JP2007263632A - Method and kit for measuring chelating agent - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To simply know the concentration of a water treatment agent on the spot where a heat device is installed. <P>SOLUTION: A method includes a step of collecting sample water, a step of respectively adding a first chemical solution containing a metal indicator and a second chemical solution containing a pH controller to the collected sample water, a step of dripping a third chemical solution, which contains a metal salt for discoloring the metal indicator, on the sample water to which the first chemical solution and the second chemical solution are added and counting a dripping number until the sample water is discolored and a step of specifying the concentration of the chelating agent in the sample water on the basis of the dripping number of the third chemical solution. The measuring kit includes a first container in which the first chemical solution containing the metal indicator is housed, a second container in which the second chemical solution containing the pH controller is housed and a third container in which the third solution containing the metal salt for discoloring the metal indicator. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for measuring a chelating agent and a kit for measuring a chelating agent, and more particularly to a measuring method and a measuring kit for easily quantifying a chelating agent contained in water to which a water treatment agent is added.

  In thermal equipment such as boilers and cooling towers, a water treatment agent is generally added to makeup water in order to suppress corrosion of heat transfer surfaces and scale generation due to moisture. In recent years, as disclosed in Patent Document 1, a water treatment agent comprising a food additive and containing silica, an alkali agent and a scale inhibitor is used in the boiler. Here, the silica is blended for the purpose of forming a film on the heat transfer surface and protecting it from corrosion due to moisture. The alkali agent is typically an alkali metal hydroxide, and is blended for the purpose of adjusting moisture to a pH range (pH 11 to 12) in which the heat transfer surface is hardly corroded. Further, the scale inhibitor is a chelating agent capable of forming a complex with hardness components (calcium ions and magnesium ions), copper ions, zinc ions, iron ions, and the like, which are scale promoting components in the makeup water, and the heat transfer surface. It is formulated for the purpose of suppressing the scale formation on the contact surface of water.

  The supply amount of the water treatment agent is such that the concentration of the water treatment agent in the thermal device is within a predetermined range based on the quality of makeup water, the operating conditions of the thermal device (for example, the concentration ratio in the boiler), and the like. Set to In order to maximize the effect of the water treatment agent, it is important that the concentration of the water treatment agent is maintained within a predetermined range. When the concentration of the water treatment agent is insufficient or excessive Therefore, it is necessary to promptly readjust the supply amount of the water treatment agent. For this reason, it is essential for maintenance managers and users to know the water treatment agent concentration regularly at the site where the thermal equipment is installed.

Japanese Patent Laid-Open No. 2003-159597

  By the way, in order to know the concentration of the water treatment agent, if it is attempted to quantify all the components supplied as the water treatment agent individually, a great amount of labor and labor are required. In addition, when trying to quantify a specific component supplied as the water treatment agent, for example, in the case of the water treatment agent disclosed in Patent Document 1, silica forms a film on the heat transfer surface, so There is a problem that the calculated density does not match the actual density. Furthermore, since alkali metal hydroxide is also generated when an alkali component such as sodium hydrogen carbonate in the make-up water is thermally decomposed, the concentration calculated from the supply amount and the actual concentration are particularly high in the boiler. There is a problem that they do not match. For these reasons, the actual situation is that the concentration of the water treatment agent cannot be easily known at the site where the thermal equipment is installed.

  The present invention has been made in view of the above circumstances, and the problem to be solved is to easily know the concentration of the water treatment agent at the site where the thermal equipment is installed.

This invention was made in order to solve the said subject, and the invention of Claim 1 is the measuring method of the chelating agent which quantifies the density | concentration of the chelating agent in sample water, Comprising: The process of extract | collecting sample water Adding the first chemical solution containing the metal indicator and the second chemical solution containing the pH adjuster to the collected sample water, and the sample water to which the first chemical solution and the second chemical solution are added. A step of dropping a third chemical solution containing a metal salt that changes the color of the metal indicator, counting the number of drops until the sample water changes color, and the concentration of the chelating agent in the sample water based on the number of drops of the third chemical solution And a step of identifying the feature.

  According to invention of Claim 1, when said 3rd chemical | medical solution is dripped at the sample water to which said 1st chemical | medical solution and said 2nd chemical | medical solution were added, the said chelating agent will be a specific metal ion from the said metal salt. And preferentially form a complex. When the total amount of the chelating agent forms a complex with the specific metal ion, the metal indicator forms a complex with an excess of the specific metal ion, and the sample water changes color. Since the supply amount of the specific metal ion until the sample water is discolored corresponds to the abundance of the chelating agent, the concentration of the chelating agent is specified based on the number of drops of the third chemical solution. Therefore, if this measuring method is used, the concentration of the water treatment agent in the thermal apparatus can be easily known using the chelating agent contained in the water treatment agent as an index.

  According to a second aspect of the present invention, in the first aspect, the chelating agent is ethylenediaminetetraacetic acid and a salt thereof, and the metal indicator, the pH adjuster, and the metal salt are xylenol orange, nitric acid, and bismuth nitrate, respectively. It is characterized by that.

  According to invention of Claim 2, when said 3rd chemical | medical solution is dripped at the sample water to which said 1st chemical | medical solution and said 2nd chemical | medical solution were added, ethylenediaminetetraacetic acid (EDTA) is bismuth from bismuth nitrate. Preferentially forms complexes with ions. When the total amount of EDTA forms a complex with bismuth ions, xylenol orange forms a complex with excess bismuth ions, and the sample water changes color. Since the supply amount of bismuth ions until the sample water changes color corresponds to the amount of EDTA present, the concentration of EDTA is specified based on the number of drops of the third chemical solution. Therefore, if this measurement method is used, it is possible to easily know the concentration of the water treatment agent in the thermal apparatus using EDTA contained in the water treatment agent as an index.

  The invention described in claim 3 is characterized in that in claim 1 or claim 2, it further includes a step of adding a masking agent to the collected sample water.

  The invention described in claim 4 is characterized in that, in claim 3, the masking agent is o-phenanthroline.

  According to invention of Claim 3 and Claim 4, when the said 3rd chemical | medical solution is dripped in presence of the said masking agent, for example, o-phenanthroline, the ferrous ion complexed with the said chelating agent And copper ions preferentially form a complex with the masking agent. For this reason, the total amount of the chelating agent rapidly forms a complex with the specific metal ion, and the reaction time until the sample water changes color is shortened. Therefore, if this measuring method is used, the concentration of the water treatment agent in the thermal equipment can be quickly and accurately known using the chelating agent contained in the water treatment agent, for example, EDTA as an index.

  The invention described in claim 5 is characterized in that, in claim 3 or 4, the method further comprises the step of adding a reducing agent to the collected sample water.

  The invention described in claim 6 is characterized in that, in claim 5, the reducing agent is ascorbic acid and an alkali metal salt thereof.

According to invention of Claim 5 and Claim 6, when the said reducing agent, for example, ascorbic acid and its alkali metal salt, are added, the ferric ion in sample water will be reduce | restored to a ferrous ion. And this ferrous ion is sealed by the said masking agent. For this reason, it is prevented that the said metal indicator, for example, xylenol orange forms a color with a ferric ion, and the normal hue of sample water is ensured. Therefore, if this measuring method is used, the concentration of the water treatment agent in the thermal equipment can be known more accurately using the chelating agent contained in the water treatment agent, for example, EDTA as an index.

  The invention according to claim 7 is a chelating agent measurement kit for quantifying the concentration of the chelating agent in the sample water, comprising a first container containing a first chemical solution containing a metal indicator, and a pH adjusting agent. And a third container containing a third chemical containing a metal salt that changes the color of the metal indicator.

  According to invention of Claim 7, while adding said 1st chemical | medical solution from said 1st container with respect to sample water, after adding said 2nd chemical | medical solution from said 2nd container, said 3rd container from said 3rd container When the third chemical solution is dropped, the chelating agent preferentially forms a complex with the specific metal ion from the metal salt. When the total amount of the chelating agent forms a complex with the specific metal ion, the metal indicator forms a complex with an excess of the specific metal ion, and the sample water changes color. Since the supply amount of the specific metal ion until the sample water is discolored corresponds to the abundance of the chelating agent, the concentration of the chelating agent is specified based on the number of drops of the third chemical solution. Therefore, if this measurement kit is used, the concentration of the water treatment agent in the thermal apparatus can be easily known using the chelating agent contained in the water treatment agent as an index.

  The invention according to claim 8 is characterized in that, in claim 7, the first chemical solution or the second chemical solution further contains a masking agent.

  According to the invention described in claim 8, when the masking agent is added to the sample water by the first chemical solution or the second chemical solution, and then the third chemical solution is dropped, the complexing agent and the chelating agent are complexed. The ferrous ions and copper ions that have been formed preferentially form a complex with the masking agent. For this reason, the total amount of the chelating agent rapidly forms a complex with the specific metal ion, and the reaction time until the sample water changes color is shortened. Therefore, if this measurement kit is used, the concentration of the water treatment agent in the thermal apparatus can be quickly and accurately known using the chelating agent contained in the water treatment agent as an index.

  The invention according to claim 9 is characterized in that, in claim 8, the first chemical liquid further contains a reducing agent.

  According to invention of Claim 9, when the said reducing agent is added by said 1st chemical | medical solution, the ferric ion in sample water will be reduce | restored to a ferrous ion. And this ferrous ion is sealed by the said masking agent. For this reason, it is prevented that the said metal indicator forms a complex with a ferric ion, and color development is prevented, and the normal hue of sample water is ensured. Therefore, if this measurement kit is used, the concentration of the water treatment agent in the thermal apparatus can be more accurately known using the chelating agent contained in the water treatment agent as an index.

  Furthermore, the invention described in claim 10 is characterized in that in claim 8, a fourth container in which a powdery reducing agent is accommodated is provided.

  According to the invention described in claim 10, when the powdery reducing agent is added from the fourth container, ferric ions in the sample water are reduced to ferrous ions. And this ferrous ion is sealed by the said masking agent. For this reason, it is prevented that the said metal indicator forms a complex with a ferric ion, and color development is prevented, and the normal hue change of sample water is ensured. Therefore, if this measurement kit is used, the concentration of the water treatment agent in the thermal apparatus can be more accurately known using the chelating agent contained in the water treatment agent as an index.

  According to the present invention, the concentration of the water treatment agent can be easily known at the site where the thermal equipment is installed. As a result, it is possible to determine on site whether or not the amount of water treatment agent supplied to the thermal equipment is appropriate, and the maintenance management related to water treatment can be made more efficient.

  Hereinafter, embodiments of the present invention will be described in detail. The chelating agent measurement method and measurement kit according to the present invention are used to manage the supply amount of a water treatment agent to a thermal apparatus such as a boiler or a cooling tower. Specifically, the concentration of the water treatment agent in the thermal equipment is specified using the chelating agent blended in the water treatment agent as a tracer, and the supply amount of the water treatment agent is determined based on the concentration of the water treatment agent. Used to determine suitability.

  In the water treatment agent, the chelating agent seals hardness components (calcium ions and magnesium ions), copper ions, zinc ions, iron ions, and the like, which are scale promoting components in water, on the heat transfer surface of the thermal device. Formulated to suppress scale formation. As such a chelating agent, for example, organic aminocarboxylic acid compounds and tricarboxylic acid compounds, and inorganic polymerized phosphoric acid compounds are used.

  Specific examples of the aminocarboxylic acid compounds include ethylenediaminetetraacetic acid (EDTA) and salts thereof; nitrilotriacetic acid (NTA) and salts thereof; hydroxyethylethylenediaminetriacetic acid (HEDTA) and salts thereof; trans-1,2- Examples include diaminocyclohexanetetraacetic acid (CyDTA) and salts thereof. Specific examples of the tricarboxylic acid compound include citric acid and its salts. Furthermore, specific examples of the polymerized phosphoric acid compound include hydroxyethylidene diphosphonic acid (HEDP) and salts thereof. Among these compounds, alkali metal salts of EDTA are suitably used because they are compounds that do not promote scale formation on the heat transfer surface. Furthermore, among the alkali metal salts of ethylenediaminetetraacetic acid, disodium ethylenediaminetetraacetic acid is a particularly suitable compound because it is a safe compound that can be used as a food additive.

  Now, the said measurement kit is used in order to quantify the density | concentration of the said chelating agent, for example, EDTA, in sample water by the titration method. The measurement kit contains a first container containing a first chemical containing a metal indicator, a second container containing a second chemical containing a pH adjuster, and a metal salt that changes the color of the metal indicator. And a third container in which the third chemical liquid is stored.

  Said 1st container, said 2nd container, and said 3rd container are containers comprised so that a chemical | medical solution could be dripped at sample water while accommodating a chemical | medical solution, for example, the nozzle was mounted | worn with the resin bottle A dripping bottle with a nozzle can be used. This dripping bottle with a nozzle is of a type in which a predetermined amount of chemical solution is dripped by pressing the body of the bottle during use. The first container, the second container, and the third container may be a dropper bottle with a dropper in which a dropper is attached to a bottle cap. The dropping bottle with a dropper is of a type in which a chemical solution in the bottle is sucked up by the dropper when used, and then a predetermined amount of the chemical solution is dropped. Furthermore, the first container, the second container, and the third container may be a container with a dropper in which a dropper is attached separately from the bottle. The container with a dropper is of a type in which a chemical solution in the bottle is sucked up by the dropper and a predetermined amount of the chemical solution is dropped during use.

The bottle is formed of a material that does not elute impurities (for example, polyethylene or glass) from the viewpoint of not contaminating or deteriorating the first chemical solution, the second chemical solution, and the third chemical solution during storage. It is desirable to be shielded from light. Moreover, it is preferable that the capacity | capacitance of the said bottle is set to the range of 25-100 ml from a viewpoint of the ease of handling and the ease of conveyance.

  Next, the first chemical solution, the second chemical solution, and the third chemical solution will be described. First, the first chemical solution will be described. The metal indicator contained in the first chemical is a dye-based chelate substance that changes color by reacting with the metal salt contained in the third chemical, and is used for detecting an end point in the titration operation. . In the titration operation using the chelating agent as a quantification target, the metal ions constituting the metal salt (hereinafter referred to as “specific metal ions” in order to be distinguished from the metal ions contained in the sample water) are given priority over the chelating agent. Complex must be formed. For this reason, the metal indicator is selected from chelate substances having a smaller stability constant with the specific metal ion than the chelating agent. As such a chelating substance, for example, when EDTA is to be quantified, xylenol orange (chemical name: 3,3′-bis [N, N-di (carboxymethyl) aminomethyl] -o-cresolsulfophthalein, Disodium salt) and methylthymol blue (chemical name: 3,3′-bis [N, N-di (carboxymethyl) aminomethyl] thymolsulfophthalein, disodium salt) can be used.

  The content of the metal indicator in the first chemical solution is not particularly limited because, as will be described later, when the first chemical solution is added to the sample water, operation is performed so that a predetermined amount of the metal indicator is supplied. Usually, from the viewpoint of solubility and economy, it can be appropriately set in the range of 0.1 to 0.6% by weight.

  Moreover, in order to seal the ferrous ion and copper ion in sample water, the said 1st chemical | medical solution can be made to contain a masking agent. Since ferrous ions and copper ions derived from makeup water and piping materials are usually strongly complexed with the chelating agent, substitution with the specific metal ions is unlikely to occur, and it is long for determining the end point in titration operations. It may take time. On the other hand, if the first chemical solution contains the masking agent, ferrous ions and copper ions preferentially form a complex with the masking agent. For this reason, the total amount of the chelating agent rapidly forms a complex with the specific metal ion, and the reaction time until the sample water changes color is shortened. Here, the masking agent has a greater stability constant with ferrous ions and copper ions than the chelating agent, and when the ferrous ions and copper ions are sealed, the color change of the metal indicator is changed. Selected from chelating substances that do not interfere with discrimination. As such a chelating substance, o-phenanthroline or the like can be used when EDTA is to be quantified.

  As will be described later, the content of the masking agent in the first chemical solution is not particularly limited because it is operated so that a predetermined amount of the masking agent is supplied when the first chemical solution is added to the sample water. Usually, from the viewpoint of solubility and economy, it can be appropriately set in the range of 0.5 to 5% by weight.

Further, the first chemical solution may contain a reducing agent in order to prevent the metal indicator from forming a complex with ferric ions in the sample water and discoloring. For example, xylenol orange in an acidic solution is yellow at pH 6 or lower, but turns blue when complexed with ferric ions. For this reason, a normal hue change does not occur during the titration operation, and the quantification of the chelating agent becomes impossible. On the other hand, when ferric ions are reduced to ferrous ions, xylenol orange shows the original hue. Here, the reducing agent is selected from reducing substances that have the action of reducing ferric ions to ferrous ions and that are turbid in the sample water and do not cause precipitation and coloring. As such a reducing substance, for example, ascorbic acid and an alkali metal salt thereof, an alkali metal salt of sulfurous acid, an alkali metal salt of bisulfite, and hydroxylamine chloride can be used.

  As will be described later, the content of the reducing agent in the first chemical liquid is not particularly limited because the operation is performed so that a predetermined amount of the reducing agent is supplied when the first chemical liquid is added to the sample water. Usually, from the viewpoint of solubility and economy, it can be appropriately set in the range of 0.1 to 10% by weight.

  The first chemical solution can be produced by uniformly dissolving the metal indicator and other additives (the masking agent and the reducing agent) in water or alcohol as a solvent. For example, in the first chemical solution for quantifying EDTA, xylenol orange is dissolved in water, and o-phenanthroline dissolved in alcohol is added and mixed, or powdered ascorbic acid is added. It can be manufactured by mixing.

  Next, the second chemical solution will be described. The pH adjuster contained in the second chemical solution is used to adjust sample water to an acidic region in which the metal indicator changes its color sharply. As the pH adjuster, an acid or a buffer composed of an acid and a salt thereof is usually used. The acids that can be used here are inorganic acids such as nitric acid, hydrochloric acid and sulfuric acid, and organic acids such as acetic acid. The acid salts that can be used here are alkali metal salts such as nitric acid, hydrochloric acid, sulfuric acid and acetic acid. Two or more kinds of acids or acid salts can be used in combination.

  Since the content of the pH adjusting agent in the second chemical solution is manipulated so that the pH of the sample water after the addition is within a predetermined range when the second chemical solution is added to the sample water, as will be described later, It is not limited. Usually, from the viewpoint of ensuring the safety of handling, it is preferable that the content does not correspond to a deleterious substance. In addition, when the water treatment agent contains an alkali metal hydroxide, the sample water is in the alkaline region, so that an amount of acid that can be neutralized and adjusted to the acidic region is added to the pH adjusting agent. It is preferable to contain as.

  The second chemical solution may contain the masking agent in order to seal ferrous ions and copper ions in the sample water. Here, the masking agent is usually contained in either the first chemical solution or the second chemical solution. As will be described later, the content of the masking agent in the second chemical solution is not particularly limited because it is operated so that a predetermined amount of the masking agent is supplied when the second chemical solution is added to the sample water. Usually, from the viewpoint of solubility and economy, it can be appropriately set in the range of 0.5 to 5% by weight.

  The second chemical solution can be produced by uniformly dissolving the pH adjuster and other additives (the masking agent) in water or alcohol as a solvent. For example, the second chemical solution for quantifying EDTA can be produced by dissolving nitric acid in water, adding o-phenanthroline dissolved in alcohol to this solution, and mixing.

Next, the third chemical solution will be described. The metal salt contained in the third chemical solution is used for supplying the specific metal ion to the sample water to which the first chemical solution and the second chemical solution are added. The metal salt is selected from inorganic salts of polyvalent metals capable of supplying the specific metal ion capable of changing the metal indicator to a predetermined hue after preferentially forming a complex with the chelating agent. As such an inorganic salt of a polyvalent metal, for example, when the metal indicator is xylenol orange, bismuth nitrate can be used. Here, the sample water to which xylenol orange is added is yellow at a pH of 6 or less, but changes to red when xylenol orange is complexed with bismuth ions. Therefore, the end point of the titration operation is determined based on this hue change. . In addition, when o-phenanthroline (that is, the masking agent) encapsulated with ferrous ions and copper ions coexists in the sample water, the sample water is orange instead of yellow, but xylenol orange is complexed with bismuth ions. Since the color changes to red when it is converted, the end point of the titration operation is determined based on this hue change.

  The content of the metal salt in the third chemical solution is set according to the resolution of the quantitative value of the chelating agent. That is, the content of the metal salt is adjusted in advance so that the metal salt contained in one drop of the second chemical liquid discharged from the nozzle or the dropper reacts with a predetermined amount of the chelating agent. For example, under the condition that the sample water is 10 ml and one drop of the third chemical discharged from the nozzle or the syringe is 0.035 gram, the free and complex EDTA contained in the sample water is reduced. When quantifying EDTA-2Na with a resolution equivalent to 0.05 mg per drop, the content of bismuth nitrate is set to 0.168% by weight.

  Further, the third chemical solution may contain a surface tension reducing agent in order to make the discharge amount per drop of the nozzle or the dropper constant. For example, when the bottle body of the dripping bottle with nozzle is pushed slowly and quickly, the amount of the third chemical solution discharged increases when pushed slowly. On the other hand, when the surface tension reducing agent is contained in the third chemical solution, the surface tension at the tip of the nozzle can be reduced, and the discharge amount per drop can be made constant. Here, the surface tension reducing agent is selected from substances that have an action of reducing the surface tension of the aqueous solution and do not react with the metal salt. As such a substance, an alcohol compound and a nonionic surfactant can be used. Examples of preferable alcohol compounds include glycols such as ethylene glycol and propylene glycol. Examples of preferable nonionic surfactants include polyoxyethylene alkyl ethers and polyalkylene alkyl ethers.

  The content of the surface tension reducing agent in the third chemical solution is preferably set in the range of 20 to 40% by weight from the viewpoint of suppressing fluctuations in the discharge amount per drop to ± 5% or less.

  The third chemical solution can be produced by uniformly dissolving the metal salt and other additives (the surface tension reducing agent) in water or a dilute acid as a solvent. For example, the third chemical solution for quantifying EDTA can be produced by dissolving bismuth nitrate in dilute nitric acid and, if necessary, propylene glycol or the like.

  The measurement kit includes a fourth container in which the reducing agent in powder form is accommodated together with the first container, the second container, and the third container without containing the reducing agent in the first chemical solution. It can also be configured as follows. Depending on the type of the reducing agent, there is a property that is susceptible to oxidation over time when stored in an aqueous solution. For example, it can withstand short-term storage for 1 to 3 months, but for long-term storage for 1 year. It may not be tolerable. When the reducing agent having such properties is used, it can be stored for a long period of time by storing it in the fourth container in a powder state.

  The fourth container can be used without any particular limitation as long as it is a container of a type that can prevent air oxidation by a sealed stopper. Moreover, it is preferable that the capacity | capacitance of a said 4th container is set to the range of 25-100 ml from a viewpoint of the ease of handling and the ease of conveyance. Furthermore, it is more preferable that a measuring spoon is attached to the fourth container. When the measuring spoon is attached, since a certain amount of the reducing agent can be measured and added to the sample water, the operability is improved.

Next, a method for measuring the chelating agent using the measurement kit will be described. First, a part of the water stored inside the thermal device is collected as sample water. When the thermal apparatus is a boiler, a part of the boiler water is collected from a blow device or the like. In addition, when the thermal device is a cooling tower, a part of the circulating water is collected from a spray device or the like. Here, when the collected sample water exceeds 40 degreeC, it is preferable to cool sample water to 40 degrees C or less from a viewpoint of ensuring the safety | security in titration operation. Further, when the collected sample water is turbid, it is preferable to filter the sample water from the viewpoint of accurately identifying the hue change of the sample water in the titration operation. In order to use the collected sample water for the titration operation, a predetermined amount (for example, 10 to 50 milliliters) is collected in advance with a graduated cylinder and then transferred to a beaker.

  Subsequently, the first chemical solution is added to the collected sample water and mixed uniformly. The amount of the first chemical solution added is usually 0.0001 to 0.003 parts by weight of the metal indicator and 0.001 to 0.5 parts by weight of the reducing agent with respect to 100 parts by weight of sample water. The number of drops from the first container is adjusted as described above. Also, the second chemical solution is added to the sample water and mixed uniformly. The amount of the second chemical solution added is usually such that the pH of the sample water is 6 or less, more preferably the pH adjusting agent is in such an amount that it is less susceptible to the effects of divalent metal ions or rare earth metal ions. The number of drops from the second container is adjusted so that it is added. Further, when the first chemical solution or the second chemical solution contains the masking agent, 0.005 to 0.5 parts by weight of the masking agent is added from the first container or the second container. Adjust the number of drops. The addition order of said 1st chemical | medical solution and said 2nd chemical | medical solution is not specifically limited, Both can also be added simultaneously.

  Here, when the addition amount of the metal indicator is less than 0.0001 part by weight, the color of the sample water is light and it is difficult to identify the hue change near the end point of the titration operation. On the other hand, if the amount of the metal indicator added exceeds 0.003 parts by weight, the sample water titrant is highly colored, making it difficult to identify a hue change near the end point of the titration operation.

  Moreover, when the addition amount of the said reducing agent is less than 0.001 weight part, it may become impossible to reduce | restor all the ferric ions contained in sample water. On the other hand, when the addition amount of the reducing agent exceeds 0.5 parts by weight, the excess reducing agent does not contribute to the reduction of ferric ions, which may be uneconomical.

  Moreover, when the pH of sample water exceeds 6, there exists a possibility that the said metal indicator may not show a predetermined | prescribed hue.

  Furthermore, when the addition amount of the masking agent is less than 0.005 parts by weight, all of the ferrous ions and copper ions contained in the sample water cannot be sealed, and an accurate quantitative value may not be obtained. . On the other hand, when the addition amount of the masking agent exceeds 0.5 parts by weight, the excess masking agent does not contribute to the sealing of ferrous ions and copper ions, which may be uneconomical.

  In the step of adding the first chemical solution, when the first chemical solution is configured not to contain the reducing agent, the powder is normally supplied from the fourth container to the sample water immediately before adding the first chemical solution. The reducing agent is added and mixed uniformly. The amount of the reducing agent added at this time is controlled so as to be 0.001 to 0.5 parts by weight with respect to 100 parts by weight of the sample water, as in the case where the reducing agent is contained in the first chemical solution. To do.

When the first chemical containing the reducing agent is added to the sample water, or the powdery reducing agent is added, ferric ions in the sample water are reduced to ferrous ions. This ferrous ion preferentially forms a complex with the masking agent. For this reason, it is prevented that the said metal indicator, for example, xylenol orange forms a complex with a ferric ion and discolors, and the normal hue of sample water is ensured.

  Next, the third chemical solution is dropped from the third container to the sample water to which the first chemical solution and the second chemical solution are added, and the number of drops until the sample water is discolored is counted. At this time, the third chemical solution is dropped while shaking the beaker so that the sample water and the third chemical solution are uniformly mixed.

  When the third chemical solution is dropped into the sample water to which the first chemical solution and the second chemical solution are added, the chelating agent preferentially forms a complex with the specific metal ion. When the total amount of the chelating agent forms a complex with the specific metal ion, the metal indicator forms a complex with an excess of the specific metal ion, and the sample water changes color. For example, when the chelating agent is EDTA and an alkali metal salt thereof, when the third chemical solution is dropped into the sample water to which the first chemical solution and the second chemical solution are added, EDTA is preferentially bismuth ions. To form a complex. When the total amount of EDTA forms a complex with bismuth ions, xylenol orange forms a complex with excess bismuth ions, and the sample water is yellow (when o-phenanthroline combined with ferrous ions coexists, it is orange) The color changes from red to red.

  When the third chemical solution is dropped in the presence of the masking agent, the ferrous ions and copper ions complexed with the chelating agent preferentially form a complex with the masking agent. For this reason, the total amount of the chelating agent rapidly forms a complex with the specific metal ion, and the reaction time until the sample water changes color is shortened.

  Next, the concentration of the chelating agent in the sample water is specified based on the number of drops of the third chemical solution required until the end point of the titration operation. As described above, since the third chemical solution is prepared so that the metal salt contained in one drop reacts with a predetermined amount of the chelating agent, it corresponds to the chelating agent per one drop of the third chemical solution. The concentration of the chelating agent in the sample water can be calculated from the amount, the number of drops of the third chemical solution, and the amount of sample water taken.

  By the way, in the thermal apparatus, the chelating agent is dissolved in water in a free state or in a state of forming a complex with a hardness component. The water stored inside the thermal equipment is usually blown to the outside intermittently or regularly supplied with replenishing water so as to maintain a predetermined concentration ratio. There is no possibility that it will crystallize in water or precipitate on the heat transfer surface. For this reason, the concentration of the chelating agent in the thermal device is correlated with the concentration of the water treatment agent, and the concentration of the water treatment agent is easily determined from the concentration of the chelating agent and the mixing ratio of the chelating agent in the water treatment agent. Identified. Therefore, it is possible to determine whether the supply amount of the water treatment agent is appropriate based on the concentration of the water treatment agent.

  As described above, according to the embodiment of the present invention, the water treatment agent concentration can be easily known at the site where the thermal equipment is installed. As a result, it is possible to determine on site whether or not the amount of water treatment agent supplied to the thermal equipment is appropriate, and the maintenance management related to water treatment can be made more efficient.

(Preparation of the first chemical)
Using a xylenol orange as a metal indicator, o-phenanthroline as a masking agent, distilled water and ethanol as a solvent, these components were mixed in the contents shown in Table 1 to prepare a first chemical solution. After the preparation, the first chemical solution was filled in a dropping bottle (capacity 100 ml; hereinafter referred to as “first container”) made of polyethylene. The dropping amount per drop of the first chemical liquid using the first container was 0.035 grams (average value).

(Preparation of the second chemical)
A 10% nitric acid aqueous solution was used as a pH adjuster to prepare a second chemical solution. The second chemical solution was filled in a dropping bottle with a nozzle made of polyethylene (capacity: 100 ml; hereinafter referred to as “second container”). The dropping amount per drop of the second chemical solution using the second container was 0.035 gram (average value).

(Preparation of third chemical)
Using a bismuth nitrate pentahydrate as a metal salt and a 0.5 mol / liter nitric acid aqueous solution as a solvent, each of these components was mixed in the contents shown in Table 2 to prepare a third chemical solution. After the preparation, the third chemical solution was filled into a polyethylene-made dripping bottle (capacity: 100 ml; hereinafter referred to as “second container”). The drop amount per drop of the third chemical solution using the third container is 0.035 g (average value), and the third chemical solution is equivalent to 0.05 mg of EDTA-2Na in one drop. To do.

(Sample water collection)
Of the once-through boilers that supply a water treatment agent containing ethylenediaminetetraacetic acid disodium (EDTA-2Na) as a scale inhibitor, 67 units were randomly extracted from across the country, and samples were taken from a continuous blower during operation. Water was collected. The water treatment agent was mixed with an alkali metal hydroxide as a corrosion inhibitor together with EDTA-2Na, and the pH of the collected sample water was in the range of 10.5-12. After each sample water was cooled to room temperature, 10 milliliters were dispensed into a beaker using a graduated cylinder to prepare first sample water for 67 samples. Further, 5 ml of each sample water was dispensed into a beaker using a graduated cylinder to prepare second sample water for 67 samples.

(Measurement of EDTA by simple titration method)
20 mg of powdered ascorbic acid as a reducing agent was added to the first preparative sample water and dissolved uniformly. To the first preparative sample water to which the reducing agent has been added, add one drop of the first chemical solution from the first container, and then add five drops of the second chemical solution from the second container to uniformly The water to be titrated was prepared by mixing. Next, the third chemical solution was dropped from the third container into the titrated water, and the number of drops until the titrated water changed from orange to red was counted. And the density | concentration of EDTA-2Na in sample water was computed from the equivalent amount of EDTA-2Na per said 3rd chemical | medical solution drop, the dripping number of the said 3rd chemical | medical solution, and the amount of sample water fractionated. In the above operation, the time required for measurement per specimen was 1 to 3 minutes.

(Measurement of EDTA by high performance liquid chromatography)
In order to compare with the quantitative value of EDTA by a simple titration method, EDTA was measured by high performance liquid chromatography (HPLC method) on the second preparative sample water. First, a commercially available 0.01 mol / liter aqueous solution of disodium ethylenediaminetetraacetate (EDTA-2Na) is diluted with distilled water to obtain 0 mg / liter, 10 mg / liter, 20 mg / liter, 40 mg / liter and 80 mg / liter. Standard solutions were prepared respectively. Further, 0.27 g of ferric chloride hexahydrate was dissolved in 0.01N hydrochloric acid to make a total volume of 100 ml to prepare a 0.01 mol / liter ferric chloride solution.

After adding 5 ml of a 0.01 mol / liter ferric chloride solution to 5 ml of each standard solution and filtering with a 0.2 μm membrane filter, high-performance liquid chromatography was performed on 10 microliters of each solution. Then, a calibration curve was created from the obtained peak heights and concentrations. Here, the conditions of high performance liquid chromatography are as follows.

Column size: ID 4.6mm, length 150mm
◎ Stationary phase: Fully porous silica gel with octadecyl group chemically modified ◎ Mobile phase: 0.01 mol / liter tetra-n-butylammonium hydroxide solution adjusted to pH 3.0 with acetic acid ◎ Transfer Phase flow rate: 1.0 ml / min ◎ Selectable wavelength of detector: 255 nm

  Next, 5 ml of a 0.01 mol / liter ferric chloride solution is added to the second preparative sample water, filtered through a 0.2 μm membrane filter, and then 10 microliters of each solution has the same conditions as the standard solution. Was used for high-performance liquid chromatography, and the peak height was measured. Then, the concentration of EDTA-2Na in the sample water was calculated based on a calibration curve prepared in advance. In the above operation, the time required for the measurement per specimen was 25 minutes.

(Evaluation)
For each sample water, a graph in which the quantitative values obtained by the simple titration method are plotted against the quantitative values obtained by the HPLC method is shown in FIG. According to FIG. 1, the quantitative value obtained by the simple titration method may cause a difference of about 5 mg / liter on the plus side with respect to the quantitative value obtained by the HPLC method. This is because the resolution of the quantitative value in the simple titration method is set to 5 mg / liter. The quantitative value of the simple titration method shows an almost linear correlation with the quantitative value of the HPLC method, which indicates that the reliability is high. The simple titration method is effective for on-site measurement because it can be measured in a short time without using a special instrument.

The graph which shows the correlation with the quantitative value of EDTA-2Na by HPLC method, and the quantitative value of EDTA-2Na by a simple titration method.

Claims (10)

A chelating agent measurement method for quantifying the concentration of a chelating agent in a sample water,
Collecting the sample water;
Adding a first chemical solution containing a metal indicator and a second chemical solution containing a pH adjuster to the collected sample water, and
Dropping a third chemical solution containing a metal salt that changes the color of the metal indicator into the sample water to which the first chemical solution and the second chemical solution are added, and counting the number of drops until the sample water changes color;
And a step of specifying the concentration of the chelating agent in the sample water based on the number of drops of the third chemical solution. The chelating agent is ethylenediaminetetraacetic acid and salts thereof;
The method for measuring a chelating agent according to claim 1, wherein the metal indicator, the pH adjuster, and the metal salt are xylenol orange, nitric acid, and bismuth nitrate, respectively.   The method for measuring a chelating agent according to claim 1 or 2, further comprising a step of adding a masking agent to the collected sample water.   The method for measuring a chelating agent according to claim 3, wherein the masking agent is o-phenanthroline.   The method for measuring a chelating agent according to claim 3 or 4, further comprising a step of adding a reducing agent to the collected sample water.   The method for measuring a chelating agent according to claim 5, wherein the reducing agent is ascorbic acid and an alkali metal salt thereof. A chelating agent measurement kit for quantifying the concentration of a chelating agent in sample water,
A first container containing a first chemical containing a metal indicator;
a second container containing a second chemical containing a pH adjuster;
A chelating agent measurement kit comprising: a third container containing a third chemical solution containing a metal salt that changes the color of the metal indicator.   The chelating agent measurement kit according to claim 7, wherein the first chemical solution or the second chemical solution further contains a masking agent.   The chelating agent measurement kit according to claim 8, wherein the first chemical solution further contains a reducing agent.   The chelating agent measurement kit according to claim 8, further comprising a fourth container in which a powdery reducing agent is accommodated.

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