JP2004333413A - Moisture measuring method and moisture measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a moisture measuring method by the Karl Fischer's method improved so that a problem of a measurement failure caused by a detection electrode can be solved surely by a simple operation. <P>SOLUTION: In this moisture measuring method by the Karl Fischer's method, conditioning of the detection electrode wherein a low-frequency alternating voltage is applied to the detection electrode dipped in a titration solvent or an anolyte before measurement is performed at every time of exchange of the titration solvent or the anolyte. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a moisture measuring method and a moisture measuring device, and more particularly, to a moisture measuring method and a moisture measuring device by a Karl Fischer method.
[0002]
[Prior art]
A water content measuring method and a water content measuring device by the Karl Fischer method (KF method) are well known. There are two methods of measuring water content by the KF method: volumetric titration and coulometric titration. The outline of each method is as follows.
[0003]
In the volumetric titration method, a sample is added to a titration solvent (also called a dehydrated solvent) contained in a titration tank, titrated with a KF reagent (mainly composed of iodine, sulfur dioxide, and a base), and a detection electrode immersed in the titration solvent. This is a method of detecting the end point by using The measurement of moisture in a sample is started by adding a measurement sample after dropping a KF reagent necessary for dehydrating the inside of a titration tank.
[0004]
FIG. 2 is an explanatory diagram of an example of a known volumetric type automatic moisture titrator. A detection electrode (11) is arranged inside the titration tank (10), a sample inlet (12) is provided on the upper side, and a rotor rotated by a magnetic stirrer (13) is provided on the bottom. A drying pipe (15) is connected to the upper lid, and a titration nozzle (22) connected to the end of a pipe extending from the automatic switching valve (21) is installed on the upper lid. On the other hand, a burette (20) and a reagent container (30) are connected to the automatic switching valve (21) by a pipe, and a drying tube (31) is connected to the internal space of the reagent container (30). A drive unit (not shown) for the burette / automatic switching valve is provided below the burette (20). The detection of the signal from the detection electrode (11) and the automatic control of the volume titration are performed by the detection unit (41) and the control unit (42), and the results are displayed by the display unit (43) and the recording unit (44). It is processed. The titration solvent (5) is contained in a titration tank (10), and the KF reagent (6) is contained in a reagent container (30).
[0005]
On the other hand, the coulometric titration method is a method using an electrolytic solution in which iodine in a KF reagent is replaced by iodide ions, and is suitable for an anode solution and a cathode solution provided in a titration tank, respectively. This is a method in which an anolyte solution and a catholyte solution are accommodated, and a sample is added to an anode chamber in which a detection electrode is arranged to perform electrolytic oxidation. In the anode chamber, the electrolyte functions as a KF reagent by iodine generated by electrolytic oxidation and reacts with water in the sample. Therefore, the measurement of the moisture in the sample is started by adding the measurement sample after converting the iodide ion to iodine by electrolytic oxidation in the anode chamber and dehydrating the inside of the titration tank. Then, the measurement is continued until the water in the measurement sample is consumed by the iodine converted by the electrolytic oxidation.
[0006]
FIG. 3 is an explanatory view of an example of a known coulometric automatic moisture titrator. A detection electrode (11) is arranged inside the titration tank (10), a sample inlet (12) is provided on the upper side, and a rotor rotated by a magnetic stirrer (13) is provided on the bottom. (14) is arranged. The titration tank (10) is divided into an anode chamber (10a) having an anode (16) and a cathode chamber (10b) having a cathode (17), and the anode (16) and the cathode (17) are separated by a diaphragm ( 18), the detection electrode (11) is arranged in the anode compartment (10a). Drying tubes (19a) and (19b) are connected to the internal spaces of the anode chamber (10a) and the cathode chamber (10b), respectively. Each of the above electrodes is connected to an electrolytic current power supply (40), and detection of a signal from the detection electrode (11) and automatic control of coulometric titration (electrolytic oxidation) are performed by a detection unit (41) and a control unit (42). These results are processed by the display unit (43) and the recording unit (44). The anolyte (7) and the catholyte (8) are contained in the anolyte compartment (10a) and the catholyte compartment (10b).
[0007]
As described above, the principle of moisture measurement in the volumetric titration method and the coulometric titration method is the same in that the Karl Fischer reagent is used. The detection electrode used is the same in both the volume titration method and the coulometric titration method. Basically, two platinum rods (diameter: about 1 mm, length: 5 mm) are inserted from the tip of the glass tube. 〜１０10 mm). The end point of the reaction (excess iodine) is monitored by monitoring a voltage generated between two platinum rods when a current of, for example, 25 μA is applied to the detection electrode.
[0008]
In the moisture measurement method by the KF method, after the first moisture measurement is completed, the next sample is added to the titration solvent in the titration tank (in the case of coulometric titration, the electrolytic solution in the anode chamber) in the case of the volumetric titration method. The second moisture measurement can be performed, and thereafter, a plurality of moisture measurements can be quickly performed in the same manner, so that it is used in various fields.
[0009]
However, in the continuous measurement as described above, there is an inconvenience that normal measurement cannot be performed, for example, an overtitration state occurs and the water content of the sample becomes high. In addition, depending on the history of the detection electrode, there is a symptom that the dehydration does not end even though the KF reagent is excessively titrated.
[0010]
Although the details of the cause of the measurement malfunction as described above are not yet clear, it is considered that the malfunction is caused by the detection electrode. As a countermeasure, a method of cleaning the detection electrode, specifically, a method of removing adhered substances with ethanol (or acetone) and wiping the glass boundary surface of the platinum tip with soft paper (for example, there is adopted) (See Non-Patent Document 1)
[0011]
However, in the above-described cleaning method, it is necessary to remove the detection electrode each time, and the operation is complicated, and there is a possibility that the platinum tip may be inadvertently damaged. In some cases, the recovery from the measurement failure may not be performed smoothly.
[0012]
[Non-patent document 1]
"Automatic Moisture Analyzer (Karl Fischer Volumetric Titration Automatic Moisture Analyzer) KF-100 Instruction Manual" (March 25, 1998, published by Mitsubishi Chemical Corporation, page 8-4)
[0013]
[Problems to be solved by the invention]
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for measuring water content by the Karl Fischer method, which has been improved so as to be able to solve the problem of measurement malfunction caused by a detection electrode with a simple operation and reliably. And a moisture measuring device.
[0014]
[Means for Solving the Problems]
The present inventors have conducted intensive studies and found that if a predetermined conditioning process is performed on a detection electrode before measurement, the above object can be easily achieved, and the present invention has been completed. Reached.
[0015]
That is, the first gist of the present invention is that the low-frequency AC voltage is applied to the detection electrode immersed in the titration solvent or the anolyte solution before the measurement every time the titration solvent or the anolyte solution is replaced in the moisture measurement method by the Karl Fischer method. The method for moisture measurement is characterized in that conditioning of a detection electrode to which is applied.
[0016]
The second gist of the present invention is to apply a constant voltage or a small current to a detection electrode immersed in a titration solvent or an anolyte to react the Karl Fischer reagent with water in the titration solvent or the anolyte. In a moisture measurement device equipped with a mechanism that monitors the progress of the reaction by monitoring the current or voltage in the system and performs moisture measurement, every time the titrant or anolyte is replaced, immerse it in the titrant or anolyte before measurement And a conditioning device for applying a low-frequency AC voltage to the detection electrode.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail.
[0018]
First, the moisture measurement method of the present invention will be described. The feature of the moisture measurement method of the present invention resides in the conditioning of the detection electrode before measurement. Therefore, the moisture measurement method itself can be performed in exactly the same manner as the conventional Karl Fischer moisture measurement method. Then, any of the capacitance method and the coulometric method may be used.
[0019]
The titration solvent used in the volumetric method is appropriately selected according to the type of the sample. Specific examples thereof include lower alcohols such as methanol and ethanol, chloroform, formamide, dimethylformamide, propylene carbonate and the like. As the electrolytic solution used in the coulometric method, a conventionally known electrolytic solution can be used.
[0020]
The shape and size of the detection electrode are not particularly limited and can be arbitrarily selected. A constant voltage or a small current is applied to the detection electrode, and the progress of the KF reaction is grasped by monitoring the current and voltage in the reaction system (reaction system between the KF reagent and water) generated at that time. For example, when water is present, the detection voltage is high, and when water is exhausted, the detection voltage is close to zero.
[0021]
In the present invention, a low-frequency AC voltage is applied to the detection electrode as conditioning of the detection electrode in order to solve the problem of measurement malfunction caused by the detection electrode. It is important that such conditioning be performed prior to measurement for the purposes of the present invention. In this respect, the present invention is different from the cleaning of the detection electrode performed after the measurement is completed. In the present invention, “before measurement” of the timing of conditioning the detection electrode means, in the case of the volumetric titration method, before dropping the KF reagent necessary for dehydrating the inside of the titration tank, and In the case of the titration method, it means before the iodide ion is converted into iodine by electrolytic oxidation in the anode chamber and the inside of the titration tank is dehydrated.
The above conditioning may be performed each time the titrant or anolyte is replaced.
[0022]
The above conditioning is performed on the detection electrode immersed in a titration solvent in the case of the volumetric method or in the anolyte in the case of the coulometric method. Therefore, in the present invention, there is no need to remove the detection electrode.
[0023]
In the above conditioning, the frequency of the low-frequency AC voltage is usually 0.01 to 100 Hz, preferably 1 to 10 Hz, and the voltage is usually 1 to 30 V, preferably 5 to 20 V. The application time of the low-frequency AC voltage is appropriately selected depending on the history of the detection electrode, the type of the measurement sample, and the type of the titration solvent, and is usually 5 to 500 seconds, preferably 30 to 200 seconds. The application of the low-frequency AC voltage can be performed by a conditioning current supply circuit.
[0024]
Next, the moisture measuring device of the present invention will be described. The moisture measurement apparatus of the present invention is a conventional Karl Fischer volumetric method (or coulometric method) automatic moisture measurement apparatus, which detects the immersion in the titration solvent or the anolyte solution before measurement every time the titration solvent or the anolyte solution is replaced. The present invention is characterized in that conditioning means for a detection electrode for applying a low-frequency AC voltage to the electrode is provided. Therefore, the configuration other than the conditioning means of the detection electrode is the same as that of the known automatic moisture titrator shown in FIG. 2 or FIG. 3, for example.
[0025]
FIG. 1 is a block circuit diagram of an example of the moisture measuring apparatus according to the present invention, and is a block circuit diagram showing both the capacity method and the coulometric method. The detection electrode (11) immersed in the titration solvent (5) accommodated in the titration tank (10) is supplied with an electrolytic conditioning low frequency AC voltage supply circuit (B) via a potential detection / electrolysis conditioning switching circuit (A). ) Is connected. The detection unit (41) is connected to the potential detection / electrolysis conditioning switching circuit (A), and the electrolysis conditioning low-frequency AC voltage supply circuit (B) and the detection unit (41) are connected to the control unit (42). . The control unit (42) is connected to a drive unit of a buret / automatic switching valve or an electrolytic current power supply (C) which is attached to each of the moisture measuring device of the capacity method and the coulometric method. In the case of the capacity method, the drive unit of the bullet / automatic switching valve functions, and in the case of the coulometric method, the electrolytic current power supply functions. Conditioning of the detection electrode is performed by applying a low frequency AC voltage from the electrolytic conditioning low frequency AC voltage supply circuit (B) to the detection electrode (11), and the control is performed by a control program of the control unit (42). Performed by function.
[0026]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist of the present invention.
[0027]
Acetone was used as a measurement sample, and a 2: 1 weight mixture of propylene carbonate and diethylene glycol monoethyl ether (KTX dehydrated solvent for ketone manufactured by Mitsubishi Chemical Corporation, using Karl Fischer volumetric method The moisture measurement was repeated a plurality of times by the measuring device, at which time the amount of the titration solvent contained in the titration tank was about 50 ml, and the amount of the sample added was 1 ml each time.
[0028]
First, a low frequency AC voltage of 15 V at 5 Hz was applied to the detection electrode for 100 seconds to condition the detection electrode. Next, a KF reagent necessary for dehydrating the inside of the titration tank was dropped, and an acetone sample was injected with a glass syringe. Then, the KF reagent was titrated to measure the moisture in the sample. Thereafter, the above-mentioned operation of "sample injection / moisture measurement" was repeated 10 times, and as a result, no measurement abnormality such as overtitration was observed in any of the measurements. After exchanging the titration solvent, the above-mentioned "conditioning" and "sample injection / moisture measurement" were again performed (10 times), but no measurement abnormality was recognized as in the above.
[0029]
Comparative Example 1
A plurality of moisture measurements were performed in the same manner as in Example 1 except that the “conditioning” operation of the detection electrode after replacing the titration solvent was omitted. As a result, in the first measurement after the exchange of the titration solvent, overtitration was performed, and the water measurement value became an abnormal value.
[0030]
【The invention's effect】
According to the present invention described above, there is provided a moisture measuring method and a moisture measuring device by the Karl Fischer method, which are improved so as to be able to solve the problem of measurement malfunction caused by the detection electrode with a simple operation and reliably. The industrial value of the invention is significant.
[Brief description of the drawings]
FIG. 1 is a block circuit diagram of an example of a moisture measuring device of the present invention. FIG. 2 is an explanatory diagram of an example of a known volumetric type automatic moisture titration device. FIG. 3 is an explanatory diagram of an example of a known coulometric type automatic moisture titration device. [Explanation of symbols]
10: titration tank 10a: anode chamber 10b: cathode chamber 11: detection electrode 12: sample inlet 13: magnetic stirrer 14: rotor 15: drying tube 16: anode 17: cathode 18: diaphragm 19a: drying tube 19b: drying Tube 20: burette 21: automatic switching valve 22: titration nozzle 30: reagent container 31: drying tube 41: detection unit 42: control unit 43: display unit 44: recording unit 5: titration solvent 6: KF reagent 7: anolyte 8 : Catholyte A: Potential detection / electrolysis conditioning switching circuit B: Electrolysis conditioning low frequency AC voltage supply circuit C: Bullet / automatic switching valve driver or electrolysis current power supply

Claims (5)

In the moisture measurement method by the Karl Fischer method, each time the titrant or the anolyte is replaced, conditioning of the detection electrode is performed by applying a low-frequency AC voltage to the detection electrode immersed in the titrant or the anolyte before measurement. A method for measuring water content, characterized in that: The moisture measurement method according to claim 1, wherein the frequency of the low-frequency AC voltage is 0.01 to 100 Hz. 3. The method according to claim 1, wherein the low-frequency AC voltage is 1 to 30 V. The moisture measurement method according to any one of claims 1 to 3, wherein the application time of the low-frequency AC voltage is 5 to 500 seconds. A constant voltage or a small current is applied to the detection electrode immersed in the titrant or anolyte, and the current or voltage in the reaction system between the Karl Fischer reagent and water in the titrant or anolyte is monitored. In a moisture measurement device equipped with a mechanism for monitoring the progress and performing moisture measurement, every time the titrant or anolyte is replaced, a low-frequency AC voltage is applied to the detection electrode immersed in the titrant or anolyte before measurement. A moisture measuring device provided with a conditioning means for detecting electrodes.

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