Mercury concentration detection device and mercury concentration detection method

Abstract

To provide a mercury concentration detection device and mercury concentration detection method capable of quickly and accurately measuring a minute amount of mercury at low cost with only pretreatment.SOLUTION: A control unit has a voltage application unit, a current measurement unit that measures a current value of a working electrode, and a calculation unit that calculates a mercury concentration based on the current value obtained by the current measurement unit. The control unit controls the voltage application unit to apply a voltage between the working electrode and a counter electrode, electro-deposit mercury contained in a test solution onto the working electrode, and measure a current value in the analysis target range corresponding to an electro-deposition potential of mercury to a predetermined sweep voltage using voltammetry. The calculation unit performs second-order differentiation of current value fluctuation spectrum data in the analysis target range, and then performs peak analysis using a maximum value as a baseline, calculates the mercury concentration based on a peak half-width, a peak voltage, and a peak intensity, and determines whether the mercury concentration exceeds a specified value.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a mercury concentration detection device and a mercury concentration detection method. [Background technology]

[0002] For example, pollutants such as heavy metals contained in soil can have a significant impact on human health. For this reason, the permissible limits of pollutants contained in soil are strictly regulated in many countries. For example, in Japan, Article 16, Paragraph 1 of the Basic Environment Law (Law No. 91 of 1993) prescribes standards for pollutants that are desirable to maintain in order to protect human health and preserve the living environment (hereinafter referred to as "environmental standards") regarding environmental conditions related to soil contamination.

[0003] Of these pollutants, even minute amounts of mercury have a significant impact on the human body and the environment, so strict environmental standards have been set for it. For example, the Appendix to Article 16, Paragraph 1 of the Basic Environment Law (Law No. 91 of 1993) stipulates that total mercury should not exceed 0.0005 mg (0.5 ppb) per liter of test solution.

[0004] Conventionally, methods for accurately measuring trace concentrations of mercury, such as those required by the environmental standards mentioned above, include, for example, a method in which a soil sample is subjected to multiple pretreatments to form a test solution, and then this test solution is analyzed using an inductively coupled plasma mass spectrometer (ICP-MS) or an atomic absorption spectrometer (AAS) (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Utility Model Application Publication No. 60-17449 [Patent Document 2] Japanese Patent Application Laid-open No. 56-100360 Summary of the Invention [Problem to be solved by the invention]

[0006] However, conventional mercury concentration measurement methods such as those described in Patent Documents 1 and 2 require expensive, large-scale analytical equipment such as ICP-MS or AAS, which means that analyzing mercury concentrations takes a long time and the analytical costs are high.

[0007] On the other hand, colorimetric methods using dithizone or methylthymol blue are known as simple methods for analyzing mercury concentrations at soil sampling sites, which is one example of a target for measuring mercury concentrations. However, these simple analyses have the problem of being difficult to detect extremely small amounts of mercury, such as concentrations of 0.5 ppb or less, and also of not being able to accurately obtain specific numerical values ​​for mercury concentrations.

[0008] The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide a mercury concentration detection device and a mercury concentration detection method that can measure trace amounts of mercury, such as concentrations of 0.5 ppb or less, quickly, accurately, and at low cost with only simple pretreatment. The configuration of the mercury concentration detection device and mercury concentration detection method of the present application can also be applied to the detection of heavy metals that can be electrochemically ionized into particles, such as mercury metals, for example, copper, zinc, cadmium, and lead. [Means for solving the problem]

[0009] In order to solve the above problems, the mercury concentration detection device and mercury concentration detection method according to one embodiment of the present invention propose the following means. (1) A mercury concentration detection device according to a first aspect of the present invention includes at least a liquid tank for accommodating a test liquid; a working electrode, a counter electrode, and a reference electrode disposed in the liquid tank; stirring means for stirring the test liquid in the liquid tank; and a control unit. The control unit includes the voltage application unit, a current measurement unit for measuring a current value at the working electrode, and a calculation unit for determining whether the mercury concentration exceeds a specified value based on the current value obtained by the current measurement unit. The control unit controls the voltage application unit to apply a voltage between the counter electrode and the working electrode to electrodeposit mercury contained in the test liquid onto the working electrode, and controls the voltage application unit to measure, by voltammetry, a current value within an analysis range corresponding to a range from the electrodeposition potential of mercury to a predetermined sweep voltage. The calculation unit performs second-order differentiation of data on the current fluctuation spectrum within the analysis range, and then calculates the mercury concentration based on the peak half-width, peak voltage, and peak intensity using the maximum value as a baseline, and determines whether the mercury concentration exceeds a specified value.

[0010] (2) A second aspect of the present invention is the mercury concentration detection device of the first aspect, wherein the working electrode is a gold nanoparticle-boron-doped diamond electrode.

[0011] (3) A mercury concentration detection method according to a third aspect of the present invention is a mercury concentration detection method using the mercury concentration detection device according to the first or second aspect, and includes the steps of: stirring the test solution in the liquid tank; applying a voltage between the counter electrode and the working electrode by sweeping the voltage across an analysis range from the electrodeposition potential of mercury to a predetermined sweep voltage; differentiating the second derivative of the current fluctuation spectrum data in the analysis range; and performing peak analysis using the maximum value of the data obtained in the differentiating step as a baseline, calculating the mercury concentration based on the peak half-width, peak voltage, and peak intensity, and determining whether the mercury concentration exceeds a specified value.

[0012] (4) A fourth aspect of the present invention is the mercury concentration detection method of the third aspect, wherein the voltage in the voltage application step is in the range of −0.9 V or more and −0.7 V or less.

[0013] (5) A fifth aspect of the present invention is the mercury concentration detection method according to the third or fourth aspect, wherein the voltage of the analysis range is 0.5 V or more and 0.8 V or less.

[0014] (6) A sixth aspect of the present invention is the mercury concentration detection method according to any one of the third to fifth aspects, wherein the voltage application time in the voltage application step is in the range of 300 seconds or more and less than 700 seconds.

[0015] (7) In an eighth aspect of the present invention, in the mercury concentration detection method of any one of the third to sixth aspects, the calculation unit determines that the mercury concentration exceeds 0.5 ppb when the peak half-width is 0.2 or more and less than 0.99, the peak voltage is in the range of 0.56±0.06 V, and the peak intensity is 0.01 or more and less than 0.25. [Effects of the Invention]

[0016] According to the present invention, it is possible to provide a mercury concentration detection device and a mercury concentration detection method that can measure trace amounts of mercury, such as concentrations of 0.5 ppb or less, quickly, accurately, and at low cost with only simple pretreatment. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a schematic diagram illustrating a mercury concentration detection device according to an embodiment of the present invention. [Figure 2] 1 is a flowchart showing a step-by-step method for detecting mercury concentration according to an embodiment of the present invention. [Figure 3] 1 is a graph showing the results of mercury electrodeposition in an example of the present invention. [Figure 4] 1 is a graph showing the results of mercury electrodeposition in a comparative example in an example. [Figure 5] 4 is a graph obtained by performing numerical processing (second-order differentiation) on the results shown in FIG. 3 in an example. [Figure 6] 1 is a graph showing the results of peak analysis of an example of the present invention in an example. [Figure 7]1 is a graph showing the results of peak analysis of a comparative example in an example. [Figure 8] 1 is a graph showing that the present invention can distinguish mercury at a concentration of 0.25 ppb at the optimum electrodeposition time (612 seconds). DETAILED DESCRIPTION OF THE INVENTION

[0018] A mercury concentration detection device and a mercury concentration detection method according to one embodiment of the present invention will be described below with reference to the drawings. Note that the following embodiment is specifically described to provide a better understanding of the gist of the invention, and does not limit the present invention unless otherwise specified. Furthermore, the drawings used in the following description may show essential parts enlarged for convenience in order to make the features of the present invention easier to understand, and the dimensional proportions of each component may not necessarily be the same as those in reality.

[0019] [Mercury concentration detection device] FIG. 1 is a schematic diagram showing the configuration of a mercury concentration detection device according to one embodiment of the present invention. The mercury concentration detection device 10 of this embodiment has at least, for example, a liquid tank 11, three electrodes contained in this liquid tank 11: a working electrode 12, a counter electrode 13, and a reference electrode 14, a stirring means 15 disposed in the liquid tank 11, and a control unit 16.

[0020] The liquid tank 11 may be any container that contains a test liquid W in a solvent containing water, for example, in which soil eluates have been dissolved, and may be made of a dielectric material such as resin or glass. In this embodiment, a circular container made of hard polyethylene and having a capacity of about 5 ml is used as the liquid tank 11.

[0021] In this embodiment, soil is described as an example of a target for measuring mercury concentration, but the target for measuring mercury concentration using the configuration of this embodiment is not limited to soil. In addition to soil, other targets for measuring mercury concentration include wastewater discharged from factories and homes, river water, various types of treated water, and eluates eluted from any solid.

[0022] The working electrode 12 is provided with a label 12a formed by forming a boron-doped diamond (BDD) thin film on a niobium or silicon substrate and modifying the BDD thin film with gold nanoparticles. When a reduction voltage is applied to the working electrode 12, mercury contained in the W in the test solution is concentrated and electrodeposited onto the label 12a.

[0023] The working electrode 12 does not necessarily have to include the label 12a, and may be, for example, an electrode made of a niobium substrate or a silicon substrate. The working electrode 12 may be made of a material other than the niobium or silicon described above, such as gold or platinum, which is reactive with the mercury to be detected. The working electrode 12 may have any shape other than a plate-like shape as in this embodiment, such as nanoparticles, a mesh, a wire, or a printed electrode, and is not limited to a specific shape.

[0024] The counter electrode 13 may be, for example, an electrode formed in a plate or coil shape and made of conductive diamond, silver, gold, platinum, or the like.

[0025] The reference electrode (standard electrode) 14 is an electrode that provides a reference point for the potential when measuring the potential. In this embodiment, a silver-silver chloride electrode (vs. Ag / AgCl) is used, which has an internal solution of potassium chloride aqueous solution and a silver wire coated with silver chloride housed in the internal solution.

[0026] In this embodiment, the stirring means 15 may be a magnetic stirrer composed of a stirring bar 15a and a stirring device main body 15b. The stirring means 15 rotates the magnet of the stirring device main body 15b, which is provided below the liquid tank 11, thereby rotating the stirring bar 15a, which is magnetically attracted via the liquid tank 11, and stirring the test solution W. As the stirring means, in addition to the magnetic stirrer described above, various stirring means such as a propeller stirrer and an ultrasonic stirrer can be used.

[0027] The control unit 16 includes a calculation unit 21, a voltage application unit 22, a current value measurement unit 23, and a display unit 24. In practice, the control unit 16 may be composed of, for example, a personal computer equipped with a CPU, memory, etc., a display, an external storage device, and an interface including a voltammetry circuit, etc.

[0028] The control unit 16 controls the voltage application unit 22 to form a reduction voltage between the counter electrode 13 and the working electrode 12, electrodeposit the mercury dissolved in the test solution W onto the marker 12a of the working electrode 12, and measure the current value in the analysis range corresponding to the mercury electrodeposition potential to a predetermined sweep voltage by square wave voltammetry.

[0029] Then, calculation unit 21, which is part of control unit 16, performs second-order differentiation of the current spectrum data in the aforementioned analysis range, performs peak analysis using the maximum value as a baseline, and calculates the mercury concentration in the soil to be analyzed based on the peak intensity, peak half-width, and peak voltage. The mercury concentration result is then displayed on display unit 24.

[0030] [Mercury concentration detection method] Next, the operation of the mercury concentration detecting device 10 of the above-described embodiment and the mercury concentration detecting method of this embodiment using the mercury concentration detecting device 10 will be described. FIG. 2 is a flowchart showing a step-by-step method for detecting mercury concentration according to one embodiment of the present invention.

[0031] When detecting mercury concentration using the mercury concentration detecting device 10 of the above-described embodiment, first, prepare soil (sample) for analyzing the mercury concentration, which is an example of a material for preparing a test solution. This sample (unit: g) is mixed with a solvent (pure water to which hydrochloric acid is added to adjust the pH to 5.8 to 6.3) at a ratio of 10% by mass, and the volume of the mixture is adjusted to 1000 mL to obtain a sample solution.

[0032] Next, the prepared sample solution was shaken by hand for about 1 minute at room temperature (20°C) and atmospheric pressure (1 atmosphere). The sample solution may also be shaken using a shaker, and the shaker settings may be, for example, 6 hours, approximately 200 shakes per minute, and a shaking width of about 4 to 5 cm.

[0033] The shaken solution is filtered, for example, through a membrane filter, and the filtrate is used as a test solution (test solution formation step S1). The pore size of the membrane filter used may be, for example, about 0.45 μm (average pore size).

[0034] The test liquid M thus obtained is placed in, for example, about 5 milliliters in the liquid tank 11 of the mercury concentration detection device 10. Then, the stirrer 15a is placed in the bottom of the liquid tank 11, and the stirrer body 15b is operated to stir the test liquid M in the liquid tank 11 (stirring step S2). The test liquid is constantly stirred during measurement to prevent sediment from forming at the bottom of the liquid tank 11.

[0035] Next, the working electrode 12, the counter electrode 13, and the reference electrode 14 are placed at a predetermined distance from one another in the liquid tank 11. Then, the control unit 16 is operated to measure the mercury concentration contained in the test liquid M in a predetermined operation mode.

[0036] First, the control unit 16 operates the voltage application unit 22 to apply a voltage between the counter electrode 13 and the working electrode 12 so as to sweep the voltage across the analysis range from the electrodeposition potential of mercury to a predetermined sweep voltage (voltage application step S3). At this time, the applied voltage (reduction voltage) is set to, for example, -0.9 V. The voltage application time in this voltage application step S3 may be, for example, in the range of 544 seconds or more and less than 700 seconds.

[0037] In the voltage application step S3, mercury contained in the test solution M is electrodeposited and concentrated on the label 12a of the working electrode 12 by applying a reducing voltage.

[0038] Then, when sweeping this analysis range, second-order differentiation is performed (differentiation step S4) using data on the current value fluctuation spectrum of the analysis range continuously measured by the current value measurement unit 23. The voltage of such an analysis range may be in the range of 0.5 V or more and 0.8 V or less.

[0039] Next, peak analysis is performed using the maximum value of the current fluctuation spectrum data obtained in the differentiation step S4 as a baseline, and the mercury concentration in the soil is calculated based on the peak half-width, peak voltage, and peak intensity (mercury concentration calculation step S5).

[0040] In this case, if all of the following conditions (1) to (3) are met: (1) the peak half-width in peak analysis is 0.2 or more and less than 0.99, (2) the peak voltage is in the range of 0.56 ± 0.06 V, and (3) the peak intensity is 0.01 or more and less than 0.25, it can be determined that the soil (sample) being analyzed for mercury concentration exceeds, for example, 0.5 ppb (the specified value), which is the regulatory limit for total mercury under Japan's Basic Environment Law.

[0041] As described above, according to the mercury concentration detection method using the mercury concentration detection device of the present invention, a test solution in which soil eluates are dissolved in a solvent containing water is used to electrodeposit the mercury to be analyzed so that it is concentrated on the working electrode, and by performing data processing such as second-order differentiation of the current value fluctuation spectrum data in the range to be analyzed and peak analysis, it is possible to accurately and quickly determine the mercury concentration in soil containing large amounts of various impurities and chemical additives with a simple configuration, even for very low mercury concentrations, such as the specified value of 0.5 ppb. In the above-described embodiment, soil is cited as an object for detecting mercury concentration, but the object for detecting mercury is not limited to soil and may be anything.

[0042] Although the embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as defined in the claims. [Example]

[0043] Hereinafter, more specific examples of the mercury concentration detection method of the present invention will be described. Using the mercury concentration detection method of the present invention, a test solution with a mercury concentration of 0.25 ppb was used. Mercury was electrodeposited for 612 seconds, the optimal electrodeposition time (544 seconds or more and less than 700 seconds), and the relationship between the reduction current and the voltage at the reference electrode (vs. Ag / AgCl) was measured. The results are shown in the graph in Figure 3.

[0044] In addition, the measurement results using a test solution containing no mercury are also shown as reference values ​​in Figure 3. Furthermore, as a comparative example, the results of measurements similar to those above were taken with an electrodeposition time of 1,200 seconds, and are shown in the graphs in Figure 4. These graphs show the results of measurements at 17 measurement points from a voltage of -0.608 V onwards as a continuous curve.

[0045] Next, a graph obtained by performing numerical processing (second-order differentiation) on the results of the present invention shown in Figure 3 is shown in Figure 5. In Figure 5, the results using a test solution to which mercury was not added are also shown as reference values.

[0046] Next, peak analysis was performed using the maximum value of the curve in Figure 5 as the baseline, and the peak half-width, peak voltage, and height from the baseline (peak intensity) were determined from the peak fit curve created. The results for a test solution with a mercury concentration of 0.25 ppb are shown in Figure 6, and the results for a test solution with no added mercury are shown in Figure 7.

[0047] From the above results, as shown in FIG. 8, it was confirmed that mercury at a concentration of 0.25 ppb could be discriminated at the optimum electrodeposition time (612 seconds). [Industrial Applicability]

[0048] The mercury concentration detection device and mercury concentration detection method of the present invention enable rapid, accurate, and low-cost measurement of trace amounts of mercury, such as concentrations of 0.5 ppb or less, without the need for complex multi-stage pretreatment of the soil to be measured and without using expensive measurement equipment such as ICP-MS or AAS, and therefore have industrial applicability. [Explanation of symbols]

[0049] 10...Mercury concentration detection device 11...Liquid tank 12...Working electrode 12a...Sign 13...Counter electrode 14...Reference electrode 15...Stirring means 16...Control unit 21...Arithmetic section 22...Voltage application section 23...Current measurement unit 24...Display section

Claims

1. The liquid test device comprises at least a liquid vessel for accommodating a test liquid, a working electrode, a counter electrode, and a reference electrode disposed in the liquid vessel, a stirring means for stirring the test liquid in the liquid vessel, and a control unit; the control unit includes a voltage application unit, a current value measurement unit that measures a current value of the working electrode, and a calculation unit that determines whether the mercury concentration exceeds a specified value based on the current value obtained by the current value measurement unit; the control unit controls the voltage application unit to apply a voltage to the counter electrode, thereby electrodepositing mercury contained in the test solution onto the working electrode, and controls the voltage application unit to measure a current value in an analysis range corresponding to a potential from the electrodeposition potential of mercury to a predetermined sweep voltage by a voltammetry method; The calculation unit performs second-order differentiation of the data of the current value fluctuation spectrum in the analysis range, then performs peak analysis using the maximum value as a baseline, calculates the mercury concentration based on the peak half-width, peak voltage, and peak intensity, and determines whether the mercury concentration exceeds a specified value.

2. 2. The mercury concentration detection device according to claim 1, wherein the working electrode is a gold nanoparticle-boron doped diamond electrode.

3. A mercury concentration detection method using the mercury concentration detection device according to claim 1 or 2, comprising: a stirring step of stirring the test liquid in the liquid tank; a voltage application step of applying a voltage between the counter electrode and the working electrode by sweeping the voltage across an analysis range from the electrodeposition potential of mercury to a predetermined sweep voltage; a differentiation step of performing second-order differentiation of the data of the current value fluctuation spectrum within the analysis range; a mercury concentration calculation step of performing peak analysis using the maximum value of the data obtained in the differentiation step as a baseline, calculating the mercury concentration based on the peak half-width, peak voltage, and peak intensity, and determining whether the mercury concentration exceeds a specified value.

4. 4. The mercury concentration detection method according to claim 3, wherein the voltage applied in the voltage application step is in the range of −0.9 V or more and −0.7 V or less.

5. The mercury concentration detection method according to claim 3 , wherein the voltage of the analysis target range is in the range of 0.5 V or more and 0.8 V or less.

6. The mercury concentration detection method according to claim 3 , wherein the voltage application time in the voltage application step is in the range of 300 seconds or more and less than 700 seconds.

7. 4. The mercury concentration detection method according to claim 3, wherein the calculation unit determines that the mercury concentration exceeds 0.5 ppb when the peak half-width is equal to or greater than 0.2 and less than 0.99, the peak voltage is in the range of 0.56±0.06 V, and the peak intensity is equal to or greater than 0.01 and less than 0.25.

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