JP6652697B2 - Residual chlorine measurement system and program - Google Patents

Description

  The present invention relates to a residual chlorine measurement system and program. More specifically, the present invention relates to a residual chlorine measuring system for measuring free chlorine by an absorption spectrophotometric method, and a program for causing a residual chlorine measuring system to perform necessary processing.

  The chlorination is performed for disinfecting various kinds of water such as clean water, sewage, industrial water, wastewater, food washing water, pool water, and the like. The chlorinating agent used in this chlorination process must be put in the water to be disinfected in a sufficient amount to disinfect it. It is not desirable to give. In recent years, in order to make tap water “delicious water”, efforts have been started to reduce the concentration of residual chlorine, which is a cause of odor. Therefore, the measurement of the residual chlorine concentration of water into which a chlorinating agent is introduced has been performed.

Residual chlorine includes hypochlorous acid (free chlorine) generated by dissolving a chlorinating agent in water and chloroamine (bonded chlorine) generated by combining this with ammoniacal nitrogen. Is the total residual chlorine concentration.
As a manual analysis method for measuring the residual chlorine concentration, an o-tolidine colorimetric method (OT method), a diethyl-p-phenylenediamine colorimetric method (DPD method), an iodine titration method and the like are used.

  However, since the manual analysis method is complicated and measurement data can only be obtained intermittently, a residual chlorine measuring apparatus using a polarographic method has been conventionally used. This polarographic method is susceptible to fluctuations in electric conductivity and pH of sample water, coexistence of bound chlorine, and the like due to the measurement principle. In addition, the electrodes used for the polarographic method need to be polished, and there is a problem that a drive unit for polishing the electrodes is required and beads generated for the polishing are generated.

Further, since free chlorine absorbs at around 290 nm and bound chlorine absorbs at around 245 nm, a method for measuring residual chlorine by an absorptiometry is also known.
However, the free chlorine concentration determined from the absorbance near 290 nm is affected by the pH. That is, the absorption at around 290 nm is that of free chlorine in the form of hypochlorite ion (ClO ⁻ ), and that of the form of hypochlorous acid (HClO) does not absorb. Since the proportion of hypochlorite ion in the free chlorine depends on the pH, the measurement of residual chlorine by the absorptiometry will depend on the pH.

Then, in patent document 1, the density | concentration calculated | required by the absorptiometry method is performed based on the pH value separately measured with the pH meter.
Further, in Patent Document 2, in order to measure the concentration of hypochlorous acid contained in the strongly acidic water produced by the electrolytic water producing apparatus, strong alkaline water generated on the cathode side is mixed with the strongly acidic water, and It has been practiced to adjust the chlorite ion concentration to a strong alkalinity at which the concentration becomes almost 100%, and then to measure by a spectrophotometric method.

JP-B-61-33605 JP 2000-343080 A

However, in the case of Patent Document 1, in addition to the absorption photometer, a pH meter using a pH electrode must be separately prepared to measure the pH.
It is also conceivable to adjust the pH as in Patent Document 2, but a pH adjusting reagent is required to adjust the pH. In Patent Literature 2, the strong alkaline water generated on the cathode side can be used for the invention relating to the electrolyzed water production apparatus. However, when measuring residual chlorine such as clean water, a pH adjusting reagent must be separately prepared. .

The present invention has been made in view of the above points, and it is an object of the present invention to provide a residual chlorine measurement system capable of determining the concentration of free chlorine by absorptiometry without using a pH adjusting reagent or an electrode type pH meter. I do.
Another object of the present invention is to provide a program for causing a residual chlorine measurement system to perform necessary processing.

The present inventor has studied the above problems, and has focused on the fact that a sample solution in which the pH and the residual chlorine concentration are always controlled can be measured assuming that the pH is constant, and arrived at the present invention described below.
[1] an absorptiometer that measures the absorbance A1 at a first wavelength λ1 (provided that 230 nm ≦ λ1 ≦ 260 nm) and the absorbance A2 at a second wavelength λ2 (provided that 270 nm ≦ λ2 ≦ 320 nm) of the sample solution;
An arithmetic unit to which the absorbance obtained by the absorptiometer is input,
The arithmetic unit determines the free chlorine concentration of the sample solution based on the absorbance A2 or the ratio of the absorbance A2 to the absorbance A1 (A2 / A1), and the absolute value or unit of the ratio of the absorbance A2 to the absorbance A1 (A2 / A1). A residual chlorine measurement system, wherein an alarm is generated when a fluctuation amount per time is out of a predetermined range.

[2] The residual chlorine measurement system according to [1], wherein the arithmetic unit further obtains a bound chlorine concentration based on the absorbance A1.
[3] The absorptiometer further measures the absorbance A3 of the sample solution at a third wavelength λ3 (provided that 600 nm ≦ λ3 ≦ 700 nm),
The residual chlorine measurement system according to [1] or [2], wherein the arithmetic unit corrects the absorbance A1 and the absorbance A2 based on the absorbance A3.

[4] an absorptiometer for measuring the absorbance A1 at a first wavelength λ1 (230 nm ≦ λ1 ≦ 260 nm) and the absorbance A2 at a second wavelength λ2 (270 nm ≦ λ2 ≦ 320 nm) of the sample solution; A program for causing a residual chlorine measurement system including an arithmetic device to which an absorbance obtained by an absorptiometer is input to execute the following processes S1 and S3.
Process S1: A process for determining the free chlorine concentration of the sample solution based on the absorbance A2 or the ratio (A2 / A1) of the absorbance A2 to the absorbance A1.
Process S3: a process of generating an alarm when the absolute value of the ratio (A2 / A1) of the absorbance A2 and the absorbance A1 or the amount of variation per unit time falls outside a predetermined range.

[5] The program according to [4], which causes the arithmetic device to execute the following process S2 in addition to the processes S1 and S3.
Process S2: A process for determining the concentration of bound chlorine in the sample solution based on the absorbance A1.
[6] The absorption spectrophotometer of the residual chlorine measurement system further measures absorbance A3 of the sample solution at a third wavelength λ3 (where 600 nm ≦ λ3 ≦ 700 nm),
The program according to [4] or [5], wherein the arithmetic unit executes each process using the absorbance A1 and the absorbance A2 corrected based on the absorbance A3.

According to the residual chlorine measurement system of the present invention, the concentration of free chlorine can be determined by an absorptiometry without using a pH adjusting reagent or an electrode type pH meter.
Further, according to the program of the present invention, it is possible to cause the residual chlorine measuring system of the present invention to perform necessary processing.

1 is an overall configuration diagram of a residual chlorine measurement system according to an embodiment of the present invention. FIG. 3 is an absorption spectrum diagram of free chlorine and bound chlorine at various pHs. 5 is a calibration curve showing the relationship between the absorbance at 290 nm and the free chlorine concentration (DPD analysis value). It is a calibration curve which shows the relationship of the free chlorine concentration (DPD analysis value) with respect to the ratio of the light absorbency in 290 nm and the light absorbency in 245 nm. 4 is a calibration curve showing the relationship between the concentration of bound chlorine (DPD analysis value) in the range of pH 6 to 8 and the absorbance at 245 nm.

<Residual chlorine measurement system>
A residual chlorine measurement system according to one embodiment of the present invention will be described with reference to FIG. The residual chlorine measurement system according to the present embodiment includes an absorptiometer 10 and an arithmetic unit 20 to which absorbance obtained by the absorptiometer 10 is input.

  The absorptiometer 10 includes a light source 11, a collimating lens 12 for converting light emitted from the light source 11 into substantially parallel light, a condensing lens 13 for collecting light converted into substantially parallel light by the collimating lens 12, A measuring cell 14 arranged on the optical path between these lenses 12 and 13, a slit 15 provided in the vicinity of the converging position of the converging lens 13, and light passing through the slit 15 is condensed, It is roughly composed of a concave diffraction grating 16 for diffracting light in a specific direction in response thereto, and a photodetector 17 for detecting the spectrum of light separated by the concave diffraction grating 16.

As the light source 11, it is preferable to use a light source including light having the following first to third wavelengths λ1 to λ3. For example, a xenon flash lamp, LED, or the like can be used.
230 nm ≦ λ1 ≦ 260 nm
270 nm ≦ λ2 ≦ 320 nm
600 nm ≦ λ3 ≦ 700 nm

The first wavelength λ1 is a wavelength at which the bound chlorine mainly absorbs. The absorbance of the first wavelength λ1 due to the bound chlorine is hardly affected by the pH. The absorbance of the first wavelength λ1 due to free chlorine is small, and the influence of pH is small.
The first wavelength λ1 preferably satisfies 240 nm ≦ λ1 ≦ 250 nm.

The second wavelength λ2 is a wavelength at which free chlorine mainly absorbs. The absorbance at the second wavelength λ2 due to free chlorine is greatly affected by pH. The absorbance of the second wavelength λ2 by the bound chlorine is extremely small.
The second wavelength λ2 preferably satisfies 280 nm ≦ λ2 ≦ 300 nm.

The third wavelength λ3 is a wavelength showing absorption depending on turbidity. The turbid material also shows absorption at the first wavelength λ1 and the second wavelength λ2. By the absorbance at the third wavelength λ3, a correction excluding the influence of turbidity at the first wavelength λ1 and the second wavelength λ2 can be performed.
Preferably, the third wavelength λ3 is 650 nm ≦ λ3 ≦ 670 nm.

The measurement cell 14 may be a bottomed cylindrical cell capable of storing a sample liquid, or may be a flow cell through which the sample liquid can flow. The portion of the measurement cell 14 arranged on the optical path is formed of a transparent material that can transmit light from the first wavelength to the third wavelength.
The slit 15 has an elongated gap extending in a direction perpendicular to the blaze direction of the concave diffraction grating 16 and allows a part of the light collected by the condenser lens 13 to pass. The slit 15 determines the spectral purity of the measured spectrum.

The concave diffraction grating 16 condenses the light passing through the slit 15 and diffracts the light in a specific direction according to the wavelength. The photodetector 17 is a multi-channel detector in which a plurality of detection channels are arranged in parallel with the blaze direction of the concave diffraction grating 16.
According to the absorptiometer 10 of the present embodiment, absorbances at a plurality of wavelengths can be obtained substantially simultaneously. In the present invention, the absorbance at the first wavelength λ1 is referred to as absorbance A1, the absorbance at the second wavelength λ2 is referred to as absorbance A2, and the absorbance at the third wavelength λ3 is referred to as absorbance A3.

  The arithmetic device 20 has a storage unit 21 and an arithmetic unit 22. The storage unit 21 stores a calibration curve, a threshold, and the like necessary for the processing performed by the residual chlorine measurement system of the present invention. The calibration curve is not limited to the form of the equation, and may be stored in the form of a table.

It is preferable that all or a part of the storage content of the storage unit 21 can be rewritten by an operation unit (not shown).
The arithmetic unit 22 incorporates the program of the present invention, and performs processing performed by the residual chlorine measurement system of the present invention based on the absorbance input from the absorptiometer 10 and the information in the storage unit 21 according to the program. It is supposed to do.

<Sample liquid>
The sample liquid in the present invention is a liquid to be measured or a calibration liquid. The measurement target liquid is a sample liquid whose residual chlorine concentration is to be determined by the residual chlorine measurement system of the present invention. The calibration liquid is a sample liquid for obtaining a calibration curve or the like in the residual chlorine measurement system of the present invention.

As the liquid to be measured, a sample whose residual chlorine concentration and pH are always controlled is preferable. For example, tap water, sewage discharge water, and overflow water are mentioned.
The pH of the liquid to be measured is preferably in the range of 6 to 9. Further, the concentration of hypochlorite ion is preferably 0.15 mg / L or more. This is because the change in the absorbance ratio in the present invention is considered to reflect the change in pH under the condition where hypochlorite ions are present. Since the hypochlorite ion concentration depends on the pH, for example, if the pH is 7.3, the free chlorine concentration is preferably 0.5 mg / L or more. The concentration of free chlorine in the liquid to be measured is preferably 5 mg / L or less.

It is preferable that the residual chlorine concentration range of the calibration liquid is dispersed in a free chlorine concentration range and a bound chlorine concentration range which can be usually taken by the liquid to be measured.
It is preferable to use a calibration solution having the same pH as the solution to be measured. For example, when the solution to be measured is controlled at around pH 7.5, it is preferable to use a calibration solution adjusted to around pH 7.5.
It should be noted that it is also possible to use a calibration liquid having a pH different from that of the liquid to be measured and to perform the correction by the method of Patent Document 1.

As the calibration liquid, it is preferable to use at least a zero liquid and a span liquid. The zero solution is a calibration solution for obtaining a zero calibration value. The span solution is a calibration solution having a chlorine concentration near the upper limit of the free chlorine concentration or the combined chlorine concentration that can be usually taken by the liquid to be measured.
In order to consider the influence of coexisting components, it is preferable that the calibration liquid is prepared based on a sample liquid equivalent to the liquid to be measured. For example, when the liquid to be measured is tap water, it is preferable to prepare the solution based on dechlorinated water from which the chlorine content of tap water has been removed and to which hypochlorite, ammonium salt, and the like are added.
Examples of the method for removing chlorine include a method for volatilizing chlorine and a method for causing chlorine to be adsorbed on activated carbon or the like.
As the zero liquid, pure water may be used in addition to dechlorinated water.
The residual chlorine concentration of the calibration solution can be confirmed by an o-tolidine colorimetric method (OT method), an iodometric method, or the like, in addition to the DPD method.

<Process performed by the system>
The method for measuring residual chlorine according to one embodiment of the present invention performs the following processes S1 to S3. The order in which the processes S1 to S3 are performed is not limited, and they may be performed simultaneously and in parallel.

[Processing S1]
The process S1 is a process for obtaining the free chlorine concentration Nf of the sample liquid based on the absorbance A2 or the ratio of the absorbance A2 to the absorbance A1 (A2 / A1). When the sample solution is measured fluid is a process based on the following formula (1) or the following formula (2), determine the free chlorine concentration Nf _X of the liquid to be measured.

Nf _X = f ₁ (A2 _X ) (1)
_{Nf X = f 2 (A2 X} / A1 X) ··· (2)
A1 _X : Absorbance A1 when the sample liquid is the liquid to be measured.
A2 _X : Absorbance A2 when the sample liquid is the liquid to be measured.
A2 _X / A1 _X : ratio of the absorbance A2 and the absorbance A1 when the sample liquid is the liquid to be measured (A2 / A1).
f ₁ : a function indicating the free chlorine concentration using the absorbance A2 as a variable, obtained using the calibration liquid as a sample liquid.
f ₂ : a function of the free chlorine concentration using the ratio of the absorbance A2 and the absorbance A1 (A2 / A1) as a variable, obtained using the calibration liquid as a sample liquid.

For example, f ₁ includes the following formula (1-1).
f ₁ (A2) = e × (A2-g) (1-1)
e: Span coefficient of free chlorine.
g: Zero calibration value of free chlorine.
As the data for obtaining the span coefficient e and the zero calibration value g, a combination of the absorbance A2 of the calibration liquid measured using an absorptiometer and the free chlorine concentration Nf obtained by a manual analysis method is used.

The f _2, for example, of the formula (2-1) can be mentioned below.
f ₂ (A2 / A1) = h × {(A2 / A1) −i} (2-1)
h: Span coefficient of free chlorine.
i: Zero calibration value of free chlorine.
As the data for obtaining the span coefficient h and the zero calibration value i, the absorbance A2 and the absorbance A1 of the calibration liquid measured using an absorptiometer and the free chlorine concentration Nf obtained by a manual analysis method are used.
The span coefficients e and h and the zero calibration values g and i may be stored in the storage unit 21 as fixed values, but are preferably updated each time a periodic calibration operation is performed.

[Processing S2]
The process S2 is a process for obtaining the bound chlorine concentration Nc of the sample solution based on the absorbance A1. When the sample solution is measured fluid is a process based on the following equation (3), obtaining the combined chlorine concentration Nc _X of the liquid to be measured.
Nc _X = f ₃ (A1 _X ) (3)
f ₃ : a function of the concentration of bound chlorine using the absorbance A1 as a variable, obtained by using the calibration liquid as a sample liquid.

The f _3, for example, the following equation (3-1).
f ₃ (A1) = n × (A1-o) (3-1)
n: span coefficient of bound chlorine.
o: Zero calibration value of bound chlorine.

As the data for obtaining the span coefficient n and the zero calibration value o, the absorbance A1 of the calibration liquid measured using an absorptiometer and the bound chlorine concentration Nc determined by a manual analysis method are used. Since the relationship between the absorbance and the concentration of bound chlorine is hardly affected by the pH, the pH of the calibration solution for obtaining the coefficients n and o does not need to be particularly considered.
The span coefficient n and the zero calibration value o may be stored in the storage unit 21 as fixed values, but are preferably updated each time periodic calibration work is performed.

[Processing S3]
The process S3 is a process for generating an alarm when the absolute value of the ratio (A2 / A1) of the absorbance A2 and the absorbance A1 or the amount of change per unit time is out of a predetermined range.
Specifically, when any one of the following equations (4-1) to (5-2) is satisfied, it is determined that an alarm should be issued, and an alarm can be issued.
Note that the alarm can be output by one or more known methods such as sound, display, and transmission signal.

A2 / A1 <K1 (4-1)
A2 / A1 ≦ K2 (4-2)
A2 / A1> K3 (4-3)
A2 / A1 ≧ K4 (4-4)
Δ (A2 / A1)> K5 (5-1)
Δ (A2 / A1) ≧ K6 (5-2)

However, K1 to K6 are thresholds that can be set arbitrarily. Δ (A2 / A1) is a fluctuation amount per unit time of the ratio (A2 / A1) of the absorbance A2 to the absorbance A1.
K1 to K4 take into account the control range of the free chlorine concentration of the sample solution, and if the ratio is within the ratio (A2 / A1) of the absorbance A2 and the absorbance A1 corresponding to the control range, no alarm is issued, and if it is out of the range. The value may be set so that an alarm is issued.
The values of K5 and K6 may be set in consideration of the required control system.

It is possible to determine the necessity of alarm generation by combining any one or two of Expressions (4-1) to (5-2).
It is preferable to use the expressions (4-1) and (4-3) in combination to determine the necessity. In addition, it is preferable to use the expressions (4-2) and (4-4) in combination to determine the necessity.

  Satisfying any one of the formulas (4-1) to (5-2) indicates that at least one of the free chlorine concentration and the pH of the sample solution may be out of the control range. Therefore, when an alarm is issued, the user can know that such a possibility has occurred. In addition, when the alarm is not issued, the concentration of free chlorine can be measured without worrying about whether the pH is controlled in a predetermined range.

The absorbances A1 and A2 used in the above processes S1 to S3 are affected when the sample solution contains a turbid substance. Therefore, it is preferable to perform turbidity correction using the following formulas (6) and (7) using the absorbance A3.
A1 = f ₄ (A1 ′, A3) (6)
A2 = f ₅ (A2 ′, A3) (7)
A1 ′: Absorbance at wavelength λ1 when the sample liquid is the liquid to be measured, directly measured by the absorptiometer.
A2 ′: Absorbance at wavelength λ2 when the sample liquid is the liquid to be measured, directly measured by the absorptiometer.
A3: Absorbance at wavelength λ3 when the sample liquid is the liquid to be measured, directly measured by the absorptiometer.
f ₄ : a function of the corrected absorbance A1 using the absorbance A1 ′ and the absorbance A3 as variables.
f ₅ : function of the corrected absorbance A2 using the absorbance A2 ′ and the absorbance A3 as variables.

The f _4, for example, of the formula (6-1) can be mentioned below.
f ₄ (A1 ′, A3) = A1′−p × A3 (6-1)
p: correction coefficient.
The f _5, for example, of the formula (7-1) can be mentioned below.
f ₅ (A2 ′, A3) = A2′−q × A3 (7-1)
q: correction coefficient.

Data for obtaining the coefficients p and q include a combination of an absorbance A1 and an absorbance A3 measured using an absorptiometer on a solution obtained by appropriately diluting a turbidity standard solution (such as kaolin, formazin, or PSL standard solution). Alternatively, a combination of the absorbances A2 and A3 is used.
Since the coefficients p and q do not change so much, they may be stored in the storage unit 21 as fixed values.
The value of the coefficient p is more than 0 and not more than 1.0, and the value of the coefficient q is more than 0 and not more than 1.0.

Note that the absorbance used in the residual chlorine measurement system of the present invention is preferably an absorbance that is zero-corrected by subtracting the absorbance of a reference sample such as pure water or air.
Therefore, the absorption spectrophotometer in the residual chlorine measurement system of the present invention may be a so-called double beam type spectrophotometer that can simultaneously measure the absorbance of the measurement sample and the reference sample. Further, a self-recording spectrophotometer that switches between the standard light beam and the measurement light beam at high speed, or an online spectrophotometer that periodically corrects zero at set intervals may be used.
Further, the absorption spectrophotometer of the residual chlorine measurement system of the above embodiment is configured to split the light after passing through the measurement cell 14, but may be split before the light enters the measurement cell 14. Further, the means for separating light is not limited to the diffraction grating, and the wavelength may be selected using, for example, a metal interference filter or the like. Further, the photodetector is not limited to the multi-channel detector, and for example, a photodiode or a photomultiplier may be used.

In the above-described embodiment, the program for causing the arithmetic unit 22 to execute each process is incorporated in the arithmetic unit 22 in the arithmetic device 20. However, some or all of the functions of the arithmetic device 20 An external computer connected directly or using a communication system may be used.
In that case, the program may be recorded in a computer in advance, or may be recorded on a computer-readable recording medium, and the program recorded on this recording medium may be read by a computer.
Further, a program recorded in a computer in advance and a program recorded in a computer-readable recording medium and read by the computer may be combined.
Further, in the residual chlorine measurement system of the above embodiment, the processes S1 to S3 are performed, but the process S2 may be omitted.

<Preparation of sample liquid>
The sample solutions used in the following Examples and Experimental Examples were prepared using the following stock solutions and the like.
Dechlorinated water: Water that has been filtered through a hollow fiber membrane after adsorbing chlorine in tap water on activated carbon.
Sodium hypochlorite stock solution: A solution of about 12% by mass of sodium hypochlorite diluted with pure water to adjust the concentration of hypochlorous acid to 1000 mg / L.
Ammonia standard solution (1000 mg / L) manufactured by Toa DKK Corporation.
NaOH solution: about 0.5% by weight aqueous solution of sodium hydroxide.
HCl solution: about 0.5% by weight hydrochloric acid.

<Measurement of residual chlorine concentration by DPD method>
The residual chlorine concentration of each sample solution by the DPD method was determined by the "iodine titration method" described in (14) Standard chlorinated water in "30.3 Absorption spectrophotometry using diethyl-p-phenylenediamine" in the 2011 Clean Water Test Method. (Hereinafter referred to as "DPD method"). Specifically, it was measured as follows.

(A) Preparation of DPD reagent 1.0 g of N, N-diethyl-phenylenediamine sulfate and 24 g of anhydrous sodium sulfate were mixed to prepare a DPD (N, N-diethyl-p-phenylenediamine) reagent.
(B) Preparation of phosphate buffer (pH = 6.5) To 100 mL of 0.2 mol / L potassium dihydrogen phosphate, 35.4 mL of a 0.2 mol / L sodium hydroxide solution was added, and trans-1,2 was added thereto. 0.13 g of cyclohexanediaminetetraacetic acid-hydrate was dissolved to prepare a phosphate buffer (pH = 6.5).

(C) Measurement of Free Chlorine Concentration 2.5 mL of the phosphate buffer was placed in a 50-mL container with a stopper, and 0.5 g of the DPD reagent was added thereto, followed by adding a sample solution to make the total volume 50 mL, and mixing.
About 3 mL of the obtained mixed solution is taken in an absorption cell, and the absorbance at a wavelength of 528 nm is measured 10 seconds after mixing using a photoelectric spectrophotometer, and the free chlorine concentration is determined from a calibration curve prepared in advance. Was.

(D) Measurement of Concentration of Bound Chlorine 2.5 mL of phosphate buffer was placed in a 50 mL container with a stopper, and 0.5 g of DPD reagent was added thereto.
About 50 g of potassium iodide was added to and dissolved in 50 mL of the obtained mixed solution. Next, about 3 mL of the solution after the addition of potassium iodide was taken into an absorption cell, and the absorbance at a wavelength of 528 nm was measured 2 minutes after the addition of potassium iodide using a photoelectric spectrophotometer. The total residual chlorine concentration was determined.
The value obtained by subtracting the free chlorine concentration obtained in (c) from the total residual chlorine concentration was defined as the bound chlorine concentration.

<Measurement of pH>
Using a WM-22P pH meter manufactured by TOA KK, pH measurement values of each sample solution were obtained.
<Measurement of absorption spectrum and absorbance>
The measurement was performed using a U-3200 self-recording spectrophotometer manufactured by Hitachi High-Technologies Corporation.

<Experimental example 1>
Absorption spectra were obtained for the following sample solutions. The results are shown in FIG.
-"F0.76mg / L pH7.35"
About 0.8 mL of sodium hypochlorite stock solution was diluted with dechlorinated water to 1000 mL. The free chlorine concentration (DPD method) of the obtained sample solution was 0.76 mg / L, and the pH was 7.35.
-"F0.76mg / L pH4.15"
While measuring the pH with a pH electrode, an HCl solution was added to the sample solution of “F 0.76 mg / L pH 7.35” so that the pH became about 4. The pH of the obtained sample solution was 4.15.
-"F0.76mg / L pH8.06"
While measuring the pH with a pH electrode, a NaOH solution was added to the sample solution of “F 0.76 mg / L pH 7.35” so that the pH became about 8. The pH of the obtained sample solution was 8.06.

-"C0.8mg / L pH6.89"
About 0.2 mL of an ammonia standard solution (1000 mg / L) manufactured by Toa DKK Corporation and about 0.8 mL of a sodium hypochlorite stock solution were diluted with dechlorinated water to 1000 mL. The obtained sample solution had a free chlorine concentration (DPD method) of about 0.04 mg / L, a bound chlorine concentration (DPD method) of 0.76 mg / L, and a pH of 6.89.
-"C 0.8 mg / L pH 4.37"
While measuring the pH with a pH electrode, an HCl solution was added to the sample solution of “C 0.8 mg / L pH 6.89” so that the pH became about 4. The pH of the obtained sample solution was 4.37.
-"C 0.8 mg / L pH 8.07"
While measuring the pH with a pH electrode, a NaOH solution was added to the sample solution of “C 0.8 mg / L pH 6.89” so that the pH became about 8. The pH of the obtained sample solution was 8.07.

  As shown in FIG. 2, absorption of free chlorine was observed at around 290 nm. Further, absorption of bound chlorine was observed at around 245 nm. The absorption of bound chlorine around 245 nm was almost the same irrespective of the pH, but it was confirmed that the absorption of free chlorine around 290 nm varied greatly depending on the pH. The absorption of free chlorine around 290 nm increases as the pH increases. This is because the absorption around 290 nm has sensitivity to hypochlorite ion and has no sensitivity to hypochlorous acid.

<Experimental example 2>
To the dechlorinated water, a sodium hypochlorite stock solution and, if necessary, a NaOH solution or an HCl solution were added to prepare various sample solutions having a pH of 6 to 8 and various free chlorine concentrations. About each prepared sample solution, the free chlorine concentration by the DPD method and the pH by the pH electrode were confirmed. In addition, the absorbance at 290 nm (290 nm Abs) of each sample solution was measured. FIG. 3 shows the relationship between the absorbance at 290 nm and the free chlorine concentration by the DPD method for each of the sample solution having a pH of 6, the sample solution having a pH of 7, and the sample solution having a pH of 8.
As shown in FIG. 3, when the pH was constant, it was confirmed that the absorbance at 290 nm and the free chlorine concentration by the DPD method showed a good correlation.

<Experimental example 3>
To the dechlorinated water, a sodium hypochlorite stock solution and, if necessary, a NaOH solution or an HCl solution were added to prepare various sample solutions having a pH of 6 to 8 and various free chlorine concentrations. About each prepared sample solution, the free chlorine concentration by the DPD method and the pH by the pH electrode were confirmed. Further, the absorbance at 245 nm and the absorbance at 290 nm of each sample solution were measured, and the ratio of the absorbance at 290 nm to the absorbance at 245 nm (290/245 nm Abs) was determined. FIG. 4 shows the relationship between the ratio of the absorbance at 290 nm to the absorbance at 245 nm and the free chlorine concentration according to the DPD method for each of the sample solution having a pH of 6, the sample solution having a pH of 7, and the sample solution having a pH of 8. Show the relationship.
As shown in FIG. 4, when the pH was constant, it was confirmed that a good correlation was exhibited between the ratio of the absorbance at 290 nm to the absorbance at 245 nm and the free chlorine concentration by the DPD method.

<Experimental example 4>
To the dechlorinated water, add a sodium hypochlorite stock solution, an ammonia standard solution (1000 mg / L) manufactured by Toa DKK Inc., and if necessary, a NaOH solution or an HCl solution. Various sample solutions having various concentrations were prepared. For each of the prepared sample solutions, the bound chlorine concentration by the DPD method and the pH by the pH electrode were confirmed. Further, the absorbance at 245 nm was determined for each sample solution. FIG. 5 shows the relationship between the absorbance at 245 nm and the concentration of bound chlorine by the DPD method for each of the sample solution having a pH of 6, the sample solution having a pH of 7, and the sample solution having a pH of 8.
As shown in FIG. 5, it was confirmed that regardless of pH, the absorbance at 245 nm and the concentration of bound chlorine by the DPD method showed a good correlation.

10: Absorbance photometer, 11: Light source, 12: Collimating lens, 13: Condensing lens,
14 measurement cell, 15 slit, 16 concave diffraction grating, 17 photodetector,
20 arithmetic unit, 21 storage unit, 22 arithmetic unit

Claims (6)

An absorptiometer that measures absorbance A1 at a first wavelength λ1 (provided that 230 nm ≦ λ1 ≦ 260 nm) and absorbance A2 at a second wavelength λ2 (provided that 270 nm ≦ λ2 ≦ 320 nm) of the sample solution;
An arithmetic unit to which the absorbance obtained by the absorptiometer is input,
The arithmetic unit determines the free chlorine concentration of the sample solution based on the absorbance A2 or the ratio of the absorbance A2 to the absorbance A1 (A2 / A1), and the absolute value or unit of the ratio of the absorbance A2 to the absorbance A1 (A2 / A1). A residual chlorine measurement system, wherein an alarm is generated when a fluctuation amount per time is out of a predetermined range.   The residual chlorine measurement system according to claim 1, wherein the arithmetic unit further obtains a concentration of bound chlorine based on the absorbance A1. The absorptiometer further measures the absorbance A3 of the sample solution at a third wavelength λ3 (where 600 nm ≦ λ3 ≦ 700 nm),
The residual chlorine measurement system according to claim 1 or 2, wherein the arithmetic unit corrects the absorbance A1 and the absorbance A2 based on the absorbance A3. An absorptiometer that measures the absorbance A1 at a first wavelength λ1 (230 nm ≦ λ1 ≦ 260 nm) and an absorbance A2 at a second wavelength λ2 (270 nm ≦ λ2 ≦ 320 nm) of the sample solution, and the absorptiometer A program for causing a residual chlorine measurement system including an arithmetic unit to which the absorbance obtained in step 1 is input to execute the following processes S1 and S3.
Process S1: A process for determining the free chlorine concentration of the sample solution based on the absorbance A2 or the ratio (A2 / A1) of the absorbance A2 to the absorbance A1.
Process S3: a process of generating an alarm when the absolute value of the ratio (A2 / A1) of the absorbance A2 and the absorbance A1 or the amount of variation per unit time falls outside a predetermined range. The program according to claim 4, wherein the program causes the arithmetic device to execute the following process S <b> 2 in addition to the processes S <b> 1 and S <b> 3.
Process S2: A process for determining the concentration of bound chlorine in the sample solution based on the absorbance A1. The absorption spectrophotometer of the residual chlorine measurement system further measures the absorbance A3 of the sample solution at a third wavelength λ3 (where 600 nm ≦ λ3 ≦ 700 nm),
The computer-readable storage medium according to claim 4, wherein the computer is configured to execute each process using the absorbance A <b> 1 and the absorbance A <b> 2 corrected based on the absorbance A <b> 3.

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