JPH09318615A - Quantitative determination method of metal ion in aqueous solution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable quantitative determination of a metal ion by measuring absorbance at a wavelength in an absorption spectral band width of a coloring matter or a water soluble dye and substituting a specific equation with the measured absorbance. SOLUTION: The coloring matter or water soluble dye is either one which forms a complex at a ratio with a metal ion in a solution which is a target to be quantitatively measured and the metal ion is a free ion, which is not bonded with a different material co-existent in the solution. An absorbance Ea at wavelength (a) in the absorption spectral band width of the coloring matter or the water soluble dye is measured and an equation is substituted with the measured absorbance Ea to obtain P as a quantitative value of the metal ion, where εa1 is a molar absorption coefficient of a coloring matter, εa2 is a molar absorption coefficient of the coloring matter which has formed a complex with a metal to be measured and εa is a molar absorption coefficient of a sample solution containing the coloring matter at a wavelength (a).

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for quantifying metal ions in a solution, particularly alkaline earth metal ions such as calcium ion in a solution containing an activator.

[0002]

2. Description of the Related Art When washing clothes with a detergent containing an anionic surfactant as a main component, the detergency thereof is affected by divalent metal ions in water, particularly calcium ions.
Therefore, the detergent has been devised to reduce the concentration of calcium ions, for example, by incorporating a builder that blocks the calcium ions in the washing liquid. Therefore, it is important to know the calcium ion concentration in the washing liquid in designing the detergent composition. As a method for measuring the calcium ion concentration, a measurement method using a calcium ion selective electrode is conventionally known. However, this method is not suitable for measurement in a system coexisting with a surfactant, and the effect of the builder, that is, the amount of sequestration of calcium ions, etc. must be estimated from the measurement value in a system containing no surfactant different from the actual conditions. Didn't get In addition, a method by titration using EDTA or the like,
Although a method in which a dye is added in a large excess and measured by a colorimetric method is also known, these can only provide information on the total amount of calcium in the solution (the sum of bound and unbound calcium). A method for easily and accurately measuring the amount of unbound calcium ions in the presence of a surfactant has not been known.

[0003]

The present invention provides a suitable method for quantifying metal ions in solution, especially alkaline earth metal ions such as calcium ions in a solution containing an activator.

[0004]

The present invention is a method for quantifying metal ions in a solution by adding a dye or a water-soluble dye, wherein the absorbance at a wavelength a within the absorption spectrum range of the dye or the water-soluble dye. Is measured, and the metal ion is quantified by obtaining P represented by the formula (1). The metal ion of the present invention means a free ion that is not bound to other coexisting substances in the solution.

[Equation 1] εa1; molar extinction coefficient of dye εa2; molar extinction coefficient of dye that forms a complex with the measurement metal εa; molar extinction coefficient of dye-containing sample solution at wavelength a

The dye or water-soluble dye used in the present invention is
A dye or a water-soluble dye that forms a complex with a metal to be measured in a solution, preferably a complex formation stability constant k
The product of d and the metal concentration in the solution [M] (mol / liter) k
d × [M] is 0.01 to 100, more preferably 0.
It is from 1 to 10. The total amount of metal in the solution can be determined by a conventional method such as titration using EDTA (JIS K0101 industrial water test method, metal chelate titration method). More preferably, it is a dye or a water-soluble dye that forms a complex with the metal ion to be measured at a constant ratio. These form a complex with a metal ion to obtain an absorption spectrum having an isosbestic point even if the concentration of the metal ion changes, and the absorbance at the isosbestic point is used to easily and accurately determine the metal ion concentration. It is possible to measure. For example, when measuring calcium ions in a low-concentration solution having a pH of 10.5 and a total calcium concentration of about 1 to 2 mM or less, dyes such as Pontachrome Violet, Murexide, Hydroxynaphthyl Blue, and Eriochrome Black T are used. It can be used suitably. In particular, hydroxynaphthyl blue with Log kd = 4.4 also [Ca] when the total calcium amount is 1 mmol.
* Kd = 25, [Ca] when 0.5 mmol * Kd =
12, preferably used. Further, Pontachrome violet having a Log kd = 3.5 with calcium at pH 10.5 has a [Ca] * Kd = 6.3 when the total calcium concentration is 2 mmol and a [C] when the total calcium concentration is 1 mmol.
a] * Kd = 3.2, [Ca] * when 0.5 mmol
Kd = 1.6, which is more preferable. The amount of the pigment or dye used is preferably not more than the metal concentration [M] (mol / liter) in the solution. If the amount is too large, the dye or dye may shift the equilibrium of the components in the solution to a non-negligible level, so that accurate quantification cannot be expected.

Next, the method for quantifying metal ions in the solution of the present invention will be described. Before performing this method, the total amount of calcium [M] (mol / liter) in the solution is measured by a conventional method, for example, a titration method using EDTA, and kd ×
It is advisable to determine a pigment or water-soluble dye whose [M] falls within the range of 0.01 to 100, more preferably 0.1 to 10. Moreover, a series of measurements in this method are all performed at a constant temperature, pH, dye amount, and salt concentration. Note that if the salt concentration becomes too high, the accuracy decreases, so the total concentration of coexisting salts, surfactants, etc. is suitably 0.1% or less.

[0007] 1. Determination of constants ε0, εa1, εa2 Metal ion concentration 0 (Sample A) and metal concentration [M]
A solution of about 5 times (mol / liter) or more (Sample B) is prepared and their absorption spectra are measured, and the wavelength a at which the difference in absorbance between A and B is maximized is determined, and The molar extinction coefficient is determined from the measured absorbance and the amount of dye added. The molar extinction coefficient (unit: liter / mol) is the value obtained by dividing the absorbance by the dye concentration. When it has an isosbestic point, the molar extinction coefficient at the isosbestic point is similarly obtained. Here, if too much dye is added to the metal to be measured, the equilibrium of the system will shift due to the dye and accurate measurement values will not be obtained, so the dye amount should be smaller than the actually measured metal amount. Is desirable.

2. Preparation of calibration curve Samples 4 to 5 for calibration curve in which the metal ion concentration is changed are prepared, and their absorption spectra are measured. The molar extinction coefficient obtained from the absorbance value Ea at the wavelength a is (1)
Substitute into the formula to find P. When the dye or water-soluble dye has an isosbestic point in the concentration change, the absorbance values at the isosbestic point and the wavelength a are measured, and the absorbance at each point is substituted into the formula (2) to obtain P. Ask.

[Equation 2] εa1; molar extinction coefficient of dye εa2; molar extinction coefficient of dye forming a complex with a measurement metal ε0; molar extinction coefficient of dye at isosbestic point Ea; absorbance of dye-containing sample solution at wavelength A E0; at isosbestic point Absorbance of dye-containing sample solution Molar extinction coefficient = absorbance / [M ′]: M ′ is a dye or water-soluble dye concentration Each metal ion concentration [M] and the value of P are plotted as a calibration curve.

3. Measurement of sample The spectrum of the sample solution is measured, and P is determined in the same manner as 2. From this P value, the metal ion concentration can be determined using the calibration curve obtained in 2.

By the above method, the amount of metal ions in the solution can be quantified. In particular, it has become possible to easily measure the calcium ion concentration in an active agent coexisting system, which was difficult to measure by the conventional method. Hereinafter, further description will be given with reference to examples.

[0010]

【Example】

(Experiment 1) Calcium ion scavenger NT in the following aqueous solution
The residual hardness when A and citric acid were added was measured. Sodium carbonate 250ppm Calcium chloride 59.4ppm Pontachrome violet 10ppm pH at this time = 10.5-10.6, measurement temperature is 2
Performed at 5 ° C. 1. Determination of εa1, εa2, ε0 Samples A and B for determining constants were adjusted as follows.
In a 100-mL volumetric flask, 70 mL of pure water at 25 ° C was placed, 5 mL of 0.5% sodium carbonate solution and 2 mL of 0.05% dye solution were added, and then water was added up to the marked line (Sample A). In a 100 ml volumetric flask, 20 ml of pure water at 25 ° C. was placed, and after adding 5 ml of 0.5% sodium carbonate solution, 60 ml of 0.099% calcium chloride solution and 2 ml of 0.05% dye solution, Water was added up to the marked line (Sample B). The absorption spectra of A and B were measured by Hitachi spectrophotometer U-3000. From the spectrum, the isosbestic point was 520 nm, and the wavelength at which the difference in absorbance between A and B was maximum was 575 nm. 575n of sample A
Table 1 shows εa1 determined from the absorbance value of m, εa2 determined from the absorbance value of sample B at 575 nm, and ε0 determined from the absorbance value at the isosbestic point.

[Table 1]

2. Preparation of calibration curve In a 100 ml volumetric flask, add 70 ml of pure water at 25 ° C, add 0.5 ml of 0.5% sodium carbonate solution 5 ml 0.099% calcium chloride solution 6 ml 0.05% dye solution 2 ml. After that, water was added up to the marked line. At this time, the calcium ion concentration of water is 0.54 mM. Similarly,
Water having a calcium ion concentration of 0.18 mM, 0.36 mM N 0.71 mM was prepared. PH of these systems
Was 10.6. 520 for these samples
Absorbance at nm (isosorption point) and 575 nm was measured by Hitachi spectrophotometer U-3000, P was obtained from the equation (2), and shown in Table 2. The relationship between calcium concentration and P is shown in FIG. From equation (1), when the calcium concentration is 0,
P = 1 and a good linear relationship with a correlation coefficient of 0.9992 passing through this point was obtained.

[Table 2]

FIG.

3. Measurement of sample solution In a 100-mL volumetric flask, add pure water 7 at 25 ° C.
Add 0 ml and add 0.5% sodium carbonate solution 5
Milliliter, 6 milliliter of 0.099% calcium chloride solution, and 2% of NTA solution adjusted to pH 10 were added to a predetermined concentration, and water was added up to the marked line. 0.
2 ml of 05% Pontachrome Violet solution was added. Similarly, a sample solution in which an aqueous citric acid solution was added instead of NTA was prepared, and the absorption spectra of both sample solutions were measured. 520nm (isosorption point) and 575
The value of P is calculated from the absorbance at nm and 2. The calcium ion concentration was determined from the calibration curve of. The residual calcium ion concentration calculated from the theoretical amount of trapped calcium of NTA and citric acid was calculated, and the results are shown in Table 3 and FIG. Pkca in the calculation of the theoretical amount of trapped calcium ions is NTA: 6.
6, citric acid: The numerical value of 4.1 was used, and the theoretical value is shown by the dotted line in FIG.

[0013]

[Table 3]

[Fig. 2] From Table 3 and FIG. 2, it can be seen that the calcium ion amount could be accurately measured by the present invention.

(Experiment 2) The residual hardness when the calcium ion scavenger NTA and citric acid were added to the following aqueous solution containing an activator was measured. Sodium dodecylbenzene sulfonate (LAS-N
a) 200 ppm Sodium carbonate 250 ppm Calcium chloride 59.4 ppm Pontachrome violet 10 ppm At this time, the pH was 10.5 and the measurement temperature was 25 ° C. 1. Determination of εa1, εa2, ε0 The values of (Experiment 1) were used. 2. Preparation of calibration curve The value of (Experiment 1) was used. 3. Measurement of sample solution 70 ml of pure water at 25 ° C in a 100 ml volumetric flask
, 0.5% LAS-Na 4 ml, 0.5% sodium carbonate solution 5 ml, 0.099% calcium chloride solution 6 ml, 0.5% NTA aqueous solution 2 ml adjusted to pH 10 were added, and water was added up to the marked line. added. 0.05 for this
2 ml of a% Pontachrome Violet solution was added. Similarly, a sample solution in which the same amount of citric acid aqueous solution was added instead of NTA was prepared, and the absorption spectra of both sample solutions were measured. 520nm (isosorption point) and 575nm
Calculate the value of P from the absorbance of 2. The calcium ion concentration was determined from the calibration curve of, and the results are shown in Table 4.

[0015]

[Table 4] From Table 4, according to the present invention, the amount of calcium ions could be measured even in the system coexisting with the active agent.

(Experiment 3) Calcium ion concentrations of 0.36, 0.54, 0.71,
The relationship between P and calcium concentration was investigated at 0.89 mM. The experiment method is the same as that of Experiment 1 except that only the dye to be added is different. Here, the value of [M] kd is
The calculated value at M = 0.5 mM is shown in Table 5 and FIG.
It was shown to. There is a good linear relationship between P and the calcium ion concentration, and the calcium ion can be accurately measured.

[0017]

[Table 5]

[Figure 3]

Claims (1)

[Claims] 1. A method for quantifying metal ions in a solution by adding a dye or a water-soluble dye, which comprises an absorbance E at a wavelength a within the absorption spectrum of the dye or the water-soluble dye.
A method for quantifying metal ions in an aqueous solution, which comprises quantifying metal ions by measuring a and determining P represented by the formula (1). εa1; molar extinction coefficient of dye εa2; molar extinction coefficient of dye that forms a complex with the measurement metal εa; molar extinction coefficient of dye-containing sample solution at wavelength a