JP3531436B2 - Acidity measuring device - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an acidity for measuring the acidity of free fatty acids contained in edible oil, malic acid or tartaric acid contained in fruit drinks, acids contained in alcoholic drinks, or caffeic acid contained in coffee. The present invention relates to a measuring device.

[0002]

2. Description of the Related Art In recent years, foods have been required to have a certain level of quality in terms of health and safety. Above all, the acid contained in the food has a great influence on the quality of the food. Also, from the health boom, it is often considered that alkaline foods are better, and recently, foods with low acidity tend to be preferred.

As described above, the acidity of various foods has a great influence on the consumption of foods, but the degree of the effect and the measuring method differ depending on the foods. So,
As a typical example of such foods, edible oils, fruit drinks such as juices, whiskey and liquor, alcoholic drinks such as wines, coffee, and what kind of each acid was conventionally measured and explain how To do.

First, the acid contained in edible oil will be described. The eating habits of our country are changing rapidly, but looking at the trend, it seems that there is a major trend of instantization, and secondly a trend of diversification represented by handmade tastes. . In particular, instant orientation can be said to reflect the times, and many processed foods are on the rise. Above all, the increase in fried foods is remarkable. This is because fried foods are also favored by taste and have the property of being relatively resistant to decay.

However, when this fried food is also exposed to an environment affected by temperature and light for a long time, oxygen in the air automatically oxidizes fats and oils to cause deterioration odor and other deterioration of quality. . For these reasons, there is generally increasing interest in the deterioration and deterioration of edible oils and fats and oil processed products.For example, the local food certification system for fried foods has been established, or the regulation of oil confectionery has been implemented. Legal regulations regarding deterioration of fats and oils are also being considered in the guidance guidelines for lunch boxes and prepared foods.

By the way, as a method of knowing the degree of damage to oils and fats, especially the degree of deterioration of heated oils and fats, there are several analytical methods for measuring acid value, peroxide value, viscosity, iodine value and the like. Here, as described above, it is temperature, humidity, and light that have a great influence on the deterioration of food, and considering that the change in acidity is large at the beginning of deterioration, the acidity of these that directly measures acidity The measurement is suitable for making a judgment of thermal deterioration, and is usually used.

Next, the acid of drinking water will be described. Fruit drinks such as juice are juices obtained by squeezing raw fruit, but most fruit drinks use concentrated fruit juice or frozen fruit juice as a raw material rather than using fresh fruit juice as it is. There are many. For example, in the case of orange juice, after removing the diseased fruits and unripe fruits of mandarin oranges, the epidermis is washed, and this is squeezed to take out the flesh and the juice, and then the fruit skin, the acacia and the like are removed from the juice. At this point, sugar content, acidity, etc. are blended so as to meet the Japanese Agricultural Standards, and the acidity is measured at that time. When making orange juice from concentrated juice or frozen juice, acidity is measured when water is added to the concentrated juice or frozen juice to make orange juice.

Next, the alcoholic beverage will be described. Distilled liquor, such as whiskey and shochu, is repeatedly used to increase the yield of ethanol, or brewed liquor obtained by fermenting and filtering the raw materials such as liquor and wine, and other fruit liquor There are various kinds of alcoholic beverages such as happoshu such as beer and beer, and the manufacturing processes thereof are also different. However, in the production of any alcoholic beverage, the acidity is measured during the process in order to ensure the quality of the product.

Finally, the acid of coffee will be described.
There are various kinds of substances that give the sourness that influences the taste of coffee, as described below, but the acid content is important as an index for evaluating the sourness of coffee. Representative of the acids contained in coffee are chlorogenic acids. Its content also changes during the process of roasting coffee beans. In addition, there are many compounds such as caffeic acid, quinic acid, and citric acid that are involved in the sourness of coffee. And, it is considered that the delicate balance and the total amount are the decisive factors for the sourness, although the content of each acid is very small.

As described above, in various foods, the acidity of each food is measured in the manufacturing process, but there are various measuring methods.

As an example of the conventional acid measuring method, the method defined by the standard oil and fat analysis method, the Japanese Agricultural Standards, JIS, the Japanese Pharmacopoeia oil and fat test method, the hygiene test method, the food and drink test method, the water test method, etc. However, in all cases, the basic measurement method is the neutralization titration method using phenolphthalein as an indicator. Therefore,
In order to explain this neutralization titration method, the neutralization titration method defined by the tap water test method and the standard oil and fat analysis method will be described below.

The acidity in the water supply test method is defined as the mg number when the acid is converted to the calcium carbonate contained in 1 liter of the sample. Specifically, 100 mL of test water
And then add phenolphthalein indicator about 0.2
mL is added, and 0.02 mol / L sodium hydroxide solution is further added. Then, when the red color disappears by tightly plugging and shaking, the neutralization end point is determined when the titration is continued until the slight red color remains without disappearing, and the mL number a of sodium hydroxide is determined. The acidity at that time is given by acidity (calcium carbonate conversion mg / L) = 10a.

Next, the neutralization titration method specified by the standard oil and fat analysis method will be described. The definition of acidity in the standard oil and fat analysis method is
It refers to the number of mg of potassium hydroxide required to neutralize the free fatty acid contained in 1 g of the sample. In the case of a liquid sample, the sample should have its estimated acidity (for example, if the acidity is 1 or less, 20 g is sampled,
When the acidity exceeds 1 and 4 or less, 10 g is sampled, and when the acidity exceeds 4 and 15 or less, 2.5 g is sampled. To this, add 100 mL of a neutral solvent and shake well until the sample is completely dissolved. However, the neutral solvent referred to here is ethyl ether, ethanol 1: 1.
Approximately 0.3 mL of a phenolphthalein indicator was added to 100 mL of the mixed solvent of 1 and neutralized with a 1 / 10N (N) potassium hydroxide-ethanol solution immediately before use.

In the case of a solid sample, it is melted by heating on a water bath and then dissolved by adding a solvent. This is 1/10 rule (N)
It is titrated with a potassium hydroxide-ethanol standard solution, and the end point of neutralization is defined when the color change of the indicator continues for 30 seconds. Then, the mg number of potassium hydroxide at this time is calculated.

Regarding the measurement of fatty acids, there is a method of measuring the acidity by voltammetry, instead of the neutralization titration method.

This is disclosed in Japanese Unexamined Patent Publication No. 5-264503, and a measurement electrolytic solution in which a free fatty acid and a naphthoquinone derivative coexist is measured by voltammetry according to a potential regulation method. The magnitude of the current value of the reduction precursor wave of naphthoquinone derivatives is proportional to the concentration of free fatty acid for all fatty acids from lower fatty acids such as formic acid to higher fatty acids such as oleic acid and linoleic acid The fact that the value obtained by superimposing the values corresponds to the total concentration of fatty acids is used. That is, the acid concentration is measured by measuring the magnitude of the current value of the reduction pre-wave of the naphthoquinone derivative.

The data measured by this method are shown in FIG. Here, FIG. 10 is a graph showing a current-potential relationship in acidity measurement by voltammetry of a measurement electrolyte solution in which a conventional naphthoquinone derivative coexists.

In FIG. 10, the horizontal axis represents the potential of the working electrode (hereinafter referred to as "electrode potential") with respect to the reference electrode when silver-silver chloride was used for the reference electrode and glassy carbon of φ3 was used for the working electrode. The axis indicates the current value flowing through the counter electrode at this time. However, the current value changes depending on conditions such as the size and roughness of the surface area of the working electrode and the concentration of acid. On the other hand, the voltage value on the abscissa is negligible although it varies slightly depending on the acid concentration.

In FIG. 10, A is a pre-peak showing a reduction pre-wave which is proportional to the acid concentration, and D is the main peak of the naphthoquinone derivative.

By the way, when measuring the acidity using the technique disclosed in Japanese Patent Laid-Open No. 5-264503, it is generally necessary to control voltammetry using a potentiostat or the like.

Here, the operating principle of the potentiostat will be described with reference to FIG. FIG. 11 is a schematic circuit diagram of the potentiostat.

In FIG. 11, the sweep voltage setting power supply 31 is connected to the positive terminal which is the non-inverting input terminal of the operational amplifier 32.
However, the reference electrode connection terminals R ′ are respectively connected to the negative terminals which are the inverting input terminals. Further, a counter electrode connection terminal C ′ is connected to the output terminal. Operational amplifier 32
A resistor 29 is provided between the output terminal of C and the counter connection terminal C ′, and the voltage amplifier circuit 3 is provided at both ends of the resistor 29.
0 is connected. The working electrode connection terminal W'is at ground potential.

When the electrode potential is swept by such a potentiostat and the current I ₁ flowing through the counter electrode at that time is to be measured, the sweep voltage setting power supply 31 is first set to a predetermined voltage V ₁ . Then, the feedback circuit including the operational amplifier 32 applies a voltage to the counter electrode connection terminal C ′ such that the voltage V ₁ = the reference electrode voltage V ₂ . Then, the current I ₁ flowing through the counter electrode is converted into the voltage V ₃ by the resistor 29, further amplified by the voltage amplifier circuit 30, and output as the voltage V ₄ . By recording this voltage V ₄ on a plotter or the like, a relative graph of the electrode potential and the counter electrode current I ₁ is completed.

Here, in the conventional acidity measuring device, a cylindrical carbon material is used for the working electrode. The surface condition of the working electrode has a great influence on the measurement results.For example, when electrolytic polymerization of the surface of the working electrode or formation of deposits on the working surface by the measurement solution occurs due to overpotential sweep, the current in voltammetry is reduced. The waveform is disturbed, which causes a problem that the acidity is erroneously measured or cannot be measured.

The reference electrode portion is composed of an electrode, a buffer solution and a liquid junction portion. The electrode is made by coating silver with silver chloride and immersed in the buffer solution, and is brought into contact with the measurement solution through the liquid junction portion. ing. When such a reference electrode section is used for a long time,
As in the case of the working electrode, a problem such as erroneous measurement or unmeasurable occurs, because the buffer solution decreases, the electrode coating material is missing, or the liquid junction is clogged.

[0026]

As described above,
The conventional acidity measuring device measures the acidity by using the neutralization titration method, and the color change due to the phenolphthalein indicator is judged as the end point of the titration. In some cases, the acidity was not objectively determined.

According to the neutralization titration method for fatty acids of the standard oil and fat analysis method, a mixed solution of ether and ethanol is used as a neutral solvent, and the boiling point of ether is 34.6 ° C., which is easily inflammable, and thus handled. Is difficult. Moreover, for example, when the color of the sample is dark such as oil of a large amount of fried food, or when the material itself is colored such as juice or wine, the color of phenolphthalein near the titration end point I couldn't accurately grasp the changes,
There was a problem in that the measured value varied due to the wrong reading of the end point. Furthermore, the amount of sample is several tens of grams, and the neutral solvent is 100 mL.
There is also a problem that an increase in the number of measurements is a burden because a large amount of sample is required for one measurement.

Further, in the technique of measuring using a potentiostat disclosed in Japanese Patent Laid-Open No. 264503/1993, handling of the potentiostat is not easy and specialized knowledge is required. take time. Furthermore, in the circuit configuration, the voltage at the W terminal is 0
Since it is fixed at V, it is necessary to use both positive and negative power supplies as the power supply for the entire system so that the voltage at the C terminal can be applied positively and negatively. It is equipped with an analog voltage output circuit etc. that has a wide range output function. There was a problem that had to be.

Further, when the current waveform is disturbed and the acidity cannot be calculated, various factors such as electrode abnormality, measurement system failure, contact failure, etc. can be considered. In the past, however, it was necessary to identify the cause. It took time. This is because almost all of the factors cannot be confirmed visually, so experience was required. For example, regarding the electrode problem mentioned above,
There are a limited number of items that can be visually checked, and by recording voltammetric data of the current value output from the potentiostat on a plotter, etc., and confirming the current waveform in detail, it is possible to detect electrode abnormalities for the first time. It was almost.

Here, the technique for judging the electrode abnormality from the current waveform requires some experience and, in addition, the disturbance of the current waveform due to the failure of the measurement system is also considered. Therefore, the abnormality of the electrode was found by the technique. It wasn't easy to do.

If an abnormality cannot be determined from the current waveform, there is a possibility of erroneous measurement.

Therefore, it is an object of the present invention to provide an acidity measuring device which is capable of promptly determining an electrode abnormality with a simple structure and notifying the user of the abnormality.

[0033]

In order to solve this problem, the present invention provides a measuring container for accommodating a coexisting electrolytic solution in which an electrolytic solution and an acid-containing solution to be measured are mixed, and a measuring container attached to the measuring container. the working electrode is immersed in the co electrolyte Te, and the counter and reference electrode section, acts to calculate the acidity of the test liquid
An acidity measuring device including a control unit capable of detecting an abnormality of an electrode and an informing unit for informing a user of the detected electrode abnormality.
Therefore, the control unit controls the electrode voltage when no voltage is applied to the counter electrode.
The potential of the reference electrode before the sweep is different from the theoretical value under normal conditions
At the same time, the potential of the reference electrode is swept after the electrode potential is swept.
When the potential converges to a convergence value that differs from the theoretical value in the normal state
In this case, this is detected as an abnormality in the comparison electrode section . In addition, the control unit controls the reference electrode during the electrode potential sweep.
Sweeper where the electric potential of the control part or the counter electrode is output from the control part
If this is not the case, it is detected as an abnormality of the working electrode.
It is something.

This makes it possible to promptly judge an electrode abnormality with a simple structure and notify the user of the measuring apparatus of the abnormality.

In this acidity measuring apparatus, the control section is the reference electrode section before the electrode potential sweep in which no voltage is applied to the counter electrode.
Potential differs from the theoretical value under normal conditions, and the electrode potential sweep
After pulling, the potential of the reference electrode is normal from the sweep potential
When the value converges to a convergence value different from the value , this can be detected as an abnormality in the comparison electrode unit. Further, when the potential of the comparison electrode portion or the counter electrode during the sweep of the polar potential is different from the sweep pattern output from the control portion, this can be detected as an abnormality of the working electrode.

[0036]

BEST MODE FOR CARRYING OUT THE INVENTION The invention according to claim 1 of the present invention comprises a measuring container for accommodating a coexisting electrolytic solution in which an electrolytic solution and an acid-containing solution to be measured are mixed, and attached to the measuring container. the working electrode is immersed in the coexistent electrolyte, a counter electrode and reference electrode portion, the working electrode to calculate the acidity of the test liquid different
An acidity measuring device comprising a control unit capable of detecting a normal state and an informing means for informing a user of a detected electrode abnormality ,
The control unit is not applying voltage to the counter electrode Before sweeping the electrode potential
The potential of the reference electrode of
In addition, after the electrode potential sweep, the reference electrode potential is
From the normal value to a convergence value different from the theoretical value,
This is an acidity measuring device that detects this as an abnormality in the reference electrode section.If an acidity measurement is attempted while the electrode is still abnormal, or if acidity measurement is impossible, an abnormality is detected in the control section and the abnormality. It is possible to promptly judge the abnormality of the electrode with a simple structure and notify the user of the measuring device of the abnormality by the notifying means for notifying the abnormality of the electrode.
Is automatically determined and notified to the user.
It has an effect of preventing erroneous measurement and enabling highly accurate acidity measurement .

[0037]

The invention according to claim 2 of the present invention comprises a measuring container for accommodating a coexisting electrolytic solution in which an electrolytic solution and an acid-containing solution to be measured are mixed, and a coexisting electrolytic solution attached to the measuring container. Calculates the acidity of the working electrode, counter electrode and reference electrode to be dipped, and the solution to be measured, and detects abnormalities in the working electrode.
A control unit, and an acidity measuring device having a notifying unit for notifying the user of the detected electrode abnormality , wherein the control unit is
The potential of the reference electrode or the counter electrode during the electrode potential sweep is
If the sweep pattern output from the control unit is different,
This is an acidity measuring device that detects this as an abnormality of the working electrode.The abnormality of the working electrode due to the formation of deposits on the electrode surface is automatically determined and notified to the user, making it impossible to measure the acidity. In case of
It has an effect that the acidity can be efficiently measured with high accuracy.

FIG. 1 shows the embodiment of the present invention.
9 to 9 will be described. In addition, in these drawings, the same members are denoted by the same reference numerals, and duplicate description is omitted.

FIG. 1 is an external perspective view showing an acidity measuring device according to one embodiment of the present invention, FIG. 2 is an external perspective view showing a state in which the upper lid is opened in the acidity measuring device of FIG. 1, and FIG. Sectional drawing which shows the measuring container in an acidity measuring device, FIG. 4 is a graph which shows the current-potential relationship of the acidity measurement by the voltammetry of the coexisting electrolyte solution which mixed the benzoquinone derivative, and FIG. FIG. 6 is a graph showing the relationship, FIG. 6 is a block diagram showing the control system of the acidity measuring device of FIG. 1, FIG. 7 is a graph showing voltage waveforms when the reference electrode is normal and when it is abnormal, and FIG. 8 is a case where the working electrode is normal. 9 is a graph showing the voltage waveform of the reference electrode in FIG. 9, and FIG. 9 is a graph showing the voltage waveform of the reference electrode when the working electrode is abnormal.

In FIG. 1, the main body portion 7 of the acidity measuring device A is shown.
An upper lid 1 that covers the internal space in which the measurement container 8 (FIG. 2) is set is attached to the. An opening button 2 for unlocking the lock of the upper lid 1 is provided adjacent to the upper lid 1. Further, the main body portion 7 is provided with the display portion 3 for displaying the measured acidity and for notifying the abnormality of the electrode,
The display unit 3 is, for example, an LCD. Furthermore, a switching button 4 for switching the region depending on the degree of acidity, a start / stop button 5 for starting the measurement, and a power button 6 for turning on / off the power of the apparatus are arranged. Then, when the release button 2 shown in FIG. 1 is pressed,
As shown in FIG. 2, the upper lid 1 is opened and the set measurement container 8 is exposed. The measuring container 8 is detachable.

As shown in FIG. 3, the counter electrode 11, the working electrode 9 and the reference electrode portion 1 are provided on the container cover 15 of the measuring container 8.
2 is attached. In addition, in the solution containing portion 14 to which the container cover 15 is attached, the coexisting electrolyte solution 13 in which the quinone derivative, the organic solvent, the electrolyte and the solution to be measured are mixed.
Is housed. As the quinone derivative, an orthobenzoquinone derivative or a parabenzoquinone derivative is desirable. According to these quinone derivatives, the pre-peak value of the voltammetric current waveform appears to shift from the reducing current waveform of dissolved oxygen, and the influence of reduction of dissolved oxygen can be cut off. Then, by mounting the container cover 15 on the solution storage unit 14, one end of the counter electrode 11, the working electrode 9, and the comparison electrode unit 12 is projected to the outside, and the other end is immersed in the coexisting electrolyte solution 13. Here, as the material of the working electrode 9 whose side surface is covered with the furan resin 10, glass-like carbon called carbon or glassy carbon, or plastic foam called PFC is used.
Carbon sintered at ℃ to 2000 ℃ is suitable. The material of the counter electrode 11 is preferably platinum, graphite, or gold, which is chemically stable and does not corrode in the coexisting electrolyte solution 13, but stainless steel, aluminum, a platinum-containing alloy or the like, which does not corrode, may be used. Although not shown in FIGS. 1 and 2, the main body 7 is provided with a connector for connecting the counter electrode 11, the working electrode 9, the electrodes of the comparison electrode unit 12 and a control circuit described later.

As shown in FIG. 3, the reference electrode section 12 includes a container 16 made of, for example, glass, a reference electrode 17 protruding from the container 16, a buffer solution 18 contained in the container 16, and a container 16. It is composed of a liquid junction portion 19 provided on the bottom surface.

Here, the material of the comparison electrode 17 is silver-
Silver chloride is preferable, but saturated calomel, saturated calomel chloride, silver-silver ion, mercury-saturated mercury sulfate, and copper-saturated copper sulfate may be used. Note that, for example, a display such as silver-silver chloride indicates that the surface of the reference electrode 17 made of silver is covered with silver chloride.

The spontaneous potential generated between the reference electrode 17 and the working electrode 9 differs depending on the material of the reference electrode 17. This is because the electrode potential is different from that of the standard hydrogen electrode, and for example, the difference between the case where silver-silver chloride is used for the reference electrode 17 and the case where silver-silver ion is used is less than 600 mV. In this embodiment, silver-silver chloride is used for the reference electrode 17, and the natural potential of the working electrode 9 with respect to the reference electrode 17 is +300 to +500 mV.

As a material of the buffer solution 18, a chloride compound such as silver chloride, sodium chloride, lithium chloride, acetonitrile, copper sulfate, or any other solution having a buffer action in the redox reaction of the reference electrode 17 is suitable.

The liquid junction 19 is located between the buffer solution 18 and the coexisting electrolytic solution 13, and has the function of suppressing passage of these solutions as much as possible and allowing electrons or ions to pass therethrough. It is composed of ceramics and porous Vycor glass.

Next, the coexisting electrolytic solution 13 contained in the solution container 14 will be described. In this embodiment, lithium perchlorate is used as the electrolyte. The coexisting electrolyte solution 13 of the present embodiment uses 65% ethanol as a solvent.
Was mixed with 35% of isooctane to 10 mL, and 10 mM of orthobenzoquinone and 50 mM of lithium perchlorate were melted, and the measurement liquid was mixed with this solvent.

Here, in the embodiment of the present invention, the orthobenzoquinone derivative or the parabenzoquinone derivative is mixed in the coexisting electrolyte solution 13 as described above.

Therefore, next, the acidity measurement by voltammetry of the electrolytic solution in which such a benzoquinone derivative coexists will be described.

In FIG. 4, the horizontal axis represents the potential of the working electrode with respect to the reference electrode when silver-silver chloride was used as the reference electrode and φ2 plastic foam carbon was used as the working electrode, and the lapse of time, and the vertical axis at this time was the counter electrode. Is the value of the current that flows through the. Here, the current value varies depending on the conditions such as the surface area of the working electrode and the acid concentration, but the voltage value on the horizontal axis is negligible although it varies slightly depending on the acid concentration. The solid line is the voltammetric current waveform of the benzoquinone derivative, and the broken line is the reduction waveform of dissolved oxygen.

As shown in FIG. 4, the voltammetric current waveform of the benzoquinone derivative having a side chain on the benzene ring is:
It appears with a large shift from the region where the reduction waveform of dissolved oxygen appears. According to FIG. 4, the pre-peak waveform is 0 m
It exists from near V to the positive potential side and is shifted by about 400 mV from the negative potential side where the reduction waveform of dissolved oxygen exists.

In FIG. 5, the horizontal axis is the acidity of the solution to be measured, and the vertical axis is the current value of the pre-peak shown in FIG. As shown in the figure, there is a proportional relationship between the current value giving the pre-peak value and the acidity of the acid mixed in the measured liquid.

A method of operating the acidity measuring device A of this embodiment will be described. First, 0.5 g of deteriorated oil, which is the liquid to be measured, is mixed with 10 mL of the solvent described above and stirred,
This is stored in the solution storage unit 14. Then, the counter electrode 11,
The container cover 15 having the working electrode 9 and the reference electrode portion 12 is attached to the solution storage portion 14. When the preparation of the measurement container 8 is completed in this way, the measurement container 8 is set in the acidity measuring device A, and the upper lid 1 is closed to bring it into a measurable state.

Then, the power button 6 is pressed to turn on the power, and the start / stop button 5 is pressed to start the measurement. Then, the remaining time of the measurement is displayed on the display unit 3 in units of seconds, for example, the acidity is displayed when it becomes "0", and the series of acidity measurement operation is completed.

However, when there is an abnormality in the electrode, when the start / stop button 5 is pressed, the fact is displayed by the display section 3 which is an abnormality notifying means of the working electrode 9 or the comparison electrode section 12. Here, a sound source such as a buzzer may be used as the notification means for notifying the electrode abnormality. Further, in the present embodiment, the means for notifying the measured acidity value and the means for notifying the electrode abnormality are the same, but they may be separate bodies.

When the abnormality of the electrode is notified, the user of the measuring device promptly replaces the electrode according to the display and restarts the measurement.

Next, the operation of the acidity measuring apparatus A of this embodiment will be described. For the acidity measurement operation, the electrode potential is +5
The acidity is calculated from the current waveform flowing through the counter electrode 11 by sweeping at a speed of 3 to 10 mV / s in the range of 00 mV to −300 mV. Where +500 mV to -3
The range of 00 mV is a region where the influence of the above-mentioned dissolved oxygen is not so large and the pre-peak value of the current can be accurately measured. Then, the sweep speed is 3 to 10 mV /
When a predetermined potential difference is swept with s, a stable voltammetric current waveform as shown in FIG. 4 can be obtained.

At this time, if the sweep rate is set to 10 mV / s or more, a stable current waveform cannot be obtained because the potential sweep rate is faster than the electrode reaction rate. On the other hand, if the sweep rate is less than 3 mV / s, the reaction on the electrode surface will occur excessively and a stable potential cannot be obtained. Therefore, it is necessary to set the potential sweep rate to 3 to 10 mV / s.

By carrying out such a sweep, the peak of the acid reduction current appears at a potential near 0 mV. This is the pre-peak, and this potential shifts to the negative side as the acid concentration increases. But even if there is a shift +50
By setting the range of 0 mV to -300 mV, it is possible to measure any concentration of acidity.

Next, the control system of the acidity measuring apparatus A of the present embodiment that executes the above operation will be described.

As shown in FIG. 6, a microcomputer
It is composed of etc. and performs acidity calculation and electrode abnormality judgment
The controller (control unit) 20 is connected to the power supply shown in FIG.
Operation consisting of switch 5 and start / stop button 6
And display measurement results and electrode abnormalities
A display unit (informing means) 26 is connected. Also,
The controller 20 has a voltage detector for detecting the potential of the reference electrode.
Predetermined output from the intelligence unit 28 and the controller 20
To the counter voltage control circuit 21 by the signal ₂Output
The D / A converter 22 is connected. Reference electrode
To control the voltage of the counter electrode by monitoring the voltage value of
The input terminal of the voltage control circuit 21 was connected to the reference electrode.
The reference electrode connection terminal R is connected to the output terminal as well as the counter electrode.
The counter electrode connection terminals C are connected to each other.

A resistor 27 is provided between the counter voltage control circuit 21 and the counter connection terminal C, and a voltage amplifying circuit for measuring the voltage value between the resistors 27 and amplifying the voltage across the resistor 27. 23 is connected. The output terminal of the voltage amplification circuit 23 is connected to the controller 20, and the controller 20 calculates the acidity based on the voltage value from the voltage amplification circuit 23. A power supply 24 for supplying electric power to the working electrode is connected to the working electrode connection terminal W connected to the working electrode.

According to such a control system, when the power button 6 (FIG. 1) of the operation unit 25 is pressed, the controller 20
Is sent to drive the display unit 26. Next, when the start / stop button 5 (FIG. 1) of the operation unit 25 is pressed, the controller 20 sends a digital signal of a predetermined comparison electrode voltage set value to the D / A converter 22.

This digital signal is sent to the D / A converter 22.
Is converted into an analog signal by the counter electrode voltage control circuit 21.
A voltage of E ₂ (V) is output to. In the counter electrode voltage control circuit 21, the voltage value E ₂ input from the D / A converter 22 is compared with the voltage value E ₃ of the comparison electrode connection terminal R, and E
_A voltage is applied to the counter electrode terminal C so that ₂ = E ₃ . At this time, the voltage value E ₃ of the comparison electrode connecting terminal R is
It is also sent to the controller 20 via. Then, in the controller 20, the abnormality of the electrode is determined based on the signal input from the voltage detection unit 28. The determination method will be described later.

With the above configuration, the electrode potential is swept by changing the comparison electrode voltage set value sent from the controller 20 to the D / A converter 22.

The current I _a flowing between the counter electrode connecting terminal C and the working electrode connecting terminal W due to the sweeping of the electrode potential is
_Is converted into _a voltage E _a by. Here, the converted voltage E _a is amplified by the voltage amplifier circuit 23 and input to the controller 20 as the voltage E _b . The controller 20 reads the change with time of the current I _a from the voltage E _b, judges the pre-peak value I _p shown in FIG. 4, and calculates the acidity θ.

Next, the procedure for calculating the acidity will be described.
As shown in FIG. 5, the pre-peak value I _p is proportional to the acidity θ of the acid mixed in the liquid to be measured. That is, there is a relation of acidity θ = current value I _p × constant K + constant B. Therefore, the proportional constant K obtained by measuring two or more standard reagents whose acidity is known in advance,
If B is stored in the controller 20, the acidity θ can be obtained by substituting the current value I _p measured by the controller 20 into the above equation when measuring an arbitrary acidity.

Here, the determination procedure when the abnormality of the electrode occurs will be described in the order of the comparison electrode and the working electrode.

When an abnormality occurs in the reference electrode section, it differs from the case where the natural potential of the reference electrode is normal. Therefore, it is possible to determine the abnormality of the comparison electrode by reading the voltage value of the comparison electrode connection terminal R when the voltage is not applied to the counter electrode by the voltage detection unit 28.

In FIG. 7, the difference in the natural potential of the reference electrode between the normal state and the abnormal state will be described. In FIG. 7, the working electrode voltage is 1000 mV, and the electrode potential is from +500 mV to −3.
It shows the voltage change of the reference electrode when it is swept up to 00 mV. The solid line is the waveform when the reference electrode is normal, and the broken line is the waveform when silver chloride, which is the coating material of the reference electrode, has fallen off. As can be seen from FIG. 7, there is a large difference between the two before and after the sweep. That is, in the normal case, the voltage of the reference electrode converges to 600 to 700 mV, whereas in the abnormal case where the coating material of the reference electrode, silver chloride, falls off, it converges to a value below 500 mV. There is. Moreover, when the buffer solution is insufficient, the voltage of the reference electrode is not stabilized at any value. in this way,
The abnormality of the comparison electrode section can be determined by checking whether the converged value of the comparison electrode voltage is within a predetermined range in the state where the voltage is not applied to the counter electrode.

On the other hand, if an abnormality occurs in the working electrode, the electrode abnormality can be determined by reading the voltage value of the comparison electrode or the counter electrode during the sweep. This is because when an abnormality occurs in the working electrode, the current value flowing through the working electrode is dropped or cut off, and the sweep of the electrode potential becomes uncontrollable.

Here, FIG. 8 and FIG. 9 show voltage waveforms when the electrode potential is actually swept.

In FIG. 8 and FIG. 9, the solid line is the controller 2
It is the set value of the comparison electrode voltage output from 0, and the broken line is the actual value of the comparison electrode voltage sent from the voltage detection unit 28 to the controller 20 as a digital signal. Also, FIG.
Is a graph when the working electrode is normal, and FIG. 9 is a graph when an abnormality occurs in the working electrode.

As shown in FIG. 8, when the working electrode is normal, the set value and the actual value of the reference electrode voltage draw an approximate line. On the other hand, when an abnormality occurs in the working electrode shown in FIG. 9, the actual value of the reference electrode voltage is disturbed regardless of the set value.

Therefore, by comparing the voltage setting value of the comparison electrode with the actual value, the abnormality of the working electrode can be determined. Also, when the actual voltage of the reference electrode cannot be controlled, the voltage waveform of the counter electrode is also disturbed, so the voltage value of the counter electrode is measured, and if the amount of change is large or the actual voltage value exceeds the predetermined range. In some cases, this can be determined as an abnormality of the working electrode.

In the present embodiment, the abnormality of the comparison electrode portion and the working electrode is detected, but only one of the abnormality may be detected.

[0078]

As described above, according to the present invention, when an attempt is made to measure the acidity while the electrode is still abnormal, or when the acidity cannot be measured, the control unit for detecting the electrode abnormality and the abnormality are detected. With the notification means for notifying the user, it is possible to obtain an effective effect that the abnormality of the electrode can be promptly determined and the user of the measuring device can be notified of this with a simple configuration.

As a result, it is possible to obtain an advantageous effect that it is possible to obtain a highly accurate acidity measuring device which can prevent erroneous measurement and realize efficient acidity measurement.

[Brief description of drawings]

FIG. 1 is an external perspective view showing an acidity measuring device according to an embodiment of the present invention.

FIG. 2 is an external perspective view showing a state in which the upper lid is opened in the acidity measuring device of FIG.

FIG. 3 is a sectional view showing a measuring container in the acidity measuring device of FIG.

FIG. 4 is a graph showing a current-potential relationship in acidity measurement by voltammetry of a coexisting electrolyte mixed with a benzoquinone derivative.

FIG. 5 is a graph showing the relationship between acidity and reduction current of the acidity measuring device.

6 is a block diagram showing a control system of the acidity measuring device of FIG.

FIG. 7 is a graph showing voltage waveforms of a reference electrode in a normal state and an abnormal state.

FIG. 8 is a graph showing a voltage waveform of the reference electrode when the working electrode is normal.

FIG. 9 is a graph showing a voltage waveform of the reference electrode when the working electrode is abnormal.

FIG. 10 is a graph showing a current-potential relationship in acidity measurement by voltammetry of a measurement electrolyte solution in which a conventional naphthoquinone derivative coexists.

FIG. 11 is a schematic circuit diagram of a potentiostat.

[Explanation of symbols]

3 Display unit (informing means) 8 measuring vessels 9 Working electrode 11 opposite poles 12 Reference electrode part 13 Coexisting electrolyte 20 Controller (control unit)

─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A-5-264503 (JP, A) JP-A 61-169755 (JP, A) JP-A 54-44593 (JP, A) JP-A 62- 242849 (JP, A) Tetsuo Fuse, 2 others, Determination of total free fatty acids in fats and oils by voltammetry, analytical chemistry, Japan, January 5, 1995, Vol. 44, No. 1, p. 29-33 (58) Fields investigated (Int.Cl. ⁷ , DB name) G01N 27/48 G01N 27/416 G01N 27/26 JISST file (JOIS)

Claims (2)

(57) [Claims] 1. A measuring container containing a coexisting electrolytic solution in which an electrolytic solution and an acid-containing solution to be measured are mixed, a working electrode attached to the measuring container and immersed in the coexisting electrolytic solution, a counter electrode, and comprising a reference electrode portion, the said action abnormality can be detected controller of electrodes to calculate the acidity of the target solution, and informing means for informing the sensed electrode anomalies user
Acidity measuring device, wherein the control unit applies an electric current to the counter electrode.
Of the reference electrode section before sweeping the electrode potential without applying pressure
The potential is different from the theoretical value when normal, and the electrode potential is swept.
After that, when the potential of the reference electrode is normal from the sweep potential,
If it converges to a convergence value different from the theoretical value,
Acidity measurement characterized by detection as abnormality of the reference electrode
Stationary device. 2. A measuring container containing a coexisting electrolytic solution in which an electrolytic solution and an acid-containing solution to be measured are mixed, a working electrode attached to the measuring container and immersed in the coexisting electrolytic solution, a counter electrode, and comprising a reference electrode portion, the said action abnormality can be detected controller of electrodes to calculate the acidity of the target solution, and informing means for informing the sensed electrode anomalies user
Acidity measuring device, wherein the control unit sweeps the electrode potential.
The potential of the reference electrode portion or the counter electrode in the
If the sweep pattern output from the control unit is different,
This is detected as an abnormality of the working electrode.
Acidity measuring device.