in anion analysis, sodium hydroxide used as the electrolyte of the eluent is converted to water, sodium carbonate or potassium carbonate is converted to carbonic acid, and the ionic component AX to be measured is converted to HX. As a result, the conductivity of the eluent that is not measured decreases, and the conductivity of the ion component HX generated after the conversion increases. Therefore, the highly sensitive ion component is reduced by both changes in noise level and signal intensity. Can be detected. However, it is known that the ionic component HX is based on its dissociation characteristics (pKa), and the dissociation state varies depending on the concentration. Therefore, depending on the ionic species, the calibration curve is bent, and the quantification accuracy is greatly affected. . This tendency is particularly noticeable in weakly acidic and weakly basic ionic components, and at the same time, there is a problem of causing a decrease in detection sensitivity (see Non-Patent Document 1).

  As a detection method other than the suppressor method-electric conductivity detection method, there is an absorbance detection method. Since the absorbance detection method is not easily affected by the dissociation state due to the concentration change, the calibration curve has excellent linearity and high quantitative accuracy. However, when direct absorbance detection is performed, applicable objects are limited to ionic species having light absorption. Indirect absorptiometry is known as a method for solving this problem. This is a detection method using an eluent with absorbance and a negative peak for ionic species that do not absorb light in a high background absorption state, but the type, concentration, and combination with the column of the eluent are limited. There are also problems such as the occurrence of a system peak derived from the eluent, and there has been a problem in general use.

As another method using absorbance detection, a post-column reaction derivatization-absorptiometry is used. This is a technique of detecting by performing a post-column reaction only with a specific ion species, and can detect the ion species to be measured with high selectivity. However, since the post-column reaction is performed online, setting of the system configuration and post-column reaction conditions is complicated, and there is a problem that it can be used only as an analysis method with limited measurement ion species. (Non-Patent Document 1)
On the other hand, Mori et al. Discloses a method of detecting absorbance after subjecting an ion to be analyzed to salt exchange (see Patent Documents 3 and 4). In this method, after ion components are separated by ion-exclusion chromatography using water as an eluent, ions that absorb UV from the effluent from the column are introduced to an immobilized ion exchange resin, and the ions to be analyzed or their counter ions are UV-dissolved. Absorbance is detected after conversion to an absorbing salt. This method has the advantage that the absorbance detection method can be widely applied to separable ionic species, but since the eluent is limited to water, it is limited to the application to chromatography using a column that can be separated only with water. Therefore, there has been a problem in application to ion exchange chromatography used for general ion analysis.

Japanese National Patent Publication No. 7-505960 Japanese Patent No. 4122228 Japanese Patent No. 3924618 Japanese Patent No. 3924622

Okada et al., Separation analysis of ionic species by chromatography, 2002, pp. 69-104, 135-151

  The present invention has been made in view of the problems of the prior art, and an object thereof is to provide a method and apparatus for converting an ionic component constituting an ionic compound and finally converting the ionic species into an ion species capable of detecting absorbance. It is in.

  As a result of intensive studies to achieve the above object, the present invention has been completed.

That is, the present invention includes the following [1] to [4].
[1] A method for converting an ion B of an ionic compound AB (wherein one of A and B represents a cation and the other represents an anion),
(1) A step of exchanging AB with an ion exchange medium to obtain AC (wherein C represents an H ⁺ ion or an OH ⁻ ion),
(2) A step of converting AC obtained in step (1) into AD (wherein D is an ion capable of detecting absorbance and having the same charge as C) by a salt exchanger. And how to.
[2] The method according to [1], wherein the ion exchange medium and / or the salt exchanger is an ion exchange column or an ion exchange membrane.
[3] An apparatus for converting an ion B of an ionic compound AB (wherein one of A and B represents a cation and the other represents an anion),
(1) an ion exchange medium that converts AB to AC (wherein C represents an H ⁺ ion or an OH ⁻ ion), and (2) the AC obtained in (1) above is converted to AD (formula An ion conversion apparatus comprising a salt converter for converting D into ions capable of detecting absorbance and having the same charge as C).
[4] The ion conversion device according to [3], wherein the ion exchange medium and / or the salt exchanger is an ion exchange column or an ion exchange membrane.

  In the present invention, the ionic compound AB is not particularly limited, and examples thereof include sodium chloride, sodium sulfate, and potassium dihydrogen phosphate.

The ion exchange medium used in the present invention is used in the step of primary conversion of the ionic compound AB to AC. Specifically, in anion analysis, a strong basic anion exchange column, a weak basic anion exchange column, and a cation analysis may be exemplified by a strong acid cation exchange column and a weak acid cation exchange column. it can. Other examples include an amphoteric ion exchange column having both an anion exchange group and a cation exchange group, a separation column for reverse phase chromatography, a separation column for hydrophilic interaction chromatography, and the like.
In addition, the primary conversion is defined in the present invention in order to distinguish it from a step of further converting ions by a salt converter described later. Moreover, it does not prevent having another conversion process before the said primary conversion by a well-known method.

In the salt converter used in the present invention, an ion D capable of detecting absorbance is immobilized, and is used when the primary-converted AC is converted to AD. Here, examples of the ions D capable of detecting absorbance include nitrate ions, bromide ions, and iodide ions.
The ions D converted by the method of the present invention are guided to an absorbance detector, and can be detected by setting a detection wavelength adapted to the light absorption characteristics of the ions D. From the detected peak area or height of the ion D, a quantitative value of the ion A is calculated, and a concentration analysis result can be obtained.

Hereinafter, an example in which the present invention is applied to an ion chromatography system will be described with reference to FIG.
For analysis, the sample injected from the autosampler 3 is introduced into the separation medium 5 together with the eluent 1. Each introduced ionic species is separated by the principle of ion chromatography.

  In the present invention, the eluent 1 allows the eluent containing an electrolyte to pass through the separation medium 5 so that each ionic component to be analyzed introduced into the separation medium 5 is separated due to the difference in interaction with the separation medium 5. A difference occurs in the moving speed in the medium 5, and the ions are separated according to the type of each ion, and flow out from the outlet of the separating medium in order of increasing moving speed. At that time, the effluent flowing out of the separation medium 5 contains the electrolyte derived from the eluent 1 and the ionic component A.

  Here, the separation medium is used in the step of primary conversion of the ionic compound AB to AC. Specifically, in anion analysis, a strong basic anion exchange column, a weak basic anion exchange column, and a cation analysis may be exemplified by a strong acid cation exchange column and a weak acid cation exchange column. it can. Other examples include an amphoteric ion exchange column having both an anion exchange group and a cation exchange group, a separation column for reverse phase chromatography, a separation column for hydrophilic interaction chromatography, and the like.

  Next, in the ion exchange medium 6, the electrolyte derived from the eluent present in the effluent is converted into water, which has a very low dissociation degree and is the same substance as the eluent so as not to interfere with the absorbance analysis. . As a result, the ions derived from the eluent 1 do not exist in the effluent from the ion exchange medium 6, and the effluent containing only the ions A derived from the injected sample flows out from the ion exchange medium 6.

The meaning of the “electrolyte” in the “eluent containing an electrolyte” means an electrolyte that can be converted into water. For example, when sodium hydroxide is used as the electrolyte of the eluent, ^This means that ⁺ and Na ⁺ are ion-exchanged and converted to water with H ⁺ + OH ⁻ = H ₂ O.

When HCl is used as the electrolyte of the eluent, it means that OH ⁻ and Cl ⁻ are ion-exchanged by hydroxide ions of the anion exchange resin and converted to water with H ⁺ + OH ⁻ = H ₂ O. .

  The salt converter 7 is used when primary exchanged ions C contained in the effluent flowing out of the ion exchange medium 6 are converted into ions D whose absorbance can be detected. In this salt converter 7, the ion species capable of detecting the absorbance is immobilized, and the ion B can be converted into the ion D capable of detecting the absorbance after the step of the primary conversion of the ions B by the ion exchange medium. The ion D that has flowed out is guided to the absorbance detector 8 and is detected by setting a detection wavelength adapted to the light absorption characteristics of the ion D. A quantitative value is calculated as the ion A from the peak area or peak height of the detected ion D, and an analysis result of the concentration of the ion component can be obtained.

  Further, such an analyzer can be applied to a method of analyzing a plurality of different analyte ions in a sample solution to be used.

  According to the present invention, the ion B of the ionic compound AB can be finally converted into an ion D whose absorbance can be detected. By applying the present invention to an ion chromatography system using an eluent containing an electrolyte, the ionic component separated can be quantified by applying an absorbance detection method regardless of its light absorption characteristics. .

  Since ions can be separated and detected by ion chromatography using an electrolyte that can be converted into water in this way, the present invention can be applied to analysis of ions using various separation columns such as an ion exchange column. In addition, by controlling the separation by freely adjusting the electrolyte concentration, it can be applied to ion analysis of a wide range of actual samples such as environmental samples, chemicals, foods, and pharmaceuticals.

  In the conventionally used suppressor method-ion chromatography method based on electrical conductivity detection, there are cases in which detection sensitivity and quantitative accuracy are problematic due to the dissociation characteristics of ionic components. For example, since all the same ion species are detected by their absorbance, the detection sensitivity can be improved, and an effect of obtaining a highly accurate quantitative analysis result can be expected.

It is a typical flowchart of the apparatus to which this invention is applied. 1 is a diagram showing an ion chromatogram obtained in Example 1. FIG. 6 is a diagram showing an ion chromatogram obtained in Example 2. FIG. It is a figure which shows the ion chromatogram which used the absorbance detector in the comparative example 1. It is a figure which shows the ion chromatogram which used the electrical conductivity detector in the comparative example 1.

  FIG. 1 shows a simplified apparatus configuration for carrying out an embodiment of the present invention.

  In FIG. 1, 1 indicates an eluent. The electrolyte used for the eluent is one that can be converted into water by passing through the ion exchange medium 6.

  In the case of anion analysis, it is possible to use an alkaline aqueous solution having a hydroxide ion as a counter ion. Specifically, sodium hydroxide, potassium hydroxide, ammonium hydroxide, lithium hydroxide, hydroxide An electrolyte such as tetraalkylammonium can be exemplified. In the cation analysis, it is possible to use an acid aqueous solution having a hydrogen ion that can be converted into water as a counter ion. Specifically, hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, methanesulfonic acid, p-toluenesulfone. An electrolyte such as an acid can be exemplified. The concentration of the electrolyte in the eluent 1 is preferably 0.01 mmol / L or more and 500 mmol / L or less, and more preferably 0.1 mmol / L or more and 200 mmol / L or less. As the eluent 1, one having a single composition or two or more kinds of compositions having different concentrations can be used stepwise or continuously mixed. The eluent 1 may contain a water-soluble organic solvent, and specific examples include alcohols such as methanol, ethanol, and propanol, acetonitrile, and the like.

  The eluent 1 is fed by a liquid feed pump 2, passed through an autosampler 3, and introduced into a separation medium 5 in a column oven 4. As the separation medium 5, a chromatography separation column using an electrolyte can be used. Specifically, in anion analysis, a strong basic anion exchange column, a weak basic anion exchange column, and a cation analysis may be exemplified by a strong acid cation exchange column and a weak acid cation exchange column. Other examples include amphoteric ion exchange columns having both an anion exchange group and a cation exchange group, a separation column for reverse phase chromatography, a separation column for hydrophilic interaction chromatography, and the like. For analysis, the sample injected from the autosampler 3 is introduced into the separation medium 5 together with the eluent 1. Each introduced ionic species is separated by the principle of ion chromatography.

  The ion exchange medium 6 can be a column type filled with an ion exchange resin or a membrane type using an ion exchange membrane. Specifically, in anion analysis, a column filled with a hydrogen ion-type cation exchange resin that can convert cations contained in the eluent to hydrogen ions or a hydrogen ion is supplied to remove cations. A membrane type suppressor having a cation exchange membrane that can be used. In cation analysis, a column filled with a hydroxide ion type anion exchange resin that can convert anions contained in the eluent to hydroxide ions or a hydroxide ion is supplied, and the anion is removed. A membrane type suppressor having a cation exchange membrane that can be exemplified.

  Next, as a material used for the salt converter 7 for performing salt conversion, a column or ion exchange membrane filled with an ion exchange resin can be used. Specifically, in the case of an ion exchange resin, an ion species having absorption characteristics for ultraviolet light or visible light is used as a counter ion, and a nitrate ion type anion exchange resin and a nitrite ion type anion exchange resin are used. , Iodide ion type anion exchange resin, bromide ion type anion exchange resin, sulfite ion type anion exchange resin, thiosulfate ion type anion exchange resin, sulfonate ion type anion exchange having aromatic functional groups Resin, metal-metal ligand complex ion type anion exchange resin, quaternary ammonium ion type cation exchange resin having aromatic functional group, sulfonium ion type cation exchange resin, metal-metal ligand complex An ion type cation exchange resin etc. can be illustrated. In addition, when it is difficult to convert ion species flowing out from the ion exchange medium 6 into an ion component having light absorbance by direct ion exchange reaction in the salt converter 7, preliminary salt conversion is performed before the salt converter. Can be used by connecting the device. A column or ion exchange membrane packed with an ion exchange resin containing an ion exchange medium can be used as a preliminary salt converter.

  As the absorbance detector 8, a detector whose detection wavelength can be set in a range of 190 nm to 700 nm can be used.

  The absorbance detector 8 is provided with a data processor 9, and the absorbance data detected by the absorbance detector 8 is processed and output as a chromatogram.

  Hereinafter, examples will be described to describe the present invention in more detail, but the present invention is not limited to these examples. In the examples, analysis examples using salt conversion treatment are shown.

Example 1
According to the schematic diagram of FIG.

  As the eluent of 1, 2 mmol / L methanesulfonic acid was used and fed at a flow rate of 0.5 mL / min. DP-8020 type pump (manufactured by Tosoh Corporation) for the liquid feed pump 2, AS-8020 type autosampler (manufactured by Tosoh Corporation) for the autosampler 3, CO column for the column oven 4 A -8020C column oven (manufactured by Tosoh Corporation) was used.

  In addition, as measurement conditions for performing cation analysis, TSKgel SuperIC-Cation HSII (inner diameter 4.6 mm, length 5 cm) is used as the separation medium 5, and hydroxide ions are paired as the ion exchange medium 6. A strongly basic ion exchange resin (TSKgel Suppress IC-C, manufactured by Tosoh Co., Ltd.) as an ion packed in a column having an inner diameter of 4.6 mm and a length of 5 cm was used. In the salt converter of No. 7, a counter ion of a strongly basic ion exchange resin (TSKgel Suppress IC-C, manufactured by Tosoh Corporation) was used as an iodide ion and packed in a column having an inner diameter of 4.6 mm and a length of 1 cm. used.

  The UV-820 UV-Visible Absorbance Detector (manufactured by Tosoh Corporation) is used as the absorbance detector 8 and a dedicated workstation LC-8020model II is used as the data processor 9 for instrument control and chromatograms. Data collection and analysis were conducted.

  The measurement temperature was 25 ° C., and the detection wavelength was set to UV 230 nm for absorbance detection. FIG. 2 shows a chromatogram obtained by injecting 20 μL of a mixed solution of sodium chloride and potassium chloride as a sample (concentration is 10 mg / L for sodium ions and potassium ions, respectively) from an autosampler.

  Peaks derived from sodium ions and potassium ions are observed in the absorbance detector. Immediately after elution from the ion exchange medium, each ion is present as sodium hydroxide, potassium hydroxide, and sodium iodide, It shows that it was converted into potassium iodide and detected by an absorbance detector.

Example 2
Using the system shown in FIG. 1, a counter ion of a strongly basic ion exchange resin (TSKgel Suppress IC-C, manufactured by Tosoh Corporation) is used as a nitrate ion and packed in a column having an inner diameter of 4.6 mm and a length of 1 cm. The wavelength at the time of absorbance detection was set to UV 210 nm. Otherwise, cations were analyzed in the same manner as described in Example 1, and the resulting chromatogram is shown in FIG.

  As a result, as in Example 1, the peaks derived from sodium ions and potassium ions were observed with the absorbance detector, converted into sodium nitrate and potassium nitrate by the salt converter, and detected by the absorbance detector.

Comparative Example 1
Using the system of FIG. 1, the counter ion of a strongly basic ion exchange resin (TSKgel Suppress IC-C, manufactured by Tosoh Corporation) is a chloride ion whose absorbance cannot be detected, and an inner diameter of 4.6 mm and a length of 1 cm. What was packed in the column was used, and the wavelength at the time of absorbance detection was set to UV 210 nm. Otherwise, cations were analyzed in the same manner as described in Example 1, and the obtained chromatogram is shown in FIG.
For reference, a chromatogram obtained by connecting an electrical conductivity detector behind the absorbance detector is shown in FIG.

  As a result, although peaks derived from sodium ions and potassium ions were observed in the electrical conductivity detector in FIG. 5, no peaks were observed in the absorbance detector in FIG. That is, the peak was not detected in the absorbance detection because it was converted into sodium chloride and potassium chloride by the salt converter.

DESCRIPTION OF SYMBOLS 1 Eluent 2 Liquid feed pump 3 Autosampler 4 Column oven 5 Separation medium 6 Ion exchange medium 7 Salt converter 8 Absorbance detector 9 Data processor 10 Sodium-derived peak
11 Potassium-derived peak

Claims (4)

Method of converting an ion B of an ionic compound AB (wherein one of A and B represents a cation and the other an anion) into an ion D capable of detecting absorbance, separating the ion D by ion chromatography, and detecting the absorbance Because
(1) A step of exchanging AB with an ion exchange medium to obtain CB (wherein C represents an H ⁺ ion or an OH ⁻ ion),
(2) CD by the resulting CB salt exchanger in step (1) (wherein, D is a absorbance detectable ions, having the same charge as B) viewed including the step of converting into,
The eluent used for ion chromatography is any of sodium hydroxide, potassium hydroxide, ammonium hydroxide, lithium hydroxide, tetraalkylammonium hydroxide, hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, methanesulfonic acid, and p-toluenesulfonic acid. Or an eluent containing one or more electrolytes . The method according to claim 1, wherein the ion exchange medium and / or the salt exchanger is an ion exchange column or an ion exchange membrane. The method according to claim 1 or 2, wherein the concentration of the electrolyte is 0.01 mmol / L or more and 500 mmol / L or less. The method according to any one of claims 1 to 3, wherein the eluent contains a water-soluble organic solvent.

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