JP2017015669A - Residual chlorine measurement method and residual chlorine measurement device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To precisely measure a residual chlorine concentration.SOLUTION: There is provided a residual chlorine measurement device 1 comprising an injection valve 2 and a flow cell 3. A liquid feed pump 9 pumps a carrier liquid to the injection valve 2. Sample water is injected into the carrier liquid circulating through the injection valve 2, and the carrier liquid including the sample water is supplied to the flow cell 3. The flow cell 3 is provided with a working electrode, a reference electrode and a counter electrode, a potentiostat keeps the potential of the working electrode constant relative to the reference electrode, and a current (or electric charge) flowing between the working electrode and counter electrode is measured. A residual chlorine concentration in the sample water is measured on the basis of the measured electric charge.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a residual chlorine measuring method and a residual chlorine measuring device. In particular, the present invention relates to a method and an apparatus for measuring residual chlorine by flow injection analysis using an electrochemical measurement method as a detection system.

  Disinfection with chlorine is widely used worldwide for disinfection of clean water and sewage because of its high disinfection effect and easy maintenance. In Japan, it is obligated to disinfect tap water, and sewage treated water is also used for disinfecting high-quality treated water in fine weather and simple treated water in rainy weather. Therefore, measurement of residual chlorine is an important measurement item in managing water quality in waterworks and sewers.

  Residual chlorine refers to free effective chlorine existing in water (free residual chlorine) and bound effective chlorine (bonded residual chlorine) such as chloramine combined with ammonia. Residual chlorine concentration refers to free residual chlorine. It is the total amount of chlorine concentration and combined residual chlorine concentration.

  As for the measurement method of residual chlorine, the inspection method of free residual chlorine and combined residual chlorine specified by the Minister of Health, Labor and Welfare is stipulated in the waterworks based on the provisions of Article 17 Paragraph 2 of the Water Supply Law Enforcement Regulations (Ministry of Health, Labor and Welfare). For free residual chlorine, (1) diethyl-p-phenylenediamine method (hereinafter referred to as DPD method), (2) current method, (3) absorptiometry, (4) absorptiometry using a continuous automatic measuring instrument, 5) The polarographic law is established. In addition, (1) DPD method, (2) current method, and (3) absorptiometric method are defined for bonded residual chlorine. In the sewerage system, (1) DPD method, (2) orthotolidine method (OT method), (3) orthotolidine arsenite method (OTA method), and (4) iodine titration method are described (for example, non- Patent Document 1).

  In addition, a method for quantifying residual chlorine by flow injection / electrochemical detection (for example, Non-Patent Document 2) and a method for quantitative analysis of free chlorine using an anodic oxidation reaction (for example, Non-Patent Document 3) have been proposed. . The electrochemical measurement method is a method for measuring a current or voltage change accompanying an oxidation-reduction reaction on an electrode, and is used in a wide range of fields such as inorganic chemistry, analytical chemistry, organic chemistry, biology, and medicine. The flow injection analysis method, for example, performs volume measurement by flowing a reagent solution at a constant flow rate, injects a certain amount of sample into the flow of the reagent solution, and connects a pipe made of fluororesin or the like to a reaction such as a flask or beaker. This is a method of mixing and reacting both liquids as if they were containers. The flow injection analysis method is easy to implement because it has few moving parts and moves as a solution.

  The flow injection analysis method generally includes a method of providing two flow paths of a reagent solution and a carrier liquid such as distilled water that does not affect the measurement, and introducing the sample solution into the flow of the carrier liquid. On the other hand, when using a method called reverse flow injection analysis, in which the sample solution and the carrier liquid are flowed at a constant flow rate instead of the reagent solution, and the reagent solution is introduced into the carrier liquid flow, or when an expensive reagent is used. After introducing the reagent solution into the carrier liquid, a multi-component flow system with multiple carrier liquids and reagent solutions is provided for a stopped flow system in which the flow is stopped once at the detector or a single sample flow path. There are various methods such as analysis methods.

  Also, several types of residual chlorine meters used for monitoring chlorine have been commercialized (Patent Documents 1 to 3). Furthermore, in the continuous measurement type residual chlorine meter, a polarographic method using a rotating microelectrode is mainly employed. In this measurement method, by applying a certain voltage optimum for electrolytic reduction of residual chlorine in the target sample water to the working electrode (detection electrode) and counter electrode of the detector attached to the water receiving tank, the water receiving tank When sample water is passed through, a reduction current (diffusion current) proportional to the residual chlorine concentration flows between the working electrode and the counter electrode, and this current is detected to measure the residual chlorine concentration.

  In addition, a reagent-based system is used because sewage and wastewater generally contain a large amount of combined residual chlorine. In the reagent-based system, the measurement of total residual chlorine and free residual chlorine is properly used by selecting the reagent to be used, but there are types that can separately measure free residual chlorine, combined residual chlorine, and total residual chlorine with the same reagent. is there. For water supply, the reagentless method is used to measure only free residual chlorine.

JP 2010-185864 A JP 2009-085749 A JP 2005-345222 A JP 2010-197383 A JP 2000-119885 A

"Sewage test method, first volume 2012", Japan Sewerage Association, December 2012, p365-372 “Analytical Chemistry”, Japan Analytical Chemical Society, 1999, Vol. 48, no. 12, pp 1123-1129 “Analytical Chemistry”, Japan Analytical Chemical Society, 2009, Vol. 58, no. 7, pp583-594

  However, the inspection method for free residual chlorine and bound residual chlorine specified in the Enforcement Regulations of the Water Supply Law and the measurement method described in Non-Patent Document 1 use various inorganic acids and organic compounds. Is complicated. In addition, the orthotolidine method (OT method) is designated as a specific chemical substance because it has carcinogenicity and moderate acute toxicity, and has been deleted from April 1, 2002. The orthotolidine arsenite method (OTA method) uses sodium meta arsenite as a reagent, but it is a toxic substance specified by the Poisonous and Deleterious Substances Control Law, and is approved by the prefectural governor at the time of disposal. It is necessary to entrust the treatment to an industrial waste supplier, which is difficult to handle.

  When measuring residual chlorine in waterworks and sewers by the DPD absorption photometry method, a portable type residual chlorine meter is widely used. When continuously measuring residual chlorine, a polarographic continuous measurement residual chlorine meter using a rotating microelectrode is employed. However, when measuring continuously, the working electrode is contaminated by the reduction reaction, so a motor is attached to the working electrode and rotated so that the electrode surface does not become dirty by rubbing with ceramic beads or glass beads placed in the solution. It is always necessary to polish. Therefore, there is a problem that the electrode surface is worn by being rubbed with ceramic beads or glass beads, and the life of the electrode is deteriorated.

  In view of the above circumstances, an object of the present invention is to provide a measurement method and a measurement apparatus that accurately measure the residual chlorine concentration in sample water.

  The residual chlorine measurement method of the present invention that achieves the above object is a residual chlorine measurement method for measuring the residual chlorine concentration of sample water, wherein pure water is circulated as a carrier liquid, and the sample water is injected into the carrier liquid. The carrier liquid injected with the sample water is supplied to the flow cell at a predetermined speed, and the residual chlorine in the sample is determined based on the current or charge detected by applying a voltage between the electrodes arranged in the flow cell. It is characterized by measuring the concentration.

  In addition, the residual chlorine measuring apparatus of the present invention that achieves the above object is detected by applying a voltage between the flow cell into which the sample water injected into the carrier liquid is introduced at a predetermined speed and the electrode disposed in the flow cell. Measuring means for measuring the residual chlorine concentration in the sample water based on the electric current or electric charge, and the carrier liquid is pure water.

  According to the above invention, the residual chlorine concentration in sample water can be measured accurately.

It is the schematic of the residual chlorine measuring apparatus which concerns on 1st Embodiment of this invention. It is a figure which shows the influence of the applied voltage which acts on the amount of electricity. It is a figure which shows the influence of the carrier liquid flow velocity which acts on an electric quantity. It is a figure which shows the measurement result of sodium hypochlorite by an electrochemical method. It is a figure which shows the measurement result of 0-1 mg / L sodium hypochlorite solution. It is a figure which shows the measurement result of 0-0.08 mg / L sodium hypochlorite solution. It is a figure which shows the continuous measurement result of sodium hypochlorite (1 mg / L). It is a figure which shows the measurement result of a 10-100 mg / L sodium hypochlorite solution. It is a figure which shows the measurement result of a 50-800 mg / L sodium hypochlorite solution. It is a figure which shows the fluctuation | variation of the electric quantity with respect to reaction time. It is a figure which shows the influence of ammonium chloride which acts on a free residual chlorine concentration. It is the schematic of the residual chlorine measuring apparatus which concerns on 2nd Embodiment of this invention. It is a figure which shows the effect of potassium iodide concentration. It is a figure which shows the addition effect of potassium iodide which acts on a joint residual chlorine measurement. It is a figure which shows the comparison with an electrochemical method and DPD method. It is a figure which shows the electrochemical measurement result by two flow paths of the sample water in which free chlorine and combined chlorine are mixed. It is a figure which shows the comparison with an electrochemical method and DPD method. It is a figure which shows the relationship between the total chlorine concentration of the sample water in which free chlorine and combined chlorine are mixed, and an electric quantity.

  A residual chlorine measuring method and a residual chlorine measuring device according to an embodiment of the present invention will be described in detail with reference to the drawings. In addition, when there is description as residual chlorine in description of embodiment, it shall mean the total chlorine which is the total amount of free residual chlorine and combined residual chlorine. In addition, regarding the effective chlorine concentration display (mg / L) of sodium hypochlorite and the display of free residual chlorine concentration and residual chlorine concentration (mg / L), unless otherwise specified, the chlorine concentration (Cl mg) in the sample. / L).

  In the residual chlorine measuring method of the present invention, the residual chlorine concentration in sample water (for example, clean water or sewage) is measured by flow injection analysis using an electrochemical measurement method as a detection system.

[First Embodiment]
FIG. 1 is a schematic view of a residual chlorine measuring apparatus 1 according to the first embodiment of the present invention. The residual chlorine measuring device 1 includes an injection valve 2 into which a carrier liquid and sample water are injected, and a flow cell 3.

  The injection valve 2 is an injection means for introducing sample water into the carrier liquid flow. The illustrated injection valve 2 is a six-way rotary valve type, but the injection means is not limited to this form. In the description of the embodiment, the sample water is manually injected directly into the injection valve 2, but a thin tube for injecting the sample water into the injection valve 2 can also be provided. Thin tubes 4 to 8 are connected to the injection valve 2 as flow paths. The narrow tube 4 is a tube constituting a flow path for injecting the carrier liquid. The thin tube 4 is provided with a liquid feed pump 9. The thin tube 5 is a tube constituting a sample loop. The narrow tube 6 is a tube constituting a flow path for supplying a carrier liquid containing sample water to the flow cell 3. The thin tubes 7 and 8 are tubes for transferring the sample water overflowed from the sample loop (the thin tube 5) or the injection valve 2 to the drain bottle 10 which is a drain portion.

  The liquid feeding pump 9 is provided in the thin tube 4 and feeds the carrier liquid to the injection valve 2 and the flow cell 3. As the carrier liquid, for example, pure water (water from which impurities have been removed through a reverse osmosis membrane or an ion exchange resin, distilled water, or the like) is used. A damper 11 is provided between the liquid feed pump 9 and the injection valve 2. The damper 11 absorbs and eliminates the pulsating flow of the liquid feed pump 9, so that a more sensitive and stable analysis can be performed.

  The flow cell 3 quantifies the residual chlorine concentration in the sample water. As the flow cell 3, for example, a flow column type electrolytic synthesis cell as shown in Patent Document 5 can be applied. Although not shown in FIG. 1, the flow cell 3 is provided with, for example, a working electrode, a reference electrode, and a counter electrode. Potentiostats are connected to these electrodes, and the arithmetic unit calculates the residual chlorine concentration in the sample water based on the potentiostat measurement data. For example, the potential of the working electrode with respect to the reference electrode is always kept constant by a potentiostat, and the current (or charge) flowing between the working electrode and the counter electrode is measured. Specifically, an electrode made of glassy carbon and carbon fiber as described in Patent Document 5 is used as the working electrode. That is, carbon fibers (for example, 100 or more) are densely filled in the porous glass tube in the axial direction, and an electrode rod made of glassy carbon or the like is connected to the carbon fibers to form a working electrode. As the reference electrode, for example, Ag / AgCl, and as the counter electrode, for example, an electrode made of stainless steel (SUS 316) is used. Each electrode is not limited to this example, and a working electrode, a counter electrode, and a reference electrode that do not hinder measurement are appropriately selected and used.

  In the residual chlorine measuring device 1, the carrier liquid placed outside the device is sent to the inside of the device via the thin tube 4 by the liquid feed pump 9. Then, the carrier liquid is fed from the damper 11 to the injection valve 2 to the flow cell 3 to the drain bottle 10 at a constant speed by adjusting the rotation speed of the liquid feeding pump 9.

  Here, an example in which the residual chlorine concentration in the sample water is measured by the residual chlorine measuring device 1 will be shown, and the residual chlorine measuring method according to the embodiment of the present invention will be described in detail.

  First, the amount of sample introduced from the injection valve 2 into the flow path (the narrow tube 6 and the flow cell 3) was examined by the same method as the study described in Patent Document 4. That is, when the residual chlorine concentration was measured in the sample amount range of 50 to 600 μL, the same linear relationship as in Patent Document 4 was obtained. Therefore, the sample amount introduced into the flow path from the injection valve 2 was selected to be 400 μL, which is a sample amount in which the amount of electricity is relatively proportional to the amount of sample and the amount of electricity is as large as possible.

  As a reagent, a sodium hypochlorite solution (product code number: 197-02206) manufactured by Wako Pure Chemical Industries, Ltd. was used. Sodium hypochlorite is a disinfectant used for disinfecting water and sewers. A commercially available sodium hypochlorite solution is a strong alkaline solution having a free effective chlorine concentration of 5 to 12 wt% and a pH of 12.5 to 13.5, which is injected into treated water or the like at a predetermined injection rate. In addition, the effective chlorine concentration of a sodium hypochlorite solution can be calculated | required by the method described in the nonpatent literature 1. In the following examples, when measuring the residual chlorine concentration of the sample water, the effective chlorine concentration of the sodium hypochlorite solution is obtained in advance by the method described in Non-Patent Document 1, and the pure chlorine based on this value is obtained. Sample water prepared by diluting with water to obtain an effective chlorine concentration of each sodium hypochlorite was used. The pH of the sample water after preparation was 6-9.

[Working electrode potential]
The potential of the working electrode (vs Ag / AgCl) affects the background, sensitivity, etc., so an optimal potential must be selected. Under the conditions of Table 1, a sodium hypochlorite solution having an effective chlorine concentration of 1 mg / L is introduced as sample water from the injection valve 2 into the flow path, and the working electrode is set to have a potential of 0 to 80 mV. A voltage was applied to the counter electrode, and the relationship between the applied voltage and the amount of electricity was determined. In the following description, the numerical value of the applied voltage indicates the potential of the working electrode when a voltage is applied to the working electrode and the counter electrode.

  As shown in FIG. 2, when the applied voltage (potential of the working electrode) is increased, the amount of electricity decreases. Therefore, in the range of 0 to 80 mV, the applied voltage can be measured with the highest sensitivity when the voltage is 0 mV. Yes.

[Carrier liquid flow rate]
In the flow injection analysis method, since the flow rate of the carrier liquid (ie, sample water) generally affects the sensitivity of the measurement value, an optimal flow rate must be selected. The carrier liquid flow rate affects the reduction reaction rate on the working electrode in the flow cell 3. The reduction current pattern becomes sharper as the carrier liquid flow rate increases and becomes broader as the carrier liquid flow rate decreases.

  Under the conditions shown in Table 2, a sodium hypochlorite solution having an effective chlorine concentration of 1 mg / L is introduced as sample water from the injection valve 2 into the flow path, and the carrier liquid flow rate is changed to 0.40 to 0.85 mL / min. Thus, the relationship between the carrier liquid flow rate and the amount of electricity was determined.

  FIG. 3 shows the measurement results of the quantity of electricity flowing at different hypochlorous acid concentrations when the carrier liquid flow rate was 0.40 mL / min. Table 3 shows the correlation between the sodium hypochlorite concentration and the amount of electricity for each carrier liquid flow rate.

The correlation between the sodium hypochlorite concentration and the quantity of electricity was good when the carrier liquid flow rate was 0.50 mL / min or less, with the coefficient of determination (R ² ) being R ² > 0.98. The measurement pattern of the current value was not good because it did not look like a Gaussian distribution. On the other hand, when the carrier liquid flow rate is 0.55 to 0.85 mL / min, the correlation between the sodium hypochlorite concentration and the electric quantity is good when the determination coefficient (R ² ) is R ² > 0.99. The measurement pattern of the current value with respect to the measurement time was also good with a Gaussian distribution. That is, when the carrier liquid flow rate was up to 0.85 mL / min, it was confirmed that a good correlation was obtained in the relationship between the sodium hypochlorite concentration and the amount of electricity.

  Therefore, it is considered that any flow rate may be used as long as the carrier liquid flow rate is in the range of 0.55 to 0.85 mL / min. However, it is desirable to suppress the consumption amount of the carrier liquid as much as possible. As such, the carrier liquid flow rate was set to 0.60 mL / min.

[Comparison with residual chlorine concentration measured by DPD method]
With the residual chlorine measuring device 1 in FIG. 1, a sodium hypochlorite solution having a concentration range of 0 to 10 mg / L was measured.

  In sewage, sodium hypochlorite is used to disinfect the treated water in the final treatment process at the water reclamation center. There is no regulation on the injection rate of sodium hypochlorite, and the sewerage law regulates that the number of coliforms in the effluent is 3,000 / mL or less. In general, in the water reclamation center, the injection rate of sodium hypochlorite for high-grade treated water in fine weather is about 0.5 mg / L, and the injection rate of sodium hypochlorite in treated water during rainy weather is 3-7 mg / L. On the other hand, the water supply law stipulates that the residual chlorine concentration is 0.1 mg / L or more at the tap terminal in tap water. Therefore, practically, it is considered that the measurement range of sodium hypochlorite is 0 to 10 mg / L.

  First, the sodium hypochlorite solution is diluted with pure water, and the effective chlorine concentration of the sodium hypochlorite solution is set to 0, 0.1, 0.5, 1, 2, 3, 4, 5, 7. 5 and 10 mg / L. Then, the residual chlorine concentration of the sodium hypochlorite solution prepared for each effective chlorine concentration was measured under the conditions shown in Table 2 except that the carrier liquid flow rate was 0.6 mL / min. In measuring the residual chlorine concentration, the sodium hypochlorite solution having the same concentration was measured three times, and the average value of the three points was plotted.

As shown in FIG. 4, the correlation between the amount of electricity and the sodium hypochlorite concentration is in the range of 0 to 10 mg / L, and the coefficient of determination (R ² ) is good when R ² = 0.9984. there were. Therefore, based on this correlation, it can be seen that the residual chlorine concentration of the sample water can be accurately detected based on the amount of electricity detected in the flow cell 3.

  In addition, the residual chlorine concentration of 0.1, 0.5, 1, and 2 mg / L sodium hypochlorite solutions prepared from commercially available sodium hypochlorite was measured by the DPD method for comparative verification. In the measurement by the DPD method, a pocket residual chlorine meter (Pocket Colorimeter II) manufactured by HACH was used.

  Since the measurement range of HACH's pocket residual chlorine meter is 0.02 to 2 mg / L, comparison was made up to 2 mg / L. Since this sample water was prepared from commercially available sodium hypochlorite, it does not contain bound chlorine, but both free chlorine (Free) and total chlorine (Total) were measured.

  As shown in Table 4, the effective chlorine concentration prepared in each sodium hypochlorite solution corresponds to the residual chlorine concentration measured by the DPD method, and the flow injection analysis using the electrochemical measurement method as the detection system. It can be seen that the residual chlorine concentration can be measured by the method. In addition, since the sample water this time does not contain bound chlorine, free residual chlorine is a measurement target. Therefore, it can be seen that the residual chlorine measuring device 1 can measure residual chlorine in a concentration range of 0 to 10 mg / L.

[Measurement of residual chlorine concentration in sample water with different residual chlorine concentration (low concentration)]
A sodium hypochlorite solution is diluted with pure water, and the effective chlorine concentration of sodium hypochlorite is 0, 0.1, 0.2, 0.3, 0.4, 0.6, 0.8. , 1.0 mg / L. The residual chlorine concentration of the sodium hypochlorite solution prepared for each effective chlorine concentration was measured under the conditions shown in Table 2 except that the carrier liquid flow rate was 0.60 mL / min. In measuring the residual chlorine concentration, the sodium hypochlorite solution having the same concentration was measured three times, and the average value of the three points was plotted.

As shown in FIG. 5, the correlation between the quantity of electricity and the sodium hypochlorite concentration is in the range of 0 to 1.0 mg / L, and the coefficient of determination (R ² ) is good when R ² = 0.9987. It was a relationship. Therefore, based on this correlation, it can be seen that the residual chlorine concentration of the sample water can be accurately detected based on the amount of electricity detected in the flow cell 3.

  Further, the sodium hypochlorite solution is diluted with pure water to prepare a sodium hypochlorite solution having an effective chlorine concentration of 0, 0.02, 0.04, 0.06, 0.08 mg / L, Residual chlorine concentration was measured in each sample. In measuring the residual chlorine concentration, the sodium hypochlorite solution having the same concentration was measured three times, and the average value of the three points was plotted.

As shown in FIG. 6, the correlation between the quantity of electricity and the sodium hypochlorite concentration is in the range of 0 to 0.08 mg / L, and the coefficient of determination (R ² ) is good when R ² = 0.9976. It was a relationship. Therefore, based on this correlation, it can be seen that the residual chlorine concentration of the sample water can be accurately detected based on the amount of electricity detected in the flow cell 3.

  From the results of FIGS. 5 and 6, it was found that the residual chlorine measuring device 1 can also measure sodium hypochlorite having a concentration of 1.0 mg / L or less. In addition, since the sample water this time is a sample prepared using a commercially available sodium hypochlorite solution, the sample water does not contain bound chlorine. Therefore, the measurement target of the residual chlorine measuring device 1 is free residual chlorine, and the measurement range is 1.0 mg / L or less, and the measurement of free residual chlorine concentration of at least 0.02 mg / L is possible. is there.

[Continuous measurement of residual chlorine concentration]
Residual chlorine concentration was continuously measured with the residual chlorine measuring device 1.

  A sodium hypochlorite solution was diluted with pure water to prepare a sodium hypochlorite solution having an effective chlorine concentration of 1.0 mg / L. Then, the residual chlorine concentration of the prepared sample water was continuously measured under the conditions shown in Table 2 except that the carrier liquid flow rate was 0.60 mL / min.

  As shown in FIG. 7, the coefficient of variation (CV) for all 70 measurements was CV = 4.89%. Thereby, it can be seen that the residual chlorine measuring device 1 is sufficiently accurate even when continuous measurement is performed.

[Measurement of residual chlorine concentration in sample water with different residual chlorine concentration (high concentration)]
The sodium hypochlorite solution was diluted with pure water to prepare sodium hypochlorite solutions having effective chlorine concentrations of 10, 20, 30, 40, 50, 60, 70, 80, 90, and 100 mg / L. And the residual chlorine measuring apparatus 1 measured the residual chlorine concentration of the prepared sample water. The measurement conditions were the same as those in Table 2 except that the carrier liquid flow rate was 0.60 mL / min. In measuring the residual chlorine concentration, sodium hypochlorite having the same concentration was measured three times, and the average value of three points was plotted.

As shown in FIG. 8, the correlation between the amount of electricity and the sodium hypochlorite concentration is in the range of 0 to 100 mg / L, and the coefficient of determination (R ² ) is a good relationship with R ² = 0.9973. there were. Therefore, based on this correlation, it can be seen that the residual chlorine concentration of the sample water can be accurately detected based on the amount of electricity detected in the flow cell 3.

  Also, dilute sodium hypochlorite solution with pure water to prepare sodium hypochlorite solutions with effective chlorine concentrations of 50, 100, 200, 400, 600, and 800 mg / L, and measure residual chlorine under the same conditions. The residual chlorine concentration was measured with the apparatus 1. In measuring the residual chlorine concentration, sodium hypochlorite having the same concentration was measured three times, and the average value of three points was plotted.

As shown in FIG. 9, the correlation between the amount of electricity and the sodium hypochlorite concentration is in the range of 50 to 800 mg / L, and the coefficient of determination (R ² ) is a good relationship with R ² = 0.9989. there were. Therefore, based on this correlation, it can be seen that the residual chlorine concentration of the sample water can be accurately detected based on the amount of electricity detected in the flow cell 3.

  Even in the case of an electrolyte solution, the amount of electricity and the concentration are not in a proportional relationship up to a high concentration. When the concentration is high, it becomes difficult to ionize, and current does not flow easily due to interaction between ions, and the proportional relationship is lost. It is estimated to be. However, from the results shown in FIG. 8 and FIG. 9, it was confirmed that the relationship between the amount of electricity and the concentration was proportional up to an effective chlorine concentration of 800 mg / L. In addition, since this sample water was prepared from a commercially available sodium hypochlorite solution, it does not contain bound chlorine. That is, the residual chlorine measuring device 1 can accurately measure the free residual chlorine concentration at least until the effective chlorine concentration is 800 mg / L.

[Influence of ammonium chloride on free residual chlorine]
Sodium hypochlorite and ammonium chloride were reacted, and the amount of electricity with respect to the reaction time was measured by the residual chlorine measuring device 1. By this measurement, it was confirmed whether the measurement target of the residual chlorine measuring device 1 is only free residual chlorine or measuring residual chlorine containing combined residual chlorine.

  First, 500 mL of a 1 mg / L sodium hypochlorite solution and 50 mL of a 1 mg / L ammonium chloride solution were mixed, and the change over time in the residual chlorine concentration was measured in the mixed solution. The measurement results are shown in FIG.

  Moreover, the free residual chlorine concentration in the mixed solution by DPD method was measured using the pocket residual chlorine meter made from HACH. FIG. 11 shows the relationship between the free residual chlorine concentration and the amount of electricity.

  As shown in FIG. 10, it was confirmed that the amount of electricity measured as the reaction time passed decreased. It is presumed that the amount of electricity decreased with the generation of bound chlorine as the reaction time passed and the concentration of sodium hypochlorite (free chlorine) decreased. Moreover, as shown in FIG. 11, the quantity of electricity detected by the flow cell 3 is correlated with the free residual chlorine concentration measured by the DPD method, and the residual chlorine measuring device 1 measures the free residual chlorine. Suggests that.

  According to the residual chlorine measuring apparatus 1 according to the first embodiment of the present invention as described above, free residual chlorine in the sample water can be measured with high accuracy. Further, the residual chlorine concentration can be measured easily and in a short time (for example, about 5 minutes) without requiring a complicated operation requiring specialized knowledge and skill.

  That is, by using a flow injection analysis method in which an electrochemical measurement method using a coulometric type flow cell 3 is used as a final detection system for residual chlorine concentration, the residual chlorine concentration is continuously and accurately measured. be able to. The electrochemical measurement method is capable of high-sensitivity measurement, but there is a problem that the reproducibility is reduced due to contamination of the electrode surface. However, if the coulometry method is used, the total amount of the target component in the sample solution is detected. The problem that the reproducibility deteriorates can be improved.

  In addition, since the residual chlorine detection system is not a rotating electrode, there is no wear of the electrode surface due to rubbing of the ceramic or glass beads with the electrode surface when the rotating electrode is used, and the life of the electrode is shortened. Absent. In addition, a carrier liquid (for example, pure water) always flows through the working electrode, and is configured to inject several hundred μL of sample water at the time of measurement. The measurement path and the working electrode are not easily contaminated. As described above, the device configuration with little deterioration with time of the measurement path and the flow cell can measure the residual chlorine concentration without lowering the detection accuracy even if the measurement is continuously performed.

  In addition, since no reagent is used for measuring the residual chlorine concentration, there is no need for complicated reagent preparation, and reagent costs are not generated. Further, since operations such as colorimetry and titration are not required, the residual chlorine concentration can be measured quickly and accurately even if the sample water is colored.

  In the measurement system of the present invention, a strong oxidizing agent such as ozone is assumed as an interfering substance. However, the measurement system of the present invention can be applied if the oxidant other than the chlorinated chemical is not used as the bactericidal agent. For example, the discharge after sterilization of the sewage treatment plant into which sodium hypochlorite has been injected. It was confirmed that the water measurement can be performed without any problem (the same applies to the residual chlorine measuring apparatus according to the second embodiment).

[Second Embodiment]
FIG. 12 is a schematic view of a residual chlorine measuring device 12 according to the second embodiment of the present invention. The residual chlorine measuring device 12 of the second embodiment differs from the residual chlorine measuring device 1 of the first embodiment in that it has a path (capillary tube 13) for injecting potassium iodide into the sample water sent to the flow cell 3. . Therefore, the same components as those in the residual chlorine measuring device 1 in FIG.

  As shown in FIG. 12, the residual chlorine measuring device 12 of the second embodiment includes an injection valve 2 into which a carrier liquid and sample water are injected, and a flow cell 3.

  Thin tubes 4 to 8 are connected to the injection valve 2 as flow paths. A mixing container 14 is provided between the narrow tube 6 and the flow cell 3.

  The mixing container 14 mixes a carrier solution into which sample water is injected and a reagent solution (for example, potassium iodide solution). A liquid feed pump 15 is connected to the mixing container 14 via a thin tube 13, and a reagent solution is injected by the liquid feed pump 15. A damper 16 is provided between the liquid feed pump 15 and the mixing container 14, and the damper 16 absorbs and eliminates the pulsating flow of the liquid feed pump 15.

  As described above, the residual chlorine measuring device 12 is configured with two flow paths, that is, a path for sending sample water to the flow cell 3 (thin tube 6) and a path for injecting the reagent solution into the sample water (thin tube 13). Then, the carrier liquid placed outside the apparatus is sent to the inside of the apparatus by the liquid feed pump 9 through the thin tube 4, and the carrier liquid is made to be the damper 11 at a constant speed by adjusting the rotation speed of the liquid feed pump 9. → Injection valve 2 → Feed to mixing container 14, reagent solution is mixed in mixing container 14, and then fed to flow cell 3 → drain bottle 10.

  Here, an example in which the residual chlorine concentration in the sample water is measured by the residual chlorine measuring device 12 will be shown, and the residual chlorine measuring method according to the embodiment of the present invention will be described in detail. In the residual chlorine measuring device 12 as well, the influence of the carrier liquid flow rate on the relationship between the sodium hypochlorite concentration and the quantity of electricity showed the same tendency as the residual chlorine measuring device 1 in FIG.

[Potassium iodide concentration injected into sample water]
First, the optimum potassium iodide concentration was examined.

  To 50 mL of a 3.2 mg / L sodium hypochlorite solution, 10 mL of a 3.2 mg / L ammonium chloride solution was added and reacted for exactly 5 minutes to produce chloramine. That is, a mixed liquid in which free chlorine and combined chlorine were mixed was prepared.

  5 mL of this mixed solution was dispensed into a test tube, 0.5 mL of potassium iodide prepared in various concentrations was added and mixed with a test tube mixer, and the amount of electricity was measured using the mixed solution as sample water.

  As shown in FIG. 13, when the concentration of the potassium iodide solution added to the mixed solution was 0.2 mol / L or more, a stable measurement value was shown. Therefore, in the following residual chlorine concentration measurement, the potassium iodide concentration was set to 0.25 mol / L. In addition, the potassium iodide concentration to be added is appropriately set according to the combined chlorine concentration contained in the sample water.

[Effect of potassium iodide on the measurement of residual chlorine concentration]
Next, the effect of adding potassium iodide on the measurement of residual chlorine concentration was examined.

  Add 10 mL of 3.2 mg / L ammonium chloride solution to 50 mL of sodium hypochlorite solution adjusted to 0, 2, 4, 6, 8, 10 mg / L effective chlorine concentration of sodium hypochlorite And reacted exactly for 5 minutes to produce chloramine. That is, a mixed liquid in which free chlorine and combined chlorine were mixed was prepared.

  5 mL of this mixed solution was dispensed into a test tube, 0.5 mL of 0.25 mol / L potassium iodide was added and mixed with a test tube mixer, and the amount of electricity was measured using the mixed solution as sample water.

  As shown in FIG. 14, even in the sample water in which free chlorine and combined chlorine are mixed, it is possible to measure combined chlorine by adding potassium iodide.

That is, since free residual chlorine has a strong oxidizing power, it can be directly measured by the flow cell 3 in the same manner as the residual chlorine measuring apparatus 1 of the first embodiment. On the other hand, bonded residual chlorine is weak in oxidizing power, but when potassium iodide is added, I ⁻ is easily oxidized to I ₂ . Since the electric quantity when I ₂ becomes I ⁻ can be measured by the flow cell 3, it is considered that the combined residual chlorine can be measured based on the electric quantity.

[Comparison with residual chlorine concentration measured by DPD method]
100 mL of 1.6 mg / L ammonium chloride solution was added to 470 mL of sodium hypochlorite solution prepared to 1.6 mg / L, and the amount of electricity and total chlorine concentration (residual chlorine concentration) were changed every 30 minutes. The measurement was performed both when potassium chloride was added and when pure water was added.

  In the measurement of the electrochemical method, 10 mL of a mixture of a sodium hypochlorite solution and an ammonium chloride solution is taken into an appropriate container every 30 minutes, and 1 mL of potassium iodide or pure water is added and mixed. The quantity of electricity was measured in a batch test using the flow cell 3.

  In the DPD method, the total chlorine concentration was measured with a pocket residual chlorine meter manufactured by HACH.

  FIG. 15 shows the relationship between the measurement result of the residual chlorine measuring device 12 and the measurement result of the residual chlorine concentration by the DPD method.

As shown in FIG. 15, by adding a potassium iodide solution and measuring the residual chlorine concentration, even when free chlorine and combined chlorine are mixed, the correlation between the amount of electricity and the total chlorine concentration by the DPD method Was highly correlated with R ² = 0.9847, and a stable result was obtained. On the other hand, when pure water was added without adding the potassium iodide solution, when free chlorine and bonded chlorine were mixed, there was no linearity and the amount of electricity was unstable.

  That is, by adding potassium iodide to the sample water, it becomes possible to measure bound chlorine and to measure the total chlorine concentration.

[Measurement of residual chlorine concentration in sample water with different residual chlorine concentrations]
Using the residual chlorine measuring device 12, the residual chlorine concentration was measured for sample water having different residual chlorine concentrations. In measuring the residual chlorine concentration, the measurement conditions were set in the same manner as the residual chlorine measuring device 1. That is, the measurement conditions were set according to the measurement conditions of the first embodiment.

  For example, the carrier liquid flow rate was set to 0.6 mL / min as in the first embodiment. In addition, when the influence of the flow rate of the reagent solution on the relationship between the sodium hypochlorite concentration and the quantity of electricity was examined, it showed the same tendency as the carrier solution flow rate, so the flow rate of the reagent solution was set to 0.6 mL / min. did. That is, since the flow rates of the carrier liquid and the reagent solution were each set to 0.6 mL / min, the liquid feeding amount to the flow cell 3 was 1.2 mL / min as the total amount of the carrier liquid and the reagent solution. The applied voltage was set to 0 V as in the first embodiment. Table 5 shows the test conditions of the residual chlorine measuring device 12.

  10 mL of 35.2 mg / L ammonium chloride solution was added to 50 mL of sodium hypochlorite solution prepared so that the effective chlorine concentration of sodium hypochlorite was adjusted to 0, 2, 4, 6, 8, 10 mg / L. For exactly 5 minutes to produce chloramine. That is, sample water in which free chlorine and combined chlorine are mixed and sample water having different effective chlorine concentrations was prepared, and the residual chlorine concentration of each sample water was measured.

  FIG. 16 shows the relationship between the effective chlorine concentration of sample water and the amount of electricity. FIG. 17 shows the measurement result of the total chlorine concentration measured by the DPD method.

From the results shown in FIG. 16, a highly correlated linearity and a determination coefficient R ² are obtained, and a highly reliable measurement is expected. Moreover, even if it is a case where free chlorine and combined chlorine are mixed by making it react with potassium iodide from the result of FIG. 17, the correlation between the amount of electricity and the total chlorine concentration by the DPD method is R ² = 0.9998. A high correlation was obtained, and a stable result was obtained. Therefore, based on this correlation, it can be seen that the residual chlorine concentration of the sample water can be accurately detected based on the amount of electricity detected in the flow cell 3.

[Measurement of residual chlorine concentration in sample water with different residual chlorine concentrations]
Sample water was prepared by changing the concentration of the ammonium chloride solution added to the sodium hypochlorite solution, and the residual chlorine concentration was measured under the measurement conditions shown in Table 5.

  First, 0, 3.2, 6.4, 9 was added to 50 mL of sodium hypochlorite solution prepared by adjusting the effective chlorine concentration of sodium hypochlorite to 0, 2, 4, 6, 8, 10 mg / L. , 12.8, 16.0, 22.4, 28.8, 35.2 mg / L of ammonium chloride solution of each concentration, 10 mL each was added and reacted for exactly 5 minutes to give different concentrations of chloramines Was generated. That is, sample water in which free chlorine and combined chlorine are mixed and sample water having different free residual chlorine concentration and combined residual chlorine concentration was prepared, and the residual chlorine concentration of the prepared sample water was measured.

As shown in FIG. 18, by adding potassium iodide to the sample water, the correlation between the amount of electricity and the total chlorine concentration by the DPD method is R ² = The correlation was as high as 0.9917. Therefore, based on this correlation, it can be seen that the residual chlorine concentration of the sample water can be accurately detected based on the amount of electricity detected in the flow cell 3. That is, the residual chlorine measuring device 12 can stably measure the residual chlorine concentration of the sample water in which free chlorine and combined chlorine are mixed.

  According to the residual chlorine measuring apparatus 12 according to the second embodiment of the present invention as described above, even when the sample water contains bound residual chlorine, the residual chlorine (total residual chlorine, free residual chlorine, combined residual chlorine) can be accurately obtained. ) Can be measured.

  That is, by mixing a reagent that reacts with bound residual chlorine in the sample water into the sample water, it is possible to measure the total residual chlorine including the bound residual chlorine. Moreover, since only free residual chlorine can also be measured by the same method as the residual chlorine measuring apparatus 1 according to the first embodiment, the combined residual chlorine concentration obtained by removing free residual chlorine from all residual chlorine can also be calculated. it can.

  Further, similarly to the residual chlorine measuring apparatus 1 according to the first embodiment, it is possible to measure the residual chlorine concentration easily and quickly with high accuracy without requiring a complicated operation requiring specialized knowledge and skill. Even if the sample water is colored, the chlorine concentration can be measured quickly and accurately. In addition, the residual chlorine concentration can be measured continuously and accurately, and measurement with little abrasion of the electrode surface, contamination of the measurement path and working electrode can be performed.

  The residual chlorine measuring method and the residual chlorine measuring apparatus of the present invention are not limited to the embodiments, and can be appropriately changed in design without impairing the features of the invention. Belongs to the technical scope of

  For example, in the description of the embodiment, sodium hypochlorite is used as a chlorinating agent having a bactericidal effect, but in addition to sodium hypochlorite, measurement of residual chlorine concentration when potassium hypochlorite is used. Can be applied to. In addition to sodium hypochlorite, it can also be applied to chlorinated chemicals such as calcium hypochlorite and liquefied chlorine, which are recognized as disinfectants in the Water Supply Law.

  In the description of the embodiment, the sample water is manually injected. However, by automatically injecting the sample water every predetermined period, the automatic measurement of the residual chlorine concentration of the sample water and the residual chlorine concentration are performed. Can be monitored.

DESCRIPTION OF SYMBOLS 1,12 ... Residual chlorine measuring device 2 ... Injection valve 3 ... Flow cell 4-8, 13 ... Thin tube 9, 15 ... Liquid feed pump 10 ... Drain bottle 11, 16 ... Damper 14 ... Mixing container

Claims (5)

A residual chlorine measurement method for measuring the residual chlorine concentration of sample water,
Distribute pure water as carrier liquid,
Injecting the sample water into the carrier liquid,
Supplying the carrier liquid injected with the sample water to the flow cell at a predetermined speed;
A residual chlorine measurement method, comprising: measuring a residual chlorine concentration in the sample based on a current or a charge detected by applying a voltage between electrodes arranged in the flow cell. The residual chlorine measuring method according to claim 1, wherein a potassium iodide solution is injected into a carrier liquid supplied to the flow cell. The residual chlorine measuring method according to claim 1 or 2, wherein a flow rate of the carrier liquid is 0.55 to 0.85 mL / min. A flow cell into which the sample water injected into the carrier liquid is introduced at a predetermined rate;
Measuring means for measuring a residual chlorine concentration in the sample water based on a current or a charge detected by applying a voltage between the electrodes arranged in the flow cell;
The residual chlorine measuring device, wherein the carrier liquid is pure water. 5. The residual chlorine measuring apparatus according to claim 4, further comprising means for injecting a potassium iodide solution into the carrier liquid introduced into the flow cell.

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