JP2557152B2 - Concentration measurement method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a concentration measuring method, and more particularly to a concentration measuring method suitable for continuously measuring the concentration of a substance which dissociates into ions in a solution and has a vapor pressure in a non-dissociated state. .

[0002]

2. Description of the Related Art Conventionally, as a method for automatically measuring the concentration of a substance to be measured such as ammonia, carbonic acid and hydrochloric acid in a sample solution,
A method is known in which an acid, an alkali, or a pH buffer solution is added to a sample solution to increase the vapor pressure of the substance to be measured in the sample, and then a gas measuring electrode with a diaphragm is immersed in the vapor pressure for measurement. However, the above measuring method requires a cylinder pump or a stirrer for injecting a fixed amount of acid, alkali or pH buffer solution into the sample solution, which complicates the apparatus and causes many measurement error factors. There is a problem that the measurement accuracy is lowered and the cost of the device is increased.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a concentration measuring method which eliminates the above-mentioned problems of the prior art, simplifies the apparatus, and enables highly accurate measurement.

[0004]

The present invention increases the vapor pressure of a substance to be measured by adjusting the pH of a solution containing the substance to be measured which dissociates ions in a solution and has a vapor pressure in a non-dissociated state. When continuously measuring the concentration of the substance to be measured in the solution with a gas electrode with a diaphragm, the pH of the solution is continuously adjusted with the solution and an acid solution, an alkaline solution or a pH buffer solution through an ion exchange membrane. The present invention relates to a method for measuring concentration, which is characterized in that the concentration measurement is carried out by contacting them physically.

The method of the present invention is used to measure the concentration of a substance which dissociates ions in a solution and has a vapor pressure in a non-dissociated state, such as ammonia, carbonic acid or hydrochloric acid. In the present invention, when measuring the concentration of a substance to be measured, the pH of the solution containing the substance is adjusted in advance in order to increase the vapor pressure of the substance and gasify it in the electrode chamber. The pH is adjusted by continuously contacting the solution with an acid solution, an alkaline solution or a pH buffer solution through an ion exchange membrane. For example, an acid solution, an alkaline solution, or a pH buffer solution for pH adjustment is injected into one of the chambers or passages, at least one surface of which is partitioned by an ion exchange membrane, and the other chamber or the other chamber facing the ion exchange membrane is provided. The solution containing the substance to be measured is continuously passed through the passage. When the substance to be measured is ammonia, the pH is adjusted to 11 or higher. The solution adjusted to a predetermined pH is introduced into the electrode chamber of the gas electrode with a diaphragm, and the concentration of the gasified target component is continuously measured by the gas electrode.

As the ion exchange membrane, an anion or cation exchange membrane based on a fluororesin, a polyethylene sulfonic acid type ion exchange membrane and the like are preferably used. Further, as the ion exchange membrane tube, for example, Nafion 117 (trade name of fluorinated resin cation exchange membrane) manufactured by DuPont is used. As the gas electrode with a diaphragm, a commercially available electrode such as an ammonia electrode or a carbon dioxide electrode is used.

FIG. 1 is an explanatory view of a concentration measuring apparatus showing an embodiment of the present invention. This apparatus includes a pH adjusting container 3 having an ion exchange membrane tube 2 therein, a sample solution inlet 5 for introducing a sample solution into the ion exchange membrane tube 2 via a cleaning solution switching valve 9A, and an electrode chamber 4. Gas electrode 1
And a liquid feed tube 7 connecting the ion exchange membrane tube 2 and the electrode chamber 4 via a cleaning liquid switching valve 9, and a cleaning liquid tank 10 connected to the cleaning liquid switching valve 9.

In such a structure, the sample solution is injected from the sample solution injection port 5 and passes through the ion exchange membrane tube 2 in the pH adjusting container 3. In the pH adjusting container 3, p
Since the H adjusting solution (acid solution, alkaline solution or pH buffer solution) is injected, the sample solution is the ion exchange membrane tube 2
When passing through the inside, the pH is adjusted through the ion exchange membrane. The pH-adjusted sample liquid is guided to the electrode chamber 4 through the liquid feeding tube 7, and a voltage is applied to the gas electrode 1 by the lead wire 8 to measure the concentration of the substance to be measured in the sample liquid. After that, the sample solution is discharged from the sample solution discharge port 6 to the outside of the system. When deposits are deposited on the ion exchange membrane tube 2, the solution sending tube 7 or the electrode chamber 4 by continuous flow of the sample solution, the cleaning solution switching valves 9A, 9 are switched to inject the cleaning solution from the cleaning solution tank 10, Cleaning is performed.

FIG. 2 is a structural explanatory view showing an example of a pH adjusting cell using the ion exchange membrane sheet used in the present invention. This cell is obtained by sequentially stacking spacers 14A and 14B and holding plates 15A and 15B on both sides of the ion exchange membrane sheet 13, and inserting bolts into the bolt through holes 16 to connect them. Spacer 14A
The sample solution inlet 5 and the outlet 6 are provided in the spacer 14B.
Is provided with a pH adjusting liquid inlet 11 and an outlet 12, and the sample liquid and the pH adjusting liquid are continuously injected from the respective inlets and come into contact with each other through the ion exchange membrane sheet 13 to adjust the pH. Done.

According to the method of the present invention, it is not necessary to inject the acid or alkali for pH adjustment with a pump, and it is not necessary to stir after the injection, so that the structure of the apparatus can be simplified, and It is possible to maintain high analysis accuracy.

[0011]

EXAMPLES The present invention will be described in detail below with reference to examples. Example 1 The ammonia concentration in seawater was continuously measured using the apparatus shown in FIG. Nafion 1 for ion exchange membrane tubes
17, a 2N-NaOH solution was used as the alkalinity adjusting solution, and a diaphragm type pH electrode for ammonia detection was used as the detection electrode. The temperature of the signal obtained at the detection electrode was corrected. As a result of the measurement, ammonia was not detected in seawater,
Ammonia was added to seawater so as to have an ammonia concentration of 0.5 ppm and 1.0 ppm, respectively, and then measured. As a result, the ammonia concentration could be measured within the concentration measurement error of ± 0.05 ppm.

Example 2 Using the apparatus shown in FIG. 1, the total carbonic acid concentration of an aqueous NaHCO ₃ solution was measured under the following conditions. Ion exchange membrane tube: Nafion 117 Acidity adjusting solution: pH 4 Phosphate-sodium phosphate buffer Detection electrode: diaphragm type glass electrode for CO ₂ measurement As a result of the measurement, NaHCO _{3 having} a concentration of 0.05 to 5% by weight.
It was possible to measure with an error within ± 0.01%.

Example 3 In Example 2, the acidity adjusting liquid was changed to 10 NH₂SO_Four
HC in the aqueous solution under the same conditions as in Example 2 except that
Measured l concentration and confirmed that HCl can be quantified
did. Example 4 In Example 1, the ion-exchange membrane membrane was subjected to long-term continuous operation.
Since brown deposits were found in the tube, the cleaning liquid switching valve in Fig. 1
Cleaning liquid (0.5N-H ₂S
O_Four), All deposits were washed away.
Was.

Example 5 The same procedure as in Example 2 was repeated except that the pH adjusting container 3 shown in FIG. 1 was replaced with a cell using an ion exchange membrane sheet shown in FIG.
The total carbonic acid concentration of the HCO ₃ aqueous solution was measured, and the same results as in Example 2 were obtained. Example 6 A temperature controller was attached to the pH adjusting container 3 shown in FIG. 1 to omit the temperature correction of the detector signal, and the ammonia concentration was measured in the same manner as in Example 1, but the ammonia concentration was as accurate as in Example 1. The concentration could be measured.

[0015]

According to the concentration measuring method of the present invention, (1)
Install a cylinder pump or stirrer for pH adjustment
Since it does not need to be installed, the device is simple, lightweight and low cost.
(2) Easy cleaning of ion exchange membrane and detection electrode
Therefore, maintenance and inspection of the device is easy and
The time can be greatly reduced, and (3) CO₂, NH
₃It is easy to achieve higher sensitivity than before when measuring
In addition, (4) by making the pH adjustment container into a constant temperature bath,
This eliminates the need for temperature correction and improves measurement accuracy.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a concentration measuring device showing an embodiment of the present invention.

FIG. 2 is a structural explanatory view of a pH adjusting cell using the ion exchange membrane sheet used in the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Gas electrode, 2 ... Ion exchange membrane tube, 3 ... pH adjustment container, 4 ... Electrode chamber, 5 ... Sample liquid inlet, 6 ... Sample liquid discharge port, 7 ... Liquid sending tube, 8 ... Lead wire, 9A, 9 ... Cleaning liquid switching valve, 10 ... Cleaning liquid tank, 11 ... pH adjusting liquid inlet, 12 ... pH adjusting liquid discharge port, 13 ... Ion exchange membrane sheet, 14A, 14B ... Spacers, 15A, 15B
... Presser plate, 16 ... Bolt through hole.

Claims (1)

(57) [Claims] 1. The pH of a solution containing a substance to be measured which dissociates ions in the solution and has a vapor pressure in a non-dissociated state.
When continuously measuring the concentration of the substance to be measured in the solution by adjusting the gas electrode with a diaphragm, the pH of the solution is adjusted with the acid solution, the alkaline solution or the pH buffer solution by an ion exchange membrane. A method for measuring concentration, which is characterized in that it is continuously contacted via the method.