JP2017067661A - Ion conversion method and ion conversion device for ion compound - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide ion analysis devices based on an ion chromatography-mass detection method which are convenient and applicable to various kinds of ion analyses, and analysis methods employing the devices.SOLUTION: The method is characterized in that an ion compound AB (where one of A and B is a cation and the other is an anion) is converted with a salt converter 7 to obtain DB (where D is an ion which can be detected with a mass detector).SELECTED DRAWING: Figure 1

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 suppressor-type electric conductivity detection method.

  The analytical device consists of a chromatographic separation process using an eluent containing electrolyte and a separation medium, a suppression process for suppressing the electrical conductivity derived from the electrolyte in the eluent, and an electrical conductivity detector for separating and eluting ionic components. It is comprised by the detection process detected by.

  As a measure for the analysis of weakly acidic ions such as organic acids, the liquid eluted from the suppressor is introduced into the first electrical conductivity detector to detect strong acidic ions, and then alkali metal ions from the effluent containing weakly acidic ions. To a salt converter containing a cation exchange resin with a counter ion as a counter ion, converting the counter ion from a hydrogen ion to an alkali metal ion, and then introducing it into the second electrical conductivity detector. Methods for detecting sensitivity are disclosed (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 sodium bicarbonate is converted to carbonic acid, and the ionic compound AX to be measured is converted to HX. As a result, the conductivity of the eluent decreases, and the conductivity of the ionic compound HX generated after the conversion increases. Therefore, highly sensitive detection of ionic components is achieved by changes in both noise level and signal intensity. Is possible. However, since the dissociation state of ionic compound HX varies depending on the concentration based on its dissociation characteristics (pKa), it is known that the calibration curve bends depending on the ionic species and affects its quantitative accuracy. This tendency is particularly noticeable in weakly acidic and weakly basic ion components, and at the same time, there is a problem of causing a decrease in detection sensitivity (Non-patent Document 1).

  As a detection method other than the suppressor method-electric conductivity detection method, an absorptiometric detection method, an electrochemical detection method, a fluorescence detection method, and the like are also used. Since these detection methods are not easily influenced by the dissociation state due to the concentration change, the calibration curve has excellent linearity and high quantitative accuracy. However, this is a method for selectively detecting a specific ion species that matches the detection principle, and there has been a problem in general use.

  On the other hand, Mori et al. Discloses a method for detecting the absorbance of a target ion after a salt conversion treatment (Patent Documents 3 and 4). In this method, after ion components are separated by ion exclusion chromatography using water as an eluent, the effluent from the column is introduced into an ion exchange resin on which ions having UV absorption are immobilized, and the ions to be analyzed or their counter ions Is converted to a salt having UV absorption, followed by absorbance detection. This method has the advantage that the absorbance detection method can be widely applied to separable ionic compounds, 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.

  In recent years, as a highly sensitive detection method having a constant performance, a detection method using a mass spectrometer is also widely used in HPLC, but due to interference caused by detection noise caused by an eluent or a matrix in a sample, it is inorganic. In the detection of ions, there is a problem that it is not suitable for detection of low molecular weight ions such as sodium ions and chloride ions due to limitations on applicable molecular weights.

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 of the present invention is to convert an ionic component constituting an ionic compound and finally convert it into an ionic species that can be detected by a mass detector, and its An analyzer is provided.

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 ions,
An ionic compound AB (wherein one of A and B is a cation and the other is an anion) is converted by a salt converter to obtain DC (wherein D is an ion detectable by a mass detector). Ion conversion method.
[2]
In the method for converting ions according to [1],
A method in which an ionic compound AB is converted by an ion exchange medium to AC (wherein C represents H + ion or OH− ion), and then converted by a salt converter to obtain DC.
[3]
The method according to [1] or [2], wherein the ion exchange medium and / or the salt converter is an ion exchange column or an ion exchange membrane.
[4]
An apparatus for detecting ions with a detector,
A means for converting an ionic compound AB (wherein one of A and B is a cation and the other is an anion) to DC (wherein D is an ion detectable by a mass detector) and a mass detector An ion detector.
[5]
Means for converting the ionic compound AB to DC are:
[4] including an ion exchange medium that converts an ionic compound AB to AC (wherein C represents H + ion or OH− ion) and a salt converter that converts AC to DC. The device described.
[6]
The ion detection device according to [4] or [5], wherein the ion exchange medium and / or the salt converter 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, potassium nitrate, 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 the anion analysis, a strong base cation exchange column, a weak base anion exchange column, and in the cation analysis, a strong acid cation exchange column and a weak acid cation exchange column can be exemplified. . 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, and a separation column for hydrophilic interaction chromatography.

  Further, the primary conversion is defined in the present invention in order to distinguish a process of changing ions further 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.

  The salt converter used in the present invention is used when the ion D capable of mass detection is immobilized and the ionic compound AC is converted to DC. Here, the ion D capable of mass detection can be exemplified by an ion paired with the ion B such as tetrabutylammonium ion or pyridium ion, but is not limited thereto. Moreover, it can also be used when, for example, the ion A of the ionic compound AC is converted to another ion after the primary conversion, and the other ion is finally converted to an ion D capable of mass detection.

  The ion D converted from the ionic compound AB to DC by the method of the present invention is guided to the mass detector, and the ion D can be detected by setting m / z according to the molecular weight of the ion D. That is, the quantitative value of the ions A is indirectly calculated from the peak area or peak height of the ions D detected by the mass detector, 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, each ion component in the sample injected from the autosampler 3 is introduced into the separation medium 5 together with the eluent 1, and the respective ion components are separated by the ion chromatography principle.

  In the present invention, the eluent 1 passes an eluent containing an electrolyte through the separation medium 5, so that each ionic component to be analyzed introduced into the separation medium 5 is caused by a difference in interaction with the separation medium 5. Thus, a difference occurs in the moving speed in the separation medium 5. As a result, each of the ion components is separated by the separation medium 5 and flows out from the separation medium outlet in the order of the moving speed among the ion components. At that time, the effluent flowing out of the separation medium 5 includes the electrolyte derived from the eluent 1 and the ions A and B.

  Specifically, the separation medium used here is a strong base cation exchange column, a weak base anion exchange column in anion analysis, a strong acid cation exchange column, or a weak acid in cation analysis. A cation exchange column can be exemplified. 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, and a separation column for hydrophilic interaction chromatography.

  The ion exchange medium 6 is used in the step of primary conversion of the ionic compound AB to AC. At this time, the electrolyte derived from the eluent present in the liquid flowing out from the ion exchange medium 6 in the ion exchange medium 6 can be prevented from interfering with mass detection. Specifically, the dissociation degree of the eluent is extremely small, and the eluent is converted to water, which is the same substance as the eluent.

The meaning of the “electrolyte” in the “eluent containing 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 to convert the ions A into ion species capable of mass detection. In this salt converter 7, ion species capable of mass detection are fixed, and specifically, ions A are converted into ions D. That is, in the present invention, the salt converter can convert the ionic compound AC obtained by the primary conversion by the mass-detectable ion D and convert it into the mass-detectable DC. Moreover, as long as it is finally converted to ions capable of mass detection, the ions in the ionic compound may be converted by the salt converter any number of times, and there is no particular limitation. After being converted by the salt converter, the ionic species flowing out of the salt converter are guided to the mass detector 8 and detected by setting m / z suitable for the molecular weight of the ionic species. From the peak height or peak area of the detected ion species, a quantitative value is calculated for the ion species as ion A, and an analysis result of the concentration of the ion component can be obtained. In addition, a salt converter can also be used when converting ions B to ions C before converting ions A to ion species capable of mass spectrometry.

  In addition, the analyzer employing the present invention can be applied to a method for simultaneously analyzing a plurality of different analyte ions in a sample solution to be used. Specifically, as will be described later in the embodiment, for example, due to a difference in interaction with the separation medium 5 for each ion component in the sample, a difference in moving speed for each ion component in the sample in the separation medium 5 occurs. Cause. Next, for example, NO3 and Cl can be converted into ions D that can be detected by a salt converter while simultaneously performing primary conversion of NO3 and Cl while causing a difference in moving speed for each ion component in the sample. As a result, each ion component can be detected by the detector while the respective ion components are separated by the difference in moving speed.

  In the present invention, there is no limit to the number of primary conversions and / or salt converters used. For example, when NaCl is used as an ionic compound, it is converted to NaOH by primary conversion, and then converted into sodium chloride, potassium chloride, and potassium nitrate by adopting three types of salt converters, and the potassium ions are detected by a mass detector or the like. It can be detected by a detector by converting it into ion species detectable by the detector.

It was suggested that mass detection of each cation was possible by direct detection.
Specifically, it has become possible to detect low molecular weight ions such as sodium ions and potassium ions and to simultaneously analyze a plurality of different analyte ions in a sample solution.

  In the conventionally used suppressor method-ion chromatography method based on electric 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 are detected as the same ion species by the m / z, the detection sensitivity is improved, and an effect of obtaining a highly accurate quantitative analysis result can be expected.

  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.

3 is a schematic flow chart of an apparatus for carrying out the present invention. 1 is a diagram showing an MS chromatogram obtained in Example 1. FIG. 2 is a diagram showing an MS chromatogram obtained in Example 2. FIG. 2 is a diagram showing an MS chromatogram obtained in Comparative Example 1. FIG. 6 is a diagram showing an MS chromatogram obtained in Comparative Example 2. FIG.

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 component is separated by the principle of ion chromatography.

  The ion exchange medium 6 is used in order to prevent the ion component derived from the eluent from affecting the detection by the detector even if it passes through the salt converter. Therefore, this is not the case when an eluent that does not affect the detection of H2O or the like is used.

  Also, a column type packed with an ion exchange resin or a membrane type using an ion exchange membrane can be used. 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, the salt converter 7 for performing the salt conversion is an ion in which a difference in the moving speed of each ion component in the sample in the separation medium 5 can be detected by a detector such as a mass detector. It can be detected by a detector by converting it to a seed. Moreover, as a material used for the salt converter, it is possible to use a column or ion exchange membrane packed with an ion exchange resin. Specifically, if it is an ion exchange resin, the ion species that can be detected by the mass detector is a counter ion, and an iodide type anion exchange resin, a bromate ion type anion exchange resin, an iodate type Anion exchange resin, sulfonate ion type anion exchange resin having an aliphatic and / or aromatic functional group, metal-metal ligand complex ion type anion exchange resin, alkylammonium ion type cation exchange resin, pyridinium Examples thereof include ionic cation exchange resins, sulfonium ion cation exchange resins, metal-metal ligand complex ion cation exchange resins, and the like.

  As a method of use, when it is difficult to convert ion components flowing out from the ion exchange medium 6 into ion species capable of mass detection by direct ion exchange reaction in the salt converter, a preliminary salt is used before the salt converter. A converter can be connected and used. A column or ion exchange membrane filled with an ion exchange resin containing an ion exchange medium can be used as a preliminary salt converter, and a plurality of salt converters are used as long as they do not depart from the gist of the present invention. It is also possible.

  It is also possible to employ a salt converter that combines the function of the ion exchange medium 6 that converts ion components in the eluent and the function of converting ion components into ion species that can be detected by a detector such as a mass detector. Is possible.

  As the mass detector 8, one that can set m / z in the range of 50 to 1000 can be used.

  The mass detector 8 is provided with a data processor 9, and the data of the intensity of each m / z detected by the mass 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
Cation analysis was performed with the system of FIG. As the eluent of 1, 2 mmol / L methanesulfonic acid was used and fed at a flow rate of 0.2 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.
TSKgel SuperIC-Cation HSII (inner diameter: 4.6 mm, length: 5 cm) is used as the separation column of No. 5, and a strongly basic ion exchange resin (TSKgel Suppress IC with a hydroxide ion as a counter ion is used as the ion exchange medium of No. 6). -C, manufactured by Tosoh Corporation) was packed in a column having an inner diameter of 4.6 mm and a length of 5 cm. In the salt converter of No. 7, the counter ion of a strongly basic exchange resin (TSKgel Suppress IC-C, manufactured by Tosoh Corporation) having hydroxide ions as counter ions is 1-ethylpyridinium ion, and the inner diameter is 4.6 mm. What was packed in a 1 cm long column was used.

  High-speed liquid chromatograph mass spectrometer LCMS-8030 (manufactured by Shimadzu Corporation) is used for the mass detector 8 and dedicated workstation LabSolution LCMS is used as the data processor 9 for instrument control and chromatograms. Data collection and analysis were conducted.

  The measurement temperature is 25 ° C., and mass detection is performed in an ESI positive mode with an interface voltage of −4.5 kV, a DL temperature of 250 ° C., and a heat block temperature of 400 ° C. , Product ion m / z was set to 108.15, and detection was performed in MRM mode.

  FIG. 2 shows an MS chromatogram obtained by injecting 20 μL of a mixed solution of sodium chloride and potassium chloride as a sample (concentrations are 10 mg / L for sodium ions and potassium ions, respectively) from an autosampler.

Peaks derived from sodium ions and potassium ions were observed in the mass detector. Immediately after elution from the ion exchange medium, each ion is present as sodium hydroxide and potassium hydroxide, and each ion is converted into 1-ethylpyridinium hydroxide by a salt converter. -Indicates that ethylpyridinium ions were detected in the mass detector.
Example 2
Using the system shown in FIG. 1, an ion exchange resin (TSKgel Suppress IC-A, manufactured by Tosoh Corp.) using tetrabutylammonium ions as a counter ion as a salt converter is packed in a column having an inner diameter of 4.6 mm and a length of 1 cm. Column was used.

In mass detection, ionization is performed at a positive interface mode of ESI at an interface voltage of −4.5 kV, a DL temperature of 250 ° C., and a heat block temperature of 400 ° C., a precursor ion m / z is 242.45, and a product ion m / z. Was set to 242.45, and detection was performed in the MRM mode.
Other than that, anion analysis was carried out under the same conditions as described in Example 1, and the obtained MS chromatogram is shown in FIG.

  Even when only one salt transducer is used, as in Example 3, it is shown that tetrabutylammonium ions derived from each separated anion were detected by the mass detector.

Comparative Example 1
Mass detection was performed using the system of FIG. 1 without using a salt transducer.
For mass detection, ionization was performed at 4.5 kV interface voltage, DL temperature of 250 ° C., heat block temperature of 400 ° C. in positive mode of ESI, and the precursor ion m / z was 23.00 for direct detection of sodium ions. Set m / z of product ion to 23.00, set m / z of precursor ion to 39.10, and m / z of product ion to 39.10 for direct detection of potassium ion, in MRM mode Detection was performed. As a sample, 20 μL of a mixed solution of sodium chloride and potassium chloride (concentrations were 10 mg / L for sodium ions and potassium ions, respectively) was injected from an autosampler.
Otherwise, cations were analyzed in the same manner as described in Example 1, and the resulting MS chromatograms are shown in FIGS.
As a result, in FIG. 4, the peak of the sodium ion itself was directly detected by mass detection without converting the sodium ion into other ion components. Compared to Example 1, the noise was large and the chromatogram was low in detection sensitivity.
Moreover, in FIG. 5, the peak of potassium itself was detected by mass detection, without converting potassium ion into another ion component. Since sodium ions have a smaller mass number than potassium ions and the like, when detected directly with a mass detector, the detection sensitivity was lower than the result of Example 1. That is, when detecting ions having a small mass number such as sodium ions, it is shown that sufficient sensitivity can be obtained in mass spectrometry by converting to other ion species having a larger mass number.

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 Mass detector 9 Data processor 10 Peak derived from sodium ion 11 Peak derived from potassium ion

Claims (6)

A method for converting ions,
An ionic compound AB (wherein one of A and B is a cation and the other is an anion) is converted by a salt converter to obtain DC (wherein D is an ion detectable by a mass detector). Ion conversion method. The method of converting ions according to claim 1,
A method in which an ionic compound AB is converted by an ion exchange medium to AC (wherein C represents H + ion or OH− ion), and then converted by a salt converter to obtain DC. The method according to claim 1 or 2, wherein the ion exchange medium and / or the salt converter is an ion exchange column or an ion exchange membrane. An apparatus for detecting ions with a detector,
A means for converting an ionic compound AB (wherein one of A and B is a cation and the other is an anion) to DC (wherein D is an ion detectable by a mass detector) and a mass detector An ion detector. Means for converting the ionic compound AB to DC are:
5. An ion exchange medium for converting ionic compound AB to AC (wherein C represents H + ion or OH− ion) and a salt converter for converting AC to DC. The device described. 6. The ion detection apparatus according to claim 4, wherein the ion exchange medium and / or the salt converter is an ion exchange column or an ion exchange membrane.

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