JPH1164281A - Apparatus and method for measuring acidity - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an apparatus and a method for measuring an acidity, whereby an acidity can be measured compactly and highly accurately through a simple operation even when an acid concentration is low. SOLUTION: This acid measuring apparatus includes a measurement container 7 which has a liquid to be measured containing an acid, a quinone derivative, an organic solvent, an electrolyte and a measurement solution wherein a standard acid is mixed to increase by a predetermined amount an acidity of the liquid to be measured, an operating electrode 9, an opposite electrode 8, and a comparison electrode 10 all dipped in the measurement solution. The apparatus also has a control unit which measures a peak current value of a waveform of the measurement solution prior to a voltammogram reduction, and calculates an acidity of the liquid to be measured by subtracting an acidity of the standard acid.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention measures the acidity of free fatty acids contained in edible oils, citric acid, malic acid, tartaric acid contained in fruit drinks, acids contained in alcoholic drinks, or coffee acid contained in coffee. The present invention relates to an acidity measuring device and an acidity measuring method that can be used.

[0002]

2. Description of the Related Art In recent years, foods have been required to have a quality above a certain level from the viewpoint of health and safety. Above all, acids contained in foods have a great effect on food quality. Alkaline foods are often considered better due to the health boom, and foods with a low acidity tend to be exclusively preferred these days. As described above, the acidity of various foods has a great influence on the consumption of foods, and the degree of the influence and the measuring method vary depending on the foods.

[0003] In the following, typical examples of such foods are as follows: what kinds of acids are used for fruit drinks such as edible oil and juice, alcoholic drinks such as whiskey, liquor and wine, and coffee. An explanation of the prior art is given below.

[0004] First, the acid contained in the edible oil will be described. Japan's dietary habits are changing rapidly, but it appears that there is a large trend of instantization first and a diversification trend represented by handmade tastes in the first place. . In particular, this instant orientation reflects 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 preferred in taste and are relatively resistant to spoilage. However, when this fried food is exposed to an environment that is affected by temperature and light for a long time, the fats and oils are automatically oxidized by oxygen in the air to produce a perishable odor and other quality deterioration.
For these reasons, there has been general interest in the deterioration and deterioration of edible fats and oils and processed fats and oils, for example, the establishment of a regional food certification system for fried foods, or the regulation of oil confectionery, and Legal regulations are also being considered for deterioration of fats and oils in the guidelines for lunches and prepared dishes.

There are several analytical methods for measuring the degree of damage of fats and oils, especially the degree of deterioration of heated fats and oils, by measuring acidity, peroxide value, viscosity, iodine value and the like. Considering that temperature and light have a significant effect on food deterioration, measuring acidity by directly measuring the degree of oxidation is appropriate for determining thermal deterioration, and this is often used. ing.

Next, the acid of drinking water will be described. Fruit drinks, such as juice, are juices obtained by extracting raw fruit through a juicer.Many fruit drinks use concentrated juice or frozen juice as a raw material rather than using fresh fruit juice as it is. There are many.

[0007] In the case of orange juice, for example, after removing diseased fruits and immature fruits of oranges, the epidermis is washed, and squeezed to take out the pulp and juice, and further, the peel,
The carcass membrane is removed. At this point, the sugar content and the acidity are adjusted so as to conform to the Japanese Agriculture and Forestry Standards. At that time, the acidity is measured. Further, when making orange juice from concentrated juice or frozen juice, the acidity is also measured when making orange juice by adding water to the concentrated juice or frozen juice.

Next, an alcoholic beverage will be described. Distilled liquor, such as whiskey and shochu, which increases the yield of ethanol by repeating distillation many times, or fermented material itself, such as liquor and wine, is used. There are various types of alcoholic beverages, such as brewed liquor obtained by filtration, and other low-malt beer such as fruit liquor and beer, and the production process is also varied. However, in the production of any alcoholic beverage, acidity is measured in the process to ensure product quality.

Next, the acid of coffee will be described.
As described below, there are various types of substances that impart sourness that affects the taste of coffee, but the acid content is important as an index for evaluating the sourness of coffee. Representative of acids contained in coffee include chlorogenic acids. Its content also varies during the roasting of coffee beans. There are many other compounds that contribute to the sourness of coffee, such as caffeic acid, quinic acid, and even citric acid. And, although the content of each acid is very small, it is considered that the delicate balance and the total amount are decisive factors for the acidity.

As described above, in various kinds of foods, the acidity of each food is measured in the production process, and there are various measuring methods. Examples of conventional acidity measurement methods include the methods specified in the standard method for analyzing fats and oils, Japanese Agricultural Standards, JIS, the Japanese Pharmacopoeia oil and fat test method, the hygiene test method, the food and drink test method, and the water supply test method. ,
In each case, the basis of the measurement is a neutralization titration method using phenolphthalein as an indicator. Then, in order to explain this neutralization titration method, the neutralization titration method specified in the clean water test method and the standard fat and oil analysis method will be described below.

The acidity in the tap water test method is defined as the number of mg when acid is converted to calcium carbonate contained in one liter of a sample. Specifically, test water 100mL
And add about 0.2 mL of the phenolphthalein indicator to the test water, add a 0.02 mol / L sodium hydroxide solution, stopper tightly and shake gently. The end point of the neutralization was defined as the time when the titration was continued until the sodium hydroxide remained.
Ask for. The acidity at that time was calculated as follows: Acidity (mg / L in terms of calcium carbonate) = a x 0.02 x
10 is calculated.

Next, the neutralization titration method specified in the standard fat and oil analysis method will be described. The definition of acidity in the standard fat and oil analysis method refers to the number of mg of potassium hydroxide required to neutralize the free fatty acid contained in 1 g of a sample. In the case of a liquid sample, the sample is weighed at its estimated acidity (eg, 20 g
The acidity is more than 1 and 4 or less, 10 g is collected, and the acidity is more than 4 and 15 or less, 2.5 g is collected. Add neutral solvent 10
Add 0 mL and shake thoroughly until the sample is completely dissolved.

However, the neutral solvent referred to here is about 0.3 mL of a phenolphthalein indicator added to 100 mL of a mixed solvent of ethyl ether and ethanol 1: 1. Immediately before use, 1/10 normal (N) potassium hydroxide Neutralized with ethanol solution.

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

By the way, only for the measurement of the fatty acid,
Instead of such a neutralization titration method, there is a method of measuring the acidity by voltammetry. This is disclosed in JP-A-5-26.
No. 4503, in which a measurement electrolyte solution in which a free fatty acid and a naphthoquinone derivative coexist is measured by voltammetry by a potential regulation method. The magnitude of the current value of the pre-reduction wave of the naphthoquinone derivative is proportional to the concentration of free fatty acids 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 superimposed value 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 pre-reduction wave of the naphthoquinone derivative. The data measured by this method is shown by the solid line in FIG.

FIG. 10 is a current-potential relationship diagram for measuring the acidity by voltammetry of a conventional electrolytic solution in which a naphthoquinone derivative coexists. In FIG. 10, the horizontal axis represents the potential of the working electrode with respect to the comparative electrode when silver-silver chloride was used as the comparative electrode and glassy carbon of φ3 was used as the working electrode, and the vertical axis represents the current value flowing through the counter electrode. However, the current value changes depending on conditions such as the surface area of the working electrode and the acid concentration. On the other hand, the voltage value on the horizontal axis is negligible although there is a slight variation depending on the acid concentration. A in FIG. 10 is a pre-peak showing a pre-reduction wave, and C is a main peak of a naphthoquinone derivative. The acid can be quantified by utilizing the fact that the pre-peak current value is proportional to the acid concentration.

However, this pre-peak current value has a smaller peak when the acid concentration is low, and the waveform of the pre-reduction wave is shown in FIG.
As shown by the broken line of 0, the pre-peak is hardly discriminated. Therefore, the reason will be described below. FIG. 11 is a pre-peak waveform diagram when measuring the acidity by voltammetry of a conventional electrolyte solution in which a naphthoquinone derivative coexists, and FIG. 12 is a peak waveform diagram when measuring the acidity by voltammetry in a conventional electrolyte solution in which a naphthoquinone derivative coexists. It is. In the case of voltammetry, a pre-peak appears as a combination of the pre-peak waveform and the main peak waveform.However, when the acid concentration is low, the pre-peak waveform is small because the pre-peak waveform is small. It will be obscured. As described above, when the acid concentration is low in the conventional method, the pre-peak is unclear and the measurement is difficult, which hinders practical use.

[0018]

As described above, since the conventional acidity measuring apparatus uses the neutralization titration method, the measurer judges the color change due to the phenolphthalein indicator and determines the end point of the titration. Depending on the measurer, the end point may vary, and the acidity may vary from measurer to measurer. In addition, when the color of the sample is dark, for example, when the material itself, such as oil or juice or wine, which is fried in large quantities, is colored, the change in the color of phenolphthalein near the end point of the titration is accurately grasped. There was a problem that the reading could not be performed, and the end point was read incorrectly, and the measured values varied. Further, the amount of the sample is required to be several tens g, the neutral solvent is required to be 100 mL, and a large amount of the sample is required for one measurement.

Further, according to the technique disclosed in Japanese Patent Application Laid-Open No. 5-264503, when the acid concentration is low, a clear pre-peak is not seen and the peak current value is accurately measured as shown by the broken line in FIG. However, there is a problem that measured values vary and reliability is lacking. As described above, even though the technology is excellent in principle, it has a problem that it is difficult to make it a practical measuring device.

The present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to provide an acidity measuring apparatus which is compact, can be easily operated, and can measure acidity with high accuracy.

In addition, the present invention provides a method for producing a composition having a low acid concentration,
An object of the present invention is to provide an acidity measuring method capable of measuring acidity with high accuracy.

[0022]

In order to solve such a problem, an acidity measuring apparatus according to the present invention comprises:
A container provided with a quinone derivative, an organic solvent, an electrolyte, and a measurement solution obtained by mixing a standard acid for increasing the acidity of the liquid to be measured by a predetermined amount, a working electrode immersed in the measurement solution, a counter electrode, and a comparison electrode unit And a controller for measuring the peak current value of the pre-wave of the voltammogram reduction of the measurement solution, and calculating the acidity of the liquid to be measured by subtracting the acidity of the standard acid.

As a result, the pre-peak current value can be accurately measured even when the acid concentration is low,
It is easy to operate and can measure acidity with high accuracy.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION The invention described in claim 1 of the present invention relates to an acid-containing solution to be measured, a quinone derivative, an organic solvent,
Electrolyte, a measurement solution obtained by mixing a standard acid for increasing the acidity of the liquid to be measured by a predetermined amount, a container provided with a working electrode, a counter electrode, and a comparison electrode portion immersed in the measurement solution, Measure the peak current value of the voltammogram reduction pre-wave, is an acidity measuring device equipped with a control unit to calculate the acidity of the liquid to be measured by subtracting the acidity of the standard acid, because the standard acid is previously mixed In addition, even when the acid concentration of the acid-containing liquid to be measured is low, the pre-peak of the voltammogram clearly appears, and the control unit can easily measure the pre-peak value of the current.

According to a second aspect of the present invention, in the acidity measuring apparatus according to the first aspect, the standard acid is an organic acid, and citric acid, malic acid or tartaric acid contained in fruit drinks is used. In addition, the acidity of alcoholic beverages or the acidity of coffee such as caffeic acid in coffee can be accurately measured even when the acid concentration is low.

According to a third aspect of the present invention, there is provided the acidity measuring apparatus according to the second aspect, wherein the organic acid is a fatty acid and the free fatty acid contained in the edible oil has a low acid concentration. However, it has the effect of being able to measure accurately.

According to a fourth aspect of the present invention, an acid-containing solution to be measured is mixed with a quinone derivative, an organic solvent, an electrolyte and a standard acid for increasing the acidity of the solution to be measured by a predetermined amount. By voltammetry of the co-existing electrolyte, measuring the peak current value of the reduction pre-wave of the current flowing through the co-existing electrolyte, and measuring the acidity of the solution to be measured, the peak current value of the reduction pre-wave is This is an acidity measurement method in which the acidity of a standard acid is shifted and measured.Even when the acid concentration of the solution containing acid is low, the pre-peak of the voltammogram clearly appears, and the pre-peak value of the current can be easily measured. Having.

According to a fifth aspect of the present invention, in the acidity measuring method according to the fourth aspect, the standard acid is an organic acid, and citric acid, malic acid or tartaric acid contained in fruit drinks is used. In addition, the acidity of alcoholic beverages or the acidity of coffee such as caffeic acid in coffee can be accurately measured even when the acid concentration is low.

According to a sixth aspect of the present invention, in the acidity measuring method according to the fifth aspect, the organic acid is a fatty acid, and the free fatty acid contained in the edible oil has a low acid concentration. However, it has the effect of being able to measure accurately.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. (Embodiment 1) First, an acidity measuring apparatus according to Embodiment 1 of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic external perspective view of an acidity measuring device according to Embodiment 1 of the present invention, FIG. 2 is a schematic external perspective view of the acidity measuring device with an upper lid opened, and FIG. 3 is a measuring container in the acidity measuring device. FIG. 4 is an explanatory view of a comparative electrode part in the acidity measuring device.

As shown in FIG. 1, the acidity measuring device comprises an upper cover 1 for covering the measuring section, an opening button 2 for opening the upper cover 1, and an LCD 3 as display means for displaying the measured acidity. A range switching button 4 for switching the region according to the degree of acidity, a start / stop button 5 for starting the measurement, and a power supply of the apparatus.
A power button 6 for turning off the power is provided, and a main body cover 14 is provided.

When the upper lid 1 is slid in FIG.
As shown in FIG. 2, the upper lid 1 is opened, and the measurement container 7 is set in the internal space of the acidity measuring device. This measuring container 7 is removable. As shown in FIG. 3, the measurement container 7 accommodates a coexisting electrolytic solution obtained by mixing a quinone derivative, an organic solvent, an electrolyte, a standard acid, and a liquid to be measured, and includes a counter electrode 8, a working electrode 9, a comparative electrode Unit 10 is combined. Specifically, the coexisting electrolytic solution is accommodated in the measuring container 7, and the container cover to which the counter electrode 8, the working electrode 9, and the comparative electrode unit 10 are attached is attached to the measuring container 7 with each electrode immersed in the coexisting electrolytic solution. Have been.

The material of the counter electrode 8 is preferably platinum, graphite and gold which are chemically stable without corrosive even in the co-existing electrolyte, but may be non-corrosive stainless steel, aluminum and alloys thereof such as platinum-containing alloy. As a material of the working electrode 9, glassy carbon called carbon or glassy carbon, or carbon obtained by sintering a plastic foam called PFC at 1000 ° C. to 2000 ° C. is suitable.

Next, the comparison electrode section 10 will be described. As shown in FIG. 4, the comparative electrode unit 10 includes an electrode 11 protruding into a glass container and a buffer solution 12 contained in the glass container.
And a liquid junction 13 provided in the glass container.

As a material for the electrode 11, silver-silver chloride is preferable, but saturated calomel, saturated calomel chloride, silver-silver ion,
Mercury-saturated mercury sulfate or copper-saturated copper sulfate may be used. In addition,
For example, “silver-silver chloride” indicates that the surface of the silver electrode 11 is covered with silver chloride.

As a material of the buffer solution 12, a chlorine compound such as silver chloride, sodium chloride, and lithium chloride, acetonitrile, copper sulfate, and other solutions having a buffering action in the oxidation-reduction reaction of the electrode 11 are suitable.

The liquid junction 13 is located between the buffer solution 12 and the co-existing electrolyte, and has the function of not allowing these solutions to pass but allowing electrons or ions to pass.
It is made of porous ceramics, porous Vycor glass, or the like.

Next, the coexisting electrolyte contained in the measurement container 7 will be described. In the first embodiment, orthobenzoquinone is used as the quinone derivative, lithium perchlorate is used as the electrolyte,
Palmitic acid is used as the standard acid. As the quinone derivative, an orthobenzoquinone or parabenzoquinone derivative is suitable. According to these quinone derivatives, the voltammogram appears shifted from the dissolved oxygen reduction waveform, so that the influence of dissolved oxygen can be cut off. The coexisting electrolyte solution of the first embodiment is a solution obtained by mixing 35% isooctane with 65% ethanol as a solvent to make 10 mL, and melting 3 mM orthobenzoquinone, 50 mM lithium perchlorate, and 0.85 mM palmitic acid. Is mixed with the liquid to be measured.
Ethanol can easily melt the electrolyte and also has the effect of cleaning the electrode surface. Further, isooctane can be melted even if it has been thermally degraded oil, and has good compatibility with ethanol. However, the thermally degraded oil has an isooctane content of 35.
%, Isooctane must be mixed at least 35%. When the degree of thermal deterioration of the oil increases, the isooctane content needs to be increased accordingly. By mixing isooctane at 35% or more in this way, the deteriorated oil can be melted in ethanol, which is a protic organic solvent, and the acidity can be measured without stirring and centrifuging as in the prior art. Become.

By the way, in the present invention, the coexisting electrolyte is
It is characterized in that a standard acid for increasing the acidity of the liquid to be measured by a predetermined amount is mixed. FIG. 5 is a current-potential relationship diagram of the acidity measurement by voltammetry of a measurement electrolyte solution in which an orthobenzoquinone derivative coexists.

In FIG. 5, 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 plastic foam carbon of φ2 was used as the working electrode, and the vertical axis represents the current flowing through the counter electrode at this time. is there. However, the current value changes depending on conditions such as the surface area of the working electrode and the acid concentration. On the other hand, the voltage value on the horizontal axis is negligible, though slightly fluctuated depending on the acid concentration.

FIG. 5A shows data when palmitic acid was dissolved at 0.85 mM, B shows data when 0.425 mM was dissolved, and C shows data when no acid was mixed. It can be seen from FIG. 5 that the lower the concentration of palmitic acid, the less the pre-peak value of the voltammogram becomes. In other words, it is difficult to accurately measure the pre-peak current value when measuring a liquid to be measured containing a small amount of acid (low acid concentration).

Therefore, by mixing a predetermined amount of acid in advance (in the case of the first embodiment, palmitic acid is added to 0.1%).
(85 mM), even when measuring a solution to be measured containing a small amount of acid, the pre-peak clearly appears, and the pre-peak current value can be easily and accurately measured.

Since the pre-peak current value varies depending on the surface area of the working electrode and the measurement conditions, the concentration of the standard acid to be mixed must be adjusted to a concentration at which the pre-peak clearly appears under the conditions. .

Now, the operation of the acidity measuring device of the first embodiment when the device is operated will be described. 10m of the above solvent
After mixing 0.5 g of the degraded oil, which is the liquid to be measured, with L, stirring the mixture, put it in the measurement container 7, and then attach the measurement cover provided with the counter electrode 8, the working electrode 9, and the comparison electrode unit 10. The acidity measuring device is set inside the measuring device, and the upper cover 1 of the acidity measuring device is closed to be ready for measurement. So power button 6
When the measurement is started by pressing the start / stop button 5, the controller 15 described later sets the potential of the working electrode 9 in the range of +200 mV to −200 mV with respect to the potential of the electrode 11 of the comparison electrode unit 10 which is a silver-silver chloride electrode. 3-1
A voltage is applied between the working electrode 9 and the counter electrode 8 so as to sweep at a sweep speed of 0 mV / s. Sweep speed 3-10
When a predetermined potential difference is swept at mV / s, a stable voltammetric current waveform as shown in FIG. 5 can be obtained as described later. By performing such a sweep, the peak of the reduction current of the acid 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 + 200m
If it is set in the range of V to -200 mV, the acidity can be measured at almost any concentration.

Next, a control section for controlling the acidity measuring apparatus according to the first embodiment will be described. FIG. 6 is a block diagram of a control unit in the acidity measuring device according to the first embodiment of the present invention.

In FIG. 6, reference numeral 5 'denotes a start / stop switch operated by the start / stop button 5, and 6' denotes a power ON-O which operates when the power button 6 is pressed.
FF switch, 15 is a controller composed of a microcomputer or the like, 16 is an oscillator, 17 is a frequency divider, 18 is timer means, 19 is a D / A converter, 20
Is an operational amplifier, 21 is a monitoring circuit, 22 is a resistor, 23 is a differential amplifier, 24 is an A / D converter, 25
Is an acidity calculating means.

When the power button 6 in FIG. 1 is pressed, the LCD 3 becomes operable. Next, when the start / stop button 5 is pressed, the controller 15 generates a clock internally by the frequency dividing circuit 17 based on the signal generated by the oscillator 16.
The clock is counted and the timer means 18 starts counting time. The timer 18 measures time in units of one second.
The controller 15 sends a digital signal (pulse) of a predetermined voltage to the D / A converter 19 in synchronization with the timer means 18.
Send. The D / A converter 19 converts the digital signal into an analog signal and outputs it to the operational amplifier 20.

FIG. 7 is an output diagram from an operational amplifier of a control circuit in the acidity measuring device according to the first embodiment of the present invention, and FIG. 8 is an output diagram from an integrating circuit of the control circuit in the acidity measuring device.

As shown in FIG. 7, when the voltage is swept at 5 mV / s, the time is 1 second, 2 seconds, 3 seconds,. , The voltage changes to 5 mV, 10 mV, 15 mV,...
Then, the signal output from the operational amplifier 20 is integrated by passing through the RC integration circuit, becomes the analog signal shown in FIG. 8, and is input to the monitoring circuit 21. Here, the controller 15 determines the potential of the working electrode 9 and the reference electrode 10.
A voltage is applied between the working electrode 9 and the counter electrode 8 while monitoring the potential difference between the working electrode 9 and the counter electrode 8.
If the sweep is performed at 0 mV / s or more, a stable current waveform cannot be obtained because the potential sweep speed is faster than the electrode reaction speed. Conversely, if the sweep speed is less than 3 mV / s, an excessive reaction occurs on the electrode surface, and a stable potential cannot be obtained. Therefore, the potential sweep speed is 3
It is necessary to make it to 〜１０10 mV / s.

In the monitoring circuit 21, the voltage C of the counter electrode 8 on the output terminal side is controlled in accordance with an analog signal by utilizing the imaginary short of the operational amplifier constituting the monitoring circuit. 1
1 is made to be the same as the analog signal. Thereby, the potential difference between the electrode 11 and the working electrode 9 falls within a predetermined value range of +200 mV to -200 mV. On the other hand, the current flowing through the counter electrode 8 is converted to a voltage by passing the voltage between both ends of the resistor 22 through a differential amplifier 23, and is converted from an analog signal to a digital signal via an A / D converter 24. 15 is input. In addition, a connector (not shown in FIGS. 1 and 2) for connecting the counter electrode 8, the working electrode 9, and the electrode 11 of the comparison electrode unit 10 to the circuit side is provided.

The controller 15 compares the input digital signal with the voltage swept at a predetermined sweep speed as shown in FIG. 8 to obtain a current value giving a pre-peak represented by A in FIG. Is detected. The acidity calculation means 25 calculates the acidity based on the pre-peak value of the current, and the value is displayed on the LCD 3.

Here, a method of calculating the acidity of the acidity measuring apparatus according to the first embodiment will be described. FIG. 9 is a diagram illustrating the relationship between the acidity and the reduction current in the acidity measuring device according to the first embodiment of the present invention.

In FIG. 10, a voltage E is a potential difference between the working electrode 9 and the electrode 11 of the comparison electrode unit 10, and a current I is a current flowing through the counter electrode 8.

The current value I giving the pre-peak value indicated by A in the waveform of FIG. 10 and the acidity θ of the acid mixed into the liquid to be measured have a proportional relationship as shown in FIG. That is, there is a relationship of I = Kθ between the prepeak current value and the acidity. The acidity calculating means 25 measures a co-existing electrolytic solution having a predetermined acidity such that the acidity becomes 1, 2, or 3, and calculates and stores the proportional constant K from the relationship between the acidity and the prepeak current value. Then, when it is desired to measure an arbitrary acidity, the acidity calculating means 25 calculates the acidity θ of the liquid to be measured from the pre-peak current value I of the liquid to be measured. The final acidity can be derived by subtracting the acidity of the standard acid mixed in advance from the calculated acidity.

[0056]

The acidity measuring apparatus according to the present invention comprises a measuring solution obtained by mixing an acid-containing solution to be measured, a quinone derivative, an organic solvent, an electrolyte and a standard acid for increasing the acidity of the solution to be measured by a predetermined amount. Since it is used, highly accurate acidity can be measured. A control unit that sweeps the potential of the working electrode from the electrode potential of the comparison electrode unit at a potential within a predetermined potential difference, detects a pre-peak value of the current, and subtracts the acidity of the standard acid to calculate the acidity of the liquid to be measured. Since it is equipped, it can be easily operated and can automatically determine the acidity,
A highly accurate and highly accurate acidity can be measured.

Further, according to the acidity measuring method of the present invention, the prepeak value can be easily detected, and the acidity can be measured with high accuracy.

[Brief description of the drawings]

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

FIG. 2 is a schematic external perspective view of the acidity measuring device with an upper lid opened.

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

FIG. 4 is an explanatory view of a comparative electrode part in the measurement container.

FIG. 5 is a current-potential relationship diagram of acidity measurement by voltammetry of a measurement electrolyte solution in which an orthobenzoquinone derivative coexists.

FIG. 6 is a block diagram of a control unit in the acidity measuring device.

FIG. 7 is an output diagram from an operational amplifier of a control unit in the acidity measuring device.

FIG. 8 is an output diagram from an integration circuit of a control unit in the acidity measurement device.

FIG. 9 is a diagram showing the relationship between acidity and reduction current in the acidity measuring device.

FIG. 10 is a current-potential relationship diagram of a conventional electrolytic solution in which a naphthoquinone derivative coexists with acidity measurement by voltammetry.

FIG. 11 is a diagram showing a pre-peak waveform at the time of measuring the acidity by voltammetry of a measurement electrolyte solution in which a conventional naphthoquinone derivative coexists.

FIG. 12 is a peak waveform chart of a conventional electrolytic solution in which a naphthoquinone derivative coexists when the acidity is measured by voltammetry.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Top cover 2 Button for opening 3 LCD 4 Button for range switching 5 Start / stop button 5 'Start / stop switch 6 Power button 6' Power ON-OFF switch 7 Measuring vessel 8 Counter electrode 9 Working electrode 10 Reference electrode section 11 Electrode Reference Signs List 12 buffer solution 13 liquid junction 14 body cover 15 controller 16 oscillator 17 frequency dividing circuit 18 timer means 19 D / A converter 20 operational amplifier 21 monitoring circuit 22 resistor 23 differential amplifier 24 A / D converter 25 acidity calculating means

Claims (6)

[Claims] 1. A measurement solution in which an acid-containing solution to be measured, a quinone derivative, an organic solvent, an electrolyte, and a standard acid for increasing the acidity of the solution to be measured by a predetermined amount are mixed, and the sample is immersed in the measurement solution. A container provided with a working electrode, a counter electrode, and a reference electrode unit, and a control for measuring the peak current value of the pre-wave of the voltammogram reduction of the measurement solution and calculating the acidity of the liquid to be measured by subtracting the acidity of the standard acid. An acidity measuring device comprising a part. 2. The acidity measuring device according to claim 1, wherein the standard acid is an organic acid. 3. The acidity measuring device according to claim 2, wherein the organic acid is a fatty acid. 4. An acid-containing solution to be measured, a quinone derivative, an organic solvent, an electrolyte, and a standard acid for increasing the acidity of the solution to be measured by a predetermined amount are mixed, and the coexisting electrolytic solution is subjected to voltammetry. When measuring the peak current value of the pre-reduction wave of the current flowing through the electrolyte and measuring the acidity of the solution to be measured,
An acidity measuring method, wherein the peak current value of the reduction pre-wave is shifted to the position of the acidity of the standard acid for measurement. 5. The method according to claim 4, wherein the standard acid is an organic acid. 6. The method according to claim 5, wherein the organic acid is a fatty acid.