JP2005127906A - Instrument and method for measuring concentration - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a concentration measuring instrument and a concentration measuring method capable of measuring a concentration with high sensitivity, using an electrode easy to be handled and high in durability. <P>SOLUTION: This instrument/method is provided with the first electrode 1, the second electrode 2, a voltage impression part 3, a current measuring part 4, and a concentration value outputting part 5. In the first electrode 1, a surface of a substrate (base body) 10 comprising metal such as, for example, titanium metal and aluminum metal, or a conductor is coated with a ferroelectric substance thin film 11, and the surface has the sufficient durability against an acid or a base contained in a solution 7 and a substance of a measuring object. An alternating current is impressed to the first electrode 1 and the second electrode 2 from the voltage impression part 3. A dielectric polarization is generated in the ferroelectric substance thin film 11 on the surface of the first electrode 1, and the substance or an ion of the measuring object is adsorbed in the vicinity of the surface of the ferroelectric substance thin film 11, attracted with a charge therein. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a concentration measuring apparatus and a concentration measuring method for performing concentration determination of substances and ions such as urea determination.

  Conventionally, in clinical laboratory analysis, a variety of methods such as a method using a so-called test paper and a method using a large-scale complicated multi-item simultaneous analysis system performed by a specialist or the like can be used as an example of urea determination. There is.

  Among such conventional clinical laboratory analysis methods, many of those actually used have been analysis by an absorptiometric method using an enzyme. In addition to the absorptiometry, there is an ion measurement method. In the ion measurement method, a glass film or a metal is used as an electrode. Alternatively, an analysis (measurement) method using an ISFET (Ion Sensitive Field Effect Transistor) sensor has been proposed in order to improve the drawbacks of the absorptiometry and ion measurement methods. In this ISFET sensor, the gate electrode of ISFET is covered with a nitride film, soaked in a solution to be measured together with a counter electrode, and a reference voltage resulting from a change in conductivity generated in the channel of ISFET due to contact between the gate electrode and the solution. Is extracted as an electrical signal, and the ion concentration is detected based on the potential difference. Such an ISFET sensor is easy to handle and has relatively good durability, and is also used in, for example, a pH meter.

  However, the conventional techniques as described above have the following problems. In other words, the ISFET sensor is easy to handle, but has a low sensitivity, so that it is difficult to realize highly sensitive measurement (analysis). In the method using a glass membrane electrode, high-sensitivity measurement is possible, but there is a problem that handling is required and the usage method tends to be complicated. In the method using a metal electrode, the sensitivity is low, and depending on the substance to be measured (solution, etc.), the substance and the metal electrode react with each other (metal oxidation, etc.), preventing accurate measurement, There is a problem that the metal electrode may become unusable in a short time.

  In addition, in the analysis using an absorptiometric method using an enzyme, the enzyme is made disposable, and the cost due to it occupies most of the total cost in the measurement (analysis) process, which hinders cost reduction. There is. In addition, if the enzyme is made disposable every time such measurement is performed, waste is frequently generated, and there is a problem that adverse effects on the environment are concerned.

  The present invention has been made in view of such problems, and a first object thereof is a concentration measuring apparatus and a concentration which can perform highly sensitive concentration measurement using an electrode that is easy to handle and has high durability. It is to provide a measurement method.

  In addition, a second object of the present invention is to provide a concentration measuring apparatus and a concentration measuring method capable of performing measurement without making the enzyme disposable when performing measurement or analysis using the enzyme. is there.

  The concentration measuring apparatus according to the present invention includes a first electrode having a dielectric layer on the surface, a second electrode serving as a counter electrode of the first electrode, an AC voltage or a pulsating voltage or the like applied to the first electrode and the second electrode. A voltage applying means for applying a step voltage; and a current measuring means for measuring a current generated between the first electrode and the second electrode via the substance or ion to be measured in response to the application of the voltage. I have.

  In the concentration measurement method of the present invention, the first electrode having a dielectric layer on the surface and the second electrode as a counter electrode of the first electrode are immersed in a solution or sample having a substance or ions to be measured or An AC voltage, a pulsating voltage, or a step voltage is applied to the first electrode and the second electrode in a face-to-face relationship, and the object to be measured is between the first electrode and the second electrode in response to the application of the voltage. The current value generated via the substance or ion is measured, and the concentration value of the substance or ion to be measured is quantified corresponding to the current value.

  In the concentration measuring apparatus or concentration measuring method of the present invention, the surface of the first electrode immersed in or facing the solution or sample containing the substance or ions to be measured has higher durability against acids and bases than a metal electrode or the like. Since the dielectric layer is provided, the surface of the first electrode can be prevented from reacting with the substance or ions to be measured and being oxidized or deteriorated.

  Then, a solution or sample to be measured is interposed between the first electrode and the second electrode, and an alternating voltage or a half-wave pulse in which the polarity of the sinusoidal waveform is inverted between the first electrode and the second electrode. When a voltage such as a step voltage whose current voltage or voltage level changes sharply with time is applied, a charge having a polarity opposite to that of the applied voltage is generated by the polarization action of the dielectric layer on the surface of the first electrode. The substance or ion to be measured is attracted by the ion and adsorbed. The transient current or synchronous current associated with ion adsorption at this time differs depending on the ion concentration in the solution and the ion adsorption speed. Therefore, by detecting (measuring) this current, The concentration of substances and ions can be quantified.

  Here, it is a desirable aspect to quantify the above density value by a circuit including a lock-in amplifier. This is because it is possible to measure density values with less error due to disturbances and the like.

  It is desirable to provide a dielectric layer not only on the first electrode but also on the surface of the second electrode. By doing so, the surface of the second electrode can be prevented from being oxidized or deteriorated by reacting with the substance or ions to be measured, and the second electrode is also the same as the first electrode. In addition, it is possible to generate a current accompanying ion adsorption by applying a voltage such as an alternating voltage whose voltage level changes.

  The first electrode as described above can be formed by oxidizing a surface of a base made of a metal or a conductive material to form a dielectric layer. As described above, by forming the dielectric layer on the surface of the first electrode by the surface oxidation treatment, the first electrode according to the present invention can be manufactured by a very simple manufacturing method.

As the dielectric layer, for example, a thin film of BaTiO _3, SrTiO _3, or Al ₂ O ₃ is suitable.

  In addition, when the measurement target is a compound, it is desirable that an enzyme for separating (so-called cutting out) the substance or ion to be measured from the compound to be measured is fixed to the surface of the first electrode and used. . By doing in this way, it becomes possible to measure, without making an enzyme disposable.

  When the measurement target is a compound, the first flow path including a column formed by fixing an enzyme that separates the measurement target substance or ions from the measurement target compound, and the first flow not including the column. A first electrode, a second electrode, a voltage applying means, and a current measuring means are provided in both the first flow path and the second flow path, respectively, and measurement is performed in the first flow path. Based on the comparison between the measured current value and the current value measured in the second flow path, the concentration value of the substance or ion to be measured may be quantified. This also makes it possible to measure without making the enzyme disposable.

  Note that the substance or ion to be measured can be, for example, urea, ammonium, phosphoric acid, or phosphate ion. However, it goes without saying that substances other than these can be measured.

  According to the concentration measuring apparatus or the concentration measuring method of the present invention, since the dielectric layer is provided on the surface of the first electrode, the surface of the first electrode reacts with the substance or ions to be measured and is oxidized or deteriorated. Can be prevented. In addition, since a voltage such as an AC voltage is applied to the first electrode and the second electrode, a charge having a polarity opposite to the applied voltage is generated by the polarization action of the dielectric layer on the surface of the first electrode. The substance or ion to be measured is attracted to the target, and the transient current or synchronous current associated with this ion adsorption is measured, so that the concentration of the substance or ion to be measured can be quantified corresponding to the current. . That is, it is possible to perform concentration measurement with sufficient sensitivity using an electrode that is easy to handle and highly durable.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a configuration of a main part of a concentration measuring apparatus according to an embodiment of the present invention. The concentration measuring method or manufacturing method according to an embodiment of the present invention is embodied by the operation or action of the concentration measuring apparatus, and will be described below together.

  The concentration measuring apparatus includes a first electrode 1, a second electrode 2, a voltage applying unit 3, a current measuring unit 4, and a concentration value information output unit 5 as main components.

  The first electrode 1 has a surface of a substrate (base) 10 made of a metal or conductor such as a copper metal or aluminum metal, for example, a ferroelectric thin film (dielectric layer) 11 such as BaTiO 3 or SrTiO 3. It is covered with.

  The ferroelectric thin film 11 may be formed by being deposited on the surface of the substrate 10 by, for example, a CVD (Chemical Vapor Deposition) method, or a film of the ferroelectric thin film 11 separately manufactured. May be deposited on the surface of the substrate 10. Alternatively, for example, the surface of the substrate 10 made of Ti (titanium) may be anodized, for example, to form BaTiO 3 and used as the ferroelectric thin film 11 of the first electrode 1. Thus, the first electrode 1 can be manufactured very easily by forming the ferroelectric thin film 11 by anodizing the surface of the substrate 10.

  Regardless of which material is used, the ferroelectric thin film 11 is formed on the surface of the first electrode 1, so that the first electrode 1 has sufficient durability against the acid 7 or base contained in the solution 7 or substance to be measured. It has become a thing. At the same time, the concentration of substances and ions to be measured can be electrochemically measured by the action described below. In addition, an electrode using the ferroelectric thin film 11 can be generally manufactured at a lower cost than an electrode using a noble metal such as a platinum electrode, and is more acid than other metals (for example, copper and aluminum). And has a very favorable advantage of high durability against bases.

  In addition to the metal and the conductive material, a glass plate or the like can be used as the substrate 10. However, in that case, a conductive film is deposited on the surface of the glass plate so that a voltage is applied to the entire substrate 10 without a bias (or an electric field is distributed), and a ferroelectric film is formed thereon. It is desirable to provide a film of the body thin film 11 or the like.

  The second electrode 2 is used as a counter electrode of the first electrode 1 and is made of a material that is less likely to be oxidized by the measurement target solution 7 such as platinum (Pt).

  It is desirable to provide the ferroelectric thin film 11 on the surface of the second electrode 2 as well. By doing so, the second electrode 2 also oxidizes or deteriorates by reacting with the substance or ions to be measured without using an electrode made of a rare and expensive noble metal material as a resource such as a platinum electrode. It becomes possible to prevent this. At the same time, the second electrode 2 can generate an electric current accompanying ion adsorption by applying an alternating voltage as in the case of the first electrode 1, and further increase the sensitivity of concentration measurement. It becomes possible.

  The solution 7 (or a liquid sample or the like) is a solution obtained by dissolving a substance to be measured or ions in a buffer solution such as HEPES (Hydroxyethyl piperazinyl ethanesulfonic acid), or a substance that does not require a buffer solution. Is a general aqueous solution of the substance, but is contained in a watertight container-like test bath 6, and the first electrode 1 and the second electrode 2 are immersed in the solution 7.

  The voltage application unit 3 applies, for example, a rectangular wave AC voltage as shown in FIG. 3 to the first electrode 1 and the second electrode 2. At the same time, a reference signal is output every time the rectangular wave AC voltage rises. The reference signal is transmitted to the density value information output unit 5.

  Needless to say, the AC voltage waveform output from the voltage application unit 3 is not limited to a rectangular wave or a step voltage waveform as shown in FIG. In addition, for example, a sine wave or a triangular wave is also possible.

  The current measuring unit 4 measures the apparent current generated between the first electrode 1 and the second electrode 2 via the substance or ion to be measured in response to the application of the alternating voltage by the voltage applying unit 3. is there.

  The concentration value information output unit 5 quantifies the concentration value of the substance or ion to be measured based on the current value measured by the current measuring unit 4, and outputs the information on the concentration value or a signal carrying the information. Output. More specifically, between the concentration of the substance or ion to be measured and the measured current value (however, in FIG. 3, the current value is converted into a voltage value (ΔVoltage) by the lock-in amplifier). There is a correlation (function relationship) as shown in FIG. Therefore, in accordance with such a correlation, the concentration value of the substance or ion to be measured can be quantified based on the measured current value. The density value information output unit 5 includes a lock-in amplifier, and can perform measurement with higher sensitivity than a case where the lock-in amplifier is not included.

  In general, a lock-in amplifier performs high-sensitivity (high-precision) amplification based on the principle that noise power is proportional to a frequency band. In other words, in order to measure the magnitude of a signal while minimizing the influence of noise, how to realize a stable bandpass filter that selectively amplifies only the vicinity of the measurement frequency is highly sensitive. One of the most important techniques for amplification is a lock-in amplifier.

  FIG. 5 is a block diagram showing an example of the configuration of the most basic lock-in amplifier. An input signal (SIG INPUT) 51 is amplified by an AC amplifier (AC AMP) 52 and sent to a PSD (Phase Sensitive Detector) 53. On the other hand, the reference signal (REF INPUT) 54 is subjected to waveform shaping and phase adjustment by a reference signal processing circuit (REF CKT) 55 and sent to the PSD 53. The PSD 53 performs multiplication (multiplication) of two signal waveforms of the input signal 51 and the reference signal 54.

  The frequency spectrum of the output of the PSD 53 is a convolution of the frequency spectrum of the input signal 51 and the reference signal 54, and shifts to a sum and difference spectrum. Therefore, in the two signals, components having the same frequency and the same phase are converted into DC (direct current) waveforms, and other asynchronous components (here, noise components) are converted into AC (alternating current) waveforms.

  Therefore, by removing the AC waveform by the low-pass filter (LPF) 56 in the next stage, only the component synchronized with the reference signal 54, that is, the component not including noise can be detected. The bandwidth that determines the noise removal capability is determined by the band of the low-pass filter 56. Since the bandwidth of the low-pass filter 56 can be narrowed without impairing the stability, it is theoretically possible to make the noise removal capability almost infinite (in other words, the noise is almost zero). The component not including noise is voltage-converted and amplified by a DC amplifier (DC AMP) 57 and output as a voltage waveform 58.

  Next, the operation of the concentration measuring apparatus and the operation in the first electrode 1 will be described. FIG. 2 schematically shows the action of the concentration measuring apparatus, particularly the first electrode 1.

  The first electrode 1 and the second electrode 2 are immersed in the solution 7 accommodated in the test bath 6, and the measurement target solution 7 is interposed between the first electrode 1 and the second electrode 2.

  When a rectangular wave-like AC voltage as shown in FIG. 3A is applied to the first electrode 1 and the second electrode 2 from the voltage application unit 3, a ferroelectric thin film on the surface of the first electrode 1 is applied. 11, dielectric polarization occurs, and a charge having a polarity opposite to the applied voltage appears on the surface. Attracted by the charge, the substance or ion to be measured is adsorbed.

  Along with the ion adsorption at this time, for example, a transient current (or synchronous current) as shown in FIG. 3B is generated. This transient current varies depending on the ion concentration in the solution 7 and the ion adsorption rate. Therefore, the current at this time can be measured by the current measuring unit 4, and the concentration of the substance or ion to be measured corresponding to the current can be quantified by the concentration value information output unit 5.

In addition, after applying the waveform on the positive electrode side as shown in FIG. 3 (A) to generate a current with a steep response waveform like a differential circuit as shown in FIG. 3 (B), the current waveform is Asymptotically settles to 0 (apparent current virtually stops flowing). However, when a reverse polarity voltage is applied next as an AC voltage, a current waveform having a polarity opposite to that shown in FIG. 3 is generated (not shown). By repeating this, the transient current generated corresponding to the ion concentration and ion adsorption speed in the solution 7 is repeatedly measured in a pulsating manner, and the concentration of the ion or substance to be measured is determined based on the measured current value. It can be measured (quantified) with high sensitivity. When a lock-in amplifier is used, an AC signal needs to be input, so it is desirable to perform measurement by applying such a repetitive voltage. In addition to the AC voltage, a voltage having a waveform such as a step voltage waveform or a pulsation in which the voltage level changes with time although the polarity does not change is applied, and the current change that occurs in response to the voltage change is measured. It may be.

  In practice, when measurement is performed using the lock-in amplifier shown in FIG. 5, the output from the lock-in amplifier has a voltage waveform corresponding to the input current. However, since the voltage waveform is obtained by converting a current value that is originally measured into a voltage value, the concentration measurement device according to the present embodiment is essentially based on the measured current value. It goes without saying that the concentration of ions or substances to be measured is measured.

  Here, the graph of FIG. 4 will be described in further detail. The vertical axis of this graph is the output voltage [mV] of the lock-in amplifier and the offset is subtracted. Therefore, the transient current can be calculated by dividing the voltage value on the vertical axis by the load resistance. This graph shows an example of the correlation between the transient current value (voltage value obtained by converting) measured when ammonia is the measurement target and the ammonia concentration, and the correlation is not linear, Since a one-to-one correspondence is established, a functional relationship condition that can be used to quantify the concentration from the transient current is satisfied. Therefore, it is possible to perform highly sensitive measurement of the concentration of the substance or ions to be measured by linearizing the nonlinear correlation based on a predetermined calibration rule and outputting the signal or display. Can do.

  Further, in this concentration measuring apparatus, the first electrode 1 having the ferroelectric thin film 11 on the surface is used as the electrode to be immersed or faced in the solution 7 or sample having the substance or ions to be measured. It is possible to prevent the surface of the electrode 1 from being oxidized or deteriorated by reacting with the substance or ions to be measured. Furthermore, by providing the ferroelectric thin film 11 on the surface of the second electrode 2, the surface of the second electrode 2 can be measured without using an expensive electrode made of a noble metal such as a platinum electrode. It can be prevented from reacting with the target substance or ion to be oxidized or deteriorated.

  Note that the frequency of the alternating voltage applied to the first electrode 1 and the second electrode 2 is desirably set as appropriate in accordance with the response speed of ions in the solution 7 to be measured. For example, the present inventors conducted an experiment in which the measurement object was ammonium, and in the result at that time, it was possible to perform concentration measurement with higher sensitivity by using a low frequency of about 20 [Hz]. . This is because the response speed of ammonium to the dielectric polarization action of the ferroelectric thin film 11 on the surface of the first electrode 1 is slow, so that the measurement conditions can be optimized by applying an AC voltage having a low frequency suitable for it. It is thought that it was because of.

  In the concentration measuring apparatus or the concentration measuring method according to the present embodiment as described above, for example, when urea determination is performed, a highly sensitive concentration that sufficiently satisfies 50 [mg / L] required as clinical sensitivity. Measurement can be realized.

  Further, in the present embodiment, even when compared with an ammonia ion measuring apparatus using the diaphragm electrode method, measurement is performed with a sensitivity comparable to the minimum displayable sensitivity (for example, 0.1 [mM (mmol))] using the diaphragm electrode method. In the case of the diaphragm electrode method, a response time of 90% and within 1 minute can be always measured in real time with almost no waiting time.

  Further, according to the concentration measuring apparatus according to the present embodiment, since an AC voltage is applied, there is no possibility of causing a DC drift or the like due to the DC voltage application. Measurement is possible.

  When the measurement target is a compound, an enzyme for separating (so-called cutting out) the substance or ion to be measured from the measurement target compound is fixed on the surface of the ferroelectric thin film 11 of the first electrode, for example. A thin film (not shown) as a medium may be provided and fixed on the surface. By doing in this way, it becomes possible to measure, without making an enzyme disposable.

  Alternatively, as shown in FIG. 6, a first flow path 61 having a column formed by fixing an enzyme for separating a substance or ion to be measured from a compound to be measured to glass or silica beads, and the enzyme And a second flow path 62 that is not fixed, and measurement systems 64 and 65 are provided in both the first flow path 61 and the second flow path 62, respectively, to measure the respective current values. The concentration value of the substance or ion to be measured may be quantified based on the difference between the current values. This also makes it possible to measure without making the enzyme disposable.

  Here, in addition to the apparatus configuration shown in FIG. 6, as shown in FIG. 7, one measurement system 66 is used by providing a delay coil 63 in one flow path 62 and time-shifting its output. It is also possible to detect the difference between the current values detected from the two flow paths 61 and 62 and quantify the concentration of the substance or ions to be measured based on the difference value.

  In both configurations of FIG. 6 and FIG. 7, the enzyme is fixed to the column, so that the measurement can be performed without making the enzyme disposable.

  Note that the concentration measuring apparatus or concentration measuring method according to the present embodiment is acidic with respect to urea or ammonium, or phosphoric acid or phosphate ions, phosphoric acid-containing substances (for example, glycerin phosphoric acid, phosphoric acid-based agricultural chemicals, etc.) as substances or ions to be measured. It can also be applied to the determination of the concentration of substances and ions such as phosphoric acid excised using phosphatase. However, it goes without saying that substances other than these can be measured.

In order to further enhance the so-called passivation of the surface of the ferroelectric thin film 11, for example, a silicon nitride oxide film or an Al ₂ O ₃ film (both not shown) is additionally provided on the surface of the ferroelectric thin film 11. You may make it do. Alternatively, it is possible to further increase the number of layers by covering the surfaces of the first electrode 1 and the second electrode 2 with a thin film (not shown) made of other materials. Further, as the dielectric layer provided on the surface of the first electrode or the second electrode, since the measurement sensitivity is good, it is preferable to use the ferroelectric thin film 11 made of the so-called ferroelectric thin film as described above. In addition to the ferroelectric thin film 11, it is possible to use a general dielectric having a dielectric constant lower than that of a ferroelectric such as Al ₂ O ₃ or a thick film.

  It can be suitably used as a concentration measurement device or concentration measurement method for highly sensitive measurement of ion concentration, etc., in solutions to be measured, such as urea and bio-related substances, in medical, industrial and other fields. It is.

It is a figure showing the structure of the principal part of the density | concentration measuring apparatus which concerns on one embodiment of this invention. It is the figure which represented typically the effect | action in the 1st electrode among the density | concentration measuring apparatuses of FIG. It is a figure showing an example of the alternating voltage waveform applied to a 1st electrode and a 2nd electrode from a voltage application part. It is a figure showing an example of the correlation established between the density | concentration of the substance or ion of a measuring object, and the measured electric current value. It is a block diagram showing an example of composition of a lock-in amplifier. It is a figure showing an example of composition of a concentration measuring device. It is a figure showing the other structural example of the density | concentration measuring apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... 1st electrode, 2 ... 2nd electrode, 3 ... Voltage application part, 4 ... Current measurement part, 5 ... Concentration value information output part, 6 ... Test bath, 7 ... Solution, 10 ... Substrate, 11 ... Ferroelectric material Thin film

Claims (19)

A first electrode having a dielectric layer on the surface;
A second electrode as a counter electrode of the first electrode;
Voltage applying means for applying an alternating voltage, a pulsating voltage or a step voltage to the first electrode and the second electrode;
A concentration measuring device comprising: current measuring means for measuring a current generated between the first electrode and the second electrode via the substance or ion to be measured in response to the application of the voltage. . Concentration value output means for quantifying the concentration value of the substance or ion to be measured corresponding to the current value measured by the current measurement means, and outputting the information of the concentration value or a signal carrying the information The concentration measuring apparatus according to claim 1, further comprising: The concentration measuring apparatus according to claim 1, wherein the current measuring unit or the concentration value output unit includes a lock-in amplifier. The concentration measuring apparatus according to claim 1, wherein the substance or ion to be measured is urea, ammonium, phosphoric acid, or phosphate ion. The concentration measuring apparatus according to any one of claims 1 to 4, wherein the second electrode is an electrode having a dielectric layer on a surface thereof. The measurement object is a compound, and an enzyme for separating a measurement object substance or ions from the measurement object compound is used by being immobilized on the surface of the first electrode. The density | concentration measuring apparatus of any one of Claims. The measurement target is a compound, a first flow path including a column on which an enzyme that separates a substance or ion to be measured from the measurement target compound is fixed, and a second channel on which the enzyme is not fixed With a flow path,
Both the first flow path and the second flow path include the first electrode, the second electrode, the voltage application means, and the current measurement means,
Based on the comparison between the current value measured in the first flow path and the current value measured in the second flow path, the concentration value output means calculates the concentration value of the substance or ion to be measured. The concentration measurement apparatus according to claim 1, wherein the concentration measurement device outputs a signal obtained by carrying out quantification and holding the information of the concentration value or the information. A delay coil is provided in the subsequent stage of the second flow path,
The difference between current values detected from the delay coil and the first flow path is detected, and the concentration of the substance to be measured is detected based on the difference value. Concentration measuring device. The concentration measurement according to any one of claims 1 to 8, wherein the first electrode has a dielectric layer formed by oxidizing a surface of a base made of a metal or a conductive material. apparatus. The first electrode is formed by depositing a thin film of BaTiO _3, SrTiO _3, or Al ₂ O ₃ on the surface of a substrate made of a metal or a conductive material as the dielectric layer. 10. The concentration measuring apparatus according to any one of claims 1 to 9. A first electrode having a dielectric layer on the surface and a second electrode serving as a counter electrode of the first electrode are immersed or faced in a solution or sample having a substance or ions to be measured, and the first electrode and the An AC voltage, a pulsating voltage or a step voltage is applied to the second electrode, and a current value generated via a substance or ion to be measured between the first electrode and the second electrode in response to the application of the voltage And measuring the concentration value of the substance or ion to be measured corresponding to the current value. The concentration measurement method according to claim 11, wherein the concentration value is measured using a circuit including a lock-in amplifier. The concentration measuring method according to claim 11 or 12, wherein the substance or ion to be measured is urea, ammonium, phosphoric acid or phosphate ion. The concentration measuring method according to any one of claims 11 to 13, wherein an electrode having a dielectric layer on a surface thereof is used as the second electrode. The measurement target is a compound, and an enzyme for separating a measurement target substance or ions from the measurement target compound is used by being immobilized on the surface of the first electrode. The concentration measurement method according to any one of the above items. The measurement target is a compound, the first flow path including a column on which an enzyme that separates the substance or ion to be measured from the measurement target compound is fixed, and the measurement target on which the enzyme is not fixed The current value is measured in both of the second flow path in which the compound of
The current value measured in the first flow path is compared with the current value measured in the second flow path, and the concentration value of the substance or ion to be measured is determined based on the result of the comparison The concentration measuring method according to any one of claims 11 to 14, wherein: A delay coil is provided in the subsequent stage of the second flow path,
The difference between current values detected from the delay coil and the first flow path is detected, and the concentration of the substance to be measured is detected based on the difference value. Concentration measurement method. The concentration measurement according to any one of claims 11 to 17, wherein the first electrode has a dielectric layer formed by oxidizing a surface of a substrate made of a metal or a conductive material. Method. The first electrode is obtained by providing a thin film of any one of BaTiO _3, SrTiO _{3, and} Al ₂ O ₃ on the surface of a base made of a metal or a conductive material as the dielectric layer. Item 19. The concentration measuring method according to any one of Items 11 to 18.

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