JPS61108964A - Quantitative determination of trace calcium in aqueous solution - Google Patents

Abstract

PURPOSE:To make possible the exact and automatic quantitative determination of the concn. of trace calcium with a simple operation by adding an adequate masking agent to a sample soln. and utilizing a blank soln. with which the calcium-component is hardly detectable. CONSTITUTION:The sample soln. added at least with the masking agent for masking the calcium is used as a blank soln. and the quantitative determination of the trace calcium in an aq. soln. is executed in a colorimetric spectrochemical analysis method of the calcium. An ordinary chelate reagent to be used as a titrating reagent for chelate titration, for example, ethylenediaminetetraacetic acid is used for the masking agent. An ordinary colorimetric spectrochemical analysis method is used for the quantitative determination method. The aq. soln. contg. calcium ion is prepd. as the sample liquid and alizarin acid black SN is added as a color forming agent into the test liquid. Such liquid added with the masking agent is subjected as the blank soln. to colorimetry. Since the backgrounds of both the sample liquid and the blank soln. are commonly used, the errors by the liquid nature of the sample liquid are offset.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a method for quantifying trace amounts of calcium in an aqueous solution.

(Prior Art and Problems) Chelate titration, colorimetric analysis, atomic absorption spectrometry, tip spectrometry, and the like have been widely used as methods for quantifying calcium concentration in aqueous solutions.

When measuring trace calcium concentration, it is possible to measure a sample that does not contain coexisting salts, but it is difficult to measure when it contains coexisting salts, especially when the salt concentration is high.

Chelate titration is not suitable for trace analysis due to its high detection limit.

Recently, plasma emission spectroscopy has been proposed, but this method requires a large amount of argon gas and has drawbacks such as difficulty in incorporating it into the manufacturing process.

In particular, strict purification control is required for the supply and brine used in the alkali chloride salt electrolysis method using an ion exchange membrane, and along with this, a method for quantifying trace calcium concentrations on the order of 0.01 ppm is required. It's here.

The inventors first improved the colorimetric spectroscopic analysis method (Japanese Unexamined Patent Publication No. 1983-
5956), this problem has been addressed, but there are still issues to be considered.

(Purpose of the Invention) In view of the above points, the inventors conducted extensive studies with the aim of obtaining a method for accurately quantifying microm calcium concentration with simple operations. As a result, the inventors discovered that the above objective can be fully achieved by using a sample solution with a certain reagent added as a blank solution in the colorimetric spectroscopic analysis of calcium compounds, leading to the completion of the present invention. It is something.

(Structure of the Invention) That is, the present invention is characterized in that a trace amount of calcium in an aqueous solution is used as a blank solution in a colorimetric spectroscopic analysis method for calcium. This is a quantitative method. In this specification, the term "trace calcium" refers to not only a trace amount of calcium alone but also a case in which a trace amount of magnesium is present together.

The masking agent used in the present invention includes common chelating reagents used as titration reagents in chelate titration, such as ethylenediaminetetraacetic acid (hereinafter referred to as EDTA), ethylene glycol bis(2-aminoethyl)etherdiaminetetraacetic acid (hereinafter referred to as GEDTA), and ethylenediaminetetraacetic acid (hereinafter referred to as EDTA). ), tra
ns -1,2-cyclohexanediaminetetraacetic acid, diethylenetriaminepentaacetic acid, triethylenethe1-raminhexaacetic acid, oxyethylethylenediaminetriacetic acid M (hereinafter referred to as HE
It's called DTA. ), ethylenediaminetetramethylenetetraphosphoric acid, etc. or salts thereof, or 2,3-dimercapto-
Examples include masking agents such as 1-propatool (hereinafter referred to as BAL). The amount of the masking agent to be added may be as long as it is necessary to mask calcium, and there is no adverse effect even if a large amount is added, but usually 0,002% by weight or more in the test solution is sufficient.

When GEDTA, HEDTA, and BAL among the above-mentioned masking agents are added to the sample liquid and used as a blank solution, only the calcium content in the sample liquid is masked, but the magnesium content is not masked. Therefore, if a sample solution is subjected to colorimetric spectroscopic analysis using this as a blank solution, only the calcium concentration can be determined.

When using masking agents other than those mentioned above, such as EDTA, not only the calcium content but also the magnesium content is masked.
The calcium concentration can be determined by adding up the magnesium concentration converted to the calcium concentration.

To carry out the present invention, a conventional method for quantifying calcium concentration using colorimetric spectrometry is applied.

For example, as a sample solution, calcium ion 0.005 to 1
,0OE) DI-containing aqueous solution p)-111,5-13
．． 0, and added Alizarin Acid Black SN as a coloring agent to o,ooot~0.01% by weight in the test liquid, and to this, 0,002% by weight or more of the masking agent in the test liquid was added as a blank. Measurement wavelength 5 as a solution
After adjusting 100 at 47rv (0 for absorbance),
Compare colors. In this case, the addition m of the coloring agent is o, o in the test solution.
If it is less than 0.01% by weight, no color will develop, and if it exceeds 0.01% by weight, excessive coloration will occur, making absorbance measurement difficult.

In addition, when the DH of the test solution is less than 11.5, alizarin acid black SN and calcium ions do not react, so no discoloration occurs, and when it exceeds 13.0, alizarin acid black SN is hydrolyzed, resulting in poor reproducibility. Good absorbance cannot be obtained.

(Actions and Effects of the Invention) The present invention uses a blank solution based on a sample solution,
Since the background of both the sample solution and blank solution is the same, errors caused by the liquid properties of the sample solution can be canceled out, and a calibration curve passing through the origin can be shared for the same type of sample. .

In particular, it is an effective quantitative method for sample solutions containing a large amount of coexisting salts, such as the above-mentioned highly concentrated alkali chloride brine for ion exchange membrane electrolysis.

The present invention makes it possible to use a blank solution in which almost no calcium is detected by adding an appropriate masking agent to the sample solution. 11) Range below DI, especially number 1) I)
This enabled calcium analysis of b.

The present invention can accurately quantify the concentration of trace amounts of calcium even in sample solutions containing coexisting ions other than magnesium by appropriately selecting measurement conditions such as the type of masking agent and the measurement wavelength.

Since the present invention can be quickly and easily automatically quantified, it can be incorporated into production processes.

As described above, the present invention is extremely useful industrially because it allows the concentration of trace amounts of calcium in an aqueous solution to be determined accurately with a simple operation.

In particular, the present invention has great utility as a method for determining the concentration of calcium in salt water, such as salt water for ion-exchange membrane chloride alkali electrolysis, which is greatly influenced by the concentration of trace amounts of calcium.

The present invention will be specifically explained in detail with reference to Examples below. All concentration percentages in the text are based on heavy ff1l.

Example 1 A series of standard coloring solutions prepared by adding specific amounts of calcium ions and magnesium ions to saturated saline solution and a series of blank solutions prepared by adding masking agents respectively were prepared, and each was measured using a spectrophotometer. Obtain the absorbance reading, and separately measure the calcium concentration using a plasma emission spectrophotometer to create a calibration m-line.

Preparation of solution j Salt solution purified with chelating resin (Na C13009/
f) J of magnesium ion and calcium ion
IS standard reagent was added to adjust the magnesium concentration to 0. O5p
Calcium concentration in pm is 0.01 and 0.15, respectively.
, 0.3G, 0.45, 0.60E)l
) - Make a standard stock solution. Take 50w of the solution in a beaker, add 10% Na 0f-1 aqueous solution, and adjust the pH to 12.
, adjusted to 8 l 001% Alizarin Acid Black S
Standard coloring solutions were prepared by adding 2 ml of N aqueous solution and adding pure water to make 100 ml.

Preparation of Blank R Solution 1 Take 50 x 4 of the above standard stock solution into a beaker, and add 10%N
a After adjusting the pH to 12.8 by adding an OH aqueous solution, add 2 e of an M/100 GEDTA aqueous solution as a masking agent, and add 0.1% Alizarin Acid Black S in the same manner as above.
N aqueous solution 2- was added, and pure water was added to make the solution for 100 s (l), each of which was used as a blank solution.

1 Cliff 11 Sushi L Using a self-recording spectrophotometer (LIV204 manufactured by Shimadzu Corporation), the absorbance of the standard coloring solution was measured at a measurement wavelength of 547rv after 100% adjustment (0 in absorbance) with each of the above blank solutions. .

Creating a calibration curve Calcium concentration of the above standard stock solution was measured using a plasma emission spectrophotometer (ICAP 575M manufactured by Nippon Jarrell Atshu Co., Ltd.).
FIG. 1 shows a calibration line created by plotting the values measured with ARK 2 (type 2) on the horizontal axis and the absorbance measurements described above on the vertical axis.

Separately, the magnesium concentration of the above stock solution was measured using a plasma emission spectrophotometer, and the calcium concentration was 0.0
51. 0.05G, 0,052. It was 0.051°0.050 ppm.

In order to create a calibration curve for calcium levels, the calibration curve was created in the same manner except that EDTA was used as the above-mentioned masking agent, and the obtained calibration curve was a straight line with almost the same slope as in Figure 1. . However, the unit of the horizontal axis is the calcium concentration (which is the sum of the magnesium concentration converted to the calcium concentration).
ppm) was used.

Example 2 7% Na2 with trace amounts of calcium and magnesium
A test solution and a blank solution were prepared in the same manner as in Example 1, except that 50 μa of SOa aqueous solution was placed in a beaker and 2 μC of M/100 EDTA aqueous solution was used as a masking agent.

The absorbance of the test solution was measured in the same manner as in Example 1 and was found to be 0.
．． 026, and the calcium concentration was 0.113 ppm+ from the M line in Figure 1. (However, the units on the horizontal axis in the M-line in Figure 1 are read as calcium concentration (DI) I). ) Separately, the calcium and magnesium concentrations of the test solution were measured using a plasma emission spectrophotometer, and found to be 0.1105 pp+ of calcium and 0.1 pp+ of magnesium.
It was 0.015 ppm.

In conventional colorimetric spectroscopy, it is necessary to investigate the liquid properties of the rimple and prepare a calibration curve based on an aqueous solution with the same liquid properties.
In the present invention, a blank solution is obtained by adding GEDTA, HEDTA, or BAL as a masking agent to the sample for quantifying the concentration of trace calcium, and adding the above-mentioned masking agent such as EDTA to the sample for quantifying the concentration of trace calcium. Calcium concentrations can be determined quickly and easily using a calibration curve.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between absorbance and calcium concentration in the method of the present invention.

Claims (3)

[Claims] (1) A method for quantifying trace amounts of calcium in an aqueous solution, which comprises using a sample solution to which at least a masking agent for masking calcium is added as a blank solution in colorimetric spectrometry of calcium. (2) Claim 1 in which alizarin acid black SN is used as a coloring agent in the colorimetric spectroscopic analysis method.
Quantification method described in section. (3) The quantitative method according to claim 1, wherein the sample liquid is an aqueous alkali chloride solution.