JP3200904B2 - Quantitative analysis method of trace alkaline earth metals in salt water - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION Analysis of alkaline earth metal in salt water supplied to an electrolytic cell and its process control in the ion exchange membrane method salt electrolysis industry, or seawater used as cooling water for various plants such as power plants It is industrially important to manage alkaline earth metals. The present invention relates to a method for rapid, sensitive, and highly accurate quantitative analysis of a trace amount of alkaline earth metal in an aqueous solution of an alkali metal salt.

[0002]

2. Description of the Related Art Quantitative analysis of calcium and magnesium in an aqueous solution has been conventionally performed by chelate titration, atomic absorption spectrometry, and the like.
A frameless atomic absorption method and the like are known. Alkaline earth metal determination in a system containing a large amount of an alkali metal salt exhibiting a chemical and physical behavior similar to that of an alkaline earth metal element has a problem in terms of detection sensitivity and accuracy due to the influence of the matrix. For example, Chemical Abstract 93
As shown in Volume 1006426d, quantitative analysis of calcium and magnesium in seawater by chelate titration is not satisfactory in terms of sensitivity and accuracy.

Further, Chemical Abstracts 95, 15
In the case of 55867y, calcium and magnesium in seawater are quantified by a complexometric titration method using a photometer, but the detection limit is 1 ppm, which is not sufficient in terms of sensitivity. According to the spectrophotometric method disclosed in JP-A-59-5956, quantitative analysis of calcium present in a saturated saline solution is performed at a sensitivity of several tens of ppb. This analysis method analyzes only a single component of calcium among alkaline earth metals, and cannot perform quantitative analysis of other alkaline earth metal components such as magnesium or strontium and barium which coexist. Alizarin Acid Black SN as Complexon
Since strontium not only calcium but also causes a complexing reaction at the same time to form a color, strontium is quantified as a total amount, so it cannot be said that this is a selective analysis method using only a calcium component.

Japanese Patent Laid-Open Publication No. Sho 62-266460 discloses a method for automatically analyzing trace amounts of calcium and magnesium.
Quantification of trace amounts of calcium and magnesium is performed by a flow injection analysis system by a sample pretreatment method in which coexisting large amounts of alkali metal ions are separated using a chelating resin. Since this method is also quantified by the total amount of calcium and magnesium, it cannot be said to be a selective analysis of a single component, and the reliability of analysis is poor due to the complicated pretreatment operation.

[0005] Recently, an automatic analysis method using ICP emission analysis has been proposed, but the problem with this analysis method is that the amount of sample solution sucked varies due to the relatively high viscosity of the high concentration alkali metal salt aqueous solution. And a measurement error occurs.

Since the sample contains a large amount of an alkali metal salt, precipitation of the alkali metal salt occurs in the vicinity of the torch and the nebulizer, causing blockage in the tube. For this reason, frequent cleaning of the periphery of the torch and nebulizer is required, and maintenance management is difficult.

[0007] Since a large amount of argon gas needs to be supplied, the running cost is high.

When the argon gas is turned into a plasma flame by high-frequency power, the temperature around the flame becomes extremely high and there is a danger of fire.

[0009] Based on the above, ICP is used as an automation of analysis.
There are still many problems in incorporating the method into process control. When a sample containing a large amount of alkali metal is measured by the frameless atomic absorption spectrometry, the measurement involves a background absorption such as molecular absorption and light scattering and a decrease in accuracy due to interference at the time of atomization. Therefore generally the background correction method used in, D ₂ lamp method, two wavelengths correction method,
Optical correction methods such as the Zeeman effect method have been used, but these correction methods alone are not sufficient.

As a method for removing a matrix salt, a method of measuring after separating and concentrating a target element by an ion exchange method, a coprecipitation method, a solvent extraction method or the like has been adopted. Further, for the purpose of removing the matrix and reducing the background absorption, a method of adding various modifiers such as EDTA, ascorbic acid, ammonium nitrate, nitric acid and the like and analyzing the same has been attempted.

According to a known report from Kureha Chemical Industry KK / Hitachi Ltd. KK, as a method for quantifying trace amounts of single components of calcium, magnesium, barium, iron and nickel in a salt water, a sample pretreatment and a modifier were used. The optimum conditions for removing the matrix salt in the drying and ashing stages are set without any addition, and the direct determination of the salt water is performed. Although this determination method is very simple, the problem is that a large amount of alkali metal is brought into the cuvette because of the direct determination of saturated salt water.As a result, the carbon surface of the cuvette furnace material is affected, and the cuvette life is shortened. Since it is significantly reduced, measurement accuracy is deteriorated.

Frequent cleaning is necessary because a large amount of alkali metal adheres around the cuvette.

Since no modifier is added, the morphology of the target component becomes unstable, and the quantitative target element volatilizes during the measurement, so that the reproducibility and reliability of the measured value remain uneasy.

It is necessary to set optimum conditions for each measurement element. From the above, when this method is applied to the quantitative analysis of a trace amount of alkaline earth metal in an aqueous solution of an alkali metal salt, it is not sufficiently satisfactory as a daily process control analysis method.

In the salt electrolysis industry using the ion exchange membrane method, the salt water supplied to the electrolytic cell has an alkali metal salt concentration of 200%.
The concentration is as high as about 300 g / liter, and the concentration of the alkaline earth metal coexisting therein is usually controlled at a level of several to several hundred ppb. As a method for quantitative analysis of calcium, magnesium, strontium, barium and the like in a system in which an alkali metal salt and an alkaline earth metal salt coexist at such a ratio, the above-described various analysis methods have been proposed. However, it cannot be said that a method for selectively and simply quantifying each single component of the alkaline earth metal which is the object of the present invention has not been established.

[0016]

SUMMARY OF THE INVENTION An object of the present invention is to provide an analytical method which satisfies the following requirements in the quantitative analysis of alkaline earth metals in a sample containing a large amount of alkali metals.

This is a high-sensitivity and high-precision analysis method having a detection limit of several to several tens of ppb without being affected by the alkali metal as the main component.

Quantitative analysis of the four elements calcium, magnesium, strontium and barium can be performed for each single element, and if possible, simultaneous quantitative analysis of the four elements is possible.

This is an analysis method that does not require complicated sample pretreatment.

The operation is simple and rapid.

[0021]

Means for Solving the Problems The present inventors have conducted intensive studies on the quantitative analysis of alkaline earth metals in an aqueous solution of an alkali metal salt which sufficiently satisfies the above four conditions by the frameless atomic absorption method. By adding a hydrogen peroxide solution and a modifier consisting of phosphoric acid and lanthanum to the sample and subjecting it to a flameless atomic absorption spectrometer, calcium,
The present inventors have found a method capable of rapidly, highly sensitively and accurately quantitatively analyzing alkaline earth metals such as magnesium, strontium and barium under the same conditions, and have completed the present invention.

That is, in the present invention, when quantifying an alkaline earth metal in an aqueous solution of an alkali metal salt by the flameless atomic absorption spectrometry, a complicated sample can be obtained simply by diluting the sample with a diluent containing a certain amount of a modifying agent. Alkaline earth metal quantification in aqueous alkali metal salts, characterized by the rapid, high sensitivity and high accuracy of the four elements calcium, magnesium, strontium and barium in almost direct conditions without the need for pretreatment An analysis method is provided.

Hereinafter, the present invention will be described in more detail.

The aqueous alkali metal salt solution to be analyzed in the present invention includes lithium, sodium,
Potassium, rubidium, an aqueous solution of a salt composed of an anionic species as a counter ion such as an alkali metal ion such as cesium, usually lithium chloride, sodium chloride, potassium chloride, cesium chloride, lithium bromide, sodium bromide,
Potassium bromide and the like, and the concentration of the alkali metal salt is, for example, 30 to 320 g /
One liter of aqueous solution.

The alkaline earth metals to be analyzed in the aqueous alkali metal salt solution are calcium, magnesium, strontium and barium, and the concentration thereof is not particularly limited, but is usually several ppb level. The above concentrations are quantitatively analyzed.

One of the components constituting the modifier added to the sample is aqueous hydrogen peroxide. The appropriate amount of hydrogen peroxide solution to be added is usually 20 to 50 ml as 30% hydrogen peroxide solution per liter of the alkali metal salt aqueous solution used for the measurement of flameless atomic absorption. The addition amount of the aqueous hydrogen peroxide slightly varies depending on the concentration of the alkaline earth metal salt in the measurement sample, but is not particularly limited. 20
When the amount is less than milliliter, the accuracy of the analytical value tends to decrease somewhat. Even if it is added in an amount of 50 ml or more, superior quantitative properties are not expected.

The phosphoric acid as one component of the modifier usually has a pH of 1.5 to 3, preferably 1.7, for a sample to be measured.
It is added in a range such that it becomes .about.2.5. When phosphoric acid is added more than necessary, the cuvette surface is eroded and the life is remarkably shortened. Therefore, the addition amount is usually 85% phosphoric acid 0.5% per liter of the alkali metal salt aqueous solution used for measurement.
A milliliter addition is preferred. In addition, calcium and magnesium may be present in trace amounts in the lanthanum. Therefore, in order to minimize contamination in the measurement solution, it is preferable to use a high-purity product or to add 2 to 5 mg of lanthanum. As the water for dissolving these three types of modifiers, it is preferable to use pure water treated by an ultrapure water producing apparatus, so-called ultrapure water.

The concentration of the alkali metal salt in the sample to be measured is not particularly limited, but is preferably 5 to 300 g / l, more preferably 10 to 200 g / l, for shortening the measurement time and improving the sensitivity and accuracy. . The concentration is adjusted usually with water. For example, in the case of saturated salt water, it is usually directly
30, preferably 1/3 to 1/15, and in the case of seawater, directly to 1/3.

In the present invention, the alkali metal salt is preferably prepared by dissolving the three kinds of modifiers of the present invention in water with respect to the aqueous alkali metal salt solution.
After dilution to a concentration of g / liter, more preferably 10 to 200 g / liter, the measurement is naturally included.

The analyzer may be a conventional frameless atomic absorption spectrophotometer, or a frameless atomic absorption spectrophotometer capable of simultaneously measuring four elements. An autosampler is attached to the latter type of atomic absorption apparatus main body, and the sample may be automatically diluted, mixed, and cuvette-injected by the autosampler.

The dilution, mixing, and cuvette injection of the sample may be performed artificially, and are not particularly limited. The amount of sample measured, that is, the amount injected into the cuvette, is usually 10 to 40 microliters, and is appropriately selected in consideration of sampling error, measurement accuracy, and the like.

[0032]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

Example 1 As a frameless atomic absorption spectrometer, an atomic absorption spectrophotometer capable of simultaneously analyzing four elements was used. The measurement sample was prepared by dissolving sodium chloride salt for industrial use in water, making it a saturated saline solution, and then subjecting it to a highly purified treatment obtained by chelating resin treatment and measuring a saturated saline solution with a salt concentration of 300 g / liter. The sample was provided. The salt water was set in an auto-sampler of the atomic absorption apparatus main body, and four elements of calcium, magnesium, strontium, and barium were subjected to an experimental study.
Table 1 shows the measurement conditions of the apparatus when performing frameless atomic absorption spectroscopy.

[0034]

[Table 1] In this measurement, the dilution liquid used for the 1/10 dilution of the salt water sample was a commercially available 30% hydrogen peroxide aqueous solution of 50 ml,
0.5 ml of 85% phosphoric acid and 2 mg of standard lanthanum for atomic absorption were sampled, and adjusted to 1 liter with ultrapure water containing no alkaline earth metal. Table 2 shows a diluent obtained by dissolving the three types of modifiers in a predetermined amount in ultrapure water.
The detection limit calculated from the CV value (%) and the S / N ratio obtained by automatically diluting the measurement sample to 1/10 and measuring it five times is shown.

[0035]

[Table 2] As is evident from the results in Table 2, it can be seen that the present invention has extremely high sensitivity, high accuracy, and extremely high reproducibility of analysis values.

Example 2 and Comparative Example 1 As a flameless atomic absorption spectrometer, the same atomic absorption spectrophotometer as in Example 1 capable of simultaneous analysis of four elements was used. 1 to 4 show that the measured salt water was 1/10 by using the modifier of the present invention.
The comparison example of the calibration curve of calcium, magnesium, strontium, and barium when it is diluted and when it is diluted 1/10 with only ultrapure water is shown. The measurement sample was prepared by dissolving industrial sodium chloride in water, converting the solution into saturated saline, and treating it with a highly purified salt solution obtained by chelating with a resin to dilute it to a salt concentration of 30 g / liter. Was served. In this measurement, the dilution liquid used for 1/10 dilution of the salt water sample was 50 ml of commercially available 30% hydrogen peroxide solution, 0.5 ml of 85% phosphoric acid, and 2 mg of standard lanthanum for atomic absorption. One prepared with ultrapure water containing no alkaline earth metal to 1 liter (Example 2),
Two types, which were diluted with ultrapure water containing no modifier (Comparative Example 1), were used.

As standard solutions of calcium, magnesium, strontium and barium used in this measurement, commercially available standard solutions for atomic absorption of 1000 ppm were used, and standard solutions of arbitrary three levels were prepared. The sample to be measured is an atomic absorption spectrometer
Set in the sampler, calcium, magnesium,
Comparative study was conducted on four elements, strontium and barium. From the comparison results, when the modifier of the present invention was used (Example 2), bumping or volatilization of the sample due to the alkali metal salt present in a large amount in the sample solution did not occur, and a good calibration as shown in FIG. Lines are now available.

When the salt water sample was continuously measured and the salt water was diluted only with ultrapure water containing no modifier (Comparative Example 1), the cuvette life was 40 times, whereas the cuvette life was 40 times. In this case, the cuvette life was about 150 times, and the cuvette life was greatly extended.

[0039]

EFFECT OF THE INVENTION By adding the modifier of the present invention and adjusting the alkali metal salt concentration, alkaline earth metals such as calcium, magnesium, strontium and barium can be rapidly and highly sensitive under the same atomic absorption analysis conditions.・ High-precision quantitative analysis is possible, and the life of the cuvette for continuous measurement can be extended. By using the method of the present invention, for example, the reliability of the process control of the alkaline earth metal in the salt water supplied in the salt electrolysis of the ion exchange membrane salt electrolysis can be remarkably increased, and its practicality is extremely large.

[Brief description of the drawings]

FIG. 1 is a comparison diagram of a calibration curve of a standard solution sample obtained by diluting a measured salt solution with a diluent of 1/10 with a modifier of the present invention and ultrapure water, and optionally adding a calcium standard solution. The vertical axis indicates absorbance, and the horizontal axis indicates calcium concentration.

FIG. 2 is a comparison diagram of a calibration curve of a standard solution sample obtained by diluting the measured salt water to 1/10 with two types of diluents of the modifier of the present invention and ultrapure water, and optionally adding a magnesium standard solution. The vertical axis indicates the absorbance and the horizontal axis indicates the magnesium concentration.

FIG. 3 is a comparison diagram of a calibration curve of a standard solution sample obtained by diluting the measured salt water to 1/10 with two types of diluents of the modifier of the present invention and ultrapure water and optionally adding a strontium standard solution. The vertical axis indicates absorbance, and the horizontal axis indicates strontium concentration.

FIG. 4 is a comparison diagram of a calibration curve of a standard solution sample obtained by diluting the measured salt water to 1/10 with two types of diluents of the modifier of the present invention and ultrapure water and optionally adding a barium standard solution. The vertical axis indicates the absorbance, and the horizontal axis indicates the barium concentration.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-5-157686 (JP, A) JP-A-59-193340 (JP, A) Food Research Institute Research Report, No. 55 (1991) pp. 45-48 Fresenius J. et al. Anal. Chem. 340 [9] (1991) p548-552 Anal. Chem. Acta. 215 [1/2] (1988) Anal. Sci. 3 [4] (1987) Z Ernaehrungswiss 20 [2] (1981) p119-131 Analytical chemistry 30 [6] (1981) pT65-T71 (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 21 / 00-21/01 G01N 21/17-21/74 G01N 33/00-33/46 JICST file (JOIS)

Claims (1)

(57) [Claims] When a trace amount of alkaline earth metal in an alkali metal salt water is quantitatively analyzed by a flameless atomic absorption spectrometer, a modifier consisting of hydrogen peroxide, phosphoric acid and lanthanum is added to the alkali metal salt water sample. And quantitatively analyzing the alkaline earth metal by flameless atomic absorption spectrometry.