TWI760465B - Urea quantifying method and analysis device - Google Patents

Abstract

A method for quantifying the urea in a water sample by a colorimetry method using diacetyl monoxime, wherein a reagent prepared for use in the reaction is refrigerated, and the urea is quantified using the refrigerated reagent. Specifically, an antipyrine-containing reagent solution is prepared, and the reagent solution is kept at a temperature of, for example, 20° or below until used to quantify the urea.

Description

Quantitative method and analysis device for urea

The present invention relates to a method and an analysis device for quantifying urea in water.

There is a requirement for high-precision quantification of trace urea in water. For example, when pure water is produced from raw water by a pure water production system, it is difficult to remove urea in the raw water by an ion exchange device or an ultraviolet oxidation device constituting the pure water production system. Therefore, the raw water from which urea has been removed in advance must be supplied to the pure water production system. As a method for removing urea, a method of selectively oxidizing urea by hypobromous acid is known by adding a chemical that generates hypobromous acid to raw water. However, the chemical that generates hypobromous acid also places a load on the pure water production system. The amount of drug input is as little as possible. Therefore, it is desirable to determine the necessity of urea treatment after quantifying the urea concentration in the raw water, and to inject appropriate chemicals when the treatment is necessary. Furthermore, it is also required to measure the urea concentration in the pure water obtained by the pure water production system.

As a quantitative method of urea, a quantitative method based on a colorimetric method using diacetylmonoxime is known. As an example of this quantitative method, there is a method described in "Sanitary Testing Law" (Non-Patent Document 1) issued by the Pharmaceutical Association of Japan. In the colorimetric method using diacetyl monoxime, other reagents, such as mixed solution of antipyrine and sulfuric acid, aqueous solution of hemicarbazine hydrochloride, mixed with manganese chloride and Nitric acid Aqueous solution of potassium, mixed solution of sodium dihydrogen phosphate and sulfuric acid, etc. In the case of using antipyrine in combination, diacetyl monoxime is dissolved in an acetic acid solution to prepare a diacetyl monoxime acetic acid solution, and antipyrine (1,5-dimethyl-2-phenyl-3- Dihydropyrazolone), for example, is dissolved in sulfuric acid to prepare a reagent solution containing antipyrine, a diacetoxymonoacetic acid solution and a reagent solution containing antipyrine are sequentially mixed with sample water, and the wavelength of The absorbance around 460nm was quantified by comparison with the standard solution.

The method for quantifying urea by colorimetry using diacetoxymonooxime is designed for the purpose of quantifying urea in swimming pool water or public bathing water, for example. Sensitivity is poor for quantification. Therefore, Patent Document 1 discloses a method for quantifying urea on-line continuously in a concentration range of ppb or less to several ppm by measuring absorbance by applying flow injection analysis (FIA) in accordance with a colorimetric method using diacetylmonoxime simultaneously .

[Prior Art Literature]

[Patent Literature]

Patent Document 1: Japanese Patent Application Laid-Open No. 2000-338099

[Non-patent literature]

Non-Patent Document 1: Edited by the Pharmaceutical Society of Japan, Annotation 1990.4.1.2.3(13)1 (1990 Edition No. 4 Supplementary Supplement (1995), p1028), 1995

The method described in Patent Document 1 is a method that can continuously quantify trace amounts of urea on-line, but has the problem that the urea concentration cannot be stably measured over time.

The object of the present invention is to provide a method and an analytical device for continuously quantitatively performing on-line urea stably over a long period of time.

The inventors of the present invention found that when the quantification of trace urea was continuously performed on-line by the colorimetric method using diacetyl monoxime, the reagent used for the reaction was preserved by refrigeration, especially after preparation by refrigeration. The reagent solution containing antipyrine can stably quantify the urea concentration over a long period of time, thereby completing the present invention.

Therefore, the method of the present invention is a method for quantifying urea in a sample water by a colorimetric method using diacetyl monoxime, characterized in that the reagent prepared for the reaction is refrigerated, and a refrigerated reagent is used. Reagents to quantify urea.

Furthermore, the analyzer of the present invention is an analyzer for continuously quantifying urea in sample water by a colorimetric method using diacetoxymonooxime, and includes: a storage tank for storing a reagent prepared for use in a reaction; And the cooling mechanism for cooling the storage tank.

In the present invention, refrigerating a reagent prepared for use in a reaction means that after the preparation of the reagent, the temperature of the reagent is preferably maintained at 20°C or lower, and more preferably at 3°C or higher and 20°C or lower. Preferably, it is more preferably maintained at above 5°C and below 15°C. In addition, these reagents are preferably stored in a light-shielding manner. When the refrigerating temperature is too low, there is a possibility that the reagent will freeze. The quantification of urea using diacetyl monoxime is the same as that of diacetyl mono The oxime is used in combination with a reagent for promoting the reaction, etc., and it is preferable to use antipyrine as the reagent used in combination. In the case of using antipyrine in combination, the diacetyl monoxime acetic acid solution and the reagent solution containing antipyrine are used, so the present invention in this case is the refrigerated diacetyl monoxime acetic acid solution and antipyrine-containing solution. One of Lin's test liquids, or both of them, and especially the test liquid containing antipyrine is preferably refrigerated. The reagent solution containing antipyrine is, for example, a reagent solution obtained by dissolving antipyrine in sulfuric acid.

As will be described later, the method of the present invention is suitable, for example, for continuously quantifying urea for a period of several days or more, and is particularly suitable for quantifying urea by applying the FIA method to measure the absorbance.

According to the present invention, continuous dosing of urea on-line can be performed stably over a long period of time.

10: Injection valve

11: Specimen Loop

31: Reaction Coil

32: Detector

33: Back pressure coil

40: Refrigeration Department

41, 42: Storage tank

43, 44: Mixing Department

Fig. 1 is a diagram showing the configuration of an analysis apparatus according to an embodiment of the present invention.

[FIG. 2] A graph showing the relationship between the number of days of water injection and the peak intensity in Example 1. [FIG.

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows the structure of an analysis apparatus according to an embodiment of the present invention. Here, the present invention will be described by taking, as an example, a case where the amount of raw water used for the production of pure water or the amount of urea contained in the pure water itself is quantified on-line. However, the water that contains urea and is the subject of quantitative determination in the present invention is not limited to these, and the term "raw water for producing pure water" here also includes reclaimed water recovered from a process using pure water when the pure water is recycled.

As shown in FIG. 1, the line 20 of raw water for producing pure water is provided, and in this line 20, the raw water is sent by the pump P0. The sample piping 21 branched from the line 20 of raw water is provided. The sample piping 21 is a piping for the sample water branched from the raw water, and includes an on-off valve 22 and a flow meter FI. The tip of the sample pipe 21 is provided with a sample injection valve 10 (also referred to as a syringe or an injection valve). The part including the injection valve 10 and downstream of the injection valve 10 has a structure as a flow injection analysis (FIA) device, and is actually a part related to quantitative urea.

The injection valve 10 is a structure generally used in the FIA method, and includes a six-way valve 11 and a sample loop 12 . The six-way valve 11 has six ports shown in [1], [2], [3], [4], [5] and [6] in the figure. The sample piping 21 is connected to the port [2]. In addition, the piping 23 for supplying the carrier water via the pump P1 is connected to the port [6], and the piping 25 for discharging the sample water via the pump P4 is connected to the port [3]. A sample loop 12 for taking a predetermined volume of sample water is connected between the port [1] and the port [4]. The port [ 5 ] is connected to one end of the pipe 24 at the outlet of the injection valve 11 . The carrier water system does not substantially contain urea water.

In the six-way valve 11, if the communication between the port X and the port Y is expressed as (X-Y), the six-way valve 11 can be switched to the first of (1-2), (3-4), (5-6) State 1, and State 2 of (2-3), (4-5), and (6-1). In FIG. 1 , the connection relationship between the ports in the first state is indicated by a solid line, and the connection between the ports in the second state is indicated by a dotted line. In the first state, the carrier water system flows through the pipe 23→port [6]→port [5]→pipe 24, and flows out from the injection valve 10 to the downstream side. The sample water system flows through the sample piping 21→port [2]→port [1]→sample loop 12→port [4]→port [3], and is discharged from the piping 25. When switching from the first state to the second state, the sample water system flows through the sample piping 21→port [2]→port [3] and is discharged from the piping 25, and the carrier water system flows through the piping 23→port [6]→Port [1]→Sample loop 12→Port [4]→Port [5]→Pipe 24, and flow out to the downstream side. At this time, the sample water that has flowed into and filled the sample loop 12 in the first state flows into the pipe 24 from the port [ 5 ] one step ahead of the carrier water and flows to the downstream side of the injection valve 10 . The volume of sample water flowing to the piping 24 is defined by the sample loop 12 . Therefore, by repeatedly switching the first state and the second state, for example, by rotating the six-way valve 11 in the direction of the arrow shown in the figure, a predetermined volume of sample water can be repeatedly fed into the piping 24 . The switching between the first state and the second state can be performed every predetermined time in consideration of the residence time required for the reaction described later and the time until urea is detected by the detector 32 . In addition, it is also possible to detect that the sample water introduced into the detector 32 is discharged from the detector 32 to perform switching. In this way, by automatically switching between the first state and the second state, urea can be continuously quantified.

In this analyzer, the FIA method is applied to the urea quantitative system using the colorimetric method of diacetylmonoxime. Therefore, a diacetoxymonoacetic acid solution (hereinafter also referred to as reagent A) and a reagent solution containing antipyrine (hereinafter also referred to as reagent B) were used as reaction reagents for quantifying urea. These reagents are stored in storage tanks 41 and 42 provided in the refrigerating unit 40, respectively. The reagent A can be prepared by dissolving diacetylmonoxime in an acetic acid solution, but in the present embodiment, the preparation itself is performed in the storage tank 41, or the reagent A is stored in the storage tank 41 after the preparation. Similarly, the reagent B system can be prepared by dissolving antipyrine in sulfuric acid, for example, and the preparation itself can be performed in the storage tank 42 , or the reagent B can be stored in the storage tank 42 after the preparation. The refrigerating unit 40 shields the storage tanks 41 and 42 from light and cools the storage tanks 41 and 42, thereby maintaining the temperature of the reagent A and the reagent B in the storage tanks 41 and 42 below 20°C, preferably 3 ℃ or higher and 20°C or lower, more preferably 5°C or higher and 15°C or lower. In addition, the storage tank 41 in which the reagent A is stored does not necessarily need to be arranged in the refrigerating part 40 as long as the storage tank 41 can be stored in a light-shielding manner. In addition, even if the refrigerating temperature of the reagent is lower than 5°C, there is no problem as long as the precipitation of crystals does not occur in the reagent. In addition, with respect to the antipyrine sulfuric acid solution obtained by dissolving antipyrine in sulfuric acid, it is described in Non-Patent Document 1 that it can be used for 2 to 3 months if stored in a brown bottle, and because even if crystals are precipitated and returned to It does not dissolve when warmed to room temperature, so it is not suitable for refrigerated storage; however, the inventors of the present invention have confirmed through experiments that the antipyrine sulfuric acid solution prepared according to the method described in Non-Patent Document 1, even at 3°C Nor will it crystallize.

One end of the pipe 26 is connected to the storage tank 41 , and the other end of the pipe 26 is connected to the pipe 24 via the mixing part 43 . The pipe 26 is provided with a pump P2 for feeding the reagent A into the pipe 24 at a predetermined flow rate. Similarly, one end of the piping 27 is connected to the storage tank 42 , and the other end of the piping 27 is connected to the piping 24 via the mixing unit 44 . The pipe 27 is provided with a pump P3 for feeding the reagent B into the pipe 24 at a predetermined flow rate. The mixing parts 43 and 44 have a function of uniformly mixing the reagent A and the reagent B with respect to the flow of the liquid in the pipe 24 , respectively. The other end of the piping 24 is connected to the inlet of the reaction coil 31 provided in the reaction thermostatic chamber 30 . The reaction coil 31 is in its interior, so that the chromogenic reaction caused by urea and diacetyl monooxime in the presence of antipyrine occurs, and its length and the flow rate in the interior of the reaction coil 31 can be adjusted according to. The residence time required for the reaction is appropriately selected. The reaction thermostat 30 heats the reaction coil 31 to a temperature suitable for the reaction. For example, the reaction coil 31 is heated to a temperature of 50°C or higher and 150°C or lower, preferably 90°C or higher and 120°C or lower.

Connected to the outlet of the reaction coil 31 is a detector 32 for measuring the absorbance of the color generated by the color reaction. The detector 32 obtains, for example, the peak intensity or peak area of absorbance in the vicinity of the wavelength of 460 nm. Using the absorbance of the carrier water as the baseline, the calibration curve can be obtained from the absorbance of the standard solution whose urea concentration is known, and the urea concentration in the sample water can be obtained from the absorbance relative to the sample water. . The outlet of the detector 32 is provided with a back pressure coil 33 for applying back pressure to the pipeline from the pump P1 through the injection valve 10 , the piping 24 and the reaction coil 31 to the detector 32 . A pressure gauge PI is connected to a position between the outlet of the detector 32 and the inlet of the back pressure coil 33 . The drain of the FIA device is discharged from the outlet of the back pressure coil 33 .

In the analyzer of the present embodiment, by the FIA method, the urea in the sample water can be measured on-line by the colorimetric method using diacetylmonoxime. In this case, as reagent A (ie, diacetoxymonoacetic acid solution) and reagent B (ie, reagent solution containing antipyrine) used for the reaction, especially reagent B, can be used in these After the preparation of the reagent, the temperature is kept below 20°C. As a result, as shown in the examples described later, it was possible to stably perform continuous dosing of urea over a long period of time.

The above description is for the case of using the reagent solution containing antipyrine as the reagent used in combination with diacetylmonoxime in the method for quantifying urea by the colorimetric method using diacetylmonoxime, except that The present invention does not limit the reagent used in combination to the reagent solution containing antipyrine.

[Example]

Next, the results of experiments carried out by the inventors to show the effects of the present invention will be described.

[Example 1]

Assemble the device shown in Figure 1. However, it is set so that the part from the line 20 to the flow meter FI is not provided, and the standard solution adjusted to the urea concentration of 60 ppb can be continuously supplied to the injection valve 10 as the sample water. Then, with respect to this standard solution, continuous monitoring of the urea concentration is performed. Here, when the standard solution is continuously measured, how the obtained urea concentration changes is investigated as a measurement value of the detection peak of the absorbance in the detector 32 . In this embodiment, the system is set as follows: dissolve 2g of diacetylmonoxime in 100mL of 10% acetic acid to prepare reagent A (ie, diacetylmonoxime acetic acid solution); weigh 0.2g of antipyrine , dissolved in 9 mol/L sulfuric acid, and the total amount was set to 100 mL to prepare reagent B (that is, the reagent solution containing antipyrine); immediately after the preparation, these reagents were stored in storage tanks 41 and 42, respectively, The respective reagents are continuously supplied to the piping 24 from the storage tanks 41 and 42 . It is set so that the reagents are not replenished during the continuous measurement after the respective reagents are poured into the storage tanks 41 and 42 at the beginning of the continuous measurement. In addition, the storage tank 41 of the reagent A is maintained at normal temperature. Regarding the reagent B, experiments were performed on two cases, a case where the storage temperature was set to 10°C after the preparation, and a case where the storage temperature was set to 25°C. The change in the urea concentration was confirmed by the peak intensity of the absorbance at a wavelength of 460 nm. The results are shown in FIG. 2 . It is shown in FIG. 2 that the urine of 60 ppb was measured immediately after preparing reagent A and reagent B and storing them in storage tanks 41 and 42 respectively. When the peak intensity of the standard solution is set to 100%, the measured value of the same standard solution will change over time.

As shown in Fig. 2, when the reagent B, that is, the reagent solution containing antipyrine, was maintained at 25°C, the peak intensity gradually decreased, and during the 10-day operation period for continuous measurement, the peak intensity decreased to 72%. In other words, it becomes impossible to stably measure the urea. On the other hand, when the antipyrine-containing reagent solution was refrigerated and kept at 10°C, the peak intensity did not decrease even after 10 days of continuous operation, and it was found that continuous urea can be stably performed for a long time. Quantitative.

[Example 2]

After the reagent B was prepared in the same manner as in Example 1, it was stored at 5°C, 10°C, 15°C, 20°C, and 25°C for 10 days, respectively. Then, after this storage, the reagent B is supplied to the apparatus of FIG. 1 . Immediately after the reagent B was supplied to the apparatus, a standard solution having a urea concentration of 60 ppb was measured using the apparatus, and the peak intensity was obtained. At this time, the peak intensity at the time of measuring the standard solution immediately after preparation of reagent B was set to 100%. The reagent A was prepared in the same manner as in Example 1 and stored at room temperature. The results are shown in Table 1.

As shown in Table 1, when the storage temperature was 5°C and 10°C, almost no decrease in the peak intensity was observed; when stored at 15°C, a decrease in the peak intensity of about 10% was observed. Store at 20°C The case is about a 20% reduction in the peak intensity, while at 25°C the peak intensity decreases by nearly 30%. From the above, it can be seen that, in order to continuously measure the concentration of trace amounts of urea, the reagents used for the reaction, in this case, the diacetylmonoxime acetic acid solution and the antipyrine-containing reagent solution, contain at least antipyrine. The test solution must be kept refrigerated. In this case, it is better to keep the temperature of the test solution containing antipyrine below 20°C, more preferably above 3°C and below 20°C, and above 5°C for 15°C. ℃ or lower is more preferable.

[Example 3]

The same test as in Example 2 was performed except that the reagent A of Example 2 was stored at the same storage temperature as that of the reagent B of Example 2.

When both Reagent A and Reagent B were refrigerated and measured, the same results as those obtained when only Reagent B was refrigerated (Table 1) were obtained.

Claims (6)

A method for quantifying urea, which is a method for quantifying urea in sample water by using diacetyl monooxime and a colorimetric method of a test solution containing antipyrine, characterized in that: the method is to be used for reaction Among the prepared reagents, the reagent solution containing at least antipyrine is refrigerated after preparation to maintain a temperature between 5°C and 15°C, and the refrigerated reagent is used to quantify urea. A method of quantifying urea as claimed in claim 1, wherein the refrigerated reagent is used to continuously quantify urea. The method for quantifying urea according to claim 2, wherein the urea is quantified by absorbance by applying a flow injection analysis method. The method for quantifying urea according to claim 1 or 2, wherein the sample water is water used for producing pure water or pure water. An analytical device for continuously quantifying urea in sample water by colorimetry using diacetyl monooxime and a test solution containing antipyrine, comprising: storage for use in a reaction A storage tank for the prepared reagent; and a cooling mechanism for cooling and storing the storage tank containing at least the reagent solution of antipyrine to maintain a temperature between 5°C and 15°C. The analysis device of claim 5, further comprising: a sample injection valve, which continuously supplies carrier water and sample water and continuously discharges the carrier water, and replaces a certain amount of the sample water with the carrier water by switching action and discharges it; a mixing part is provided in the Downstream of the injection valve, the water discharged from the injection valve mixes the reagent from the storage tank; a reaction coil is arranged downstream of the mixing part to make the sample water react with the reagent ; and a detector connected to the outlet of the reaction coil.

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