JP2012112736A - Electrode body and measuring apparatus using the electrode body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode body which can prevent failure of disabling measurement by being conducted between respective electrodes by, for example, a solid substance such as silver chloride even when the end point of titration is detected by a method for measuring the potential difference only by a pair of electrodes.SOLUTION: The electrode body 15 for detecting the end point of the titration by the method for measuring the potential difference only by the pair of the electrodes without using a reference electrode includes: the pair of the electrodes 153; and a body 151 on which the pair of the electrodes 153 is mounted. The thickness dimension of the electrodes 153 is set to be smaller than the diameter dimension of the electrodes 153.

Description

  The present invention relates to an electrode body for detecting the end point of titration by a method of measuring a potential difference using only a pair of electrodes without using a reference electrode, and a measuring apparatus using the electrode.

For example, when measuring COD (chemical oxygen demand) which is one of the indicators of water pollution, an oxidizable substance such as an organic compound contained in a sample solution is oxidized with potassium permanganate (KMnO ₄ ), Excess sodium oxalate (Na ₂ C ₂ O ₄ ) is added to stop the oxidation, and then back titration with potassium permanganate is performed again. In this way, the amount of potassium permanganate required to oxidize the oxidizable substance in the sample solution is measured, and the COD value is determined from the amount.

  In order to detect the end point of titration related to such oxidation-reduction reaction, a conventional COD automatic measuring apparatus as disclosed in Patent Document 1 uses a reference electrode having a liquid junction as a liquid junction, such as ceramic, and oxidation-reduction. A potential measurement electrode is immersed in a sample solution, and the end point of titration is detected by utilizing the fact that the oxidation-reduction potential changes greatly in the vicinity of the equivalence point by each electrode.

  By the way, the river water, which is the COD measurement target, and industrial wastewater contain dust and the like, so that the liquid junction of the reference electrode is clogged, and as a result, the redox potential cannot be measured well. Sometimes. In order to avoid such problems, the end point of titration is detected not by measuring the redox potential using the reference electrode but by the constant current polarization potential difference method using a twin platinum electrode having no liquid junction. It is possible.

  The constant current polarization potential difference method will be briefly described. As shown in FIG. 6, the apparatus configuration includes a test tube body 151A made of glass, and projects from the tip of the body 151A. A biplatinum electrode 15A having a pair of platinum electrodes 153A formed in a rod shape having a large thickness dimension is immersed in a sample solution so that a constant current flows between the platinum electrodes 153A at a predetermined current value. Configured. When configured in this way, when titration is performed with potassium permanganate when sodium oxalate is present in the sample solution, it is a charge bearer as sodium oxalate and potassium permanganate approach the equivalent. The amount of oxalate ions present in the sample solution is reduced by the oxidation-reduction reaction. Accordingly, as the equivalence point is approached, the charge bearer is reduced from the sample liquid, so that it is difficult for the current to flow. And since it is comprised so that a constant current may flow between each platinum electrode, the electrical potential difference between electrodes becomes large. Using this fact, it is possible to detect the titration point at which the potential difference finally takes an extreme value as the end point.

  However, even if the above-described biplatinum electrode is used, the end point of titration may not be detected well depending on the properties of the solid substance contained in the sample solution. For example, in COD measurement, in order to prevent chlorine in a sample solution from affecting the measurement, silver nitrate is added to the sample solution to convert chlorine ions into solid silver chloride. Immediately after the addition of silver nitrate, the silver chloride is fluffy and drifts in the sample solution. At this time, since stirring is performed so that silver nitrate spreads uniformly throughout the sample solution, the white cotton-like silver chloride may be caught by the twin platinum electrode immersed in the flow in the sample solution. Then, in the conventional biplatinum electrode as described above, silver chloride containing moisture may be entangled so as to bridge between a pair of rod-shaped platinum electrodes, and the polarization between each electrode is caused by conduction between the platinum electrodes. It may not occur and the potential difference cannot be measured.

JP 05-322830 A

  The present invention has been made in view of the above-described problems, and even when the end point of titration is performed by a method of measuring a potential difference with only a pair of electrodes without using a reference electrode in COD measurement or the like, for example, An object of the present invention is to provide an electrode body capable of preventing a problem in which measurement cannot be performed due to conduction between electrodes due to a solid substance such as silver chloride.

  That is, the electrode body of the present invention is an electrode body for detecting the end point of titration by a method of measuring a potential difference with only a pair of electrodes without using a reference electrode, and the pair of electrodes and the pair of electrodes are And a thickness dimension of the electrode set to be smaller than a diameter dimension of the electrode. Here, the reference electrode is an electrode used for providing a reference point of potential in measuring the electrode potential. For example, the reference electrode and the reference electrode and the reference electrode are broken.

  Here, the thickness dimension of the electrode is, for example, a dimension in a direction perpendicular to the surface of the body to which the electrode is attached or an imaginary plane including an outer edge that the electrode intersects with the body. The diameter dimension is a dimension in a direction along the surface with respect to a virtual surface including a surface of the body to which the electrode is attached or an outer edge that the electrode intersects with the body.

  If this is the case, since the amount of the electrode protruding from the body is small, even if a solid substance such as silver chloride is drifting in the sample solution that is immersed, It is possible to prevent conduction between the electrodes due to silver chloride or the like. Therefore, it is possible to prevent a situation in which the end point of titration cannot be measured even in COD measurement.

  As a specific mode for preventing conduction between the pair of electrodes, a pair of attachment holes may be formed in the body, and each electrode may be attached to the inside of each attachment hole.

  In order to accommodate and protect signal lines and the like in the body while reducing the amount of metal used for the electrodes, the body is formed in a tubular shape, and the mounting hole penetrates the wall surface of the body It is sufficient that the electrode has substantially the same shape as the attachment hole and is attached so as to close the attachment hole.

  In order to make solid matter such as silver chloride more difficult to adhere to the electrode, the electrode is a flat plate and is attached so as to close the inner side of the mounting hole formed in the body. Good.

  As a specific embodiment for preventing conduction between the pair of electrodes due to silver chloride or the like, there is a cut surface of the body between the electrodes in a cross section cut through the pair of electrodes. What should I do?

  In order to more easily prevent conduction between the pair of electrodes and the solid substance, the pair of electrodes may be attached so as to face each other with the body interposed therebetween. In such a case, since the pair of electrodes are separated from each other, even if a solid substance adheres to one of the electrodes, it is unlikely to adhere to the other electrode.

  In order to be able to detect whether the sample liquid is in the sample container without using an additional sensor when performing automatic measurement of COD, an AC voltage is applied between the electrode body and the pair of electrodes. In this case, the measurement apparatus may include a sample liquid detection unit that detects the presence or absence of the sample liquid that contacts the electrode body based on the conductivity between the pair of electrodes.

  As described above, according to the electrode body of the present invention, even if a solid material such as silver chloride drifts in the sample solution in which the electrode body is immersed, the electrode body adheres to bridge the pair of electrodes. It becomes possible to prevent the constant current polarization potential difference method from being disabled.

The schematic diagram which shows the COD automatic measuring apparatus which concerns on one Embodiment of this invention. The typical expanded longitudinal cross-sectional view of the twin platinum electrode in the embodiment. The typical expanded cross-sectional view of the twin platinum electrode in the embodiment. The typical expanded sectional view of the twin platinum electrode concerning another embodiment of the present invention. The schematic diagram of the biplatinum electrode which concerns on another embodiment of this invention. The schematic diagram which shows the conventional twin platinum electrode.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  The biplatinum electrode 15 that is the electrode body of the present embodiment and the measuring device 100 using the biplatinum electrode 15 are used for measuring COD (chemical oxygen demand), which is one of water quality indicators. More specifically, the measuring apparatus 100 of the present embodiment is a COD automatic measuring apparatus 100 based on a standard defined in JIS, and oxidizes substances such as organic substances in a sample solution in a reaction tank 101 described later. It is oxidized by heating with potassium permanganate, and the amount of potassium permanganate required to oxidize the substance to be oxidized is measured by back titration to calculate the COD value.

  The COD automatic measuring apparatus 100 includes at least a reaction vessel 101 and a control device 104 that performs various controls related to automatic measurement of COD such as introduction and discharge of a sample solution and a reagent solution into the reaction vessel. is there.

  First, each part of the reaction vessel 101 will be described.

  As shown in FIG. 1, the reaction vessel 101 includes a heat transfer body 12 into which a sample container 11 that stores a sample solution is inserted, and a heater 13 that heats the heat transfer body 12.

  The sample container 11 is a glass container having a cone shape on the bottom surface side and a cylindrical shape on the upper surface side. Inserted. In the sample container 11, the sample is only present on the bottom-side portion that has a cone shape (substantially inverted conical shape), that is, the portion whose cross-sectional area increases from the bottom surface side to the top surface side. The liquid is stored so that a certain level of liquid can be obtained even if the amount of the sample liquid is small. By doing in this way, even if there is little sample liquid, the said measurement electrode 15 and the stirring blade 16 can be immersed in a sample liquid. Further, since the cross-sectional area is maximized at the opening on the upper surface, it is possible to prevent the devices from interfering with each other even when the various devices described above are inserted, and to be easily inserted into the sample container 11. .

  Among the various reagent solution introduction tubes 24 and 25, the tip of the titration reagent solution introduction tube 25 that introduces a minute amount of potassium permanganate into the sample solution in the back titration step is stored in the sample solution. It is provided so that it may be located below the liquid level. The tip of the other reagent solution introduction tube 24 is provided so as to be positioned above the liquid level of the sample solution.

  The measurement electrode 15 is a so-called biplatinum electrode 15 and corresponds to the electrode body in the claims. The biplatinum electrode 15 includes a glass body 151, two platinum electrodes 153 attached to the body 151, and a temperature sensor 154 provided at the tip of the body 151. The biplatinum electrode 15 is used to detect the end point of back titration with potassium permanganate, which will be described later, by the constant current polarization potential difference method.

  More specifically, as shown in the longitudinal sectional view of FIG. 2, the body 151 has a substantially straight tube shape, and accommodates signal wires attached to the platinum electrode 153 and the temperature sensor 154 therein. It is configured. A pair of attachment holes 152 to which the platinum electrode 153 is attached are formed at a predetermined height from the tip of the body 151 on the side peripheral surface of the body 151, and the pair of attachment holes 152 are respectively The body 151 is provided so as to face each other.

  The mounting hole 152 is formed as a hole having a substantially cylindrical bottom extending inwardly perpendicular to the side surface of the body 151. A small hole is formed in the bottom of the mounting hole 152 so as to penetrate into the center, and the small hole is connected to the platinum electrode 153 through a signal line.

  The platinum electrode 153 has a substantially disk shape, and is a film electrode whose thickness is smaller than the radial dimension. Each platinum electrode 153 is fitted in the mounting hole 152 without a gap, and is accommodated in the mounting hole 152 so as to contact the inner peripheral surface and the bottom of the mounting hole 152. Therefore, as shown in the cross-sectional view taken along line AA in FIG. 3, the cross section of the body 151 appears between the platinum electrodes 153 in the cross section cut through the pair of electrodes 153. become. In addition, constant current control is performed between the pair of platinum electrodes 153 so that a constant current flows through the sample solution by an end point detector described later.

  The temperature sensor 154 is provided in a storage chamber formed of an adhesive at the front end of the body 151, and is used for controlling the temperature of the sample solution by the heater 13 or emptying the sample container 11 without any sample solution. It is used to prevent

  The stirring blade 16 is made of glass, and is used to make the concentration uniform by stirring the sample solution in the sample container 11 or to prevent silver chloride from precipitating and solidifying.

As shown in FIG. 1, one end of the liquid discharge pipe 18 is disposed in the vicinity of the bottom of the sample container 11. When the COD measurement is finished, the sample liquid that is no longer needed is moved out of the sample container 11. Used to discharge.
As will be described later, in order to prevent silver chloride generated when a silver nitrate aqueous solution is added to the sample solution as a pretreatment for measurement to solidify inside the sample container 11, bubbling with minute bubbles is performed from the vicinity of the bottom. A pipe (not shown) is also inserted into the sample container 11.

  As shown in FIG. 1, the heat transfer body 12 into which the sample container 11 is inserted has a substantially cylindrical outer shape formed by an aluminum thin plate, and has a substantially M-shaped cross section. More specifically, a sheet-like heater 13 is provided so as to cover the outer peripheral surface 123 of the heat transfer body 12, the sample container 11 is inserted on the upper surface side of the heat transfer body 12, and the sample container 11 is formed, and a recess 122 is formed on the bottom surface side of the heat transfer body 12.

  Next, the control device 104 will be described. The control device 104 is a so-called computer including a CPU, a memory, an input / output interface, an A / D, a D / A converter, and the like. The control device 104 controls the movement of various liquids via a pressure supply mechanism (not shown), or controls the voltage applied to the biplatinum electrode 15 to measure the sample liquid, thereby the sample container 11. A sample solution introduction step for introducing into the sample solution, a pretreatment step for removing chlorine from the sample solution, an oxidation step for introducing potassium permanganate into the sample solution and oxidizing the oxide in the sample solution, excess sodium oxalate Is introduced into the sample solution to stop the oxidation, an oxidation stop process to stop oxidation, a quantitative process to measure the amount of potassium permanganate required for oxidation by reverse titration, and a post-treatment to discharge the liquid in the sample container after calculating the COD value It is comprised so that a process may be performed in this order.

  When attention is paid to the functions of the control device 104 in the quantitative process and the post-processing process, the control device is configured to exhibit at least the functions of the end point detection unit 41 and the sample liquid detection unit 42.

  The end point detection unit 41 is configured to sequentially change and apply a voltage so that a constant current continues to flow between the platinum electrodes 153 in the determination step. The end point detection unit 41 is configured to detect the titration point at which the applied voltage is maximized as the end point at which sodium oxalate and potassium permanganate are equivalent. When the end point of the titration is detected by the end point detection unit 41, the amount of potassium permanganate necessary to oxidize the sample solution is calculated from the amount of potassium permanganate added by titration, and COD Used for value calculation.

  For example, in the post-processing step, the sample liquid detection unit 42 determines whether or not the liquid level of the sample liquid has decreased in the sample container 11 from at least the height at which the platinum electrode 153 of the biplatinum electrode 15 is provided. It is something to detect. More specifically, in the post-processing step in which the sample solution is discharged from the sample container 11, the sample solution detection unit 42 applies an alternating voltage between the platinum electrodes 153, and the conductivity (electric conduction) at that time is applied. Degree). By applying an alternating current between the platinum electrodes 153 in this way, polarization can be prevented from occurring on the surface of the platinum electrode 153 when it is in the sample solution, and the current value can be measured. In addition, as a specific configuration for detecting the presence or absence of the sample solution, for example, the reference conductivity in river water or factory wastewater used as the sample solution is measured in advance, and the measured conductivity and the reference conductivity are measured. The sample liquid detection unit 42 is configured to make a determination by comparing the two. In this way, by using the biplatinum electrode 15, whether the biplatinum electrode 15 is immersed in the sample liquid, that is, whether the sample liquid is discharged from the sample container 11 and the liquid level starts to decrease. It can be detected without using a photo sensor or another electrode for detection. Therefore, for example, an abnormality such that silver chloride is clogged in the liquid discharge pipe 18 and the drainage cannot be started can be detected without an additional sensor, and an extra sensor needs to be inserted into the sample container 11. Therefore, the sample container 11 can be downsized.

  According to the COD automatic measuring apparatus 100 and the biplatinum electrode 15 configured as described above, the film-like platinum electrode 153 is provided in the mounting hole 152 of the body 151, and the platinum electrode 153 is outward from the body 151. Therefore, silver chloride is not easily caught on the platinum electrode 153 and is difficult to adhere. Therefore, even when a large amount of silver chloride is present in the sample solution, it is possible to prevent a situation in which silver chloride adheres so as to bridge between the platinum electrodes 153 and becomes conductive. That is, since the end point of titration can be detected by the constant current polarization potential difference method without being affected by silver chloride, COD measurement can be performed without any problem even for a sample solution having a high chlorine concentration.

  Other embodiments will be described.

  In the embodiment, the biplatinum electrode 153 that is an electrode body is used to detect the end point of titration by the constant current polarization potential difference method, but other electrode bodies may be used. For example, the pair of electrodes 153 are the platinum electrodes 153, but may be electrodes formed of other metals such as gold, silver, and iron. Further, the shape of the pair of electrodes 153 is not limited to the above embodiment. For example, as shown in the enlarged view of FIG. 4A, a part of the electrode may protrude slightly from the mounting hole 152. Further, as shown in FIG. 4B, the electrode 151 may be formed on the surface of the body 151 without forming the mounting hole 152. In short, it is sufficient that the thickness dimension is smaller than the diameter dimension and the thickness dimension is such that silver chloride does not easily adhere. Furthermore, the pair of electrodes 153 may be provided not only so as to face each other with the body 151 interposed therebetween, but also, for example, arranged side by side at a predetermined distance apart. In addition, the body 151 may be tubular, and a plurality of ring-shaped electrodes 153 may be arranged in the axial direction and attached at predetermined intervals. For example, as shown in the side view of FIG. 5A and the longitudinal cross-sectional view of FIG. 5B, the shape of the mounting hole 152 formed in the body 151 is formed in a substantially thin cylindrical shape, Ring-shaped electrodes 153 and ring-shaped insulators 155 are alternately stacked and attached in the space of the hole 152. More specifically, the electrode 153 is paired with two outer poles 153 (a) on the outside in the vertical direction in the drawing and an inner pole 153 (b) in the center, and these outer poles 153 are paired. An insulator 155 is provided between each of (a) and the inner electrode 153 (b), and the end point of the titration can be known from the potential difference between the outer electrode 153 (a) and the inner electrode 153 (b). it can. Even in such a case, since it is configured such that it hardly protrudes from the electrode 153 from the inside 155 of the mounting hole, an effect that silver chloride or the like hardly adheres can be obtained.

  In the embodiment, the body is formed in a tubular shape, but may be a solid body, for example.

  In addition, various modifications and combinations of embodiments may be performed without departing from the spirit of the present invention.

100: COD automatic measuring device 15: Biplatinum electrode (electrode body)
151 ... Body 152 ... Mounting hole 153 ... Platinum electrode (electrode)
42 ・ ・ ・ Sample liquid detector

Claims (7)

An electrode body for detecting the end point of titration by a method of measuring a potential difference with only a pair of electrodes without using a reference electrode,
The pair of electrodes;
A body to which the pair of electrodes are attached,
An electrode body, wherein a thickness dimension of the electrode is set smaller than a diameter dimension of the electrode.   The electrode body according to claim 1, wherein a pair of attachment holes are formed in the body, and each electrode is attached inside each attachment hole. The body is formed in a tubular shape, and the attachment hole is formed to penetrate the wall surface of the body,
The electrode body according to claim 2, wherein the electrode has substantially the same shape as the attachment hole and is attached so as to close the attachment hole.   The electrode body according to claim 2 or 3, wherein the electrode has a flat plate shape and is attached so as to close an inner side of an attachment hole formed in the body.   5. The electrode body according to claim 1, wherein the body has a cut surface between the electrodes in a cross section cut through the pair of electrodes.   The electrode body according to claim 1, wherein the pair of electrodes are attached to face each other with the body interposed therebetween. An AC voltage is applied between the electrode body according to any one of claims 1 to 6 and the pair of electrodes, and the presence or absence of a sample solution in contact with the electrode body is determined based on conductivity between the pair of electrodes at that time. A sample liquid detection unit for detecting.