JP6512630B2 - Method and apparatus for concentration and analysis of selenium and / or arsenic - Google Patents

Description

  The present invention relates to a method of concentrating selenium (Se) and / or arsenic (As) in a solution for analysis and the like, and a method of concentrating selenium and / or arsenic by this method for highly sensitive analysis. , And apparatus for these methods.

  Selenium is handled as a raw material, a by-product, or a substance to be excluded in various manufacturing processes such as semiconductor devices and glass products, a flue gas desulfurization process in a thermal power plant, an oil refining process and the like. At present, precipitation, ion exchange membrane method, activated carbon adsorption method, etc. are known as methods for removing selenium and selenium compounds from waste water, and quantifying selenium according to the number of valences appropriately makes selenium in waste water It is necessary to process. The valence referred to here is a number indicating the oxidation state of the atom, and in the case of a selenium compound which can be present in an aqueous solution, generally + tetravalent selenium [Se (IV); eg selenite compound] and + 6-valent selenium [Se (VI); such as selenate compounds] is known. Since selenium is an element that may cause health hazards in humans, it is required to quantify trace amounts of selenium contained in drinking water, river water, sea water, groundwater, etc. according to the valence in addition to drainage as described above. It is done.

As a method of quantifying selenium according to its valence number, Patent Document 1 discloses selenite ion (SeO ₃ ^2- ) and selenate ion in a sample by ion exchange chromatography packed with strongly acidic anion exchange resin. (SeO ₄ ^2- ) were separated, sulfuric acid was added, and inductively coupled plasma mass spectrometry (ICP-MS) apparatus was used for each retention time in ion exchange chromatography, that is, the valence of selenium. For each number, a method of counting selenium atoms is shown. In the one described in Patent Document 1, for example, a 0.0001 to 0.003 mol / L aqueous solution of 1,3,5-benzenetricarboxylic acid adjusted to pH 6.6 is used as an eluent in ion exchange chromatography It is done.

  Arsenic is also handled as a raw material, a by-product, or a substance to be excluded in various manufacturing processes, a flue gas desulfurization process, an oil refining process, and the like. Among the arsenic compounds which may be present in the aqueous solution, generally + trivalent selenium [As (III); eg arsenous acid compound] and + pentavalent arsenic [As (V); eg arsenate compound] are known . Arsenic, in particular, exhibits high toxicity as is well known, and when comparing + trivalent arsenic (As (III) with + 5valent arsenic (As (V)), + trivalent is more preferable Therefore, it is required to be able to quantify arsenic by valence with high detection sensitivity, and since selenium and arsenic often coexist in waste water and environmental samples, valence of selenium and arsenic is simultaneously determined. It is useful to be able to measure with high sensitivity depending on the number.

  As a method of quantifying arsenic according to valence, Patent Document 2 transfers a solution containing As (III) and As (V) to an eluent containing a quaternary salt having an alkyl group of 3 or more carbon atoms. The phase is passed through a reverse phase column, arsenic is separated by valence in the reverse phase column, and the outlet liquid from the reverse phase column is transferred to an inductively coupled plasma emission spectroscopy (ICP-OES) instrument. A method to derive and quantify is shown.

Unexamined-Japanese-Patent No. 11-2623 gazette JP, 2013-181776, A

  The method described in Patent Document 1 separates Se (IV) and Se (VI) by ion exchange, so application to samples with high salt concentration such as seawater and drainage is difficult, and detection sensitivity is also sufficient. It can not be said that It is also conceivable to concentrate the selenium compound in the sample solution to improve the detection sensitivity, but in a general concentration method, since the anion stationary phase exchange group is to be of a cationic type, it is possible to use sample water When the salt concentration is high, anions such as chloride ions in the sample water are bound to the stationary phase, and the concentration ability of the selenium compound is reduced. In addition, in the ion exchange type concentration, in order to elute the selenium compound from the ion exchange column etc. after concentration, an organic carbon eluent as used in the above-mentioned Patent Document 1 or a high concentration salt solution such as phosphoric acid is used as an eluent. is necessary. For this reason, the eluate obtained by concentrating the selenium compound also contains these eluent components, and when the eluate is introduced into the liquid chromatograph or ICP-MS in the latter stage, separation by chromatography and It is feared that the ICP-MS detection is adversely affected, and that these devices are also adversely affected.

  Similarly, the method described in Patent Document 2 also has room for improvement in detection sensitivity. Since selenium and arsenic often coexist, simultaneous analysis of these is also effective, but no sample preparation method or analysis method for performing simultaneous analysis with high sensitivity is known.

  An object of the present invention is to provide a concentration method and apparatus capable of enhancing the concentration of selenium compounds and arsenic compounds in a sample solution containing selenium and / or arsenic to facilitate processing of the sample solution.

  Another object of the present invention is to provide a method and apparatus capable of sensitively analyzing these substances by valence by concentrating selenium and / or arsenic by the concentration method of the present invention.

  The concentration method of the present invention is a method of concentrating in a sample solution containing at least one of a selenium compound and an arsenic compound as a target substance, and the sample solution is concentrated on an ion exclusion column having an anion exchange group. The target substance in the sample solution is concentrated by passing it through a concentration column, and the eluent, which is an aqueous solution containing nitric acid and a sulfate, is passed through the concentration column to obtain a liquid in which the target substance is concentrated. And have stages.

  The analysis method of the present invention is a method of analyzing the target substance in a sample solution containing at least one of a selenium compound and an arsenic compound as a target substance according to the valence, and the target substance obtained by the concentration method of the present invention is concentrated The separated solution is injected into a separation column composed of an ion exclusion column having an anionic exchange group, and the target substance in the sample solution is separated according to the valence while flowing the eluent through the separation column; Introducing the outflowing liquid into the inductively coupled plasma mass spectrometer to quantify the target substance.

  The concentration apparatus of the present invention is an apparatus for concentrating a target substance in a sample solution containing at least one of a selenium compound and an arsenic compound as a target substance, and the concentration column comprising an ion exclusion column having an anionic exchange group Switchable between the sample introduction step and the sample discharge step, wherein the sample solution is introduced into the concentration column in the sample introduction step to concentrate the target substance in the sample solution in the concentration column; And an injector for passing the eluent through a concentration column and causing the liquid in which the target substance is concentrated to flow out of the concentration column.

  The analyzer according to the present invention is an apparatus for quantifying a target substance in a sample solution according to the valence by using at least one of a selenium compound and an arsenic compound as a target substance, a pump for feeding an eluent, an anionic exchange group A concentration column composed of an ion exclusion column having an ion exchange column, a separation column composed of an ion exclusion column having an anionic exchange group, and switching between two modes, a load mode and an inject mode, In the load mode, the eluent from the pump is sent to the separation column and the sample solution is introduced into the concentration column to concentrate the target substance in the sample solution in the concentration column, and in the inject mode, the eluent from the pump is concentrated , And an inductively coupled plasma mass spectrometer connected to the outlet of the separation column. In coupled plasma mass spectrometer for counting the corresponding atomic ions to the target material.

  As will be apparent from the examples described below, according to the present invention, it is possible to concentrate a trace amount of selenium compound and / or arsenic compound contained in a sample solution. This makes it possible, for example, to quantify the valence of trace amounts of selenium compounds and arsenic compounds in the sample solution.

It is a figure explaining the principle of ion exclusion chromatography. BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows an example of a structure of the apparatus for enforcing the determination method according to the valence of selenium of one Embodiment of this invention. It is a figure explaining operation of an injector, and (a) shows injection mode and (b) shows load mode. It is a figure which shows the structure of the apparatus used by each reference example. (A), (b) is a graph which shows the result of the reference example 1. FIG. (A), (b) is a graph which shows the result of the reference example 2. FIG. (A), (b) is a graph which shows the result of the reference example 3. FIG. 7 is a graph showing the results of Reference Example 4; 15 is a graph showing the results of Reference Example 5; (A), (b) is a graph which shows the result of the reference example 6. FIG. (A), (b) is a graph which shows the result of Example 1. FIG.

  Next, an embodiment of the present invention will be described with reference to the drawings.

  The selenium and / or arsenic concentration method and analysis method according to the present invention utilize ion exclusion chromatography using an ion exclusion column as a concentration column or separation column. Therefore, first, the principle of ion exclusion chromatography will be described. FIG. 1 illustrates the principle of ion exclusion chromatography.

  When, for example, a strongly acidic cation exchange resin of H-type is used as the stationary phase 11 in liquid chromatography, a large number of pores 12 are formed on the surface of the stationary phase 11 and the outermost surface of the stationary phase 11 Is modified with a strongly acidic anionic group 13 such as, for example, a sulfo group. Here, it is assumed that a neutral chemical species 21, a weakly acidic chemical species 22 and a strongly acidic chemical species 23 flow together with a liquid which is a mobile phase. Then, due to the negative charge possessed by the strongly acidic anionic group 13, the more negatively charged chemical species (chemical species having a smaller pKa) in the mobile phase are subjected to greater static elimination and are eluted more quickly. Further, the penetration into the pore 12 is determined by the magnitude of the negative charge, and the penetration into the pore 12 is increased as the negative charge amount is smaller, that is, as pKa is larger. As a result of these, the elution time of the neutral species 21 becomes longer, and the elution time becomes shorter as the chemical species of smaller pKa. In ion exclusion chromatography, in general, the contribution of chemisorption from the mobile phase to the stationary phase by ion exchange is negligible. After all, in ion exclusion chromatography using a strongly acidic cation exchange resin, it is generally considered that anions with smaller pKa (negative ions) elute earlier.

  The acid dissociation index (pKa) of selenium, which is a representative compound of selenium, is as follows.

HSeO ₄ ^- ⇔ H ⁺ + SeO ₄ ^2- pKa ₂ = 1.66
H ₂ SeO ₃ ⇔ H ⁺ + HSeO ₃ ^- pKa ₁ = 2.75
HSeO ₃ ^- ⇔ H ⁺ + SeO ₃ ^2- pKa ₂ = 8.50
The acid dissociation index (pKa) of arsenic and arsenous acids, which are representative compounds of arsenic, is as follows.

H ₃ AsO ₄ ⇔ H ⁺ + H ₂ AsO ₄ ^- pKa ₁ = 2.3
H ₂ AsO ₃ ^- ⇔ H ⁺ + HAsO ₄ ^2- pKa ₂ = 6.8
HAsO ₄ ^2- ⇔ H ⁺ + AsO ₄ ^3- pKa ₂ = 11.6
H ₃ AsO ₃ ⇔ H ⁺ + H ₂ AsO ₃ ^- pKa = 9.28
Considering that selenate, selenite, arsenate and arsenous acid have the above-mentioned acid dissociation index, chloride ion, sulfate ion, nitrate ion, etc. which are considered to be often present in the sample solution The strong acid anion is considered to elute faster than selenic acid, selenious acid, arsenic acid and arsenous acid when the sample solution is passed through the ion exclusion column. Therefore, by setting the flow conditions when passing the sample solution from one end of the ion exclusion column, the strongly acidic anion flows out from the other end of the ion exclusion column, but selenate, selenite, arsenate And arsenic trioxide can be left in the ion exclusion column. On the other hand, cations (cations) such as alkali metal ions in the sample solution are ion-exchanged and adsorbed on the stationary phase in the ion exclusion column. The adsorbed cations do not desorb from the ion exclusion column unless they pass through the acid at an extremely low pH. On the other hand, selenic acid, selenious acid, arsenic acid and arsenic acid remaining in the ion exclusion column can be made to flow out of the ion exclusion column by flowing a weak acidic liquid as an eluent. As a result, it is possible to concentrate the selenium compound and / or the arsenic compound by the ion removal column, excluding the influence of the strongly acidic anion and various cations. At this time, the ion exclusion column will function as a concentration column for selenium compounds and / or arsenic compounds.

  In particular, in the method according to the present invention, dilute nitric acid plus low concentration sulfate is used as a weakly acidic eluent for eluting concentrated selenium compounds and / or arsenic compounds from the concentration column which is an ion exclusion column. use. As a result, the eluate from the concentration column contains only dilute nitric acid and a low concentration sulfate in addition to the concentrated target substance which is at least one of a selenium compound and an arsenic compound, so Even if introduced into a chromatograph apparatus or ICP-MS apparatus, adverse effects on these apparatuses are unlikely to occur. That is, it can be said that the concentration method according to the present invention is a method suitable for use in combination with high sensitivity determination by an ICP-MS device.

  FIG. 2 shows an example of the configuration of an apparatus for performing quantitative analysis according to the valence of selenium as an application example of the concentration method of the present invention. The eluent stored in the eluent tank 31 is pressure-fed by the pump 32 and supplied to the injector 33. As the injector 33, a six-way valve type commonly used for injection of a sample in high performance liquid chromatography is used. The selenium compound is supplied to the injector 33 from the sample bottle 34 via the sample pump 39. Further, both ends of the concentration column 40 configured of an ion exclusion column are connected to the injector 33, and at the outlet of the injector 33, a guard column 36 and a separation column 37 which are both ion exclusion columns are connected in series in this order. Connected As described later, the guard column 36 may not be provided, but when the guard column 36 is configured by the ion exclusion column, the guard column 36 also bears part of the function as a separation column.

  The injector 33 has two modes (operating states) of a load mode and an inject mode, and can switch between the load mode and the inject mode at high speed. In the load mode, the injector 33 sends the eluent from the pump 32 directly to the guard column 36 and the separation column 37, and introduces the sample solution to the concentration column 40. At this time, only the sample solution is allowed to flow through the concentration column 40. Thereby, the selenium compound in the sample solution is concentrated in the concentration column 40. On the other hand, in the injection mode, the injector 33 first passes the eluent from the pump 32 through the concentration column 40, and sends the liquid returned from the concentration column 40 through the guard column 36 to the separation column 37. As a result, the selenium compound concentrated in the concentration column 40 is injected into the separation column 37.

  FIG. 3 is a view for explaining the operation of such an injector 33, in which (a) shows an inject mode and (b) shows a load mode. The injector 33 has six ports as shown by 1 to 6 in the drawings, and in the injection mode, the ports are connected as in 1⇔2, 3⇔4, 5⇔6, and 2 in the load mode. The ports are connected as in the case of 3, 4 5 and 6 1. Then, both ends of the concentration column 40 are connected to port 1 and port 4, respectively, port 2 is connected to the separation column 37 through the guard column 36, port 3 is supplied with the eluent from the pump 32, and port 5 is discharged. It is used for (drain), and port 6 is adapted to be supplied with a sample solution. Thus, by connecting the piping to the injector 33, the selenium compound in the sample solution is concentrated in the concentration column 40 in the load mode, and the selenium compound concentrated in the inject mode is separated through the guard column 36. It will be injected into the column 37. In the load mode and the inject mode, the flow of the liquid (sample liquid and eluent) in the concentration column 40 is reversed.

  The above-described inject mode is also a step of passing the eluent through the eluent to the concentration column and causing the selenium compound and / or the arsenic compound to flow out of the concentration column 40. Therefore, the selenium compound and / or the selenium compound in the concentration column 40 From the point of view of concentration of the arsenic compound, the injection mode can be said to be the sample discharge stage in the injector 33. On the other hand, the load mode is a step of introducing the sample solution into the concentration column 40 and concentrating the selenium compound and / or the arsenic compound in the sample solution in the concentration column 40. It can be said.

  The outlet of separation column 37 is connected to the sample inlet of inductively coupled plasma mass spectrometry (ICP-MS) apparatus 38. Here, the ICP-MS device 38 is used as a detector of elemental selenium in ion exclusion chromatography using the separation column 37 which is an ion exclusion column.

When performing determination according to the number of valences of selenium using such an apparatus, an aqueous solution containing nitric acid and sulfate is used as an eluent, and the injector 33 is placed in the load mode via the pump 32 and the injector 33. The sample solution is introduced into the concentration column 40 via the injector 33 while passing the eluent continuously through the guard column 36 and the separation column 37. Next, the injector 33 is switched to the inject mode so that the liquid in the concentration column 40 is injected into the guard column 36 while maintaining the flow of the eluent through the guard column 36 and the separation column 37. . As a result, the sample liquid introduced into the concentration column 40 and having the selenium compound and / or the arsenic compound concentrated is injected into the guard column 36 and subsequently into the separation column 37. At this time, selenous acid precedes selenious acid to flow out from the outlet of the separation column 37 according to the principle of ion exclusion chromatography described above, and the selenium compounds in the sample liquid are separated according to the valence. It will be. Then, the liquid from the outlet of the separation column 37 is introduced to the ICP-MS device 38, and atomic ions of selenium (for example, ⁷⁸ Se ⁺ ) are detected and counted in the mass analysis unit of the ICP-MS device. The count value in the ICP-MS device is totaled according to the elapsed time from the time when the sample solution is injected in the injector 33 (the time when the load mode is switched to the inject mode), and a chromatogram is obtained The quantitative determination of selenium by the valence number of

  In the loading mode, concentration of selenium compounds is performed in the concentration column 40. However, when, for example, H-type strongly acidic cation exchange resin is used as the stationary phase of the concentration column 40, cations such as alkali metal ions contained in the sample solution It will be ion-exchanged and will remain in the concentration column 40. Such a cation will remain in the concentration column 40 without detachment in the eluent as used in this embodiment. Further, as described above, strong acid anions such as chloride ion and sulfate ion are discharged from the concentrating column 40 through the port 5 of the injector 33 to the outside because the elution rate is faster than the selenium compound and the arsenic compound. , Does not remain in the concentration column 40. Therefore, according to the method of the present embodiment, the determination according to the valence number of selenium can be performed without the influence of interfering components such as the alkali metal ion and the strongly acidic anion, etc. on the separation column 37 and the ICP-MS device 38. It becomes possible to analyze the sample solution with high salt concentration with high accuracy. On the other hand, since it is not preferable that alkali metal ions and the like stay in the concentration column 40, the injector 33 is loaded again after the selenium compound switched to the injection mode is injected into the separation column 37. It is preferable to elute the substance remaining in the concentration column 40 by flowing a washing solution, for example, a concentrated acid, into the concentration column 40 instead of the sample solution. The cleaning liquid is drained from the port 5 in the example shown in FIG.

As an example of the ion exclusion column used as the separation column 37 and the concentration column 40 used in the present invention,
(1) Shim-pack (registered trademark) SCR series (for example, SCR-102H: length 300 mm, inner diameter 8 mm, particle diameter 7 μm, stationary phase is sulfo group) manufactured by Shimadzu Corporation,
(2) SH1011 and SH1821 manufactured by Shodex (for example, SUGAR SH1011: size 8 mm × 300 mm, particle size 6 μm, functional group sulfo group),
(3) KC-811 (for example, RSpak KC-811: size 8 mm × 300 mm, particle size 6 μm, functional sulfo group) manufactured by Shodex Corporation,
(4) TSKgel (registered trademark) OApak-A and OApak-P (for example, TSKgel (registered trademark) OApak-A: particle diameter 5 μm, functional group carboxymethyl group, base polymer (methacrylate type)) manufactured by Tosoh Corporation,
(5) TSKgel (registered trademark) SCX (particle diameter 5 μm, functional sulfo group, base polymer (styrene type)) manufactured by Tosoh Corporation,
(6) ICSep series manufactured by Transgenomic (eg, ICSep ION-300: pressure resistance 7 MPa, particle diameter 7 μm, functional sulfo group, counter ion H ⁺ , crosslinking rate 6%),
(7) Thermo Fisher Dionex IonPac ion exclusion column series (for example, Dionex IonPac ICE-AS 1: size 9 × 250 mm, or Dionex IonPac ICE-AS 6: size 9 × 250 mm, functional sulfo group and carboxy group)
Etc. In particular, it is preferable to use one having a strongly acidic cation exchange resin as a stationary phase, and the strongly acidic cation exchange resin is preferably in the hydrogen (H) form in ionic form. Although the guard column 36 is provided in the front stage of the separation column 37 in the one shown in FIG. 2, it is not always necessary to provide the guard column. When each of the ion exclusion column products exemplified above is used as the separation column 37, a guard column that is compatible with the ion exclusion column product is often designated, and thus the designated column is designated as the guard column 36. It may be used as In general, the guard column 36 and the separation column 37 are packed with the same kind of stationary phase.

  As the concentration column 40, the same ion exclusion column as the separation column 37 can be used. However, the concentration column 40 is not intended to separate selenium compounds according to their valence number, and for example, to concentrate selenium compounds by removing the influence of interfering ions such as cations present in a sample solution. Therefore, the column length can be shorter than that of the separation column 37. Therefore, as the concentration column 40, as long as it is an ion exclusion column, a column of the same type as the separation column 36 described above can be used.

  Next, the eluent used in the present invention will be described. In the present invention, an aqueous solution containing nitric acid and sulfate is used as an eluent. The pH of the eluent is preferably 1 or more and 5 or less. When the pH exceeds 5, separation of Se (IV) and Se (VI) in the separation column which is an ion exclusion column tends to be deteriorated. If the pH is less than 1, the strong acidity may adversely affect the separation column, the ICP-MS apparatus, and the pump for feeding the eluent. As the sulfate contained in the eluent, for example, it is preferable to use one or more compounds selected from the group consisting of sulfates of alkali metals, sulfates of alkaline earth metals, and ammonium sulfate. The term "alkali metal" as used herein refers to each element of Li, Na, K, Rb and Cs, and the term "alkaline earth metal" refers to each element of Be, Mg, Ca, Sr and Ba. Specifically, for example, sodium sulfate, calcium sulfate, ammonium sulfate and the like can be used as the sulfate. The concentration of sulfate in the eluent is preferably 0.002 mmol / L or more and 100 mmol / L or less. However, even if the concentration of sulfate is increased to a certain value or higher, the improvement of the separation performance of selenium reaches a plateau, and rather, each peak by valence in the chromatogram tends to expand and the measurement sensitivity also tends to decrease. It is more preferable to set the concentration of the sulfate in a low concentration region of, for example, 1 mmol / L or less, since the occurrence of clogging at the introduction part of the ICP-MS also occurs.

Furthermore, according to the method as described herein, arsenic (As) can be quantified according to valence simultaneously with selenium. In the case of simultaneously quantifying selenium and arsenic in a sample solution according to the number of valences for a sample solution containing selenium and arsenic, use the same guard column 36, separation column 37 and eluent as above, The solution is introduced into the guard column 36, the solution from the outlet of the separation column 37 is guided to the ICP-MS apparatus 38, and atomic ions of selenium (eg, ⁷⁸ Se ⁺ ) and arsenic atomic ions in the mass analysis unit of the ICP-MS apparatus. Detect and count (generally ⁷⁵ As ⁺ ). Then, according to the elapsed time from when the sample solution is introduced in the injector 33, the count value in the ICP-MS device is divided into selenium and arsenic and counted, and a chromatogram is obtained to obtain selenium and arsenic in the sample solution. The quantification by each valence of each of

  Next, the present invention will be described in more detail by way of examples and reference examples.

  First, experimental results were conducted on the ability to quantify selenium in a sample solution according to valence by combining an ion exclusion column, a separation column, with ICP-MS and using an aqueous solution containing nitric acid and sulfate as an eluent. It will be described as a reference example. FIG. 4 shows the configuration of the apparatus used in the reference example. Compared with the apparatus shown in FIG. 2, this apparatus is not provided with the sample bottle 34 and the sample pump 39, and the sample liquid is supplied to the injector by a microsyringe etc., and instead of the concentration column 40. The difference is that a sample loop 35 is provided. The sample loop 35 is for collecting a predetermined amount of sample solution and injecting it into the guard column 36 and the separation column 37.

  In the determination according to the number of valences of selenium using the apparatus shown in FIG. 4, an aqueous solution containing nitric acid and a sulfate is used as an eluent, and first, the injector 33 is set to the load mode, and the pump 32 and the injector 33 are used. The sample solution was introduced into the sample loop 35 via the injector 33 while passing the eluent continuously through the guard column 36 and the separation column 37. Next, the injector 33 is switched to the inject mode so that the eluent passes through the sample loop 35, thereby maintaining the flow of the eluent through the guard column 36 and the separation column 37 in the sample loop 35. The sample solution was injected into the guard column 36. As a result, the sample solution collected in a fixed amount in the sample loop 35 is injected into the guard column 36 and subsequently into the separation column 37. Then, the liquid from the outlet of the separation column 37 was introduced to the ICP-MS apparatus 38, and a chromatogram was obtained as described later, and quantification was performed. In each reference example, 50 μL of sample loop 35 was used, and the volume of the sample solution injected in one operation was 50 μL.

  Hereinafter, conditions common to each example and each reference example will be described below.

In each example and each reference example, a sample solution containing Se (IV), Se (VI), As (III) and As (V) is used. These sample solutions are selenous acid (H ₂ SeO ₃ ) manufactured by Kanto Chemical Co., Ltd. as Se (IV), and selenic acid (H ₂ SeO ₄ ) manufactured by Kanto Chemical Co., Ltd. as Se (VI), As (III) Arsenic standard solution manufactured by Kanto Chemical Co., Ltd. and SPEC-As 5 manufactured by SPEX Co., Ltd. as As (V) were mixed to obtain a predetermined concentration and diluted with ultrapure water. As nitric acid used as one component of the eluent, one having a specific gravity of 1.42 (high purity reagent Ultrapur-100 manufactured by Kanto Chemical Co., Ltd.) was used. The eluent was prepared by diluting nitric acid and added sulfate with ultrapure water.

  As the separation column 37, SCR-102H manufactured by Shimadzu Corporation was used. This is a column having an inner diameter of 8 mm and a length of 30 cm packed with a H-type strongly acidic cation exchange resin based on a hard styrene-divinylbenzene copolymer as a functional group as a sulfo group. As guard column 36, SCR 102H (inner diameter 6 mm, length 5 cm) manufactured by Shimadzu Corporation having the same stationary phase as separation column 37 was used.

As an ICP-MS apparatus, 7500 ce manufactured by Agilent Technologies is used, which has a high frequency output of 1550 W, a carrier gas flow rate of 0.75 L / min, a make-up gas flow rate of 0.3 L / min, and a hydrogen (H ₂ ) gas flow rate of 3 mL / min It operated on condition. By using ⁷⁸ Se ⁺ ions for detection of selenium and ⁷⁵ As ⁺ ions for detection of arsenic, it is possible to simultaneously detect selenium and arsenic by repeatedly switching the detection ions in the mass spectrometer at high speed. did.

  The flow rate of the eluent by the pump 32 was 1.5 mL / min.

[Reference Example 1]
Sample solution containing 50 μg / L of Se (IV) and 50 μg / L Se (VI) in terms of selenium atoms, containing 50 μg / L As (III) and 50 μg / L As (V) in terms of arsenic atoms Using sodium sulfate (Na ₂ SO ₄ ) as the sulfate salt contained in the eluent, varying the sodium sulfate concentration in the eluent, and chromatographing selenium and arsenic for each of the varied sodium sulfate concentrations. I got a gram. The nitric acid concentration in the eluent was constant at 10 mmol / L. The results are shown in FIG. Even when the sodium sulfate concentration in the eluent was changed within the range shown in FIG. 5, the pH of the eluent was constant at 2.1.

  As shown in FIG. 5 (a), with respect to selenium, when sodium sulfate was not added to the eluent at all, almost no selenium peak was observed. With the eluent containing 0.0035 mmol / L or more of sodium sulfate, Se (IV) and Se (VI) could be separated and quantified separately. The higher the sodium sulfate concentration, the larger the Se (IV) and Se (VI), and the sharper the peaks. From these, it was found that it is effective to add a sulfate to the eluent mainly composed of dilute nitric acid in the determination according to the valence of selenium.

  On the other hand, as shown in FIG. 5 (b), with regard to arsenic, As (III) and As (V) were well separated regardless of the amount of sodium sulfate. The addition of sodium sulfate gave better results in terms of peak sharpness. With regard to arsenic, it is considered better to add the addition of sulfate for separation by valence.

[Reference Example 2]
A sample solution of the same composition as in Reference Example 1 is used, sodium sulfate is used as a sulfate salt contained in the eluent, the sodium sulfate concentration in the eluent is fixed at 0.7 mmol / L, and the nitric acid concentration is changed. The pH of the eluent was changed thereby to obtain chromatograms for selenium and arsenic for each pH. The results are shown in FIG.

As shown in FIG. 6 (a), with regard to selenium, the peak of Se (VI) and the peak of Se (IV) were largely separated on the chromatogram as the pH was closer to 2. This is because the selenite pKa ₂ is 1.66 while the selenite pKa ₁ is 2.75, and this difference in pKa greatly contributes to the difference in the ion exclusion effect. It is believed that there is. From this result, it was found that the pH of the eluent is preferably 5 or less.

  As shown in FIG. 6 (b), with regard to arsenic, the peak of As (III) and the peak of As (V) were largely separated on the chromatogram without depending largely on pH.

[Reference Example 3]
A sample solution having the same composition as in Reference Example 1 was used to examine how the chromatographs of selenium and arsenic differ when different types of sulfate were added to the eluent. As sulfates, sodium sulfate, ammonium sulfate ((NH ₄ ) ₂ SO ₄ ) and calcium sulfate (CaSO ₄ ) were used. Further, as a comparative example, the case where sodium chloride (NaCl) was added to the eluent instead of the sulfate was also examined. The nitric acid concentration in the eluent was kept constant at 10 mmol / L, and the concentration of sulfate was standardized at 0.5 mmol / L in terms of sulfate ion (SO ₄ ^2- ). When sodium chloride was added, the concentration was 0.5 mmol / L. The results are shown in FIG.

  As can be seen from FIG. 7 (a), with regard to selenium, Se (IV) and Se (VI (VI) can be used regardless of the type of sulfate, provided that the volume molar concentration of sulfate in the eluent as sulfate ion is the same. Can be separated and quantified well. On the other hand, when sodium chloride was used, the selenium peak itself could not be recognized. This indicates that it is preferable to add sulfate regardless of the type for determination of selenium by valence number. Further, the absence of a selenium peak when sodium chloride is used means that the selenium compound in the concentration column 40 can not be made to flow out using the same eluent, and the concentration method of the present invention In addition, it is indicated that it is preferable to add sulfate to the eluent.

  As can be seen from FIG. 7 (b), with regard to arsenic, As (III) and As (V) can be well separated and quantified regardless of the type of sulfate, and the eluent contains sulfate. As (III) and As (V) can be separated even if sodium chloride is contained without it.

[Reference Example 4]
A sample solution of the same composition as in Reference Example 1 was used, and the sulfate salt added to the eluent was ammonium sulfate, and the concentrations were 0.7 mmol / L and 70 mmol / L, and chromatographs at these concentrations for selenium were obtained. . The nitric acid concentration in the eluent was 10 mmol / L. The results are shown in FIG. As can be seen from FIG. 8, when the sulfate concentration is extremely high, the peaks of Se (IV) and Se (VI) spread and both overlap each other. Since it will be difficult to separate and quantify if the peak overlap is large, it is understood that it is desirable to set the concentration of sulfate in the eluent to about 1 mmol / L or less.

[Reference Example 5]
What overlapped and displayed the chromatogram of the selenium and the chromatogram of the arsenic which were obtained when the sodium sulfate density | concentration in the eluent in the reference example 1 is 0.7 mmol / L is shown in FIG. It can be seen that valence-based quantification can be performed simultaneously for selenium and arsenic.

[Reference Example 6]
Sample solutions with different concentrations of selenium compound and arsenic compound were prepared, and quantification was performed by valence simultaneously for both selenium and arsenic to obtain a calibration curve. At the same time, the repeatability was also determined. As an eluent, one containing 10 mmol / L of nitric acid and 0.7 mmol / L of sodium sulfate was used. The calibration curve for selenium is shown in FIG. 10 (a), and the calibration curve for arsenic is shown in FIG. 10 (b). The coefficient of variation (CV) indicating repeatability is 4.3% for Se (IV), 4.6% for Se (VI), 3.5% for As (III), for As (V) It was 0.8%. As a result, the measurement lower limit in the apparatus shown in FIG. 4, that is, the measurement lower limit in the case where concentration is not performed in the concentration column which is also the ion exclusion column before separation by the separation column which is the ion exclusion column, is Se (IV) And 5 μg / L for Se (VI), 1 μg / L for As (III), and 1 μg / L for As (V). Moreover, it was confirmed that the reproducibility by this method is good.

Example 1
An apparatus of the configuration shown in FIG. 2 was assembled. As the concentration column 40, SCR 102H (inner diameter 6 mm, length 5 cm) manufactured by Shimadzu Corporation having the same stationary phase as the separation column 37 was used. The concentration column 40 has the same specifications as the separation column 36. As a sample solution, one containing 0.5 ppb each of Se (IV), Se (VI), As (III) and As (V) was used. When the injector 33 was in the load mode, the sample liquid was introduced into the concentration column 40 by the sample pump 39 at a flow rate of 1.5 mL / min. Thereafter, with the injector 33 in the inject mode, the concentrated selenium and arsenic compounds in the concentration column 40 are injected into the guard column 36 and the separation column 37, and simultaneous counting of selenium and arsenic is performed by the ICP-MS device 38, Chromatograms were obtained for both selenium and arsenic, respectively. The loading time, that is, the time during which the sample liquid was passed through the concentration column 40 with the injector 33 in loading mode, was changed to 1 minute, 2 minutes, and 5 minutes, and differences in chromatograms due to differences in loading time were examined. The results are shown in FIG. FIG. 11 (a) is a chromatogram for selenium, and FIG. 11 (b) is a chromatogram for arsenic. The peak observed between 190 seconds and 200 seconds is considered to be noise caused by switching the injector 33 from the load mode to the inject mode.

  As shown in FIG. 11, by increasing the loading time, that is, the concentration time in the concentration column 40, the peaks became particularly high for Se (VI), Se (IV) and As (V). It was found that the sensitivity was improved by concentration by passing the solution through a concentration column 40 which is an ion exclusion column. This means that it is possible to concentrate selenium compounds and / or arsenic compounds in the sample solution by using an ion exclusion column.

  In Reference Examples 1 to 6, selenium compounds can be separated according to valence by ion exclusion chromatography using an aqueous solution containing nitric acid and sulfate as an eluent, and selenium compounds and arsenic compounds can be simultaneously separated according to valence. It shows that it can be separated. The concentration in the concentration column as shown in Example 1 corresponds to the pretreatment by ion exclusion chromatography using an aqueous solution containing nitric acid and a sulfate as an eluent, and the reference examples 1 to 6 and the examples From the results, it can be seen from the results that according to the method of the present invention, selenium compounds and arsenic compounds in a sample can be quantified with high sensitivity by valence.

Claims (13)

A method of concentrating a sample liquid containing, as a target substance, at least one of a selenium compound which may be present as an anion in an aqueous solution and an arsenic compound which may be present as an anion in an aqueous solution ,
Passing the sample solution through a concentration column composed of an ion exclusion column having an anionic exchange group to concentrate the target substance in the sample solution in the concentration column;
Passing an eluent, which is an aqueous solution containing nitric acid and a sulfate, through the concentration column to obtain a solution in which the target substance is concentrated;
How to have it.   The method according to claim 1, wherein the pH of the eluent is 1 or more and 5 or less.   The method according to claim 1 or 2, wherein the sulfate is one or more compounds selected from the group consisting of sulfates of alkali metals, sulfates of alkaline earth metals, and ammonium sulfate.   The method according to any one of claims 1 to 3, wherein the concentration of the sulfate in the eluent is 0.002 mmol / L or more and 100 mmol / L.   The method according to any one of claims 1 to 4, wherein the flow direction of the eluent is opposite to the flow direction of the sample solution in the concentration column.   The method according to any one of claims 1 to 5, wherein the concentration column comprises a strongly acidic cation exchange resin as a stationary phase. A method of analyzing, according to valence, the target substance in a sample solution containing, as a target substance, at least one of a selenium compound which may be present as an anion in an aqueous solution and an arsenic compound which may be present as an anion in an aqueous solution ,
A liquid obtained by concentrating the target substance obtained by the method according to any one of claims 1 to 6 is injected into a separation column composed of an ion exclusion column having an anionic exchange group, and the eluent is allowed to flow through the separation column. While the target substance in the sample solution is separated according to valence,
Introducing the liquid flowing out of the separation column into an inductively coupled plasma mass spectrometer to quantify the target substance;
How to have it. The sample solution simultaneously contains selenium and arsenic, and the sample solution is introduced into the concentration column to simultaneously concentrate the selenium compound and the arsenic compound in the concentration column,
The concentrated selenium compound and arsenic compound in the concentration column are injected into the separation column, and the arsenic compound contained in the sample solution is separated according to valence simultaneously with the selenium compound,
The method according to claim 7, wherein selenium and arsenic are simultaneously quantified in the inductively coupled plasma mass spectrometer.   The method according to claim 7 or 8, wherein the separation column comprises a strongly acidic cation exchange resin as a stationary phase. An apparatus for concentrating the target substance and the target substance including the sample solution of at least one of arsenic compounds which may be present as anions selenium compound and an aqueous solution may exist as anions in the aqueous solution,
A concentration column composed of an ion exclusion column having an anionic exchange group,
It is switchable between a sample introduction step and a sample discharge step, wherein the sample solution is introduced into the concentration column in the sample introduction step to concentrate the target substance in the sample solution in the concentration column. An injector for passing the eluent through the concentration column in the sample discharging step to cause the liquid in which the target substance is concentrated to flow out of the concentration column;
A device having   The apparatus according to claim 10, wherein the concentration column comprises a strongly acidic cation exchange resin as a stationary phase. An apparatus for quantifying the target substance in a sample solution according to the valence, with at least one of a selenium compound which may be present as an anion in an aqueous solution and an arsenic compound which may be present as an anion in an aqueous solution as a target substance,
A pump for feeding the eluent;
A concentration column composed of an ion exclusion column having an anionic exchange group,
A separation column comprising an ion exclusion column having an anionic exchange group,
It is switchable between two modes, a loading mode and an injecting mode, and in the loading mode, the eluent from the pump is sent to the separation column and a sample solution is introduced into the concentration column to An injector for concentrating the target substance in the sample solution in a concentration column, and sending the eluent from the pump to the separation column through the concentration column in the inject mode;
An inductively coupled plasma mass spectrometer connected to the outlet of the separation column;
An apparatus for counting atomic ions corresponding to the target substance in the inductively coupled plasma mass spectrometer.   The apparatus according to claim 12, wherein the concentration column and the separation column contain a strongly acidic cation exchange resin as a stationary phase.

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