JP3456511B2 - Anion analysis method and anion analysis set - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an anion analysis method by non-suppressor method ion chromatography and an anion analysis set, and more specifically, to a fluoride ion and a phosphate ion in a sample using a weakly acidic eluent. Particularly, the present invention relates to an anion analysis method and an anion analysis set that can be separated well.

[0002]

TECHNICAL BACKGROUND OF THE INVENTION Phosphate ion, fluoride ion,
In recent years, ion chromatography has been used as an efficient, highly accurate and highly sensitive means for analyzing inorganic anions such as chloride ion, nitrite ion, bromide ion, nitrate ion and sulfate ion.

In ion chromatography, a sample containing ion species is injected into an ion exchange column while the eluent is being sent to the column, and the column is separated and eluted with a retention time difference. Ion (type,
Amount) is detected by a high-sensitivity detector such as an electric conductivity detector. This ion chromatography has a “suppressor method” that uses a “suppressor” and a “non-suppressor method” that does not use a suppressor. , This suppressor has the function of lowering the background when detecting ions with the conductivity detector and increasing the measurement sensitivity.

In the former "suppressor method", a separation column is followed by a cation removal system called a suppressor, which is composed of an ion exchange membrane or an ion exchange resin. Further, in this suppressor method, as the eluent, a carbonate buffer having a pH of 10 to 12, a borate buffer, and an aqueous sodium hydroxide solution are used. In this suppressor method, after the anions in the injected sample are separated in the separation column, the cations contained in the eluent are removed in the suppressor connected to the separation column, the effluent becomes low in conductivity, and then the conductivity is reduced. The ion is detected by being introduced into a detector such as a degree detector.

In the latter "non-suppressor method", an organic acid having low conductivity such as phthalic acid, p-hydroxybenzoic acid, trimesic acid, etc. is used as an eluent, and sample ions are separated in a separation column. , Direct conductivity detector. In this non-suppressor method, the background of the conductivity detector is low and highly sensitive analysis is possible. The pH of the eluent is not limited, and various separation conditions can be selected. Moreover, the non-suppressor method can be carried out by using a commonly used HPLC apparatus as it is and is excellent in economic efficiency. Therefore, although the non-suppressor method was developed after the suppressor method, it is widely applied today. It has become so.

In the non-suppressor method, conventionally, as the eluent conditions, the weakly acidic organic acid aqueous solution, which is hardly affected by the carbon dioxide in the outside air as described above, is often used, but under such conditions, Of the seven major anions measured (phosphate, fluoride, chloride, nitrite, bromide, nitrate and sulfate), retention of phosphate and fluoride Since the time (retention time) is extremely close, there is a problem that it is difficult to separate the two.

In order to solve such problems, Japanese Patent Application No.
Flat No. 4-126393 (JP-A-05-322864)
"A method for analyzing an anion component in a sample containing a fluoride ion and a phosphate ion by ion chromatography at a pH of weakly acidic or less, wherein a mobile phase (eluent)
Boric acid was added to, and the boric acid and fluorine ion were selectively reacted to generate an anionic compound, and the fluorine ion (fluoride ion) and the phosphate ion could be separated. ” Ion analysis methods have been proposed. According to the anion analysis method described in this publication, it is possible to separate fluoride ions and phosphate ions to a considerable degree, but the amount of boric acid added is 100 mM or more,
There is a problem that it takes time and labor such as heating and ultrasonic waves for a long time to dissolve. Further, according to the method described in this publication, it is difficult to completely separate the phosphate ion and the fluoride ion, which is not always satisfactory.

Therefore, the inventors of the present invention have conducted extensive studies to solve the above-mentioned problems, and as a result, when a boronic acid derivative was added to the weakly acidic eluent, phosphoric acid was selected from among the various anions described above. The retention time of fluoride ions is selectively delayed (increased and extended) as compared with the retention time of ions,
Among the various ions described above, they have found that even fluoride ions and phosphate ions can be satisfactorily separated, and have completed the present invention.

[0009]

It is an object of the present invention to solve the problems associated with the prior art as described above, and it is possible to almost completely separate anions, particularly phosphate ions and fluoride ions, in a sample. It is intended to provide an anion analysis method by the suppressor method.

Another object of the present invention is to provide an anion analysis set by the non-suppressor method which can almost completely separate anions in a sample, particularly phosphate ions and fluoride ions.

[0011]

SUMMARY OF THE INVENTION An anion analysis method according to the present invention is performed by injecting a sample containing an ionic species into an ion-exchange column while feeding the eluent into the column to remove anions separated and eluted from the column. A non-suppressor method ion chromatography for analysis by a detector, characterized in that a weakly acidic organic acid aqueous solution containing a boronic acid derivative is used as the eluent.

In a preferred aspect of the present invention, it is desirable that the ionic species include a fluoride ion and a phosphate ion. In a preferred embodiment of the present invention, it is desirable that the boronic acid derivative is a phenyl group-containing boronic acid or an alkylboronic acid.

The anion analysis set according to the present invention comprises an ion exchange column into which a sample containing anions is injected, and a weakly acidic organic acid aqueous solution containing a boronic acid derivative for separating and eluting anions from the column. , A conductivity detector that detects the separated and eluted anions, and (and, if necessary, an integrator that displays the signal detected by this conductivity detector as a chromatogram, and sends the eluent into the column. A pump for injection, an injection device for injecting the sample into the column, and a constant temperature bath to keep the column at a constant temperature)
It is characterized by consisting of.

According to such anion analysis method, the anion components (eg, phosphate ion, fluoride ion, chloride ion, nitrite ion, bromide ion, nitrate ion and sulfate ion) in the sample are analyzed. Among them, fluoride ions and phosphate ions, which have been difficult to analyze with high sensitivity in the past, can be detected with high sensitivity by non-suppressor method ion chromatography.

According to the above-mentioned anion analysis set, it is possible to detect fluoride ions and phosphate ions, which have been difficult to analyze with high sensitivity in the conventional manner, with high sensitivity by non-suppressor ion chromatography.

[0016]

DETAILED DESCRIPTION OF THE INVENTION The anion analysis method and anion analysis set according to the present invention will be specifically described below.

The anion analysis method according to the present invention is carried out by injecting a sample containing ion species into the column while feeding the eluent to an ion exchange column, and detecting the anions separated and eluted from the column. In the non-suppressor method ion chromatography, the weak acidic organic acid aqueous solution containing a boronic acid derivative is used as the eluent.

<Sample> The anion is not particularly limited.
Specifically, for example, phosphate ion (H ₂PO_Four ^-,
HPO_Four ^2-, PO_Four ^3-), Fluoride ion (F^-),chloride
Product ion (Cl ^-), Nitrite ion (NO₂ ^-), Bromide
Ion (Br^-), Nitrate ion (NO₃ ^-), Sulfate ion
(SO_Four ^2-) And I^-, S₂O₃ ^-, SCN^-, Aromatic
Rufonate ion (eg toluenesulfonic acid, xylene
Ions such as sulfonic acid), alkyl sulfonate ions
(Example: octyl sulfonic acid, decyl sulfonic acid,
Ions such as decyl sulfonic acid) and the like.

In a preferred embodiment of the present invention, it is desirable that the ionic species include a fluoride ion and a phosphate ion which can be detected with high sensitivity by the method of the present invention. <Separation column> As the separation column used in the present invention, an anion exchange column is mainly used, and the packing material (ion exchanger) for the column is a surface functional type or a porous chemical bond type. There is.

Examples of the surface functional type filler include those obtained by coating a non-porous substrate with a fine particle anion exchanger electrostatically or chemically bonded. As the substrate, sulfonated polystyrene, Polystyrene or the like is used.

As the porous chemical bond type filler, for example, porous silica gel or polyacrylate particles can be used.
The thing which chemically bonded the quaternary ammonium group is mentioned.
Each of these fillers has a low exchange capacity, and is usually 10
Is about 100 μeq / g.

The column packed with such a packing has an inner diameter of about 1 to 6 mm and a length of 5 to 25 c.
Various types are used up to about m. The material of the column is stainless steel, plastic, glass or the like which is inert to the eluent.

As the separation column, a reversed-phase column packed with octadecyl group-bonded silica gel, polystyrene gel or the like can also be applied. In this case, tetrabutylammonium or the like as an ion pair agent and a borohydride are used in the weakly acidic organic acid aqueous solution. An anion may be separated by adding an acid derivative.

<Eluent> In the present invention, as the eluent, a weakly acidic organic acid aqueous solution containing a boronic acid derivative as described above [pH is usually 3 to 6, preferably pH 3.5 to 4.
5] is used, and as the organic acid, an organic acid that dissociates under weak acidity (having a dissociation index pK ₁ of 6.5 or less) is used.

Specific examples of such an organic acid include:
For example, tartaric acid, citric acid, oxalic acid, acetic acid, phthalic acid, benzoic acid, p-hydroxybenzoic acid, hippuric acid, salicylic acid, methylhippuric acid, aspartic acid, and other carboxylic acids; octansulphonic acid, decane sulfonic acid, toluene sulfone. Examples thereof include acids, benzenesulfonic acids, and sulfonic acids such as naphthalene sulfonic acid.

In the present invention, one kind of these organic acids is usually selected and used, but two or more kinds may be appropriately combined and selected depending on the purpose. Although the concentration of the organic acid depends on its ionic output, it is usually about 0.5 to 10 mM. From the viewpoint of detection sensitivity, it is desirable that the concentration of the organic acid used is as low as possible, and an organic acid with a high elution output such as phthalic acid, salicylic acid, octansulphonic acid, etc. is used at a concentration of 1 to 3 mM. Often.

Boronic Acid Derivative The boronic acid derivative contained in the eluent in the present invention is
It acts on the fluoride ion to extend its retention time (holding time) and contributes to enhancing the separation ability between the fluoride ion and the phosphate ion.

Examples of the boronic acid derivative include phenyl group-containing boronic acids and alkylboronic acids. The phenyl group-containing boronic acids are represented by the following general formula [I]:

[0029]

[Chemical 1]

{In the formula [I], R ¹ is a halogen atom, --N
O ₂ , —NH ₂ , —OR ⁵ (R ⁵ : an alkyl group having 1 to ⁵ carbon atoms, preferably 1 to 2 carbon atoms), and some or all of hydrogen atoms are 1
Or an alkyl group having 1 to 5 carbon atoms, preferably 1 to 2 carbon atoms which may be substituted with two or more kinds of halogen atoms, n represents an integer of 0 to 5, and when n is 2 or more, , A plurality of R ^1's may be the same or different from each other. } Is represented.

The halogen atom of the phenyl group-containing boronic acid represented by the above formula [I] is F, Cl, Br or I.
And the like. Examples of -OR ⁵ include -OCH ₃ , -OC ₂ H ₅
Etc., and as the partially or fully one or more of good the alkyl group optionally substituted with a halogen atom hydrogen atom, -CF _3, -C ₂ F _5, and the like.

Specific examples of such phenyl group-containing boronic acids [I] include those shown in Table 1 below, and among them, numbered (1a), (2a), (6).
a) is preferable, and (1a) is particularly preferably used.

[0033]

[Table 1]

The alkylboronic acids are represented by the following formula [II]:

[0035]

[Chemical 2]

{In the formula [II], R ³ may be linear or branched and a part or all of hydrogen atoms may be substituted with one or more halogen atoms. Optionally represents an alkyl group having 1 to 30 carbon atoms, preferably 1 to 20 carbon atoms. } Is represented.

The alkyl group represented by the formula [II]
The halogen atom in the phosphoric acid includes F, Cl, Br,
I etc. are mentioned. Also above-R³As for -CH₃,-
C₂H _Five,-(CH₂)₃CH₃,-(CH₂)₁₃CH₃,-(C
H₂)₁₇CH₃,-(CH₂) CH (CH₃) CH₃Etc.
To be

Specific examples of such alkylboronic acids [II] include those shown in Table 2 below, and among them, the numbers (1b) and (3b) are preferably used.

[0039]

[Table 2]

The action of such a boronic acid derivative is not always clear, but it is presumed that this boronic acid derivative forms some complex with the fluoride ion and delays the elution of the fluoride ion. The concentration of the boronic acid derivative added to the eluent varies depending on its type, and therefore cannot be generally stated. However, generally, the more hydrophobic the compound, the smaller the amount added.

Any of the above phenyl group-containing boronic acids [I] can achieve the object of the present invention if incorporated in the eluent. Any of the above alkylboronic acids [II] can achieve the object of the present invention by being mixed in the eluent.

The reason for this is presumed to be that the complex of the boronic acid derivative and the fluoride ion, which is likely to be produced, is large and the elution thereof is delayed. For example, the methylboronic acid used in Example 2 (molecular weight: 59.
86) does not show much effect unless 50 mM or more is added, but the phenylboronic acid of Example 1 (molecular weight: 12
1.93) shows the effect of addition from about 2 mM, 8 mM
The purpose can be sufficiently achieved by adding.

As the pH adjusting agent for the eluent, any of aqueous solutions of inorganic bases such as sodium hydroxide and potassium hydroxide and organic bases such as trishydroxymethylaminomethane and triethanolamine can be used. When using conductivity detectors, the latter organic bases are more desirable due to the lower background.

In the present invention, as the detector, an ultraviolet-visible detector, a refractive index detector, etc. can be used in addition to the conductivity detector.

[0045]

As described above, according to the present invention, in the non-suppressor method ion chromatography using a weakly acidic eluent, a boronic acid derivative is mixed in the eluent, and therefore, seven major anions (phosphorus) are used. Acid ions, fluoride ions, chloride ions, nitrite ions, bromide ions, nitrate ions, and sulfate ions) can be satisfactorily separated.

In particular, according to the present invention, since the boronic acid derivative is mixed in the eluent, among the above-mentioned seven kinds of anions in the sample, fluoride ions and phosphorus ions, which have hitherto been difficult to perform highly sensitive analysis, can be obtained. Acid ions can be detected with higher sensitivity.

Moreover, in the present invention, since such a boronic acid derivative is used as the eluent component, a small amount of the boronic acid derivative is contained (added) in the weakly acidic eluent as compared with the case where boric acid is added. It is possible to almost completely separate the phosphate ion and the fluoride ion in the sample.

According to the above-mentioned anion analysis set, it is possible to detect fluoride ion and phosphate ion, which have been difficult to analyze with high sensitivity as described above, with high sensitivity by non-suppressor ion chromatography.

[0049]

The present invention will be described in more detail below by showing typical examples. Note that these are merely examples for description, and the present invention is not limited to these examples.

In the following examples, the anion analysis set as described above was used. That is, in this anion analysis set, the eluent is poured from the eluent tank through a pump into a column with a thermostatic chamber filled with a weakly basic ion exchanger, while the eluent is pumped between the eluent transport pump and the column. The sample is injected from the sample injection device provided in the column, and various anions that are sequentially separated and eluted from the column with a time difference are detected by the conductivity detector and recorded (displayed) by the integrator. There is.

[0051]

Example 1 Anion exchange column "Shodex IC I-524A" [Showa Denko KK, inner diameter 4.6 mm, length 10 cm, packing material: anion exchange resin] was used as a separation column, and the eluent was used. Was prepared as follows. 2.5 mmol of phthalic acid and 2.3 mmol of trishydroxymethylaminomethane were placed in a 1 liter measuring flask, and pure water was added to make 1 liter. Phenylboronic acid C ₆ H ₅ B (OH) ₂ was added to each of them in an amount of 4 m.
Two kinds of eluents containing M and 8 mM were prepared and dissolved by ultrasonic waves. The pH of each of the eluents thus prepared was 4.0.

The above two kinds of eluents were passed through the above anion separation column at 1.2 ml / min, and as a sample, phosphate ion 30 mg / liter, fluoride ion 1 mg / liter, chloride ion 5 mg / liter, nitrite. Ion 1
0 mg / liter, bromide ion 10 mg / liter,
Nitrate ion 10mg / l, Sulfate ion 10mg / l
50 μL of an aqueous solution containing 1 L was injected, and the conductivity was detected by an electric conductivity detector [Showa Denko KK, product number: CD-5].

The obtained chromatograms are shown in FIG.
Shown in (a) and (b). FIG. 1 (a) shows a chromatogram containing 4 mM of phenylboronic acid and FIG. 1 (b) shows a chromatogram containing 8 mM of phenylboronic acid. It can be seen that fluoride ions and phosphate ions are completely separated.

[0054]

Comparative Example 1 The same column as used in Example 1 was used as the separation column, and the eluent was prepared as follows. 2.5 mmol phthalic acid, 2.3 in a 1 liter volumetric flask.
Tris-hydroxymethylaminomethane was taken in mmol and pure water was added to make 1 liter. Then, three kinds of liquids containing boric acid (H ₃ BO ₃ ) of 50 mM, 100 mM and 300 mM were prepared, and heated while stirring to completely dissolve them. The pH of each of the eluents thus prepared was 4.0.

As the sample, phosphate ion 20 mg / liter, fluoride ion 2.5 mg / liter, chloride ion 2.5 mg / liter, nitrite ion 5 mg / liter, bromide ion 5 mg / liter, nitrate ion 5 m
50 μL of an aqueous solution containing g / liter and 5 mg / liter of sulfate ion was injected, and detection was performed by an electric conductivity detector.

The obtained chromatograms are shown in FIG.
Shown in (c), (d), and (e). (C) 50 boric acid
In the case of containing mM, (d) is a chromatogram in the case of containing boric acid of 100 mM, (e) is the case of containing boric acid of 300 mM, but if 100 mM or more is not added, there is no remarkable effect. However, it was not possible to completely separate the phosphate ion and the fluoride ion.
The data was also collected when 300 mM or more was added, but the separation was not further improved.

[0057]

Example 2 The same column as used in Example 1 was used as the separation column, and the eluent was prepared as follows. 2.5 mmol phthalic acid, 2.3 in a 1 liter volumetric flask.
Tris-hydroxymethylaminomethane was taken in mmol and pure water was added to make 1 liter. Then, an eluent containing 150 mM of methylboronic acid CH ₃ B (OH) ₂ was prepared, and heated while stirring to completely dissolve it. The eluent thus prepared had a pH of 4.0.

As samples, phosphate ion 20 mg / liter, fluoride ion 2.5 mg / liter, chloride ion 2.5 mg / liter, nitrite ion 5 mg / liter, bromide ion 5 mg / liter, nitrate ion 5 m
50 μL of an aqueous solution containing g / liter and 5 mg / liter of sulfate ion was injected, and detection was performed by an electric conductivity detector.

The obtained chromatogram is shown in FIG. In the case of methylboronic acid, addition of about half the amount of boric acid showed the same effect as boric acid.

[Brief description of drawings]

1 is a separation chromatogram obtained in Example 1. FIG.

2 is a separation chromatogram obtained in Comparative Example 1. FIG.

FIG. 3 is a separation chromatogram obtained in Example 2.

[Explanation of symbols]

(B): Chromatogram when the amount of phenylboronic acid added was 4 mM in Example 1 (b): Chromatogram when the amount of phenylboronic acid added was 8 mM in Example 1 (c): Amount of boric acid added in Comparative Example 1 Chromatogram at 50 mM (d): Chromatogram at a boric acid addition amount of 100 mM in Comparative Example 1 (e): Chromatogram at a boric acid addition amount of 300 mM in Comparative Example 1: Phosphate ion (H ₂ PO ₄ ^-) 2: fluoride ions ^(F -) 3: chloride ion (Cl ^-) 4: nitrite ions (NO ₂ ^-) 5: bromide ion (Br ^-) 6: nitrate ion (NO ₃ ^-) 7 : Sulfate ion (SO ₄ ^2- )

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-5-273189 (JP, A) JP-A-5-322864 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01N 30/26 G01N 30/88

Claims (5)

(57) [Claims] 1. A non-suppressor method ion chromatography in which a sample containing ion species is injected into an ion exchange column while the eluent is being sent to the column, and anions separated and eluted from the column are analyzed by a detector. A method for analyzing anions, which is a graph, wherein a weakly acidic organic acid aqueous solution containing a boronic acid derivative is used as the eluent. 2. The analytical method according to claim 1, wherein the ionic species include a fluoride ion and a phosphate ion. 3. The analysis method according to claim 1 or 2, wherein the boronic acid derivative is a phenyl group-containing boronic acid. 4. The analytical method according to claim 1, wherein the boronic acid derivative is an alkylboronic acid. 5. An ion exchange column into which a sample containing anions is injected, a weakly acidic organic acid aqueous solution containing a boronic acid derivative for separating and eluting the anions from the column, and the separated and eluted anions are detected. And an anion analysis set comprising: