JPH10332636A - Acidity measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an acidity measuring apparatus by which the acidity of various acids can be measured with high reliability by a method wherein a discrimination member which corresponds to the kind of an acid is installed at a container and a distinction part which distingushes the discrimination member is installed at a control part. SOLUTION: Protrusions 11A to 11D as discrimination members which are installed at a container 7 in a measuring container 14 can specify the kind of an acid by combining their number and their position, and 16 kinds can be specified according to how the protrusions are installed in four positions at equal intervals. When the number of the protrusions is designated as (n), (2n) kinds of acids can be distinguished. When an acidity is measured by using the measuring container 14, a coexistent electrolytic solution mixed with a liquid, to be measured, which contains an acid is housed inside the container 7, and a container cover 15 to which a container electrode 8, a working electrode 9 and a comparison electrode part 10 are attached is lidded from the upper part. Then, switches, for distinction, whose number corresponds to the protrusions 11A to 11D at the container 7 are placed on a control part at an acidity measuring apparatus, and the kind of an acid and its acidity can be determined.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method 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 coffee acid in coffee. The present invention relates to an acidity measuring device capable of producing an acidity.

[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 the quality of foods. Recently, foods with low acidity tend to be exclusively enjoyed. 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. Examples of conventional acidity measurement methods include the methods specified in the Standard Oil and Fat Analysis Method, Japanese Agricultural Standards, JIS, Japanese Pharmacopoeia Oil and Fat Test Method, Sanitary Test Method, Food and Drink Test Method, Water Supply Test Method, etc. The measurement is based on a neutralization titration method using phenolphthalein as an indicator. Then, in order to explain this neutralization titration method, the titration method specified by the clean water test method and the standard fat and oil analysis method will be described below.

[0003] The acidity in the clean 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 neutralization is defined as the time when the titration is continued until the remaining sodium hydroxide remains, and the mL number a of the sodium hydroxide is determined. 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.

[0004] Next, the neutralization titration method specified in the standard fat and oil analysis method will be described. The definition of acidity in the reference fat analysis method is
This refers to the number of mg of potassium hydroxide required to neutralize free fatty acids contained in 1 g of a sample. In the case of a liquid sample, the sample is sampled for its estimated acidity (for example, 20 g if the acidity is 1 or less, 10 g if the acidity is more than 1 and 4 or less, and 2.5 g if the acidity is more than 4 and 15 or less. And collect it in an Erlenmeyer flask. To this is added 100 ml of neutral solvent and shaken thoroughly until the sample is completely dissolved. However, the term "neutral solvent" as used herein means that about 0.3 ml of a phenolphthalein indicator is added to 100 ml of a mixed solvent of ethyl ether and ethanol 1: 1. It is a sum.

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 standard (N) / 10 potassium hydroxide-ethanol standard solution, and the end point of neutralization is determined when the color change of the indicator continues for 30 seconds. Then, the mg number of potassium hydroxide at this time is calculated.

Incidentally, in addition to the neutralization titration method described above, there is a method of measuring acidity by voltammetry. This is a method disclosed in JP-A-5-264503. In order to measure the acidity by this method, it is necessary to mix the acid in the coexisting electrolyte and then sweep the potential of the working electrode from the potential of the comparison electrode, and measure the current value at this time. Nitrogen gas or the like must be supplied to the coexisting electrolyte to remove dissolved oxygen in the coexisting electrolyte. If dissolved oxygen is not removed, a current for reducing dissolved oxygen will flow, making it difficult to determine the magnitude of the current of the pre-reduction wave detected by voltammetry, and reducing the pre-reduction wave that is related to acidity. Can hardly be determined. And in order to remove oxygen, it is necessary to install a gas cylinder such as nitrogen gas and continue to supply the gas for oxygen removal.
The size of the apparatus has been increased, which has practically hindered the practical use of this measuring method. Furthermore, even if an attempt is made to measure the degree of oxidation in order to know the deterioration of oil, etc., the oil etc. does not melt in the coexisting electrolyte, and must be extremely stirred and centrifuged, which also causes the equipment to become large. I was

In addition, since the coexisting electrolyte and the current curve by voltammetry (hereinafter referred to as voltammogram) differ depending on the type of the acid to be measured, separate calibration and mounting on the apparatus are required, and operation is difficult for inexperienced persons. There was a problem of difficulty.

[0008]

As described above, in the conventional neutralization titration method and voltammetry, the measuring method differs depending on the kind of acid, and a separate measuring device is prepared according to each measuring method. I had to put it. In this case, the measuring device takes up space, and the measurer is required to have very advanced knowledge of measurement.

The voltammetry technique disclosed in Japanese Patent Application Laid-Open No. Hei 5-264503 requires a large-sized apparatus using a nitrogen cylinder or the like, and even if oxygen is removed by this nitrogen gas or the like, a coexisting electrolytic solution or voltammogram is obtained for each acid. However, it was difficult for those with little experience to measure.

Accordingly, it is an object of the present invention to provide a small and compact acidity measuring apparatus which can measure various acids, is easy to operate even for those who have little measurement experience, and has high reliability.

[0011]

In order to solve such a problem, an acidity measuring device according to the present invention is provided with an identification member corresponding to the type of acid in a container, and a control unit for identifying the identification member. A determination unit is provided.

[0012] Thus, various acids can be measured, and even a person with little measurement experience can easily operate, and a highly reliable, small and compact acidity measuring apparatus can be provided.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention is directed to a container for accommodating a coexisting electrolyte mixed with an acid-containing solution to be measured, and provided in the container and immersed in the coexisting electrolyte. The working electrode, the counter electrode, the comparison electrode portion, and the potential of the working electrode are swept within a predetermined potential difference from the electrode potential of the comparison electrode portion, and a pre-peak value of a current flowing between the working electrode and the counter electrode is detected. Since the container is provided with a discriminating member corresponding to the type of the acid, and the control unit is provided with a discriminating unit for discriminating the discriminating member. When mounted on the acidity measuring device, the determination unit of the control unit determines the identification member provided on the container, and has the effect of specifying the type of acid.

According to a second aspect of the present invention, the identification member is a projection member composed of a combination of the number and position of the projections protruding from the outer surface of the container, and the discriminating portion is a switch corresponding to the projection. Therefore, 2 ⁿ kinds of acids can be distinguished by the number and position of the projections.

(Embodiment) An acidity measuring apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic external view of an acidity measuring device according to an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes an upper cover for covering the measuring unit, 2 is a button for opening the upper cover 1, 3 is an LCD which is a display means for displaying the measured acidity, and 4 is for switching the area according to the magnitude of the acidity. , A start / stop button 5 for starting measurement, 6 a power button for turning on / off the power of the apparatus, and 18 a body of the acidity measuring apparatus.

Next, FIG. 2 is a schematic external view of a partially crushed acidity measuring apparatus according to an embodiment of the present invention, in which an upper lid is opened, and FIG. 3 shows a measuring container of the acidity measuring apparatus according to an embodiment of the present invention. FIG. 4 is a detailed view of a comparative electrode unit of the acidity measuring device according to one embodiment of the present invention. When the upper lid 1 is slid in FIG. 1, the upper lid 1 is moved as shown in FIG.
Is opened, and the measuring container 14 is set in the internal space of the acidity measuring device. This measuring container 14 is removable. 2 and 3, reference numeral 7 denotes an organic solvent such as an orthobenzoquinone derivative or a parabenzoquinone derivative, an electrolyte,
And a container for accommodating a co-existing electrolyte mixed with a liquid to be measured containing an acid. Reference numeral 8 denotes a counter electrode, 9 denotes a working electrode, and 10 denotes a comparison electrode unit, which is immersed in the container 7. 11A to 11D are protrusions provided to protrude from the outer surface of the container 7, and are the identification members of the present invention. The measuring container 14 contains the coexisting electrolyte solution in the container 7 when measuring the acidity, and is covered by a container cover 15 to which the counter electrode 8, the working electrode 9, and the comparative electrode unit 10 are attached from above. Each electrode is mounted on the container 7 while being immersed in the coexisting electrolyte. Preferable materials for the counter electrode 8 are platinum, graphite, and gold, which are chemically stable without corrosive even in the co-existing electrolyte solution.
Aluminum or an alloy thereof may be used. As the material of the working electrode 9, glassy carbon called carbon or glassy carbon, or carbon obtained by sintering a plastic fiber 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, an internal liquid 12 housed in the glass container,
It comprises a liquid junction 13 provided in a glass container. Electrode 1
Silver-silver chloride is good as the material of No. 1, but saturated calomel,
Silver-silver ions or mercury-saturated mercury sulfate may be used. Note that, for example, “silver-silver chloride” indicates that the surface of the silver electrode 11 is covered with silver chloride. Internal liquid 1
Suitable materials for the second material include chlorine compounds such as silver chloride, sodium chloride, and lithium chloride, acetonitrile, copper sulfate, and other solutions that exhibit a buffering action in the oxidation-reduction reaction of the electrode 11. The liquid junction 13 is located between the internal 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 therethrough, such as porous ceramics and porous Vycor glass. Etc.

Next, the coexisting electrolyte contained in the container 7 will be described. In this embodiment, lithium perchlorate is used as the electrolyte. The coexisting electrolyte solution of the present embodiment is a mixture of 65% ethanol and 35% isooctane as a solvent to make 10 ml, and melts 3 mmol of orthobenzoquinone and 50 mmol of lithium perchlorate. The measurement solution is mixed and used. Orthobenzoquinone may be a derivative thereof, or parabenzoquinone or a derivative thereof. These quinone derivatives exhibit a prepeak at a position where the voltammogram is shifted from the dissolved oxygen reduction waveform when subjected to voltammetry with the liquid to be measured as described below. As described above, the coexisting electrolytic solution of the present invention may contain any solvent as long as the solvent can shift from the dissolved oxygen reduction waveform. Ethanol can easily melt the electrolyte, and at the same time, 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, thermally degraded oils and the like will not melt unless the isooctane content is 35% or more, so it is necessary to mix isooctane at least 35%. When the degree of thermal deterioration of oil or the like increases, it is appropriate to increase the isooctane content 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.

FIG. 5 is a current-potential diagram for measuring the acidity of the co-existing electrolyte containing acid by voltammetry. As shown in FIG. 5, the voltammogram of the coexisting electrolyte described above is
It appears with a large shift from the region where the dissolved oxygen reduction waveform appears. The solid line in FIG. 5 is a voltammogram of the co-existing electrolyte solution and the solution to be measured, and the dashed line is a reduction waveform of dissolved oxygen. According to FIG. 5, the position of the pre-peak is on the positive potential side, and is shifted by about 400 mV from the negative potential side where the dissolved oxygen reduction waveform exists. Even at the position of this peak, there is almost no effect of the reduction of dissolved oxygen. In this way, the pre-peak value can be measured in a region where the dissolved oxygen is not affected, so that the acidity can be accurately measured without being affected by the dissolved oxygen even if the dissolved oxygen is not removed in advance. It is.

Next, the identification unit and the discrimination unit, which are features of the present invention, will be described with reference to FIGS. 3, 6 to 8. FIG.
, The container 7 is provided with an identification member. In the present embodiment, the projections 11A to 11D are provided as the identification member. The types of the acids of the projections 11A to 11D can be specified by a combination of the number and the position. In the present embodiment, 16 types are specified depending on whether or not the projections are provided at four equally spaced positions. I can do it. Assuming that the number of protrusions is n, 2 ⁿ types of acids can be distinguished. In FIG. 3, reference numeral 15 denotes a container cover for covering a solution such as an object to be measured. Although all four of the projections 11A to 11D are provided, any or all of the projections 11A to 11D may be removed. As described above, 16 kinds of acids can be specified by the presence or absence of the protrusion at the predetermined position. In some cases, the identification member can also determine whether or not a container is mounted on the acidity measuring device. In the embodiment of the present invention, the projection is provided on the container 7, but the container cover 15
May be provided.

FIG. 6 is a schematic diagram of a discriminating unit according to an embodiment of the present invention. In FIG. 6, 17A to 17D are:
A switch that is connected to the control unit 21 of the acidity measuring device (see FIG. 9) and that can identify the type of acid by engaging with the projection on the container 7 when the measuring container 7 is mounted on the acidity measuring device. is there. When pressed, the switch is turned on. The number and position of the switches correspond to the number and position of the projections on the container. As described above, the discriminating unit of the present embodiment is a switch, but if the discriminating member of the container 7 is magnetic recording or the like,
The magnetic head or the like reading this is a discriminating unit, and does not necessarily require engagement.

FIG. 7 is a schematic external view of a container according to another embodiment of the present invention, and FIG. 8 is a schematic external view of a container according to another embodiment of the present invention mounted on a discriminating section. FIG. 7 shows the container 7 of FIG. 3 without the protrusions of 11A and 11C, and as shown in FIG.
17D has only the projections 11B and 11D in the container 7,
The projections 11B and 11D press the switches 17B and 17D to conduct and specify the type of acid.

Next, a control circuit for controlling the acidity measuring apparatus according to the present embodiment will be described. FIG. 9 is a control circuit diagram of the acidity measuring device according to one embodiment of the present invention. In FIG. 9, 5 'is a start / stop switch operated by a start / stop button 5, 6' is a power ON-OFF switch which is operated by pressing a power button 6, 2
1 is a control unit composed of a microcomputer or the like,
22 is an oscillator, 23 is a frequency dividing circuit, 24 is a timer means, 2
5 is a D / A converter, 26 is an operational amplifier, 27 is a monitoring circuit, 28 is a resistor, 29 is an operation amplifier, 3
0 is an A / D converter, 31 is an acidity calculating means composed of a microcomputer or the like as in the control section 21, 17A to
17D is a switch. First, the measurement container 1 shown in FIG.
4 is attached to the acidity measuring device, the switches 17A to 17
D is pressed by the projections 11B and 11D,
And 17D are ON, and 17A and 17C are OFF. These are input as 4-bit signals to the control unit 21, read out the type of acid stored in the storage unit of the control unit 21, and input this to the acidity calculation unit 31. Next, when the power button 6 (FIG. 1) is pressed, the LCD 3 becomes operable. When the start / stop button 5 is further pressed, the control unit 21
Is a frequency dividing circuit 23 based on a signal generated by the oscillator 22.
, A clock is generated internally, the clock is counted, and the timer 24 starts counting time. This timer 2
4 measures time in units of one second. The control unit 21 sends a digital signal (pulse) of a predetermined voltage to the D / A converter 25 in synchronization with the timer 24. The D / A converter 25 converts the digital signal into an analog signal and outputs it to an operational amplifier 26.

FIG. 10 is an output diagram from an operational amplifier of a control circuit of the acidity measuring apparatus according to one embodiment of the present invention.
1 is an output diagram from an integration circuit of a control circuit of the acidity measuring device according to one embodiment of the present invention. As shown in FIG. 10, when time is plotted on the horizontal axis and voltage is plotted on the vertical axis, the time is 1
The voltage is 5m every second, 2 seconds, 3 seconds, ...
V, 10 mV, 15 mV,... Then, the signal output from the operational amplifier 26 is integrated by passing through the RC integration circuit, becomes the analog signal shown in FIG. 11, and is input to the monitoring circuit 27. In the monitoring circuit 27, the voltage R of the electrode 11 of the comparison electrode unit 10 is fed back using the imaginary short property of the operational amplifier 26, and the potential difference between the monitoring electrode 27 and the working electrode 9 becomes a predetermined value (+200 mV to -200 mV). )
The voltage C applied to the counter electrode 8 is controlled. On the other hand, the current flowing through the counter electrode 8 is obtained by converting the voltage across the resistor 28 into a differential amplifier 29.
The signal is converted to a voltage by passing the signal through the A / D converter 30, and is converted from an analog signal to a digital signal via the A / D converter 30. Here, the control unit 2
1 detects a current value that gives a pre-peak represented by A in FIG. 5 by comparing currents with respect to a voltage swept at a predetermined sweep speed. The acidity is calculated by the acidity calculating means 31 based on the pre-peak value of the current, and the calculated value is displayed on the LCD 3. FIG. 12 is a diagram showing the relationship between the acidity and the reduction current of the acidity measuring device according to one embodiment of the present invention. In FIG. 12, a current I is a current flowing through the counter electrode 8. As can be seen from the relationship diagram of FIG. 12, the current value I giving the pre-peak value indicated by A and the acidity θ of the acid mixed into the liquid to be measured are in a proportional relationship. That is, there is a relationship of I = Kθ (K is a proportional constant) between the prepeak current value and the acidity. Therefore, by measuring the current value I of A, the acidity θ can be measured.

Now, the operation of the apparatus for measuring the acidity according to the present embodiment will be described. First, if the degraded oil to be measured is edible oil, a container 7 having an identification member corresponding to edible oil is selected. Next, for 10 mL of the above solvent,
0.5 g of the deteriorated oil, which is the liquid to be measured, is mixed and stirred. Next, the container cover 15 provided with the counter electrode 8, the working electrode 9, and the comparison electrode unit 10 is attached and set in the acidity measuring device, and when the upper lid 1 of the acidity measuring device is closed, each electrode becomes conductive and becomes ready for measurement. At the same time, the identification member of the measurement container 14 is identified by the identification unit, and the control unit 21 reads out the stored 4-bit type of acid, and calculates the proportional constant K and the like necessary for calculating the acidity according to the type of acid. Information is also read. Then, the power button 6 and the start / stop button 5 are pressed to start the measurement. The control section 21 sweeps the potential of the working electrode 9 with respect to the potential of the electrode 11 of the comparison electrode section 10 which is a hydrogen standard electrode, in a range of +200 mV to -200 mV and at a sweep speed of 3 to 5 mV / s. Thus, a voltage is applied to the working electrode 9 and the counter electrode 8. This + 200mV
The range of -200 mV indicates a region where the above-mentioned dissolved oxygen is hardly affected and in which the pre-peak value can be accurately measured. Of course, a quinone derivative having a prepeak value of the voltammogram in this range is selected as the coexisting electrolyte. When a predetermined potential difference is swept at a sweep rate of 3 to 5 mV / s, a stable voltammogram not affected by dissolved oxygen as shown in FIG. 5 can be obtained, and the reduction current of the acid peaks and falls within the above range. Appears at potential. This is the pre-peak, and this potential shifts to the negative side as the acid concentration increases. + 200m like this
If it is set in the range of V to -200 mV, it can be measured without being affected by dissolved oxygen at almost any concentration of acidity. The control unit 21 applies a voltage between the working electrode 9 and the counter electrode 8 while monitoring the potential difference between the potential of the working electrode 9 and the electrode potential of the comparison electrode unit 10. If the potential difference between the comparison electrode units 10 is swept at about 5 mV / s or more, a stable current waveform cannot be obtained because the potential sweep speed is faster than the electrode reaction speed. Conversely, the sweep speed is set to 3 mV
If it is less than / s, the reaction on the electrode surface occurs excessively and a stable potential cannot be obtained. Therefore, the potential sweep speed needs to be in the range of 3 to 5 mV / s. Control unit 2
When a measured current value I indicating a pre-peak is inputted, information such as the measured current value I and the proportionality constant K is transmitted to the acidity calculating means 3.
1 and the acidity calculating means 31 calculates the acidity θ. When the acidity θ is calculated, the control unit 21 displays this value on the LCD 3
To be displayed.

As described above, the acidity measuring apparatus according to the embodiment is
Since an identification member is provided on the measurement container 14 and a determination unit is provided on the measurement device side, the acidity according to the acid of the liquid to be measured can be automatically calculated only by setting the measurement container 14. is there.

[0027]

According to the acidity measuring device of the present invention, since the identification member corresponding to the type of the acid is provided in the container and the discriminating portion is provided in the control section, it is possible to automatically recognize various kinds of acids. Since there is no operation for inputting the kind of acid and the like, measurement is easy even for those who have little experience in measurement. In addition, since a precise measurement corresponding to each type of acid can be performed, the reliability is high, and there is no need to remove oxygen or centrifugal separation, so that a small and compact acidity measuring device can be obtained.

[Brief description of the drawings]

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

FIG. 2 is a partially crushed schematic external view of an acidity measuring device according to an embodiment of the present invention with an upper lid opened.

FIG. 3 is a diagram showing a measuring container of the acidity measuring device according to one embodiment of the present invention.

FIG. 4 is a detailed view of a comparison electrode unit of the acidity measuring device according to one embodiment of the present invention.

FIG. 5 is a current-potential relationship diagram of acidity measurement of a coexisting electrolyte containing acid by voltammetry.

FIG. 6 is a schematic diagram of a determination unit according to an embodiment of the present invention.

FIG. 7 is a schematic external view of a container according to another embodiment of the present invention.

FIG. 8 is a schematic external view in which a container according to another embodiment of the present invention is mounted on a determination unit.

FIG. 9 is a control circuit diagram of the acidity measuring apparatus according to one embodiment of the present invention.

FIG. 10 is an output diagram from an operational amplifier of a control circuit of the acidity measuring device according to one embodiment of the present invention.

FIG. 11 is an output diagram from an integrating circuit of a control circuit of the acidity measuring apparatus according to one embodiment of the present invention.

FIG. 12 is a diagram showing the relationship between the acidity and the reduction current of the acidity measuring device according to one embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Top lid 2 Button 3 LCD 4 Button 5 Start / Stop button 5 'Start / Stop switch 6 Power button 6' Power ON-OFF switch 7 Container 8 Counter electrode 9 Working electrode 10 Comparative electrode part 11A-16D Projection 12 Internal liquid 13 Liquid junction Unit 14 measuring container 15 container cover 17A to 17D switch 18 main body 21 control unit 22 oscillator 23 frequency dividing circuit 24 timer 25 D / A converter 26 operational amplifier 27 monitoring circuit 28 resistor 29 operating amplifier 30 A / D converter 31 acidity calculating means

Claims (2)

[Claims] A container for accommodating a co-existing electrolyte mixed with a solution to be measured containing an acid; a working electrode provided in the container, immersed in the co-existing electrolyte; A control unit that sweeps the potential within a range of a predetermined potential difference from the electrode potential of the comparison electrode unit, and detects a pre-peak value of a current flowing between the working electrode and the counter electrode; and the container includes a type of the acid. An acidity measuring device, characterized in that an identification member corresponding to (1) is provided, and the control section is provided with a determination section for determining the identification member. 2. The identification member according to claim 1, wherein the identification member is a projection member formed by a combination of the number and position of projections protruding from the outer surface of the container, and the determination unit includes a switch corresponding to the projection. The acidity measuring device according to claim 1, wherein: