JP4221504B2 - Chemical substance measuring method and apparatus - Google Patents

Description

  The present invention relates to a chemical substance measurement method for continuously detecting and quantifying only a chemical substance to be measured with an electrode reaction with high accuracy and high sensitivity in a sample aqueous solution containing a plurality of chemical substances, particularly industrial water, The present invention relates to a technique used for detection and quantification of chemical substances such as heavy metal ions contained in river water, seawater, groundwater, soil and the like.

As a method for qualitative and quantitative analysis of chemical substances from the oxidation-reduction potential and oxidation-reduction current at this time by directly inserting an electrode into a sample aqueous solution containing multiple chemical substances and oxidizing or reducing the chemical substances, Rography was used. (For example, see Non-Patent Document 1)
This is accomplished by using a mercury droplet loaded with voltage as an electrode, and immersing this mercury droplet directly in the sample aqueous solution and changing its potential by sweeping the electrode reaction (reduction or oxidation reaction) that occurs on the surface of the mercury droplet. ) To measure the measurement target chemical substance such as metal ions in an aqueous solution, and qualitative analysis is performed from the potential at which the reaction occurs, and quantitative analysis is performed from the current accompanying the reaction.

FIG. 8 schematically shows a current-potential curve (a diagram showing a change in current with respect to a change in potential) obtained with this measurement.
This figure shows the case of reducing three kinds of metal ions with different reduction potentials of M1 ⁺ , M2 ⁺ , and M3 ⁺ (equilibrium potential is M1 ⁺ is the most noble, the next is M2 ⁺ and M3 ⁺ is the most basic). For example, a current-potential curve is shown, and the horizontal axis of the figure is a base potential (low potential) in the right direction.
When the potential of the mercury droplet is changed in the base direction, the reduction reaction of the M1 ⁺ ion having the highest equilibrium potential starts and becomes constant after the current increases rapidly.

In the same manner, the reduction reaction of M2 ⁺ and M3 ⁺ starts from around the equilibrium potential in the same manner, and a staircase type curve is obtained. From this curve, ions can be identified from the potential at which the current rises.
Also, the current is constant because the reduction reaction rate is governed by the diffusion rate of ions to the mercury droplet surface, and the current value at this time is proportional to the ion concentration in the aqueous solution. In addition, the ion concentration (M1 ⁺ , M2 ⁺ , M3 ⁺ ion concentration) in the aqueous solution can be determined from this current (i1, i2-i1, and i3-i2).

  In this conventional polarography, the electrode for proceeding the oxidation-reduction reaction is immersed directly in the sample aqueous solution. Therefore, when multiple chemical substances are present in the sample aqueous solution, the electrode reaction (oxidation) of the chemical substance other than the purpose of measurement is performed. In the measurement using the reaction, the oxidation reaction has a lower oxidation potential than the target chemical substance, and in the measurement using the reduction reaction, the reduction reaction having the noble oxidation potential than the target chemical substance) proceeds simultaneously. However, since the current measured as shown by i3 in FIG. 8 includes an oxidation-reduction current other than the target chemical substance, it is necessary to appropriately correct this after performing a potential sweep, which complicates the operation. Above, continuous measurement is not possible.

In addition, especially when the chemical substance to be measured is smaller than the concentration of other chemical substances, the change in current associated with the electrode reaction of the chemical substance to be measured becomes minute, and this substance concentration must be accurately quantified. It becomes difficult.
As described above, the conventional example has a problem that it is difficult to continuously detect and quantify only a chemical substance to be measured with high accuracy and high sensitivity.
"Analytical Chemistry (2nd edition)", Tokyo Chemical Doujin, pp. 445-448 (Showa 55)

  This invention is made | formed in view of the above-mentioned actual condition in a prior art. That is, the object of the present invention is to continuously detect only a chemical substance to be measured with high accuracy and high sensitivity by an electrode reaction in an aqueous solution containing a plurality of chemical substances without being interfered by chemical substances other than the chemical substance to be measured. It is to provide a measurement technique that can be detected and quantified.

  As a result of intensive studies to solve the above-mentioned problems, the present inventor has paid attention to the difference in redox potential associated with the oxidation-reduction reaction between the chemical substance to be measured and the other chemical substance, and the chemical substance to be measured In addition to the electrode to measure the chemical substance, the chemical substance other than the measurement target is deposited on the electrode surface and captured, or this is changed to a chemical form that does not affect the measurement of the measurement target chemical substance. Install non-acting electrodes, hold them at different potentials, and remove the interference of chemical substances other than the measurement target among the chemical substances diffusing from the sample aqueous solution with the latter electrode. By detecting and quantifying the chemical substance with the former electrode, the chemical substance to be measured is measured while preventing interference by chemical substances other than the measurement object.

  That is, the chemical substance measuring method of the present invention provides a cavity communicating with the aqueous solution in the aqueous solution containing the chemical substance to be measured and other chemical substances, and oxidizes the chemical substance to be measured in the inner part of the cavity. Alternatively, a post electrode to be detected and quantified by a reduction chemical reaction is installed, and then a pre electrode is installed between the post electrode and the cavity entrance, and the former is sufficiently low in potential or oxidized to reduce the chemical substance to be measured. In the case of reducing the chemical substance to be measured, the latter is more noble than the reduction potential of the chemical substance to be measured, and kept at a lower potential than the reduction potential of other chemical substances. When oxidizing the chemical substance to be measured, the chemical substance that diffuses into the cavity from the aqueous solution by keeping the potential lower than the oxidation potential of the chemical substance to be measured and nobler than the oxidation potential of other chemical substances. Among them, chemical substances other than the chemical substances to be measured are captured by being deposited on the electrode surface by the oxidation or reduction reaction of the front electrode, or changed to a substance that does not cause an electrode reaction at the rear electrode. The measurement target chemical substance that passes through the front electrode and reaches the rear electrode is measured by measuring the oxidation current associated with the reduction or oxidation reaction at the rear electrode while preventing the reaction of these chemical substances at the rear electrode. Only the chemical substance to be measured is detected and quantified without being disturbed by chemical substances other than chemical substances.

  The present invention further includes a container that holds an aqueous solution containing a plurality of chemical substances, and a detector that is in communication with the aqueous solution in the container through an opening, and that has a structure that does not communicate with the aqueous solution except at the opening. A main body, a rear electrode for detecting and quantifying a chemical substance to be measured, which is installed in the inner part of the cavity of the detector main body, by an oxidation or reduction chemical reaction, and a front electrode disposed between the rear electrode and the cavity inlet And a power supply device that applies a reduction potential or an oxidation potential according to the measurement target chemical substance and the non-measurement chemical substance. Among the chemical substances that diffuse into the cavity from the aqueous solution, The chemical substance is deposited on the electrode surface by the oxidation or reduction reaction of the front electrode and captured, or changed to a substance that does not cause an electrode reaction at the rear electrode, passes through the front electrode, and reaches the rear electrode. Measurement target chemical A chemical substance measuring device characterized by detecting and quantifying a post electrode, and applying a voltage alternately to the front electrode side and the rear electrode side without simultaneously applying a voltage to the front electrode and the rear electrode This chemical substance measuring device equipped with a front electrode side changeover switch and a rear electrode side changeover switch, prevents the advection of the aqueous solution into the cavity in the flowing aqueous solution at the cavity inlet of the detector body, and only by diffusion The chemical substance measuring device with a filter that moves the chemical substance inside, the chemical substance measuring device consisting of a plurality of electrode plates with spacers inserted in the front electrode, the counter electrode and the reference electrode inside the cavity of the detector body It relates to the chemical substance measuring device installed.

  In the present invention, in the aqueous solution containing a plurality of chemical substances, only the chemical substance to be measured is detected with high accuracy and high sensitivity by the electrode reaction without being interfered by chemical substances other than the chemical substance to be measured. It has an excellent effect that it can be continuously detected and quantified.

Hereinafter, the present invention will be described in detail. FIG. 1 is a diagram for explaining a preferred arrangement of cavities and electrode systems in the present invention. Based on this diagram, the principle of measurement of chemical substances by these will be explained.
The upper part of FIG. 1 shows a preferred electrode arrangement according to the present invention, and the lower part of FIG. 1 shows an actual embodiment using this electrode.
A rear electrode 2 is disposed behind two flat plate-shaped front electrodes 1 arranged in parallel at a constant interval, and the front electrode and the rear electrode are respectively connected to separate power sources and signal processing devices 4. 3 is connected.

Actually, the front electrode and the rear electrode remain in this arrangement, and the detector body 10 having a structure in which a cavity is formed in one direction as shown in the lower part of FIG. The detector body is immersed in the sample aqueous solution 12 filled in the test tank 11 with the front electrode placed on the opening side of the cavity.
The inside of the cavity communicates with the aqueous sample solution, and the chemical substance in the aqueous sample solution diffuses between the two front electrodes from the front surface of the front electrode. In FIG. 1, metal ions 9 (M1 ⁺ , M2 ⁺ ) are shown as chemical substances contained in the sample aqueous solution. Hereinafter, the present invention will be described with reference to an example in which this is measured by a reduction reaction.

In addition to the above electrodes, the reference electrode 7 and the counter electrode 8 are immersed in the sample aqueous solution, and are connected to the front electrode and the rear electrode via the power source and the signal processing device 4 as shown in FIG. . A voltage is applied between the front electrode, the rear electrode, and the counter electrode, and a current flows between the connected front electrode-counter electrode and rear electrode-counter electrode, respectively. Detected.
The potentials of the front electrode and the rear electrode at this time are measured by the potentiometer 5 with reference to the connected reference electrode potential, and the electrode potentials measured by the potentiometer are respectively set to target values. The voltage applied between the front electrode or the rear electrode and the counter electrode is adjusted.

Here, M2 ⁺ is a metal ion to be measured, and M1 ⁺ is an ion coexisting with this in an aqueous solution. These metal ions are reduced based on the following formula when the electrode is at a base potential lower than the equilibrium potential of each oxidation-reduction reaction, and are deposited on the electrode surface.
M1 ⁺ + e ⁻ → M1 (1)
M2 ⁺ + e ⁻ → M2 (2)
Here, the equilibrium potential of the oxidation-reduction reaction of M1 ⁺ is V1, the one of M2 ⁺ is V2, and V1> V2 (V1 is more noble than V2 and is easily reduced).

If the front electrode is kept at a potential lower than V1 and nobler than V2, and the rear electrode is kept at a potential lower than V2, M1 ⁺ is reduced while diffusing between the front electrodes to become metal M1. It deposits on the surface of the electrode and the concentration decreases. M2 ⁺ is not reduced at the front electrode but diffuses between the front electrodes, reaches the back electrode, is reduced there, and is deposited as metal M2.
The same ion is detected from the current at this time and the concentration is quantified. Here, as shown in the front electrode portion of the electrode arrangement diagram in the upper part of FIG. 1, in the depth direction at the center of the electrode plate of the front electrode and the center of the interval between the two front electrodes. If x and y coordinates are set perpendicularly to the electrode plate direction, the concentration distribution of the metal ion M1 ⁺ between the two front electrode plates is a value obtained by the following equation.
C = C0exp (-πx / y0) cos (πy / y0) (3)

Here, C is the ion concentration at the position (x, y), C0 is the metal ion concentration in the aqueous sample solution, and y0 is the distance between the two front electrodes.
Therefore, the metal ion concentration after passing through the front electrode can be set to a target value by setting the ratio (x / y0) between the distance y0 between the front electrodes and the depth x.
This ratio (x / y0) is required to set the ratio of the metal ion concentration before passing through the front electrode to the metal ion concentration after passing through the front electrode as C1 / C0. Is obtained by the following equation.
x1 / y0 = (-1 / π) ln (C1 / C0) (4)

From now on, by setting this x1 / y0 to an appropriate value according to the concentration ratio of the metal ions M1 ⁺ and M2 ⁺ in the aqueous solution, the M2 ⁺ concentration can be measured at the rear electrode without being interfered by M1 ^+. Is possible.
By setting this value to 2 or more, can be the concentration of M1 ⁺ approximately 1/500 or less, in the case of substantially the same degree M1 ⁺ and M2 ⁺ ion concentration without being little interference by M1 ⁺ M2 It becomes possible to measure ⁺ concentration.

Although the above shows an example in which the two front electrodes are paired in parallel, the same effect can be obtained with only one plate electrode. In this case, y0 is the distance between one flat plate electrode and a parallel cavity wall surface, and equations (3) and (4) are (5) and (6) shown below.
C = C0exp (-πx / 2y0) cos (πy / 2y0) (5)
x1 / y0 = (-2 / π) ln (C1 / C0) (6)
Accordingly, the preferable value of x1 / y0 is 4 or more.

In this description, the case where there is only one metal ion other than the metal ion to be measured has been described, but the present invention can be applied even when a plurality of metal ions are included.
In this case, the metal ions in the aqueous solution are M1 ⁺ , M2 ⁺ ... Mn-1 ⁺ , Mn ⁺ , M1 + 1 ⁺ ..., And the equilibrium potential of each oxidation-reduction reaction is V1, V2. Vn, Vn + 1 (V1 is the most noble, the equilibrium potential is V1>V2>...>Vn-1>Vn> Vn + 1> ...), and Mn ⁺ is the metal ion to be measured At this time, the front electrode potential is set to a potential lower than Vn-1 and higher than Vn, and the potential of the rear electrode is set lower than Vn and higher than Vn + 1.

Although only metal ions have been described in the present description, the measurement method using the electrode system of the present description and formulas (3) to (6) are charged substances other than metal ions or substances having no charge such as O _2. But it is equally applicable.
Since this formula does not depend on the physical constant inherent to the substance, such as the diffusion coefficient of the substance, the above results can be applied to any chemical substance as well, and it is necessary to change the value of x1 / y0 depending on the substance. Absent.

The front electrode and the rear electrode are preferably fabricated using a noble metal such as gold, platinum, silver, etc., but other conductive iron, copper, nickel, aluminum, steel, and alloys such as brass and stainless steel It can also be made of materials or other metals. In addition, graphite, conductive polymer, and the like can be used.
The reference electrode is preferably an Ag / AgCl, saturated calomel electrode, Cu / CuSO4 electrode or the like, but this may be another electrode exhibiting a stable potential.

The counter electrode is preferably Ag, but other metal materials such as gold, platinum, iron, copper, aluminum and steel, alloy materials such as brass and stainless steel, and conductive materials such as graphite and conductive polymers Can also be used.
In the figure, the reference electrode and the counter electrode are separated from each other, but it is also possible to use a structure in which the reference electrode also serves as the counter electrode without using the counter electrode.
The detector body is preferably made of an insulating polymer such as fluororesin, polyethylene or silicon rubber, but can also be made of an insulating inorganic material such as ceramic or glass.

In this description, the post electrode is also a flat plate, but other shapes are possible for the post electrode.
In this description, an example of measuring the concentration of a chemical substance such as a metal ion using a reduction reaction has been described. However, when measuring using an oxidation reaction, the same measurement is performed by setting a potential opposite to the above. Is possible.
Therefore, the oxidation-reduction potential of the chemical substance to be measured is Vn, the other V1, V2 ... Vn-1, Vn, Vn + 1 (V1 is the most noble, the equilibrium potential is V1>V2> ... >Vn-1>Vn> Vn + 1> ...), the front electrode potential is lower than Vn and higher than Vn + 1, and the rear electrode is higher than Vn and higher than Vn-1. The base potential is set.

[Example 1]
Next, the present invention will be described in more detail with reference to examples.
FIG. 2 shows a current-potential curve for each aqueous solution (aqueous chloride solution) containing Co ²⁺ , Ni ²⁺ , and Fe ²⁺ ions when these ions are reduced by an electrode reaction using a gold electrode. The measurement results are shown. In this case, the reduction reaction proceeds based on the following formulas.
Co ²⁺ + 2e ⁻ → Co (7)
Ni ²⁺ + 2e ⁻ → Ni (8)
Fe ²⁺ + 2e ⁻ → Fe (9)

In FIG. 2, the horizontal axis is the base potential in the right direction. When the electrode potential becomes lower than the equilibrium potential of the oxidation-reduction reaction, the current increases.
From the figure, the equilibrium potential is Co ²⁺ > Ni ²⁺ > Fe ²⁺ (Fe ²⁺ is the most basic). If the ion to be measured is Fe ²⁺ , the set potential of the front electrode is lower than the equilibrium potential of Ni ^2+. In addition, the post electrode potential is lower than the Fe ²⁺ equilibrium potential, and the post electrode potential is lower than the Fe ²⁺ equilibrium potential.

FIG. 3 shows a mixed aqueous solution containing 1.0 × 10 ⁻³ mol / dm ³ of Co ²⁺ , Ni ²⁺ and various concentrations of Fe ²⁺ ions using the detector and electrode system of FIG. 1 based on the results of FIG. In this example, the Fe ²⁺ ion concentration was quantified by setting the front electrode potential at −0.8 V and the rear electrode potential at −1.05 V (relationship between Fe ²⁺ ion concentration and output current (reduction current)). Show.

In this embodiment, a parallel plate type front electrode having y / x of 3 is used, the rear electrode area in the inner part of the cavity is 0.5 cm ^2, and gold and counter electrodes are used for the front electrode and the rear electrode. A silver plate is used. As described above, other conductive materials may be used. However, when other materials are used, the current-potential curve in FIG. It is necessary to set the post-electrode and post-electrode potentials.
Further, an Ag / AgCl electrode is used as the reference electrode, but this may be another electrode exhibiting a stable constant potential as described above. A fluororesin is used for the detector body, but as described above, other materials may be used.

[Example 2 to Example 5]
Next, another embodiment of the present invention will be described with reference to FIGS. In Example 2 shown in FIG. 4, voltage is not applied simultaneously to the front electrode and the rear electrode, but voltage is alternately applied by the front electrode side changeover switch 13 and the rear electrode side changeover switch 14.
Normally, only when the front electrode side switch is closed and the rear electrode side switch is opened and the concentration of the measurement target substance is measured, the front electrode side switch is opened and the rear electrode side switch is Closed.
This prevents the deterioration of the counter electrode, and enables measurement with only one power source and signal processing device.

  In Example 3 shown in FIG. 5, a filter that prevents the advection of the aqueous solution into the cavity in the flowing aqueous solution and moves the chemical substance only by diffusion is attached to the cavity inlet of the detector body. is there. The filter 15 is made of a fiber made of a hydrophilic material, preferably a filter paper or a polyester cloth, a porous net made of resin or metal, a sintered ceramic, or the like.

In Example 4 shown in FIG. 6, a plurality of pre-electrodes are installed with spacers 16 inserted, and a voltage is simultaneously applied to all the pre-electrodes, so that the pre-electrode's ability to remove unmeasured chemical substances ( While maintaining the x1 / y0 value), by increasing the opening area, a larger amount of the chemical substance to be measured is introduced into the detector, thereby increasing the detection sensitivity of the chemical substance to be measured.
The spacer at this time can be manufactured using any of the same conductive material as the electrode and an insulating material such as resin, ceramic, and glass.

  In Example 5 shown in FIG. 7, the counter electrode and the reference electrode are installed inside the cavity of the detector, and the detector is miniaturized.

As described above, the present invention can continuously detect and quantify only the chemical substance to be measured with high accuracy and high sensitivity by the electrode reaction without being interfered by chemical substances other than the chemical substance to be measured. Has an excellent effect, especially in the aqueous solution containing multiple chemical substances such as industrial water, river water, seawater, groundwater, etc. The concentration can be quantified.
Moreover, it can be applied not only to an aqueous solution containing such a chemical substance but also to a conductive non-aqueous solution such as an acetonitrile solution containing an electrolyte, and can also be used for detection and concentration determination of a measurement target chemical substance contained therein.
It is also possible to embed the detector body in sand, soil, clay, sludge, powder sample or the like containing an aqueous solution. Therefore, its industrial significance is great.

It is a figure explaining the arrangement | positioning of the suitable cavity and electrode system in this invention. It is a figure which shows the actual measurement result of the electric current-potential curve accompanying Co ^<2+> , Ni ^<2+> and Fe ^<2+> ion reduction in aqueous solution. It is a figure which shows the Fe2 ⁺ ion concentration measurement result by the Example of this invention. It is explanatory drawing which shows the other Example of this invention which provided the changeover switch. It is explanatory drawing which shows the other Example of this invention which provided the filter in the cavity inlet_port | entrance of the detection recording main body. It is explanatory drawing which shows the other Example of this invention which shows the structure of the pre-electrode comprised from the electrode plate by inserting the spacer. It is explanatory drawing which shows the other Example of this invention which installed the counter electrode and the reference electrode inside the cavity of a detector. It is explanatory drawing (current-potential curve) which shows typically the measurement result of the polarography which is a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Front electrode 2 Rear electrode 3 Conductor 4 Power supply and signal processing apparatus 5 Voltmeter 6 Ammeter 7 Reference electrode 8 Counter electrode 9 Metal ion 10 Detector main body 11 Test tank (container)
12 Sample aqueous solution 13 Pre-electrode side switch 14 Back electrode switch 15 Filter 16 Spacer

Claims (6)

In the aqueous solution containing a plurality of chemical substances, a detector body provided with a cavity having a structure that communicates with the aqueous solution through an opening and does not communicate with the aqueous solution other than the opening, and the aqueous solution in the inner part of the cavity. A post electrode for detecting and quantifying a chemical substance to be detected and quantified by a reduction reaction or an oxidation reaction is arranged among the chemical substances of the above-mentioned chemical substances, and the post electrode and the cavity opening entrance of the detector main body are arranged. In between, a cavity and an electrode system in which a front electrode that removes a chemical substance other than the chemical substance to be measured in the aqueous solution by a reduction reaction or an oxidation reaction is disposed without hindering communication between the aqueous solution and the rear electrode In this case, the post electrode is maintained at a potential that can reduce or oxidize the chemical substance to be measured, the pre electrode is noble or base, and chemical substances other than the chemical substance to be measured are reduced or oxidized. The prefix By maintaining it at a potential that can be deposited and captured on the electrode or changed into a chemical that does not affect the reduction or oxidation reaction of the back electrode, the reduction or oxidation reaction of the back electrode and its A chemical substance measuring method for detecting and quantifying a chemical substance to be measured without being interfered by the reaction of a chemical substance other than this by an electric current generated when
The front electrode is two conductive planes facing each other, a gap between the planes is in communication with the aqueous solution, and the rear electrode is disposed in the inner part of the cavity opposite to the aqueous solution in the gap. When the chemical substance other than the measurement object diffuses in the gap, it is reduced or oxidized by the front electrode and deposited on the front electrode or removed by changing to a chemical substance that is not reduced or oxidized by the rear electrode, Only the chemical substance to be measured is detected and quantified by the reduction reaction or oxidation reaction by the post electrode,
The spacing of the plane and y, a length of up post electrode side from the solution side of the electrode and x, the chemical concentration other than the measurement target in the solution inside the C0, the measured chemicals in post electrode In order to measure without interference of other chemical substances, when the concentration of the chemical substance other than the measurement target that should be reduced after passing through the front electrode due to the reaction of the front electrode is C, the value of x / y is as follows: It is that chemicals measurement method being determined by the equation.
x / y = 1 / πln (C0 / C) 2. The chemical substance measuring method according to claim 1 , wherein the value of x / y is 2 or more. In the aqueous solution containing a plurality of chemical substances, a detector body provided with a cavity having a structure that communicates with the aqueous solution through an opening and does not communicate with the aqueous solution other than the opening, and the aqueous solution in the inner part of the cavity. A post electrode for detecting and quantifying a chemical substance to be detected and quantified by a reduction reaction or an oxidation reaction is arranged among the chemical substances of the above-mentioned chemical substances, and the post electrode and the cavity opening entrance of the detector main body are arranged. In between, a cavity and an electrode system in which a front electrode that removes a chemical substance other than the chemical substance to be measured in the aqueous solution by a reduction reaction or an oxidation reaction is disposed without hindering communication between the aqueous solution and the rear electrode In this case, the post electrode is maintained at a potential that can reduce or oxidize the chemical substance to be measured, the pre-electrode is more noble or base, and chemical substances other than the chemical substance to be measured are reduced or oxidized. do it By maintaining this at a potential that can be deposited and captured on the front electrode or changed to a form of chemical that does not affect the reduction or oxidation reaction of the rear electrode, A chemical substance measuring method for detecting and quantifying a chemical substance to be measured without interference from the reaction of other chemical substances by an oxidation reaction and a current generated at that time,
One of the front electrodes is a conductive plane, and one is an insulating plane, and the gap between the planes communicates with the aqueous solution, and the rear electrode is located in the back of the cavity opposite to the aqueous solution in the gap. When a chemical substance other than the object to be measured diffuses in this gap, it is reduced or oxidized by the front electrode and deposited on the front electrode or removed by changing to a chemical substance that is not reduced or oxidized by the rear electrode. Only the chemical substance to be measured is detected and quantified by the reduction reaction or oxidation reaction by the post electrode,
The spacing of the plane and y, a length of up post electrode side from the solution side of the electrode and x, the chemical concentration other than the measurement target in the solution inside the C0, the measurement object by using a post electrode X / y value when C is the concentration of the chemical other than the target that should be reduced after passing through the front electrode due to the reaction of the front electrode in order to measure the chemical without interference of other chemicals There be that chemicals measuring method characterized in that it is determined by the following equation.
x / y = 2 / πln (C0 / C) 4. The chemical substance measuring method according to claim 3 , wherein the value of x / y is 4 or more. A container for holding an aqueous solution containing a plurality of chemical substances, a detector body provided with a cavity having a structure that communicates with the aqueous solution in the container through an opening and does not communicate with the aqueous solution except for the opening; and the detector A post electrode for detecting and quantifying a chemical substance to be measured installed in the inner part of the cavity of the main body by oxidation or reduction chemical reaction, a front electrode installed between the post electrode and the cavity inlet, and a measurement target A power supply device that applies a reduction potential or an oxidation potential according to the chemical substance and the non-measurement chemical substance. Among the chemical substances that diffuse into the cavity from the aqueous solution, the non-measurement chemical substance is the front electrode. This is deposited on the surface of the electrode by oxidation or reduction reaction and captured, or changed to a substance that does not cause an electrode reaction at the post electrode, and the chemical substance to be measured that passes through the front electrode and reaches the post electrode is later By placement electrode Out, a chemical measurement device for quantification,
It is provided with a front electrode side changeover switch and a rear electrode side changeover switch that do not apply voltage to the front electrode and the rear electrode at the same time, and alternately apply a voltage to the front electrode side and the rear electrode side. It characterized chemicals measurement devices. 6. The chemistry according to claim 5 , wherein a filter that prevents the advection of the aqueous solution into the cavity in the flowing aqueous solution and moves the chemical substance to the inside only by diffusion is attached to the cavity inlet of the detector body. Substance measuring device.

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