JP7466864B2 - Quantitative measurement device, quantitative measurement method, quantitative measurement program, and dialysis system - Google Patents

Description

The present invention relates to a quantitative measurement device, a quantitative measurement method, and a quantitative measurement program for quantifying a target substance in a test liquid containing a target substance and a second substance having an oxidation potential close to the oxidation potential of the target substance, and in particular to a dialysis system for quantifying a target substance in a dialysis effluent as the test liquid.

The uric acid measuring device described in Patent Document 1 includes a uric acid measuring sensor body having a working electrode, a reference electrode, and a counter electrode in a space portion, a signal control detection unit that detects and controls signals from the working electrode, the reference electrode, and the counter electrode when a liquid to be measured is supplied into the space portion, and an analysis device that receives a signal detected and controlled by the detection unit and analyzes substances from the signal, and the working electrode is composed of an anodized diamond thin film electrode. With the above configuration, the uric acid measuring device in Patent Document 1 aims to clearly distinguish between uric acid and ascorbic acid in the measurement of uric acid.

JP 2001-147211 A

However, the uric acid measuring device described in Patent Document 1 requires anodizing, a process for modifying the working electrode, which complicates the manufacturing process of the device, increases manufacturing costs, and requires maintenance of the anodized film after the device begins to be used.

The present invention aims to provide a quantitative measurement device, a quantitative measurement method, and a quantitative measurement program that enable the quantitative measurement of a target substance in a test solution containing interfering substances without modifying the electrodes, and a dialysis system that enables the quantitative measurement of uric acid, which is a target substance in dialysis effluent. In particular, the inventors of the present application have investigated the possibility of selectively detecting uric acid after oxidizing and removing the interfering component ascorbic acid by multi-potential step voltammetry without modifying the electrodes, and have established a simpler and faster quantitative measurement method. In the following embodiments, examples, and reference examples, a pulse voltammetry potential waveform is used, in which a pulse cycle in which a potential is applied with a predetermined pulse width and then returned to the initial value is repeated a predetermined number of times while increasing the applied potential, and the pulse width of one pulse cycle is composed of two pulse steps, a first pulse predetermined width and a second pulse predetermined width with a higher potential, and current sampling is performed at each pulse predetermined width. A pulse cycle consisting of such steps is repeated a set number of times while increasing the potential by a predetermined amount, and the current difference between the two points is recorded for each pulse cycle, thereby realizing an apparatus etc. that accurately and easily performs the quantification of a target substance in a test liquid in which interfering substances coexist. Another object of the present invention is to provide a quantification apparatus etc. that can perform the quantification of a target substance without adjusting the pH (hydrogen ion exponent) of the test liquid.

In order to solve the above problems, the quantitative measurement device, quantitative measurement method, quantitative measurement program, and dialysis system of the present invention have the following features.
(1) The quantitative measurement device of the present invention is a quantitative measurement device that applies a voltage between a working electrode and a counter electrode in contact with a test liquid (e.g., dialysis effluent, phosphate buffer solution) containing a first substance (e.g., uric acid) as a target substance, and quantifies the content of the first substance in the test liquid based on a current value flowing due to an electrochemical oxidation reaction of the first substance at the working electrode, and includes an application unit that applies the voltage, a control unit that controls the application unit, a measurement unit that measures the current value at the working electrode, and a calculation unit that calculates the content of the first substance based on the measurement result by the measurement unit, and the test liquid contains a second substance (e.g., ascorbic acid) having an oxidation potential lower than the oxidation potential of the first substance, and the oxidation potential of the second substance is determined based on the oxidation potential of the first substance. the difference between the oxidation potential of the first substance and the oxidation potential of the second substance is equal to or less than a predetermined value, the control unit controls the application unit to apply an initial potential corresponding to the oxidation potential of the second substance to the test liquid over a first pulse potential width set based on the content of the second substance assumed to be contained in the test liquid, and after the application of the initial potential, controls the application unit to apply a target potential corresponding to the oxidation potential of the first substance to the test liquid over a second pulse potential width, and these pulse periods are repeated a number of times while increasing each potential by a predetermined potential, with this forming one pulse period, and the calculation unit calculates the content of the first substance based on the current values measured by the measurement unit when each initial potential and the target potential are applied.

(3) In the quantitative measurement device of (1) or (2) above, the first pulse potential width and the second pulse potential width are the same time.

(4) In the quantitative measurement device of (1) or (2) above, the second pulse potential width is shorter than the first pulse potential width.

(5) The quantitative method of the present invention is a quantitative method for applying a voltage between a working electrode and a counter electrode in contact with a test liquid containing a first substance, and quantifying the content of a first substance in the test liquid based on a current value flowing due to an electrochemical oxidation reaction of the first substance at the working electrode, wherein the test liquid contains a second substance having an oxidation potential lower than the oxidation potential of the first substance, and the difference between the oxidation potential of the first substance and the oxidation potential of the second substance is equal to or less than a predetermined value, and the quantitative method includes an initial potential application step of applying an initial potential corresponding to the oxidation potential of the second substance to the test liquid over a predetermined pulse potential width set based on the content of the second substance assumed to be contained in the test liquid, a target potential application step of applying a target potential corresponding to the oxidation potential of the first substance to the test liquid over the predetermined pulse potential width after the initial potential application step, and a content calculation step of calculating the content of the first substance based on the current value measured when the initial potential and the target potential are applied, characterized in that the initial potential application step and the target potential application step are repeatedly performed multiple times while increasing each potential by a predetermined potential.

(6) A quantitative determination program of the present invention is a quantitative determination program for applying a voltage between a working electrode and a counter electrode in contact with a test liquid containing a first substance, and quantifying the content of the first substance in the test liquid based on a current value flowing due to an electrochemical oxidation reaction of the first substance at the working electrode, wherein the test liquid contains a second substance having an oxidation potential lower than the oxidation potential of the first substance, a difference between the oxidation potential of the first substance and the oxidation potential of the second substance is equal to or less than a predetermined value, and an initial potential corresponding to the oxidation potential of the second substance is set by the application unit based on the control by the control unit and set based on the content of the second substance assumed to be contained in the test liquid. The method includes an initial potential application step in which an initial potential is applied to the test liquid over a predetermined pulse potential width, a target potential application step in which, after the initial potential application step, the application unit applies a target potential corresponding to the oxidation potential of the first substance to the test liquid over a predetermined pulse potential width based on control by the control unit, and a content calculation step in which the calculation unit calculates the content of the first substance based on the current values measured by the measurement unit when the initial potential and the target potential are applied, and the initial potential application step and the target potential application step are repeatedly executed multiple times while increasing each potential by a predetermined potential.

(7) The dialysis system of the present invention is a dialysis system including a dialyzer connected to a dialysis patient, a dialysis device that supplies dialysis fluid to the dialyzer and discharges dialysis effluent from the dialyzer, and a uric acid quantification device that calculates the content of uric acid in the dialysis effluent. The uric acid quantification device is a quantification device that applies a voltage between a working electrode and a counter electrode that are in contact with dialysis effluent containing uric acid as a first substance, and quantifies the content of uric acid in the dialysis effluent based on the current value that flows due to the electrochemical oxidation reaction of uric acid at the working electrode, and includes an application unit that applies the voltage, a control unit that controls the application unit, a measurement unit that measures the current value at the working electrode, and an operation unit that calculates the content of uric acid based on the measurement result by the measurement unit. and a calculation unit, the dialysis effluent contains ascorbic acid as a second substance having an oxidation potential lower than the oxidation potential of uric acid, the control unit controls the application unit to apply an initial potential corresponding to the oxidation potential of ascorbic acid to the dialysis effluent over a predetermined pulse potential width, and after the application of the initial potential, controls the application unit to apply a target potential corresponding to the oxidation potential of uric acid to the dialysis effluent over a predetermined pulse potential width, and these are regarded as one pulse cycle, and the pulse cycle is repeated multiple times while increasing each potential by a predetermined potential, and the calculation unit calculates the uric acid content based on the current value measured by the measurement unit when the initial potential and the target potential are applied.

According to the present invention, it is possible to provide a quantitative determination device etc. capable of quantitatively determining the target substance in a test liquid containing interfering substances without modifying the electrodes and without adjusting the pH (hydrogen ion exponent) of the test liquid. In particular, a method for selectively detecting the first substance of the target substance while oxidizing the second substance, which is an interfering component, by using a potential waveform of pulse voltammetry, one pulse cycle is composed of two pulse steps, a first pulse with a predetermined width and a second pulse with a higher potential, current sampling is performed at each pulse with a predetermined width, and a pulse cycle consisting of such steps is repeated a set number of times while increasing the potential by a predetermined amount, and the current difference between the two points is recorded for each pulse cycle, thereby realizing a device etc. that accurately and easily performs quantitative determination of the target substance in a test liquid containing interfering substances.

FIG. 1 is a block diagram showing the configuration of a dialysis system according to an embodiment of the present invention. 1 is a flowchart showing a procedure for measuring (quantifying) a uric acid concentration in an embodiment of the present invention. 1A is a graph showing an example of a potential pattern applied to the test liquid, FIG. 1B is an enlarged view of portion A1 of FIG. 1A, and FIG. 1C is a graph showing the current response when the potential shown in FIG. 1 is a graph in a reference example showing a change in current flowing when a working electrode and a counter electrode are brought into contact with each other and a voltage is applied between them for each of an aqueous solution of ascorbic acid, an aqueous solution of uric acid, and an aqueous solution obtained by mixing the above two aqueous solutions. 1 is a graph showing changes in current flowing when a working electrode and a counter electrode are brought into contact with an aqueous solution of ascorbic acid and a voltage is applied between them. 1 is a graph showing changes in current flowing when a working electrode and a counter electrode are brought into contact with an aqueous solution of uric acid and a voltage is applied between them. 1 is a graph showing the change in current flowing when a working electrode and a counter electrode are brought into contact with an aqueous solution containing ascorbic acid and uric acid and a voltage corresponding to the oxidation potential of ascorbic acid is applied between them. 1 is a graph showing the change in current flowing when a working electrode and a counter electrode are brought into contact with an aqueous solution containing ascorbic acid and uric acid and a voltage corresponding to the oxidation potential of uric acid is applied between them. 13 is a graph showing the change in measured current with respect to the applied value of a voltage corresponding to a target potential when the difference between the voltage when no potential is applied and the voltage corresponding to the initial potential is changed. Graphs (a) and (b) show the change in current measured when a phosphate buffer solution containing uric acid is used as a test solution, the working electrode and the counter electrode are brought into contact with each other, and a voltage is applied between them. 1 is a graph showing the change in current measured when a test liquid, a dialysis effluent containing uric acid and ascorbic acid, is brought into contact with a working electrode and a counter electrode and a voltage is applied between them. 12 is a graph showing a calibration curve illustrating the change in current versus the concentration of uric acid, which was created based on the results obtained in FIGS. 10( a ), ( b ), and FIG. 11 .

Hereinafter, a quantitative measurement device, a quantitative measurement method, a quantitative measurement program, and a dialysis system according to an embodiment of the present invention will be described in detail with reference to the drawings.
(1) Configuration of the dialysis system As shown in FIG. 1, the dialysis system 1 according to this embodiment includes a hemodialysis device 10, a dialysis fluid supplying device 20, and a uric acid content measuring device 40 as a quantitative measurement device (uric acid quantitative measurement device).
In the following description, uric acid may be referred to as "UA" and ascorbic acid may be referred to as "AA."

The hemodialysis device 10 has a dialyzer 11 as a blood purifier. The dialyzer 11 has a blood inlet 11a, a blood outlet (purified blood outlet) 11b, a dialysis fluid inlet 11c, and a dialysis fluid outlet 11d. Between the blood inlet 11a and the blood outlet 11b in the dialyzer 11, a blood flow path is provided through which blood introduced from the blood inlet 11a flows to the blood outlet 11b. A blood purification membrane is provided on the blood flow path. More specifically, the dialyzer 11 has a number of hollow fiber membranes as blood flow paths, and blood passes through the inside of the hollow fiber membranes, and these hollow fiber membranes function as blood purification membranes. In addition, between the dialysis fluid inlet 11c and the dialysis fluid outlet 11d in the dialyzer 11, a dialysis fluid flow path is formed through which the dialysis fluid introduced from the dialysis fluid inlet 11c flows to the dialysis fluid outlet 11d. More specifically, the dialysis fluid flows around the outside of the hollow fiber membrane in the opposite direction to the blood flow direction. Various known dialyzers can be used as the dialyzer 11.

The blood inlet 11a is connected to an arterial blood line 12 connected to a dialysis patient A, and the blood outlet 11b is connected to a venous blood line 13 connected to a dialysis patient A. The dialysate inlet 11c is connected to the downstream end of a dialysate inlet line (dialysate inlet piping) 14, and the dialysis effluent outlet 11d is connected to the upstream end of a dialysis effluent discharge line (dialysis effluent discharge piping) 15. The dialysate inlet line 14 and the dialysis effluent discharge line 15 are each connected to a measuring device 16 equipped with a dialysate measuring chamber, and a predetermined amount of dialysis fluid is supplied to the dialyzer 11 through the dialysate inlet line 14, and a predetermined amount of effluent is discharged through the dialysis effluent discharge line 15. At this time, the measuring device 16 measures the amount of dialysis fluid discharged, making the amount of fluid discharged greater than the amount supplied to the dialyzer 11, thereby removing water from the blood.

The hemodialysis device 10 is mainly composed of a dialyzer 11, a dialysis fluid inlet path 14, a dialysis fluid discharge path 15, a measuring device 16, a dialysis fluid delivery pump (not shown), a blood pump, a clamp, etc. The arterial blood path 12 and the venous blood path 13 may also be considered to be included in the hemodialysis device 10.

A dialysis fluid supplying device 20 is connected to the upstream end of the dialysis fluid inlet path 14. The dialysis fluid supplying device 20 is configured to supply dialysis fluid prepared to a required concentration to the dialyzer 11 via the dialysis fluid inlet path 14. Note that if the hemodialysis device 10 has a dialysis fluid preparation function, the dialysis fluid supplying device 20 is omitted.

The downstream end of the dialysis effluent discharge path 15 is connected to the dialysis effluent recovery section 30, which recovers the dialysis effluent.

A uric acid content measuring device 40 is connected to the dialysis effluent discharge path 15 between the dialysis effluent outlet 11d and the dialysis effluent recovery unit 30 inside the hemodialysis device 10 or outside as shown in FIG. 1. The uric acid content measuring device 40 will be described later. Normally, the dialysis system 1 is configured to supply dialysis fluid from one dialysis fluid supply device 20 to multiple hemodialysis devices 10, and in this case, a uric acid content measuring device 40 is provided for each hemodialysis device 10.

Each device (each part) included in the dialysis system 1 is connected to a control unit 121 configured as a computer having an arithmetic circuit. A display unit, an input/output device, etc. are connected to the control unit 121. A dialysis program and other programs are stored in a readable manner in a memory circuit built into the control unit 121. The arithmetic circuit of the control unit 121 reads out a program such as a dialysis program stored in the memory circuit, and executes each step (for example, an initial potential application step and a content calculation step described later) based on an instruction given from the read program. Thus, the dialysis procedure, dialysis conditions, uric acid concentration measurement procedure, etc. described later are controlled. In addition, the control unit 121 records the quantified uric acid concentration, displays it on a display unit connected to the control unit 121, and controls the dialysis system 1, such as the hemodialysis device 10 and the dialysis fluid supply device 20, based on the quantified uric acid concentration, and adjusts the blood flow rate, the dialysis fluid flow rate, etc.
In this embodiment, the control unit 121 is described as controlling the entire dialysis system 1, but each of the hemodialysis device 10, the dialysis fluid supply device 20, and the uric acid content measuring device 40 may be provided with a control unit and these may be linked together to form the dialysis system 1.

(2) Configuration of the Uric Acid Content Measuring Device The uric acid content measuring device 40 will be described in detail with reference to Fig. 1. The uric acid content measuring device 40 is configured to perform electrochemical measurement using a three-electrode method to calculate the content of uric acid. More specifically, the working electrode and the counter electrode are brought into contact with a test liquid containing uric acid, and a predetermined voltage is applied between the working electrode and the counter electrode to electrolyze uric acid, the value of the current flowing due to the electrolysis of uric acid is measured, and the content (concentration) of uric acid as a target substance is quantified based on the measured current value.

As described above, the uric acid content measuring device 40 is connected to the dialysis effluent discharge path 15 between the dialysis effluent outlet 11d and the dialysis effluent recovery unit 30. The uric acid content measuring device 40 has a container 41 that contains the test liquid. The container 41 is provided with a test liquid inlet 41a and a test effluent outlet 41b.

The downstream end of the test liquid inlet 41a is connected to the test liquid inlet 42, and the upstream end of the test liquid inlet 42 is connected to the dialysis wastewater discharge path 15. The test liquid inlet 42 is provided with a valve V1, which is an on-off valve. Dialysis wastewater as the test liquid is supplied from the test liquid inlet 42 to the container 41 via the valve V1.

The test effluent discharge port 41b is provided below the side wall of the container 41. The upstream end of the test effluent discharge path 45 is connected to the test effluent discharge port 41b, and the downstream end of the test effluent discharge path 45 is connected to a test effluent recovery unit 46 configured to recover the test effluent. The test effluent discharge path 45 is provided with a valve V2. A solution 54 containing dialysis effluent (test liquid), which is the test effluent, is introduced from the test effluent discharge path 45 via the valve V2 to the test effluent recovery unit 46 and recovered.

Inside the container 41, a working electrode 51, a counter electrode 52, and a reference electrode 53 are arranged so as to be in contact with (immersed in) a solution 54 containing the dialysis effluent.

The working electrode 51 can be made of, for example, glassy carbon, platinum, or conductive diamond, and can be used without anodization or other modification processes.

For example, stainless steel or platinum in a wire, mesh or coil shape is used as the counter electrode 52. For example, a silver/silver chloride electrode or a saturated calomel electrode (Hg/Hg ₂ Cl ₂ ) is used as the reference electrode 53.

In the electrolysis of uric acid described above, an electrochemical oxidation reaction occurs on the working electrode 51 when a voltage is applied between the working electrode 51 and the counter electrode 52. In the oxidation reaction in cyclic voltammetry, the maximum occurs when a voltage of about +0.34 V is applied. However, the dialysis effluent contains various components other than uric acid, and these also undergo an electrochemical oxidation reaction on the working electrode 51 when a voltage is applied between the working electrode 51 and the counter electrode 52.

Here, among the components contained in the dialysis effluent, ascorbic acid (AA) exhibits the largest electrochemical oxidation reaction when a voltage of about +0.19 V is applied. Since uric acid and ascorbic acid have close "oxidation potentials" at which the electrochemical oxidation reaction is largest, when the content of uric acid is calculated based on the change in the current value flowing due to electrolysis, the change in the current value caused by ascorbic acid is superimposed, which may hinder the calculation of the content of uric acid.
Uric acid is excreted from the blood into the dialysis fluid as a waste product, but the uric acid concentration in the blood and the dialysis fluid is highly correlated, and it is possible to estimate the uric acid concentration in the blood by measuring the uric acid concentration in the dialysis fluid. On the other hand, ascorbic acid is vitamin C, which is absorbed into the body and carried by the blood, and is excreted into the dialysis fluid during dialysis. Therefore, when measuring the uric acid concentration in the dialysis fluid, it is necessary to remove ascorbic acid from the dialysis fluid.

The working electrode 51, the counter electrode 52, the reference electrode 53, etc. are connected to a potentiostat 121A (see FIG. 1 ) provided in the control unit 121. The potentiostat 121A is configured to apply a voltage between the working electrode 51 and the counter electrode 52, measure an electrolysis current described below, and further maintain the potential of the working electrode 51 constant with reference to the potential of the reference electrode 53.
That is, the potentiostat 121A functions as an application unit that applies a voltage between the working electrode 51 and the counter electrode 52, and as a measurement unit that measures a current value at the working electrode 51. The potentiostat 121A as a measurement unit measures a current value per unit time. A program executed on the control unit 121 controls the voltage application procedure and current value measurement procedure of the potentiostat 121A. The control unit 121 also functions as a calculation unit that calculates the uric acid content based on the measurement result by the measurement unit.

(3) Method and program for measuring uric acid concentration Fig. 2 is a flow chart showing the procedure for measuring uric acid concentration, Figs. 3(a) and (b) show applied potential waveforms, and Fig. 3(c) shows a current-potential curve (voltammogram). Hereinafter, a method and program for measuring the uric acid concentration in a test liquid by electrochemical measurement in a dialysis system 1 using the above-mentioned uric acid content measuring device 40 will be described. In the following description, the operation of each component constituting the dialysis system 1, including the uric acid content measuring device 40, is controlled by the control unit 121.

When dialysis is started, blood drawn from the dialysis patient A and flowing through the arterial blood path 12 is introduced into the blood path in the dialyzer 11 through the blood inlet 11a. The blood introduced into the blood path passes through the blood path and is returned to the dialysis patient A through the blood outlet 11b and the venous blood path 13. In addition, dialysis fluid is introduced from the dialysis fluid supply device 20 into the dialysis fluid path in the dialyzer 11 through the dialysis fluid inlet 14 and the dialysis fluid inlet 11c. The dialysis fluid introduced into the dialysis fluid path passes through the dialysis fluid path and is collected in the dialysis fluid collection section 30 through the dialysis fluid outlet 11d and the dialysis fluid discharge path 15.

When blood introduced into the blood flow path passes through a hollow fiber membrane as a blood purification membrane provided in the blood flow path, the blood comes into contact with the dialysis fluid flowing in the dialysis fluid flow path outside the hollow fiber membrane through the hollow fiber membrane, and waste products and excess water in the blood are permeated into the dialysis fluid. This purifies the blood removed from dialysis patient A, and the purified blood is returned to dialysis patient A. In this embodiment, while purifying the blood of dialysis patient A, the uric acid concentration of the dialysis fluid discharged from the dialysis fluid discharge port 11d is measured using the uric acid content measuring device 40 as the dialysis fluid (dialysis fluid) flows through the dialysis fluid discharge path 15.

In the uric acid concentration measurement method and uric acid concentration measurement program using the uric acid content measurement device 40, as shown in FIG. 2, after the initial setting (step S1), an initial potential application step (step S2), a target potential application step (step S3), an initial value application step (counting step) (step S4), a content calculation step (step S5), and a judgment step (step S6) are executed in that order, and when the concentration measurement cycle of steps S2 to S5 is completed according to the judgment in the judgment step (step S6), a test waste liquid recovery step (step S6) is executed. For each step, the arithmetic circuit of the control unit 121 controls the operation of the hardware related to each step based on the command given from the program stored in the control unit 121.

(a) Initial Settings (Step S1)
In the initial setting (step S1), the rest time Ts and the initial value Ei, the base potential (potential Es in FIG. 3) when stepping from the initial value Ei to the initial potential (increasing toward the positive potential side) in order to apply the initial potential in the initial potential application step (step S2), the first pulse potential width (time t1 in FIG. 3) as the time to apply the initial potential, the pulse potential (potential ΔE in FIG. 3) when stepping from the initial potential to the target potential (increasing toward the positive potential side) in order to apply the target potential in the target potential application step (step S3), the second pulse potential width (time t2 in FIG. 3) as the time to apply the target potential, the waiting time Tw from the target potential back to the initial value Ei until the next pulse period begins, the number of repetitions n of the pulse period, and the sampling timings st1 and st2 for measuring the current value at each pulse potential width t1 and t2 are set. The setting is performed using an input device not shown, and the input result is stored in a storage device in the control unit 121. The first pulse potential width t1 is set based on the assumed amount of ascorbic acid as the second substance contained in the test liquid. By appropriately setting the first pulse potential width t1, most or all of the ascorbic acid reacting during the application of the initial potential in the pulse period can be oxidized, so that when the target potential is applied to uric acid as the first substance (target substance) after the first pulse potential width t1 has elapsed to cause an electrochemical oxidation reaction, the influence of ascorbic acid on the amount of current measured at that time can be suppressed to be small, and the amount of uric acid can be accurately quantified. Note that the initial potential applied in the initial potential application step (step S2) is the initial value Ei + base potential Es × the number of repetitions n of the pulse period, and the target potential applied in the target potential application step (step S3) is the initial value Ei + base potential Es × the number of repetitions n of the pulse period + pulse potential ΔE. In addition, the sampling timings st1 and st2 are set to be equal timings in each pulse potential width t1 and t2 in the pulse period, and in this embodiment, the current value is measured at 3/4 timing of each pulse potential width t1 and t2.

Here, "potential" corresponds to the voltage applied between the working electrode 51 and the counter electrode 52 when they are in contact with the test liquid, and assumes the potential applied to the working electrode 51 based on the potential of the reference electrode.

The target potential is a potential corresponding to the oxidation potential of uric acid as the first substance, and the initial potential is a potential corresponding to the oxidation potential of ascorbic acid as the second substance. Here, the difference between the oxidation potential of uric acid and the oxidation potential of ascorbic acid is equal to or less than a predetermined value. This "equal to or less than a predetermined value" means that the oxidation potentials are close enough to each other that the effect of the electrochemical oxidation reaction of ascorbic acid (second substance) cannot be ignored in quantification based on the current measured when an electrochemical oxidation reaction of uric acid (first substance) is caused.

In the multi-potential step voltammetry of the present invention, an initial value Ei is set as a potential at which neither uric acid (first substance) nor ascorbic acid (second substance) is oxidized, and in one pulse period in which a target potential is applied from this initial value Ei to return to the initial value Ei, an initial potential lower than the target potential is applied over a first pulse potential width t1, and then the target potential is applied over a second pulse potential width t2. Such a pulse period is repeated while the initial potential and the target potential are increased stepwise, and at predetermined sampling timings st1 and st2 for each of the first pulse potential width t1 and the second pulse potential width t2, the current value I1 of the initial potential and the current value I2 of the target potential in that pulse period are measured, and the current difference i (I2-I1) between them is calculated. The pulse period for applying the potential is such that the potential is increased stepwise from a potential at which both uric acid (first substance) and ascorbic acid (second substance) are unlikely to undergo an oxidation reaction to a potential at which an oxidation reaction occurs, and since ascorbic acid (second substance) has a lower oxidation potential than uric acid (first substance), when the applied potential is increased stepwise, the current value I1 measured at the initial potential is always strongly influenced by the oxidation of ascorbic acid (second substance). At the target potential which is increased by the pulse potential ΔE after the application of the initial potential, the oxidation of ascorbic acid (second substance) has already progressed, so the influence of uric acid (first substance) is strongly influenced by the current value I2. Furthermore, by subtracting the current value I1 from such a current value I2, the current difference i becomes a value which more clearly indicates the degree of the oxidation reaction of uric acid (first substance). The current difference i for each pulse period thus obtained is then assigned a potential shifted by the base potential Es from the initial value Ei + base potential Es + pulse potential ΔE, thereby obtaining the current-potential curve (voltammogram) shown in FIG. 3(c). The highest value (peak value of the current-potential curve) of the current difference i for each pulse period thus obtained is applied to a calibration curve created in advance, thereby making it possible to quantify the content of uric acid (first substance).

In addition, in the initial setting (step S1), a number is set as an index for repeating the uric acid concentration measurement. For example, this number may be a threshold value for the current value calculated in the content calculation step (step S5). If the current value calculated in the content calculation step is greater than the threshold value, the time for performing the initial potential application step in the repeated uric acid concentration measurement (first pulse potential width (t1 in FIG. 3)) is set to be longer than the time for the initial potential application step.

The first pulse potential width t1 and the second pulse potential width t2 may be set to the same time as the first pulse potential width t1 and the first target potential application time t2, respectively, or may be changed, depending on the calculation results in the content calculation step (step S5), for example, based on the content of ascorbic acid (second substance) assumed to be contained in the test liquid.

(b) Initial potential application step (step S2)
The valve V1 is opened, and the dialysis effluent as the test liquid is supplied from the test liquid introduction path 42 into the container 41. When a predetermined amount (for example, 5 cc) of the dialysis effluent (test liquid) is supplied into the container 41, the valve V1 is closed. Next, while the working electrode 51 and the counter electrode 52 are in contact with the test liquid containing uric acid, a voltage (initial potential: Ei+Es×n) corresponding to the oxidation potential of ascorbic acid as the second substance is applied between the working electrode 51 and the counter electrode 52 to cause an electrochemical oxidation reaction in the dialysis effluent (test liquid). The application time of this voltage is a predetermined first pulse potential width t1. The application of the voltage corresponding to the initial potential is performed by the potentiostat 121A as the application unit under the control of the control unit 121. The current value generated by the electrochemical oxidation reaction is measured at the sampling timing st1 and recorded as the current value I1.

(c) Target potential application step (step S3)
After the initial potential application step, while the working electrode 51 and the counter electrode 52 are kept in contact with the test liquid containing uric acid, a voltage (target potential: Ei+Es×n+ΔE) corresponding to the oxidation potential of uric acid as the first substance is applied between the working electrode 51 and the counter electrode 52 to cause an electrochemical oxidation reaction in the dialysis effluent (test liquid). The application time of this voltage is a predetermined second pulse potential width t2. The application of the voltage corresponding to the target potential is also performed by the potentiostat 121A as the application unit under the control of the control unit 121. The current value generated by the chemical oxidation reaction is measured at the electrical sampling timing st2 and recorded as the current value I2.
(d) Initial value application step (step S4)
After application of the target potential, an initial value Ei is applied, and the number of times a pulse cycle consisting of application of the initial potential, application of the target potential, and application of the initial value Ei is executed is counted. If a preset number of repetitions n is reached, the process proceeds to the next content calculation step; if not, application of a potential according to the next pulse cycle is continued.

(e) Content Calculation Step (Step S5)
In the initial potential application step, ascorbic acid is mainly electrolyzed, and in the target potential application step, uric acid is mainly electrolyzed, so that an apparent current (oxidation current, hereinafter, this current is also referred to as electrolysis current) flows between the working electrode 51 and the counter electrode 52. The value of this electrolysis current (amount of electrolysis current) is measured at 121 A at predetermined sampling timings st1 and st2 in both the initial potential application step and the target potential application step. Then, in the content calculation step, the current value I1 recorded in the initial potential application step for each corresponding pulse period is subtracted from the current value I2 recorded in the target potential application step for each pulse period to calculate the current difference i for each pulse period, and the current difference i with the largest value is obtained. The obtained current difference i is applied to a registered calibration curve to quantify the content of uric acid. Since an initial potential corresponding to the oxidation potential of ascorbic acid is applied over the first pulse potential width t1 in the initial potential application step prior to the target potential application step, most of the ascorbic acid, which has an oxidation potential close to that of uric acid, is oxidized by an electrochemical oxidation reaction before the start of the target potential application step. Therefore, it can be estimated that the electrolytic current flowing in the target potential application step is due to the electrochemical oxidation reaction of uric acid, enabling highly accurate quantification.

(f) Judgment step (step S6)
After the content calculation step (step S5), the control unit 121 judges whether the next cycle of concentration measurement is possible before the end of the predetermined dialysis time, and if the measurement is possible (YES in step S6), the control unit 121 executes the concentration measurement cycle again, which includes the initial potential application step (step S2), the target potential application step (step S3), the initial value application step (step S4), and the content calculation step (step S5). When the concentration measurement cycle is executed again, the valve V1 is opened and closed in the same manner as described above, the dialysis effluent is supplied again from the test liquid introduction path 42 into the container 41, and the test liquid (dialysis effluent) is accumulated in the solution 54.

Here, when the largest current value i calculated in the most recent content calculation step is larger than the threshold value set in the initial setting (step S1), it is determined that the current value is large due to the influence of remaining ascorbic acid because the oxidation of ascorbic acid in the initial potential application step is insufficient, and the execution time of the next initial potential application step is set to a time longer than the execution time of the immediately preceding initial potential application step (first pulse potential width t1).

In contrast, when the largest current value i calculated in the content calculation step is equal to or less than the threshold value set in the initial setting, the execution time of the next initial potential application step is maintained the same as the execution time (first pulse potential width t1) of the immediately preceding initial potential application step.

(g) Recovery step of test waste liquid (step S7)
In the judgment step (step S6), if it is determined that the concentration measurement for the next cycle cannot be performed before the end of the specified dialysis time (NO in step S6), the control unit 121 opens valve V2 and introduces the solution 54 in the container 41 as the test effluent from the test effluent discharge path 45 to the test effluent recovery unit 46 for recovery.

(4) Effects Obtained by the Present Embodiment According to the present embodiment, the following effects can be obtained.
(a) When the content of a first substance to be measured, e.g., uric acid, in a test solution is calculated based on the current that flows during an electrochemical oxidation reaction, even if a second substance, e.g., ascorbic acid, is present and has an oxidation potential close to that of the first substance and therefore interferes with the calculation, the content of the first substance can be calculated, i.e., quantified, simply, quickly, and accurately without modifying the electrode used in the reaction, by applying the oxidation potential of the second substance to allow the electrochemical oxidation reaction to proceed before applying the oxidation potential of the first substance.

(b) When an oxidation potential of the second substance is applied, the oxidation of the second substance proceeds, and does not interfere with the measurement of the content of the first substance, so that quantification can be performed without adjusting the pH of the aqueous solution.

(c) By adjusting the time for applying the oxidation potential of the second substance (initial potential application step), the accuracy of the quantification of the first substance can be ensured even when the content of the second substance is high.

(d) By repeating the concentration measurement cycle, the test liquid can be added or replaced while performing continuous quantification, and more reliable quantitative results can be obtained by averaging the results of continuous quantification.

The above is a detailed description of an embodiment of the present invention. However, the present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the gist of the present invention. For example, other embodiments and modifications such as the following are also possible.

In the above embodiment, the concentration of uric acid is detected by electrochemical measurement using a three-electrode method, but this is not limiting. For example, uric acid may be detected by electrochemical measurement using a two-electrode method using a working electrode 51 and a counter electrode 52 without providing a reference electrode 53.

In the above embodiment, the uric acid content measuring device 40 is provided in the dialysis system 1, but the present invention is not limited to this and may be provided in a form independent of the dialysis system 1. A sampling port may be provided in the dialysis effluent discharge path 15, and the dialysis effluent may be taken out using a syringe or the like and dripped into the container 41. In addition, the uric acid concentration may be measured not only in the dialysis effluent but also in liquid body fluids such as urine and blood.

In the above embodiment, the concentration measurement cycle is repeated as much as possible until the end of the specified dialysis time. However, if it is determined in the judgment step that the content value calculated in the most recent specified number of cycles falls within a predetermined range, the person measuring the content may be notified that the content measurement result has stabilized regardless of the remaining time of the specified dialysis time. The notification is performed by, for example, a notification device provided in the dialysis system 1 under the control of the control unit 121. The notification device has, for example, a display unit that displays the notification and a speaker unit that emits a notification sound. The above-mentioned specified number of times and the above-mentioned specified range for determining whether to make a notification are determined taking into consideration the physical condition of the subject to be measured at the time of measurement, past measurement history, etc., and the specified number of times can be 5 times, and the specified range can be a current value variation of within plus or minus 5%.

Hereinafter, experimental results that support the effects of the above-described embodiment will be described based on examples and reference examples.
Examples and reference examples relating to the potential applied in the initial potential application step or the target potential application step and the change in the measured value of the current at the working electrode due to the application will be described with reference to Figures 4 to 12. In the reference examples and examples shown in Figures 4 to 12, the potential is applied as a voltage between the working electrode 51 and the counter electrode 52, the potential is measured based on the potential of the reference electrode 53, and the current value at the working electrode 51 is measured.

(Reference example)
First, the effect on the electrolysis current when the oxidation of ascorbic acid is insufficient in the initial potential application step (step S2) will be described with reference to the cyclic voltammograms in Fig. 4. Fig. 4 is a graph showing the change in the current (vertical axis, unit μA) flowing when a voltage (horizontal axis, unit V) is applied between the working electrode and the counter electrode in contact with each other for each of an aqueous solution S1 of ascorbic acid (curve L1a), an aqueous solution S2 of uric acid (curve L1u), and an aqueous solution T (curve L1t) in which the above two aqueous solutions S1 and S2 are mixed. The aqueous solution S1 of ascorbic acid does not contain uric acid, and the aqueous solution S2 of uric acid does not contain ascorbic acid.

In aqueous solution T, which is a mixture of aqueous solutions S1 and S2, the first peak P1t of the current change occurs at approximately 0.19 V, similar to the aqueous solution S1 of ascorbic acid, and the current value at the peak P1t is approximately the same as the current value in the case of aqueous solution S1. In other words, the peak P1a of aqueous solution S1 and the first peak P1t of aqueous solution S2 almost overlap.

In the aqueous solution T, there is a second peak P1u' at approximately 0.34 V, the same as in the aqueous solution S2 of uric acid. However, the current value at this peak P1u' is significantly larger than the current value at peak P1u in the case of the aqueous solution S2, and is approximately the same current value as the first peak P1t. This shows that when the aqueous solutions S1 of ascorbic acid and S2 of uric acid are mixed, the peak P1u of the current change in the aqueous solution S2 of uric acid is significantly shifted upward due to the influence of the current that changes based on ascorbic acid.

As shown in FIG. 4, in the aqueous solution S1 of ascorbic acid, a peak P1a of the current change appears at approximately 0.19 V. In contrast, in the aqueous solution S2 of uric acid, a peak P1u of the current change appears at approximately 0.34 V, and the oxidation peak potentials of the two are very close, making it difficult to selectively detect uric acid.

Next, the relationship between the time for which the potential is applied and the measured current will be described with reference to Figures 5 and 6. Figures 5 and 6 are graphs showing the change in the current (vertical axis, unit μA) that flows when a working electrode and a counter electrode are brought into contact with each aqueous solution and a voltage (horizontal axis, unit V) is applied between them. Figure 5 is a graph for an aqueous solution of ascorbic acid, and Figure 6 is a graph for an aqueous solution of uric acid. In Figure 5, five curves L21, L22, L23, L24, and L25 show the cases where the voltage application time (pulse width of the applied waveform) is 0.3 seconds, 0.5 seconds, 1.0 seconds, 2.0 seconds, and 5.0 seconds, respectively. In Figure 6, five curves L31, L32, L33, L34, and L35 show the cases where the voltage application time (pulse width of the applied waveform) is 0.3 seconds, 0.5 seconds, 1.0 seconds, 2.0 seconds, and 5.0 seconds, respectively.

As shown in FIG. 5, in the aqueous solution of ascorbic acid, the peak of the current change appears at the same voltage value regardless of the length of application time, and the longer the application time, the smaller the current value at the peak. This tendency is also seen in the aqueous solution of uric acid shown in FIG. 6, where the peak of the current change appears at the same voltage value regardless of the length of application time, and the longer the application time, the smaller the current value at the peak. From the results shown in FIG. 5 and FIG. 6, it can be seen that there is a voltage (electric potential) at which the electrochemical oxidation reaction peaks for both ascorbic acid and uric acid. Furthermore, it can be seen that by extending the application time of the voltage, the electrochemical oxidation reaction proceeds sufficiently, and the amount of ascorbic acid or uric acid as a reactant decreases.

Next, the time for applying a voltage corresponding to the oxidation potential of ascorbic acid and the measured current will be described with reference to FIG. 7. FIG. 7 is a graph showing the change in current flowing when a working electrode and a counter electrode are brought into contact with an aqueous solution of a mixture of an aqueous solution of ascorbic acid and an aqueous solution of uric acid and a voltage (horizontal axis, unit V) is applied between them. The applied voltage is a voltage corresponding to the oxidation potential of ascorbic acid, and the three curves L41, L42, and L43 show the cases where the voltage application time (pulse width of the applied waveform) is 0.5 seconds, 1.0 seconds, and 5.0 seconds, respectively. Note that the three curves L41, L42, and L43 are displayed shifted vertically in order to compare the changes in the current value, but do not show the magnitude relationship between the current values.

As can be seen by comparing the three curves L41, L42, and L43 shown in FIG. 7, in the curve L41 with a short application time, in addition to the current peak corresponding to the oxidation potential of uric acid of about 0.3 V, there is a peak corresponding to the oxidation potential of ascorbic acid at about 0.1 V, whereas the peak corresponding to the oxidation potential of ascorbic acid becomes smaller as the application time is increased. As a result, by extending the application time of the voltage corresponding to the oxidation potential of ascorbic acid to a predetermined range, a curve with a clear peak corresponding to the oxidation potential of uric acid can be obtained. Therefore, if a voltage corresponding to the oxidation potential of uric acid is applied in this state, it becomes possible to perform highly accurate quantification using the measured current value.

The time for applying a voltage corresponding to the oxidation potential of uric acid and the measured current will be described with reference to FIG. 8. FIG. 8 is a graph showing the change in current (vertical axis) that flows when a working electrode and a counter electrode are brought into contact with an aqueous solution of a mixture of an aqueous solution of ascorbic acid and an aqueous solution of uric acid and a voltage (horizontal axis, unit V) is applied between them. FIG. 8 is a graph showing the change in current response with the change in the first pulse potential width t1. The applied voltage is a voltage corresponding to the oxidation potential of uric acid, and the three curves L51, L52, and L53 show the cases where the voltage application time (pulse width of the applied waveform) is 5 ms, 20 ms, and 100 ms, respectively. Note that the three curves L51, L52, and L53 are displayed shifted vertically in order to compare the changes in the current value, but do not show the magnitude relationship between the current values.

As can be seen by comparing the three curves L51, L52, and L53 shown in Figure 8, curve L51, which has a short application time, has a clear current peak corresponding to the oxidation potential of uric acid of about 0.22 V, whereas the longer the application time, the more prominent the peak corresponding to the oxidation potential of ascorbic acid becomes. As a result, by shortening the application time of the voltage corresponding to the oxidation potential of uric acid to within a specified range, a curve with a clear peak corresponding to the oxidation potential of uric acid can be obtained. Therefore, it is possible to perform highly accurate quantification using the current value measured based on this curve.

From these findings, it is clear that the quantification of uric acid is more pronounced when the second pulse potential width t2, which applies the target potential, is shorter than the first pulse potential width t1, which applies the initial potential. More specifically, highly accurate quantification is possible by setting the first pulse potential width t1 to 1.0-5.0 s and the second pulse potential width t2 to 5-20 ms.

Figure 9 is a graph showing the change in measured current with respect to the applied value of the voltage corresponding to the target potential when the difference (pulse potential ΔE) between the voltage when no potential is applied (base potential Es) and the voltage corresponding to the initial potential is changed. The four lines L61, L62, L63, and L64 in Figure 9 show the cases when the pulse potential ΔE is 0.50 V, 0.30 V, 0.15 V, and 0.001 V, respectively. In the results shown in Figure 9, the voltage in the state where no potential is applied before the initial potential is applied is 0.004 V, and in the initial potential application step, a voltage increased by ΔE from the above 0.0004 V is applied for 5 seconds as the voltage corresponding to the initial potential, and then the voltage corresponding to the target potential is applied for 5 ms to measure the current. Note that the four lines L61, L62, L63, and L64 are displayed shifted vertically in order to compare the changes in current value, but do not show the magnitude relationship between the current values.

As shown in FIG. 9, in curve L63 where the pulse potential ΔE is 0.15 V, a current peak corresponding to the oxidation potential of uric acid appears near 0.25 V, while in the other three lines L61, L62, and L64, no clear peak appears. Therefore, it can be seen that by setting the pulse potential ΔE within a predetermined range around 0.15 V, it is possible to perform accurate quantification of uric acid.

(Example)
10(a) and (b) are graphs showing changes in current measured when a test solution containing uric acid and a pH 7.4 phosphate buffer solution is brought into contact with a working electrode 51 and a counter electrode 52 and a voltage is applied between them by the multi-potential step voltammetry method, which is the method of the above embodiment. Fig. 10(a) shows the case where the test solution does not contain ascorbic acid, and five curves L71, L72, L73, L74, and L75 show the cases where the concentrations of uric acid contained in the test solution are 300 μM, 200 μM, 100 μM, 75 μM, and 50 μM, respectively. 10(b) shows the case where the test solution contains ascorbic acid at a concentration of 200 μM, and five curves L76, L77, L78, L79, and L80 show the cases where the concentrations of uric acid contained in the test solution are 300 μM, 200 μM, 100 μM, 75 μM, and 50 μM, respectively. In the results shown in FIG. 10(a) and (b), a voltage of 0.004 V corresponding to the initial potential in the initial potential application step is applied for 5 seconds, and then the voltage is increased by 0.15 V, and the current is measured after applying this voltage for 5 ms.

As shown in FIG. 10(a), in the phosphate buffer solution that does not contain ascorbic acid, the peak corresponding to the oxidation potential of uric acid at around 0.24 V is maintained, and the current value at the peak increases as the concentration of uric acid increases. As shown in FIG. 10(b), in the phosphate buffer solution that contains ascorbic acid, the peak corresponding to the oxidation potential of uric acid at around 0.25 V is maintained, and the current value at the peak increases as the concentration of uric acid increases.

Fig. 11 is a graph showing the change in current measured when a test liquid containing uric acid and ascorbic acid and having a pH of 7.42 is brought into contact with a working electrode 51 and a counter electrode 52 by the multi-potential step voltammetry method, which is the method of the above embodiment, and a voltage is applied between them. In Fig. 11, five curves L81, L82, L83, L84, and L85 show the cases where the concentrations of uric acid contained in the test liquid are 300 μM, 200 μM, 100 μM, 75 μM, and 50 μM, respectively. In addition to uric acid and ascorbic acid, this dialysis effluent contains ions such as Na ⁺ , K ⁺ , Ca ²⁺ , Mg ²⁺ , Cl ^- , HCO ₃ ^- , and CH ₃ COO ^{- ,} as well as glucose. In the results shown in FIG. 11, a voltage of 0.004 V corresponding to the initial potential in the initial potential application step is applied for 5 seconds, and then the voltage is increased by 0.15 V, and this voltage is applied for 5 ms, after which the current is measured.

As shown in Figure 11, similar to the case of the phosphate buffer solution shown in Figures 10(a) and (b), in the dialysis effluent, the peak corresponding to the oxidation potential of uric acid at around 0.24 V is maintained, and the current value at the peak increases as the concentration of uric acid increases.

Figure 12 is a graph showing a calibration curve showing the change in current versus uric acid concentration (horizontal axis, units: μM), created based on the results obtained in Figures 10(a), (b), and 11. The three straight lines L91, L92, and L93 in Figure 12 are calibration curves based on a phosphate buffer solution containing uric acid but not ascorbic acid (Figure 10(a)), a phosphate buffer solution containing uric acid and ascorbic acid (Figure 10(b)), and a dialysis effluent containing uric acid and ascorbic acid (Figure 11), respectively.

As shown in FIG. 12, in both the phosphate buffer solution (FIGS. 10(a) and (b)) and the dialysis effluent (FIG. 11), the uric acid concentration and the current show a linear relationship. Therefore, by setting the voltage values corresponding to the initial potential and the target potential, and the application time of these voltages within a predetermined range, it is possible to suppress the influence of ascorbic acid, which has a similar oxidation potential, and to quantify uric acid with high accuracy. Furthermore, in the cases shown by lines L91 and L92 in FIG. 12, similar to the dialysis effluent shown by line L93, voltage is applied under neutral conditions of about pH 7, and a line with approximately the same slope is obtained. Therefore, since there is no need to suppress the influence of ascorbic acid by adjusting the pH, quantification can be performed simply and quickly.

1 Dialysis system 10 Hemodialysis device (dialysis device)
11 Dialyzer 20 Dialysis fluid supply device 30 Dialysis waste fluid recovery section 40 Uric acid concentration measuring device (quantification device, uric acid quantification device)
46 Test waste liquid recovery unit 51 Working electrode 52 Counter electrode 53 Reference electrode 121 Control unit (calculation unit)
121A Potentiostat (applying part, measuring part)
A. Dialysis patients

Claims (6)

A quantitative determination device that applies a voltage between a working electrode and a counter electrode that are in contact with a test liquid containing a first substance, and determines the content of the first substance in the test liquid based on a current value that flows due to an electrochemical oxidation reaction of the first substance at the working electrode,
An application unit that applies the voltage;
A control unit that controls the application unit;
A measurement unit that measures a current value at the working electrode;
a calculation unit that calculates an amount of the first substance based on a measurement result by the measurement unit ,
the test liquid contains a second substance having an oxidation potential lower than an oxidation potential of the first substance, and a difference between the oxidation potential of the first substance and the oxidation potential of the second substance is equal to or smaller than a predetermined value;
the control unit controls the application unit to apply an initial potential corresponding to an oxidation potential of the second substance to the test liquid over a first pulse potential width set based on the content of the second substance assumed to be contained in the test liquid , and controls the application unit to apply a target potential corresponding to the oxidation potential of the first substance to the test liquid over a second pulse potential width after the application of the initial potential, and repeats the pulse period a plurality of times while increasing each potential by a predetermined potential, with this forming one pulse period;
The quantitative measurement apparatus is characterized in that the calculation unit calculates the content of the first substance based on the current value measured by the measurement unit when each of the initial potentials and the target potential is applied. 2. The quantitative measurement apparatus according to claim 1 , wherein the first pulse potential width and the second pulse potential width have the same duration. The quantitative measurement apparatus according to claim 1 , wherein the second pulse potential width is shorter than the first pulse potential width. A method for quantifying a content of a first substance in a test liquid, the method comprising: applying a voltage between a working electrode and a counter electrode that are in contact with the test liquid containing a first substance; and quantifying a content of the first substance in the test liquid based on a current value that flows due to an electrochemical oxidation reaction of the first substance at the working electrode, the method comprising:
the test solution contains a second substance having an oxidation potential lower than an oxidation potential of the first substance,
a difference between an oxidation potential of the first material and an oxidation potential of the second material is equal to or less than a predetermined value;
an initial potential application step of applying an initial potential corresponding to an oxidation potential of the second substance to the test liquid over a predetermined pulse potential width set based on the content of the second substance assumed to be contained in the test liquid ;
a target potential application step of applying a target potential corresponding to an oxidation potential of the first substance to the test liquid over a predetermined pulse potential width after the initial potential application step;
a content calculation step of calculating a content of the first substance based on a current value measured when the initial potential and the target potential are applied;
wherein the initial potential application step and the target potential application step are repeatedly performed a plurality of times while increasing each potential by a predetermined potential. A quantitative determination program for applying a voltage between a working electrode and a counter electrode that are in contact with a test liquid containing a first substance, and quantifying the content of the first substance in the test liquid based on a current value that flows due to an electrochemical oxidation reaction of the first substance at the working electrode,
the test solution contains a second substance having an oxidation potential lower than an oxidation potential of the first substance,
a difference between an oxidation potential of the first material and an oxidation potential of the second material is equal to or less than a predetermined value;
an initial potential application step of applying an initial potential corresponding to the oxidation potential of the second substance to the test liquid over a predetermined pulse potential width set based on the content of the second substance assumed to be contained in the test liquid by an application unit based on the control by a control unit;
a target potential application step of applying a target potential corresponding to an oxidation potential of the first substance to the test liquid over a predetermined pulse potential width by the application unit based on control by the control unit after the initial potential application step;
a content calculation step of calculating a content of the first substance by a calculation unit based on a current value measured by a measurement unit when the initial potential and the target potential are applied;
wherein the initial potential application step and the target potential application step are repeatedly executed a plurality of times while increasing each potential by a predetermined potential. A dialysis system comprising a dialyzer connected to a dialysis patient, a dialysis device that supplies a dialysis fluid to the dialyzer and discharges a dialysis effluent from the dialyzer, and a uric acid quantification device that calculates the content of uric acid in the dialysis effluent,
The uric acid quantitative determination device comprises:
A quantitative determination apparatus for determining the content of uric acid in a dialysis effluent based on a current value flowing due to an electrochemical oxidation reaction of the uric acid at the working electrode, the quantitative determination apparatus being configured to apply a voltage between a working electrode and a counter electrode that are in contact with the dialysis effluent containing uric acid as a first substance,
An application unit that applies the voltage;
A control unit that controls the application unit;
A measurement unit that measures a current value at the working electrode;
A calculation unit that calculates the content of the uric acid based on the measurement result by the measurement unit,
The dialysis effluent contains ascorbic acid as a second substance having an oxidation potential lower than an oxidation potential of uric acid,
the control unit controls the application unit so as to apply an initial potential corresponding to an oxidation potential of the ascorbic acid to the dialysis effluent over a predetermined pulse potential width, and controls the application unit so as to apply a target potential corresponding to an oxidation potential of the uric acid to the dialysis effluent over a predetermined pulse potential width after the application of the initial potential, and repeats the pulse period a plurality of times while increasing each potential by a predetermined potential, with the above being regarded as one pulse period;
The dialysis system according to claim 1, wherein the calculation unit calculates the uric acid content based on the current value measured by the measurement unit when the initial potential and the target potential are applied.

Images