JP2000065812A - Anion measurement method using chelating agent - Google Patents

Abstract

PROBLEM TO BE SOLVED: To analyze a sample containing fluorine ions with high quantitative precision in a wide measurement range by adding a water soluble chelating agent in a mobile phase of an ion chromatograph. SOLUTION: In an anion analysis based on an ion chromatography, a water- soluble chelating agent is added in a mobile phase. As this water-soluble chelating agent, an amino polycarboxylate chelating agent is used. A sample containing fluorine ions is analyzed. As the mobile phase, any phase separating anions from each other may be used without any specification of its sort, concentration, or pH. If an electrical conductivity detector is used, organic acid with a low ion equivalent conductivity is used. In consideration of bond stability between the chelating agent and metal ion, pH of eluting solution is desirably set to pH 3-8 approximately. Preferable concentration of the added chelating agent is about 1-500 μM for increasing fluorine ion quantitative precision effectively, and depending on a sort of the chelating agent, a concentration of about 4-100 μM is more preferable.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for analyzing anions in ion chromatography, and more particularly to a method for measuring anions with high quantitative accuracy.

[0002]

2. Description of the Related Art In recent years, when global environmental problems have been dealt with, analysis of anions contained in food, drinking water and soil has been increasingly required for maintaining health and preventing environmental pollution. The method of analyzing anions by ion chromatography is specified in official methods such as the industrial water test method, the industrial wastewater test method and the clean water test method, and is one of the analytical methods with a wide range of applications. As a means for analyzing anions, a highly sensitive and highly selective measurement method is desired. In the analysis of anions by ion chromatography, in particular, fluorine ions are difficult to be retained on the column and elute quickly, so that a negative peak at a non-retained position caused by dilution of the mobile phase due to sample injection (Water di
It overlaps with p) and the quantitative accuracy is easily impaired. In addition, the quantitative accuracy may decrease due to the influence of impurities having similar retention times, such as carbonate ions or monovalent carboxylic acids contained in the air. In addition, even when a column for anion analysis that solves the above-mentioned problem is used, a small amount of metal ions or a small amount of metal ions that elute from the wall of the flow channel tube into the mobile phase, or a small amount of metal ions containing fluorine ions in the sample. A change in the shape of the fluorine ion peak, which appears to form a complex with metal ions and the like contained in the liquid, occurs.
Quantitative precision tended to decrease.

[0003]

Generally, in order to normalize the peak shape of fluorine ions in ion chromatography and perform accurate measurement from a low concentration to a high concentration, it is necessary to perform the following steps.
If the possible contaminants are metal ions that interact with fluorine ions, before injecting the sample into ion chromatography as a pretreatment, bond the fluorine and metal by performing steam distillation or alkali pretreatment. (Intern. J. Environ. Anal. Chem. 62 191-205 1996). However, it is pointed out that when steam distillation is performed as a pretreatment, the operation is complicated and the fluorine recovery rate is low. In addition, when the alkali pretreatment is performed, there is a problem that the peak of the sodium ion used in the alkali pretreatment increases in the chromatogram, and the separation of the fluorine ions is deteriorated. The present invention has been made in view of such a situation, in particular, in ion chromatography, continuously prevents the binding of metal ions and anions, fluorine ion with high quantitative accuracy in a wide measurement range without complicated pretreatment. The purpose is to analyze a sample containing:

[0004]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above problems, and as a result, by adding a water-soluble chelating agent to the mobile phase of ion chromatography, the retention time of other ions can be reduced. It was found that it was possible to measure anions accurately without changing them,
The present invention has been completed. That is, the present invention
(1) An anion analysis method using ion chromatography, wherein a water-soluble chelating agent is added to a mobile phase, and (2) an aminopolycarboxylic acid-based chelating agent is used as a water-soluble chelating agent. The present invention relates to the method for measuring anions according to the above (1) to be used, and (3) to the method for measuring anions according to the above (1) or (2), wherein a sample containing fluorine ions is analyzed.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION In the method for analyzing anions by ion chromatography of the present invention, any ion chromatography column may be used as long as it is a column for analyzing anions. S
handexIC I-524A or ShodexIC
A column for anion analysis in which a quaternary amine is introduced into a methacrylate-based polymer gel like NI-424 can be used.

[0006] The mobile phase is not particularly limited as long as it can separate anions from each other, and its type, concentration and pH are not particularly limited. When an electric conductivity detector is used, an organic acid having low ion equivalent conductivity, for example, p-hydroxybenzoic acid, and a base for adjusting pH, for example, bis (2-hydroxyethyl) iminotris- (hydroxymethyl) methane Can be used. Further, the pH of the eluent is preferably not strongly acidic in consideration of the binding stability between the chelating agent and the metal ion, and more preferably pH 3 to 8.

The concentration of the chelating agent to be added is not particularly limited, and is preferably from 1 μM to 500 μM in order to effectively increase the accuracy of quantification of fluorine ions. Although it varies depending on the type of the chelating agent, it is generally preferably from 4 μM to 100 μM.
Since the concentration of the chelating agent added in the present invention is low,
Neither does it form a system peak that interferes with the peaks of other ions or the peak of the chelator itself. As the chelating agent to be added, a water-soluble chelating agent is preferable, and examples thereof include aminopolycarboxylic acids, oxycarboxylic acids, and inorganic compounds. Among them, aminopolycarboxylic acids are particularly preferable, and nitrilotriacetic acid (NTA), N
-Hydroxyethyliminodiacetic acid (NIMDA), ethylenediaminediacetic acid (EDDA), ethylenediaminetetraacetic acid (EDTA), N-hydroxyethylethylenediaminetetraacetic acid (HEDTA), diethylenetriaminepentaacetic acid (DTPA), 1,2-cyclohexanediaminetetraacetic acid (CyDTA), trimethylenediaminetetraacetic acid (TM
TA), ethylene glycol diethyl ether diamine tetraacetic acid (GEDTA), ethylene diamine tetrapropionic acid (EDTP), glutamic acid-N, N-diacetic acid, aspartic acid-N, N-diacetic acid, and salts thereof are preferred. Is done. Examples of oxycarboxylic acids include lactic acid, glycolic acid, citric acid, tartaric acid, and mandelic acid, and examples of inorganic compounds include pyrophosphoric acid, triphosphoric acid, and condensed phosphoric acid. The chelating agent used in the present invention is preferably an aminopolycarboxylic acid system which reacts instantaneously with a cation. For example, a method of adding 2 to 10 μM of EDTA to an eluent can be mentioned.

The anions to be analyzed in the present invention include inorganic acid ions such as phosphoric acid, fluorine, chloride, nitrous acid, bromide, nitric acid and sulfuric acid contained in an aqueous solution, and formic acid,
Organic acid ions such as acetic acid, propionic acid, lactic acid, oxalic acid, and malonic acid. The anion measurement method of the present invention is particularly suitable for analyzing a sample containing fluorine ions.
An electric conductivity detector is suitable for detecting anions,
Other detectors such as a UV detector may be used and are not particularly limited.

[0009]

The present invention will be described in more detail with reference to the following examples. FIG. 1 shows a liquid chromatography system for performing the anion measurement method of the present invention.

(Example 1) Using a liquid chromatography system shown in FIG. 1, a column: Shodex ICNI-
424, column temperature 40 ° C., mobile phase: 8 mM p-hydroxybenzoic acid, 2.7 mM bis (2-hydroxyethyl) iminotris- (hydroxymethyl) methane, 4 μm
MEDTA, eluent flow rate 1.0 ml / min, detector:
The measurement was performed under the conditions of the electric conductivity detector ShodexCD-5. As a result, a chromatogram as shown in FIG. 3 was obtained. The peaks are respectively 1: phosphate ion (PO ₄
^3- ), 2: Fluorine ion (F ⁻ ), 3: Chloride ion (Cl ⁻ ), 4: Nitrite ion (NO ₂ ⁻ ), 5: Bromide ion (Br ⁻ ), 6: Nitrate ion (NO ₃₎ ^- ), 7: Corresponds to each ion of sulfate ion (SO ₄ ^2- ).

Example 2 In the same manner as in Example 1, using the liquid chromatography system shown in FIG.
dexIC NI-424, column temperature 40 ° C, mobile phase: 8 mM p-hydroxybenzoic acid, 2.3 mM bis (2-hydroxyethyl) iminotris- (hydroxymethyl) methane, 4 μMCyDTA, eluent flow rate 1.
0 ml / min, Detector: Electrical conductivity detector Shode
The test was performed under the conditions of xCD-5. Figure 4 with an injection volume of 100 μL
Was obtained. The peaks indicate 1: fluorine ion (F ⁻ ), 2: chloride ion (Cl ⁻ ), 3: nitrite ion (NO ₂ ⁻ ).

(Comparative Example 1) As in Example 1, using the liquid chromatography system shown in FIG.
dexIC NI-424, column temperature 40 ° C., eluent flow rate 1.0 ml / min, detector: electric conductivity detector S
The mobile phase under the condition of hodexCD-5 is 8 mMp.
-Hydroxybenzoic acid, only 2.7 mM bis (2-hydroxyethyl) iminotris- (hydroxymethyl) methane were used, and no chelating agent was added, to obtain a chromatogram as shown in FIG. The peaks are respectively 1: phosphate ion (PO ₄ ³⁻ ), 2: fluoride ion (F ⁻ ), 3: chloride ion (Cl ⁻ ), 4: nitrite ion (NO ₂ ⁻ ),
5: bromide ion (Br ^-), 6: nitrate ion (N
O ₃ ⁻ ), 7: corresponding to sulfate ion (SO ₄ ²⁻ ). 8 is a shoulder peak derived from fluorine ions.

FIG. 2 is a conventional chromatogram obtained in Comparative Example 1, and FIG. 3 is a chromatogram obtained in Example 1 when the chelating agent of the present invention is added. When comparing the peaks, FIG.
It can be seen that in the conventional chromatogram, the shoulder peak (abnormal peak shape) derived from fluorine ion of peak 8 observed in the conventional chromatogram is eliminated. Further, in FIG. 4 which is a chromatogram obtained in Example 2 when the chelating agent of the present invention was added, each peak was 1: fluorine ion (F
^-), 2: chloride ion (Cl ^-), 3: nitrite ion (NO ₂ ^-) indicates respectively, 0.5 ppm, 500p
pm, 5 ppm. Thus, even when a large amount of anions other than fluorine are present, fluorine ions can be measured with high sensitivity.

[0014]

According to the method for measuring anions using a chelating agent of the present invention, an anion, particularly a fluorine ion, can be produced by adding a low concentration of a chelating agent to an eluent, while the anion, particularly fluorine ions, is encountered during ion chromatography analysis. Since the bond with the ion can be continuously avoided, impurities can be removed, and the peak shape of the fluorine ion can be improved. As a result, the accuracy of quantification of fluorine ions and the like can be improved, and anion analysis can be performed with high sensitivity and high accuracy. This is particularly useful for anion measurement in ion chromatography.

[Brief description of the drawings]

FIG. 1 is a flow diagram showing an embodiment of the present invention.

FIG. 2 is a chromatogram for anion analysis of a comparative example.

FIG. 3 is an example of a chromatogram for anion analysis in Example 1 of the present invention.

FIG. 4 is an example of a chromatogram for anion analysis in Example 2 of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Eluent 2 Pump 3 Injector 4 Column 5 Detector cell part 6 Detector main body 7 Oven (40 degreeC) 8 Recorder

Claims (3)

[Claims] 1. A method for measuring anions, comprising adding a water-soluble chelating agent to a mobile phase in anion analysis by ion chromatography. 2. The method according to claim 1, wherein an aminopolycarboxylic acid chelating agent is used as the water-soluble chelating agent. 3. The method according to claim 1, wherein a sample containing fluorine ions is analyzed.