JP4874345B2 - Electrochemical measurement method of zinc ion - Google Patents

Description

  The present invention relates to a measurement method capable of performing detection and concentration measurement of zinc ions by an electrochemical method with high accuracy and high sensitivity with a simple operation and apparatus.

  Conventionally, as a high-sensitivity measurement method for heavy metals, an electrochemical measurement method using mercury has been widely used because it is the most sensitive and simple. In particular, for metals such as zinc, which have a low redox potential, due to the relationship between the hydrogen overvoltage and the redox potential of metal ions, measurement is virtually impossible when materials other than mercury are used as the electrode material. is there. However, due to stricter regulations on mercury use, alternative measurement methods are required.

  Recently, ICP (Inductively Coupled Plasma) measurement has been used as a highly sensitive measurement method that does not use mercury, but it has been used in electrochemical measurement methods such as a large apparatus and complicated sample preparation. In comparison, there was a problem in usability.

  For this reason, a method of measuring zinc ions using a boron-doped diamond electrode has been attempted (Patent Document 1).

JP 2001-91499 A

  However, in the method described in Patent Document 1, the detection sensitivity of zinc ions is low, and results sufficient for practical use are not obtained.

  Therefore, the present invention is intended to provide a measurement method capable of performing detection and concentration measurement of zinc ions by an electrochemical method with high accuracy and high sensitivity with a simple operation and apparatus.

  That is, the electrochemical measurement method of zinc ions according to the present invention is a method of electrochemically measuring the concentration of zinc ions in a sample solution, wherein the liquid property adjustment step of adjusting the liquidity of the sample solution to alkaline, Contacting the sample solution with a counter electrode and a boron-doped diamond electrode, changing the potential of the boron-doped diamond electrode in the negative potential direction, and depositing zinc on the surface of the boron-doped diamond electrode; and A potential sweep step of sweeping the potential of the boron-doped diamond electrode in the positive potential direction and detecting a current change with respect to the potential sweep while eluting the zinc deposited on the boron-doped diamond electrode surface into the sample solution; It is characterized by being.

  In the present invention, first, the liquidity of the sample solution is adjusted to be alkaline. In particular, it is preferable to adjust to strong alkalinity of pH 12.5 or more. In the method described in Patent Document 1, the liquidity of the sample solution is adjusted to be acidic, and its detection sensitivity is low and not sufficient. On the other hand, when the liquidity of the sample solution is strongly alkaline as in the present invention, most metals other than zinc are not ionized and cannot be dissolved in the sample solution. Therefore, zinc ions are selectively sampled. It can be dissolved in a solution, and for example, interference effects of other metal ions such as Cu, Cd, and Mn can be reduced and highly accurate measurement can be performed. Further, if the sample solution is strongly alkaline, the potential window is widened to about −1.6 to −1.5 V, and the potential of the boron-doped diamond electrode is set to −1.6 to −1.5 V in the potential sweeping step. Can be swept in the positive potential direction. For this reason, even when measuring zinc ions at the same concentration, it is easier to detect the peak current when detecting zinc ions than in acidic conditions where the potential window is as narrow as about -1.3V. Sensitivity can be increased.

  In order to adjust the sample solution to be alkaline, it is preferable to use sodium hydroxide or potassium hydroxide. The sodium hydroxide and potassium hydroxide are preferably solids such as granules and powders, or are highly concentrated solutions of 0.1 M or more. The reason is that if the concentration is 0.1 M or more, the pH of the high-concentration solution as an alkalizing agent is 12.8 or more, and the pH can be easily adjusted to 12.5 or more.

  The sample solution thus adjusted to be alkaline is measured by bringing the counter electrode and the working electrode into contact with each other. In the present invention, the working electrode has a diamond thin film imparted with conductivity by mixing boron. A boron-doped diamond electrode is used.

  In a state where the counter electrode and the boron-doped diamond electrode are in contact with the sample solution, the potential of the boron-doped diamond electrode is then changed in the negative potential direction so that zinc ions are present in the sample solution on the boron-doped diamond electrode surface. Precipitate dissolved zinc. At this time, the potential of the boron-doped diamond electrode may be varied by a method of sweeping the potential at a constant rate or a method of stepping to a specified potential at regular intervals. It is preferable to hold it. By maintaining the potential of the boron-doped diamond electrode at a constant potential at which zinc is deposited for a while, zinc can be sufficiently deposited on the surface of the boron-doped diamond electrode. And the longer the potential holding time, the lower the concentration of zinc ions can be measured.

  After depositing zinc on the surface of the boron-doped diamond electrode, the potential of the boron-doped diamond electrode is swept in the positive potential direction, and the zinc deposited on the surface of the boron-doped diamond electrode is eluted as zinc ions into the sample solution. In addition, the zinc ion concentration is measured by detecting a current change with respect to the potential sweep.

  The scanning speed of the potential in the potential sweep step of the present invention is preferably 200 mV / s or more. By setting the scanning speed to 200 mV / s or more, the amount of signal at the time of measurement increases, and a lower density can be detected.

  The potential scanning method used in the potential sweeping step is not particularly limited, and any method such as cyclic voltammetry, linear sweep voltammetry, normal voltammetry, and differential pulse voltammetry may be used. Each of these methods can be appropriately selected according to the accuracy of obtaining the zinc ion concentration. For example, when the zinc ion concentration is extremely low, the differential pulse voltammetry is used to accurately detect the zinc ion concentration. be able to.

  In the present invention, it is preferable to apply a constant potential or a potential cycle to the boron-doped diamond electrode before the deposition step or after the potential sweep step. As a result, the boron-doped diamond electrode can be regenerated, the state can be kept constant, and variations in sensitivity from measurement to measurement can be reduced.

  The electrochemical measurement method for zinc ions according to the present invention may be based on a two-electrode method using a boron-doped diamond electrode and a counter electrode. However, when high-sensitivity and high-accuracy measurement is performed, a three-electrode using a reference electrode It is preferable to use the method, and the absolute value of the voltage applied between the boron-doped diamond electrode and the counter electrode may be controlled by further bringing a reference electrode into contact with the sample solution.

  The electrochemical measurement method for zinc ions according to the present invention can be carried out, for example, by a measuring apparatus having the following configuration. That is, an apparatus for electrochemically measuring the concentration of zinc ions in a sample solution, including a liquidity adjusting means for adjusting the liquidity of the sample solution to alkaline, a counter electrode and a boron-doped diamond electrode Cell, means for varying the potential of the boron-doped diamond electrode, means for detecting a current change accompanying the potential fluctuation of the boron-doped diamond electrode, and information for measuring the concentration of zinc ions from the detected current change And a processing device.

  Further, in this measuring apparatus, the cell may further include a reference electrode, and may be provided with means for controlling the absolute value of the potential of the boron-doped diamond electrode.

  As described above, according to the present invention, by detecting zinc ions under alkaline conditions, interference by other metal ions can be prevented, and the potential window is widened to about -1.6 to -1.5V. As a result, the detection of the peak current during the detection of zinc ions is facilitated, and the detection sensitivity of zinc ions can be increased.

The schematic diagram of the electrochemical measuring device which shows one embodiment of the present invention. The voltammogram obtained by performing electrochemical measurement by changing the pH of the sample solution containing zinc ions. The voltammogram obtained by performing electrochemical measurement by changing the pH of the sample solution containing zinc ions in the alkaline region.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Boron dope diamond electrode 2 ... Reference electrode 3 ... Counter electrode 4 ... Sample solution 5 ... Measurement cell 6 ... Stirrer 7 ... Potentiostat 8 ... Information Processing equipment

  Hereinafter, an embodiment of an electrochemical measurement apparatus used in the present invention will be described with reference to the drawings.

  FIG. 1 shows an embodiment of an apparatus for carrying out an electrochemical measurement method for zinc ions according to the present invention, and shows an outline of an electrochemical measurement apparatus 100 using a batch cell for electrochemical measurement. is there.

  The electrochemical measurement apparatus 100 shown in FIG. 1 includes a measurement cell 5 in which three electrodes, that is, a boron-doped diamond electrode 1, a reference electrode 2, and a counter electrode 3, are built. Is connected to the potentiostat 7, and an information processing device 8 is connected to the potentiostat 7. In addition, a stirring bar 6 for stirring the sample solution 4 is inserted into the measurement cell 5.

  In order to measure the concentration of zinc ions using the electrochemical measurement apparatus 100 shown in FIG. 1, a sample solution 4 containing zinc ions is injected into a measurement cell 5, and the boron-doped diamond electrode 1, reference electrode 2, and pair While the electrode 3 is in contact with the sample solution 4, a voltage is applied between the boron-doped diamond electrode 1 and the counter electrode 3 while stirring the sample solution 4 with the stirrer 6 to cause an electrochemical reaction. The current value (electric signal) generated by the electrochemical reaction is transmitted to the potentiostat 7 and the signals at the electrodes 1, 2, and 3 are controlled and detected. The signal detected by the potentiostat 7 is analyzed by the information processing device 8 to detect zinc ions and measure the concentration.

  The material of the measurement cell 5 is not particularly limited as long as the sample solution 4 can be stored therein. For example, the measurement cell 5 is preferably made of a resin such as polytetrafluoroethylene that can suppress the elution of impurities as much as possible.

  The measurement cell 5 is configured such that the sample solution 4 stored therein can come into contact with the boron-doped diamond electrode 1, the reference electrode 2 and the counter electrode 3.

  The boron-doped diamond electrode 1 functions as a working electrode in the electrochemical measuring device 100. The boron-doped diamond electrode 1 in which boron is doped at a high concentration in diamond has an advantageous property that a potential window is wide and a background current is low as compared with other electrode materials. The boron-doped diamond electrode 1 is also excellent in chemical resistance, durability, electrical conductivity, corrosion resistance, and the like.

The addition amount of boron mixed for imparting conductivity to diamond may be appropriately determined within a range where conductivity can be imparted to diamond. For example, conductivity of about 1 × 10 ⁻² to 10 ⁻⁶ Ωcm is given. An amount is preferred.

  Although it is possible to use the boron-doped diamond itself as an electrode regardless of the support of the base material, it is preferable to form a thin film of boron-doped diamond on the base material and connect a conductive wire to the thin film to form an electrode. . The thickness of the boron-doped diamond thin film is not particularly limited, but is preferably about 1 to 100 μm and more preferably about 5 to 50 μm.

  The shape of the boron-doped diamond electrode 1 may be either a rod shape or a planar shape. The electrode surface may be left as-grown, but may be subjected to chemical surface treatment such as hydrogen annealing or electrolytic oxidation, or physical treatment of the surface shape such as flattening by various types of polishing.

The counter electrode 3 compensates for an electrolysis current. For example, an electrode made of platinum, carbon, stainless steel, gold, diamond, SnO ₂ or the like can be used.

  A known electrode can be used as the reference electrode 2, and for example, a silver-silver chloride electrode, a calomel electrode, a standard hydrogen electrode, a hydrogen palladium electrode, or the like can be used.

  In measuring zinc ions, first, only a carrier solution not containing zinc ions to be measured is injected into the measurement cell 5 to minimize and stabilize the so-called background current. Next, a sample solution 4 containing zinc ions is injected into the measurement cell 5. Here, the sample solution 4 is previously adjusted to pH 12.5 or more using sodium hydroxide or potassium hydroxide.

  The sample solution 4 injected into the measurement cell 5 is stirred by the stirring bar 6. When the stirrer 6 stirs the sample solution 4, the efficiency at which zinc is deposited (electrodeposited) on the boron-doped diamond electrode 1 is improved. The stirrer 6 is not particularly limited in the shape and material of the wings and the operation method of the wings. However, it is preferable that the stirrer 6 can sufficiently stir the sample solution 4 and can suppress generation of impurities and fine powders as much as possible.

  While the sample solution 4 is stirred, zinc ions are deposited on the surface of the boron-doped diamond electrode 1 by using the potentiostat 7 to change the potential of the boron-doped diamond electrode 1 in the negative potential direction. At this time, by maintaining the potential of the boron-doped diamond electrode 1 at a constant potential for a while, the zinc can be concentrated and sufficiently precipitated.

  In addition to the function of keeping the potential constant, the potentiostat 7 has a function of scanning the potential at a constant speed and stepping to a specified potential at regular intervals. These functions do not need to be mounted on one unit. For example, the potential holding function and the potential scanning function may be provided in different cases.

  When zinc is deposited on the surface of the boron-doped diamond electrode 1, the stirrer 6 is stopped and the potential of the boron-doped diamond electrode 1 is swept from −1.6 to −1.5 V in the positive potential direction by the potentiostat 7. Then, zinc ions are re-eluted into the sample solution 4.

  When zinc ions are eluted, a current is generated accordingly. The current resulting from zinc ion elution is generated at −1.5 to −1.2 V, and this current (electrical signal) is transmitted to the potentiostat 7, and the signal detected by the potentiostat 7 is the information processing device 8. Is converted to a concentration. When the scanning speed of the potential at the time of the potential sweep is 200 mV / s or more, the signal amount increases, and detection of zinc ions at a lower concentration is possible.

  The information processing apparatus 8 includes a CPU, an internal memory, an external storage device such as an HDD, a communication interface such as a modem, a display, input means such as a mouse and a keyboard, and the like. Then, an electrical signal is analyzed in accordance with a program set in a predetermined area such as the internal memory or the external storage device, and zinc ions are detected and the concentration is calculated. The information processing apparatus 8 may be a general-purpose computer or a dedicated computer.

  After the potential sweep is completed, by keeping the potential of the boron-doped diamond electrode 1 at −1.2 V or more, the precipitated zinc is completely eluted, and the boron-doped diamond electrode 1 is returned to the state before measurement and regenerated. can do. The regeneration of the boron-doped diamond electrode 1 is possible not only by holding a constant potential but also by repeatedly sweeping at a wide potential.

FIG. 2 shows a boron-doped diamond electrode using a platinum wire electrode as the counter electrode 3, a silver-silver chloride electrode as the reference electrode 2, 10 ppm Zn ²⁺ as the sample solution 4, and changing the pH from pH 2.07 to 13.1. The potential of 1 is maintained at -1.4V, and zinc ions are deposited on the surface of the boron-doped diamond electrode 1, and then measured by linear sweep voltammetry, and the obtained voltammogram is shown. As shown in FIG. 2, the peak current at pH 13.1 was remarkably detected.

  FIG. 3 shows a voltammogram obtained by measuring in the same manner as in FIG. 2 except that the pH was changed in the alkaline region from pH 12.5 to 13.1. As shown in FIG. 3, it was confirmed that pH 12.5 was the detection limit of the peak current.

  In addition, this invention is not restricted to the said embodiment, For example, you may use the electrochemical measurement apparatus 100 of the stopped flow type | mold other than what is a batch type cell.

  In addition, the electrochemical measurement apparatus 100 performs measurement by the three-electrode method including the boron-doped diamond electrode 1, the reference electrode 2, and the counter electrode 3, but the electrochemical for performing the measurement method according to the present invention. The measuring apparatus 100 may be a two-electrode method including only the boron-doped diamond electrode 1 and the counter electrode 3. In the three-electrode method, the absolute value of the voltage applied between the boron-doped diamond electrode 1 and the counter electrode 3 can be controlled, so that measurement with higher accuracy and sensitivity can be performed. According to the electrode method, two electrodes, that is, a boron-doped diamond electrode 1 and a counter electrode 3 are used. Therefore, the structure of the measurement cell 5 can be simplified and reduced in size, and the measurement cell 5 is made into a chip and made disposable. It is also possible to perform simpler measurement.

  The liquidity adjustment of the sample solution 4 may not be performed in advance before the sample solution 4 is injected into the measurement cell 5, and the liquidity adjustment of the sample solution 4 may be performed in the measurement cell 5. In addition, the electrochemical measurement apparatus 100 may further include a mixing tank for mixing with the alkaline reagent before injecting the sample solution 4 into the measurement cell 5.

  When the boron-doped diamond electrode 1 is regenerated, the regeneration efficiency can be improved by making the solution liquid neutral or acidic.

  According to the present invention, detection and concentration measurement of zinc ions can be performed quickly and accurately with an inexpensive apparatus.

Claims (11)

A method for electrochemically measuring the concentration of zinc ions in a sample solution,
A liquidity adjusting step for adjusting the liquidity of the sample solution to be alkaline;
Contacting the sample solution with a counter electrode and a boron-doped diamond electrode;
Varying the potential of the boron-doped diamond electrode in the negative potential direction, a deposition step of depositing zinc on the boron-doped diamond electrode surface, and
A potential sweep step of sweeping the potential of the boron-doped diamond electrode in the positive potential direction and detecting a current change with respect to the potential sweep while eluting the zinc deposited on the boron-doped diamond electrode surface into the sample solution A method for electrochemically measuring zinc ions.   The method for electrochemical measurement of zinc ions according to claim 1, wherein the alkalinity is pH 12.5 or more.   3. The method for electrochemical measurement of zinc ions according to claim 1, wherein in the potential sweeping step, the potential of the boron-doped diamond electrode is swept in a positive potential direction from −1.6 to −1.5 V. 4.   The method for electrochemical measurement of zinc ions according to claim 1, 2 or 3, wherein sodium hydroxide or potassium hydroxide is used in the liquid property adjusting step.   The method for electrochemical measurement of zinc ions according to claim 4, wherein the sodium hydroxide and potassium hydroxide are solutions of 0.1M or more. The method for electrochemical measurement of zinc ions according to claim 1, 2, 3, 4, or 5, wherein cyclic voltammetry, linear sweep voltammetry, normal voltammetry, or differential pulse voltammetry is used in the potential sweep step.   The method for electrochemical measurement of zinc ions according to claim 1, wherein the boron-doped diamond electrode is maintained at a constant potential in the precipitation step.   The method for electrochemical measurement of zinc ions according to claim 7, wherein the constant potential is a potential at which zinc is deposited on the surface of the boron-doped diamond electrode. A step of applying a constant potential or a potential cycle to the boron-doped diamond electrode before the deposition step or after the potential sweep step is provided. The electrochemical measuring method of the zinc ion of description.   The method for electrochemical measurement of zinc ions according to claim 1, wherein a scanning speed of the potential is 200 mV / s or more in the potential sweeping step. An apparatus for electrochemically measuring the concentration of zinc ions in a sample solution,
Liquidity adjusting means for adjusting the liquidity of the sample solution to alkaline,
A cell containing a counter electrode and a boron-doped diamond electrode;
Means for varying the potential of the boron-doped diamond electrode;
Means for detecting a current change accompanying a change in potential of the boron-doped diamond electrode;
An apparatus for electrochemical measurement of zinc ions, comprising: an information processing device for measuring the concentration of zinc ions from the detected current change.

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