CN114544533A - Quantitative detection method for low-concentration urea in ultrapure water - Google Patents

Abstract

The invention discloses a method for quantitatively detecting low-concentration urea in ultrapure water, which comprises the following steps: firstly performing vacuum freeze-drying treatment on a water sample; The diacetyl monooxime solution, stabilizer and catalyst are placed in the reaction vessel at a high temperature for the reaction under the condition that the nozzle is sealed; The standard curve yields the concentration of urea in the initial water sample. The quantitative detection method of the invention can accurately detect urea with a concentration of 0.5-80ug/L in the water body; the method of the invention first performs vacuum freeze-drying treatment on the water sample containing low concentration urea, and then increases the concentration of diacetyl oxime, antipyrine/ The concentration of thiosemicarbazide increases the color of the solution after the reaction, thereby effectively reducing the detection lower limit of the urea concentration in the water body; at the same time, the method of the present invention accelerates the progress of the reaction and increases the stability of the color development by adding metal ions, so that after the reaction After standing for a period of time, the absorbance of the reaction solution has almost no decrease compared with the absorbance at 0.

Description

A kind of quantitative detection method of low concentration urea in ultrapure water

technical field

The invention relates to a quantitative detection method for low-concentration urea in ultrapure water.

Background technique

Urea is considered an important pollutant in the production of ultrapure water (UPW) in the electronics industry. After actual water testing and literature research, it is found that the content of urea in tap water is 10-30ug/L, and the content in reclaimed water is 40-100ug/L. After the tap water is treated by the conventional ultrapure water treatment system, the total organic carbon (TOC) of the terminal effluent is less than 1ug/L, which meets the effluent standard. However, if reclaimed water is used, the terminal effluent often does not meet the standard, and urea has been proved to be one of the main reasons for not meeting the standard. Additionally, urea releases ammonium when heated, which can negatively impact the lithography process. Therefore, it is necessary to develop a urea treatment process for reclaimed water, and embed the process into the end of the treatment of reclaimed water, so as to reduce the concentration of urea in the effluent and make the effluent of the treatment terminal meet the standard. In the process of new process development, the quantitative detection of urea is particularly important.

The national standard method (GB/T18204.2-2014) uses the diacetylmonoxime-antipyrine spectrophotometer to detect urea, but this method cannot accurately and quantitatively detect the concentration of 5ug/ Urea below L is obviously unable to meet the urea detection requirements of the recycled water level in the electronics industry.

SUMMARY OF THE INVENTION

Purpose of the invention: The purpose of the present invention is to provide a method for quantitatively detecting low-concentration urea in ultrapure water.

Technical scheme: The quantitative detection method of low-concentration urea in ultrapure water according to the present invention is specifically as follows: firstly, vacuum freeze-drying the water sample; Add diacetyl monooxime solution, stabilizer and catalyst, and place the reaction vessel at a high temperature to carry out the reaction under the condition of sealing the nozzle; place the reacted reaction solution in the measuring vessel, and measure the absorbance of the reaction solution with a spectrophotometer And according to the standard curve to obtain the concentration of urea in the initial water sample.

The concentration of urea in the initial water sample is positively correlated with the concentration of reaction products (diazine derivatives), and the higher the concentration of urea, the more reaction products.

Among them, before the concentration of the water sample, the urea concentration in the water sample is 0.3-0.5ug/L, and after vacuum freeze drying, the urea concentration in the water sample is 3-5ug/L.

Among them, the vacuum freeze-drying treatment is specifically as follows: take the initial water sample and place it in a closed container, pre-freeze it in a freezer at -80°C for 6 to 24 hours; then open the container and put it in a vacuum freeze dryer to dry for 12 to 12 hours. 24h, after drying, place the container at room temperature until the ice cubes in the container are completely dissolved. At this time, add water (water with the same composition as the initial water sample) to the liquid by constant volume until the liquid volume is the initial water sample. 1/10 of the volume.

Among them, in the vacuum freeze-drying process, the vacuum degree of the dryer is 0.05-0.06MPa, and the temperature is -50°C.

Wherein, the concentration of the diacetylmonoxime solution is 45g/L～50g/L.

Wherein, the stabilizer is antipyrine acid solution or thiosemiuric acid solution; in the antipyrine acid solution, the concentration of antipyrine is 15g/L～20g/L; The concentration of thiosemicarbazide is 15g/L～20g/L.

The reaction between urea and diacetyl monooxime needs to be carried out under acidic conditions. When preparing antipyrine, a large amount of sulfuric acid is added. Adding sulfate radicals can make the dissociation equilibrium reach, and there are more hydrogen ions in the water, which strengthens the acidic environment.

Wherein, the catalyst is a sulfate containing cadmium ions and/or iron ions and/or silver ions.

Among them, in the sulfate, the concentration of cadmium ions is 8g/L; the concentration of iron ions is 10g/L; the concentration of silver ions is 8g/L.

Wherein, the reaction vessel is placed in a boiling water bath and heated for 30-50 min under the condition that the nozzle is sealed. The effect of heating on the reaction is to accelerate the progress of the reaction.

Wherein, the measurement container is measured by using a 5cm-thick cuvette. Use a 5cm cuvette to increase the optical path, thereby increasing the absorbance.

The saturated vapor pressure of urea is lower than that of water. Water sublimes first due to the higher saturated vapor pressure. Due to the lower concentration of urea, there are fewer hydrogen bonds with water (in an environment with a very high content of water molecules, water molecules tend to Clusters are rarely combined with other substances, so in a very low concentration of urea aqueous solution, there are few hydrogen bonds between urea and water molecules, most of which are self-aggregated clusters between water molecules), and then sublimation . Therefore, the vacuum freeze-drying process can realize the concentration of the water sample on the one hand, and on the other hand, the vacuum freeze-drying process will not cause the loss of urea, so as to ensure the accurate measurement.

The detection principle of the present invention is as follows: under acidic conditions, urea and diacetyl monoxime undergo condensation through the catalysis of cadmium ions, ferric ions or silver ions to generate red diazine derivatives, which are unstable to light ( Diazine derivatives are prone to decomposition reactions under light, and decomposition reactions also occur after long-term storage), so the reaction needs to be carried out in a brown reaction vessel; cadmium ions, ferric ions and silver ions can improve the The color development stability of diazine derivatives means that after adding metal ions and stabilizers to the reaction system, the reacted diazine derivatives will not decompose even if they are left for 24 hours.

The reaction equation of urea and diacetyl oxime is:

Beneficial effects: compared with the prior art, the quantitative detection method of the present invention can accurately detect urea with a concentration of 0.3-80 ug/L in the water body; the method of the present invention first performs vacuum freeze drying on the water sample containing low concentration urea, and then increases the The concentration of diacetylmonoxime, antipyrine/thiosemicarbazide increases the color of the solution after the reaction, thereby effectively reducing the detection lower limit of the urea concentration in the water body; at the same time, the method of the present invention accelerates the reaction by adding metal ions and Increase the stability of color development, so that after the reaction solution is placed for a period of time, compared with the absorbance at 0, the absorbance has almost no decrease.

Description of drawings

Fig. 1 is the urea standard solution curve diagram in the embodiment.

Detailed ways

Example 1

The quantitative detection method of low-concentration urea in ultrapure water of the present invention specifically comprises the following steps:

Step (1), take 250mL of the initial water sample and put it into a PTFE plastic bottle, tighten the bottle cap, then pre-freeze it in a -80°C freezer for 24 hours, take it out, unscrew the bottle cap, and put the PTFE plastic bottle. The bottle was placed in a vacuum freeze dryer and dried for 24 hours. After drying, the polytetrafluoroethylene plastic bottle was taken out and placed at room temperature until the ice cubes in it were completely dissolved; at this time, water was added to the liquid (same as the initial water sample) by constant volume. water with the same composition), until the liquid volume is 1/10 of the initial water sample volume (ie 25mL); the vacuum degree of the dryer is 0.05MPa, and the temperature is -50℃; the urea concentration in the initial water sample is 0.3ug/L; the vacuum After freeze-drying, the urea concentration in the water sample was 3ug/L;

Step (2), prepare a diacetyl monooxime solution with a concentration of 50 g/L; specifically: take 5 g of diacetyl mono oxime and dissolve it in 10 ml of isopropanol, stir until it is completely dissolved, and then use 10% isopropanol in mass fraction. Dilute with propanol until the solution volume is 100mL, and store in a brown bottle at room temperature;

Step (3), prepare an acid solution with an antipyrine concentration of 15 g/L; specifically: take 1.5 g of antipyrine, dissolve in mixed acid (mixed acid is composed of sulfuric acid: phosphoric acid volume ratio 9:1), add water Dilute to 100mL and store in a brown bottle for later use;

Step (4), prepare a silver sulfate solution with a concentration of 8g/L: take 0.8g of silver sulfate and dissolve it in a concentration of 50vol.% sulfuric acid, add water to the volume to 100mL, and store it in a brown bottle for later use;

Step (5), digestion and color development: measure 25 mL of the concentrated water sample in step 1 and put it in a 50 mL brown colorimetric tube, and add 2 mL of diacetylmonoxime solution, 2 mL of antipyrine acid solution and 1 mL of sulfuric acid to the colorimetric tube in turn. Silver solution, and tie the nozzle tightly with raw tape and put it into a boiling water bath and heat for 50min, take it out immediately and cool it in flowing tap water (the purpose of cooling is: in the next measurement, it needs to be carried out at room temperature) 2min;

Step (6), use a 5cm cuvette at a wavelength of 460nm, measure the absorbance of the reaction solution after the reaction and obtain the concentration of urea in the initial water sample according to the standard curve; when the urea concentration in the initial water sample is 0.3ug/L; vacuum freezing After drying, the absorbance value can still be detected when the concentration of urea in the water sample is 3ug/L.

Establishment of standard curve: Measure 25mL with concentrations of 0.01mg/L, 0.02mg/L, 0.03mg/L, 0.04mg/L, 0.05mg/L, 0.06mg/L, 0.07mg/L, 0.08mg/L The urea standard solution was placed in a 50mL brown colorimetric tube, followed by adding 2mL diacetyl monooxime solution (50g/L diacetyl monooxime solution), 2mL antipyrine acid solution (antipyrine concentration 15g/L acid solution) and 1mL silver sulfate solution (8g/L silver sulfate solution), and carry out the above steps (5) and (6) to obtain a urea standard solution curve. Using the curve diagram of the standard solution, under the same concentration of the reaction reagent, the concentration of urea in the initial water sample can be quickly obtained after the absorbance value is obtained.

As shown in Figure 1, the relationship between urea concentration and absorbance within 0-80ug/L conforms to Beer's law, the linear regression equation is y=1.0058x-0.0032, the correlation coefficient r=0.9991, and the correlation of the standard curve meets the requirements.

Comparative Example 1

A kind of quantitative detection method of urea, specifically comprises the steps:

Step (1), take 250mL of the initial water sample and put it into a PTFE plastic bottle, tighten the bottle cap, then pre-freeze it in a -80°C freezer for 24 hours, take it out, unscrew the bottle cap, and put the PTFE plastic bottle. The bottle was placed in a vacuum freeze dryer and dried for 24 hours. After drying, the polytetrafluoroethylene plastic bottle was taken out and placed at room temperature until the ice cubes in it were completely dissolved; at this time, water was added to the liquid (same as the initial water sample) by constant volume. water with the same composition), until the liquid volume is 1/10 of the initial water sample volume (ie 25mL); the vacuum degree of the dryer is 0.05MPa, and the temperature is -50℃; the urea concentration in the initial water sample is 0.3ug/L; the vacuum After freeze-drying, the urea concentration in the water sample was 3ug/L;

Step (2), prepare a diacetyl monooxime solution with a concentration of 50 g/L; specifically: take 5 g of diacetyl mono oxime and dissolve it in 10 ml of isopropanol, stir until it is completely dissolved, and then use 10% isopropanol in mass fraction. Dilute with propanol until the solution volume is 100mL, and store in a brown bottle at room temperature;

Step (3), prepare an acid solution with an antipyrine concentration of 15 g/L; specifically: take 1.5 g of antipyrine, dissolve in mixed acid (mixed acid is composed of sulfuric acid: phosphoric acid volume ratio 9:1), add water Dilute to 100mL and store in a brown bottle for later use;

Step (4), prepare a silver sulfate solution with a concentration of 8g/L, weigh 0.8g of silver sulfate and dissolve it in a concentration of 50vol.% sulfuric acid, add water to dilute to 100mL, and store in a brown bottle for later use;

Step (5), digestion and color development: measure 25 mL of the concentrated water sample in step 1 and put it in a 50 mL brown colorimetric tube, add 2 mL of diacetyl monoxime solution and 2 mL of antipyrine solution to the colorimetric tube in turn, and use raw Tie the nozzle with tape and put it in a boiling water bath for 80min, take it out immediately and cool it in running tap water (the purpose of cooling is: in the next measurement, it needs to be carried out at room temperature) for 2min;

Step (6), measure with an ultraviolet spectrophotometer, use a 5cm cuvette at a wavelength of 460nm, measure the absorbance of the reaction solution after the reaction, and obtain the concentration of urea in the initial water sample according to the standard curve.

After 24h, the absorbance of the reaction solutions of Example 1 and Comparative Example 1 was measured again, and the absorbance of Comparative Example 1 without adding metal ions decreased by 12.15% (this absorbance was compared with time 0), while the example of adding metal ions The absorbance of 1 dropped by only 3%. At the same time, the heating time of Comparative Example 1 without adding metal ions also increased significantly.

Comparative Example 2

A kind of quantitative detection method of urea, specifically comprises the steps:

Step (1), preparation concentration is 50g/L diacetyl monooxime solution; Specifically: Weigh 5g diacetyl monooxime and dissolve in 10ml isopropanol, stir until completely dissolved, and then use 10% isopropyl alcohol in mass fraction. Dilute with propanol until the solution volume is 100mL, and store in a brown bottle at room temperature;

Step (2), preparing an acid solution with an antipyrine concentration of 15 g/L; specifically: take 1.5 g of antipyrine, dissolve in mixed acid (mixed acid is composed of sulfuric acid: phosphoric acid volume ratio 9:1), add water Dilute to 100mL and store in a brown bottle for later use;

Step (3), prepare a silver sulfate solution with a concentration of 8g/L, take by weighing 0.8g of silver sulfate and dissolve it in a concentration of 50vol.% sulfuric acid, add water to the volume to 100mL, and store it in a brown bottle for later use;

Step (4), digestion and color development: measure 25mL of water sample in a 50mL brown colorimetric tube, add 4mL of diacetylmonoxime solution, 4mL of antipyrine acid solution and 1mL of silver sulfate solution to the colorimetric tube in turn, and use Tighten the nozzle with raw tape and put it into a boiling water bath and heat for 50min, take it out immediately and cool it in running tap water (the purpose of cooling is: in the next measurement, it needs to be carried out at room temperature) for 2min;

Step (5), measure with an ultraviolet spectrophotometer, use a 5cm cuvette at a wavelength of 460nm, measure the absorbance of the reaction solution after the reaction, and obtain the concentration of urea in the initial water sample according to the standard curve.

Establishment of standard curve: Measure 25mL with concentrations of 0.01mg/L, 0.02mg/L, 0.03mg/L, 0.04mg/L, 0.05mg/L, 0.06mg/L, 0.07mg/L, 0.08mg/L The urea standard solution was placed in a 50mL brown colorimetric tube, and 4mL of diacetylmonoxime solution (50g/L diacetylmonoxime solution), 4mL of antipyrine acid solution (antipyrine concentration 15g/L acid solution) and 1mL silver sulfate solution (8g/L silver sulfate solution), and carry out the above steps (5) and (6) to obtain a urea standard solution curve. Using the curve diagram of the standard solution, under the same concentration of the reaction reagent, the concentration of urea in the initial water sample can be quickly obtained after the absorbance value is obtained.

The lower limit of detection of Comparative Example 2 is 5ug/L (when the urea concentration in the water sample is lower than 5ug/L, there is no absorbance value), and its measurement range is 5～80ug/L, indicating that even though Comparative Example 2 increases the reaction reagent The reaction concentration is also unable to quantitatively detect water samples with a urea concentration below 5ug/L.

Comparative Example 3

A kind of quantitative detection method of urea, specifically comprises the steps:

Step (1), take 250mL of the initial water sample and put it into a PTFE plastic bottle, tighten the bottle cap, then pre-freeze it in a -80°C freezer for 24 hours, take it out, unscrew the bottle cap, and put the PTFE plastic bottle. The bottle was placed in a vacuum freeze dryer and dried for 24 hours. After drying, the polytetrafluoroethylene plastic bottle was taken out and placed at room temperature until the ice cubes in it were completely dissolved; at this time, water was added to the liquid (same as the initial water sample) by constant volume. water with the same composition), until the liquid volume is 1/10 of the initial water sample volume (ie 25mL); the vacuum degree of the dryer is 0.05MPa, and the temperature is -50℃; the urea concentration in the initial water sample is 0.3ug/L; the vacuum After freeze-drying, the urea concentration in the water sample was 3ug/L;

Step (2), prepare a diacetyl monooxime solution with a concentration of 50 g/L; specifically: take 5 g of diacetyl mono oxime and dissolve it in 10 ml of isopropanol, stir until it is completely dissolved, and then use 10% isopropanol in mass fraction. Dilute with propanol until the solution volume is 100mL, and store in a brown bottle at room temperature;

Step (3), prepare an acid solution with an antipyrine concentration of 15 g/L; specifically: take 1.5 g of antipyrine, dissolve in mixed acid (mixed acid is composed of sulfuric acid: phosphoric acid volume ratio 9:1), add water Dilute to 100mL and store in a brown bottle for later use;

Step (4), prepare a silver sulfate solution with a concentration of 8g/L, weigh 0.8g of silver sulfate and dissolve it in a concentration of 50vol.% sulfuric acid, add water to dilute to 100mL, and store in a brown bottle for later use;

Step (5), digestion and color development: measure 25 mL of the concentrated water sample in step 1 and put it in a 50 mL colorless colorimetric tube, and add 2 mL of diacetylmonoxime solution, 2 mL of antipyrine solution and 1 mL of antipyrine solution to the colorimetric tube in turn. Silver sulfate solution, and put the pipe mouth tightly into the boiling water bath with raw tape and heat for 50min, take it out immediately and cool it in flowing tap water (the purpose of cooling is: in the next measurement, it needs to be carried out at room temperature) 2min;

Step (6), measure with an ultraviolet spectrophotometer, use a 5cm cuvette at a wavelength of 460nm, measure the absorbance of the reaction solution after the reaction, and obtain the concentration of urea in the initial water sample according to the standard curve.

By comparing the absorbance of the reaction solutions of Example 1 and Comparative Example 3, it can be found that the measured value of the reaction with a colorless colorimetric tube is 3.15% lower than the measured value of the reaction with a brown colorimetric tube, which is within the error range specified by the standard. It can be shown that the color development stability of the reaction product is increased after the addition of metal ions, and a transparent colorimetric tube can be used to replace the brown colorimetric tube.

Comparative Example 4

A kind of quantitative detection method of urea, specifically comprises the steps:

Step (1), take 250mL of the initial water sample and put it into a PTFE plastic bottle, tighten the bottle cap, then pre-freeze it in a -80°C freezer for 24 hours, take it out, unscrew the bottle cap, and put the PTFE plastic bottle. The bottle was placed in a vacuum freeze dryer and dried for 24 hours. After drying, the polytetrafluoroethylene plastic bottle was taken out and placed at room temperature until the ice cubes in it were completely dissolved; at this time, water was added to the liquid (same as the initial water sample) by constant volume. water with the same composition), until the liquid volume is 1/10 of the initial water sample volume (ie 25mL); the vacuum degree of the dryer is 0.05MPa, and the temperature is -50℃; the urea concentration in the initial water sample is 0.3ug/L; the vacuum After freeze-drying, the urea concentration in the water sample was 3ug/L;

Step (2), prepare a diacetyl monooxime solution with a concentration of 50 g/L; specifically: take 5 g of diacetyl mono oxime and dissolve it in 10 ml of isopropanol, stir until it is completely dissolved, and then use 10% isopropanol in mass fraction. Dilute with propanol until the solution volume is 100mL, and store in a brown bottle at room temperature;

Step (3), prepare an acid solution with an antipyrine concentration of 15 g/L; specifically: take 1.5 g of antipyrine, dissolve in mixed acid (mixed acid is composed of sulfuric acid: phosphoric acid volume ratio 9:1), add water Dilute to 100mL and store in a brown bottle for later use;

Step (4), prepare a silver sulfate solution with a concentration of 8g/L, weigh 0.8g of silver sulfate and dissolve it in a concentration of 50vol.% sulfuric acid, add water to dilute to 100mL, and store in a brown bottle for later use;

Step (5), digestion and color development: measure 25 mL of the concentrated water sample in step 1 and put it in a 50 mL brown colorimetric tube, and add 2 mL of diacetylmonoxime solution, 2 mL of antipyrine acid solution and 1 mL of sulfuric acid to the colorimetric tube in turn. Silver solution, and put the tube mouth tightly into the boiling water bath with raw tape and heat for 30min, immediately take it out and cool it in flowing tap water (the purpose of cooling is: in the next measurement, it needs to be carried out at room temperature) 2min;

Step (6), measure with an ultraviolet spectrophotometer, use a 5cm cuvette at a wavelength of 460nm, measure the absorbance of the reaction solution after the reaction, and obtain the concentration of urea in the initial water sample according to the standard curve.

Comparing and measuring the absorbance of the reaction solutions of Example 1 and Comparative Example 4, it can be found that the measured value of reaction 30min after adding metal ions is lower than the measured value of 50min reaction by 2.89%, which is within the error range specified by the standard. It can be shown that the reaction is accelerated after the addition of metal ions, and the reaction time is shortened by 20 min.

Example 2

The quantitative detection method of low-concentration urea in ultrapure water of the present invention specifically comprises the following steps:

Step (1), take 250mL of the initial water sample and put it into a PTFE plastic bottle, tighten the bottle cap, then pre-freeze it in a -80°C freezer for 24 hours, take it out, unscrew the bottle cap, and put the PTFE plastic bottle. The bottle was placed in a vacuum freeze dryer and dried for 24 hours. After drying, the polytetrafluoroethylene plastic bottle was taken out and placed at room temperature until the ice cubes in it were completely dissolved; at this time, water was added to the liquid (same as the initial water sample) by constant volume. water with the same composition), until the liquid volume is 1/10 of the initial water sample volume (ie 25mL); the vacuum degree of the dryer is 0.05MPa, and the temperature is -50℃; the urea concentration in the initial water sample is 0.4ug/L; the vacuum After freeze-drying, the urea concentration in the water sample was 4ug/L;

Step (2), prepare a diacetyl monooxime solution with a concentration of 50 g/L; specifically: take 5 g of diacetyl mono oxime and dissolve it in 10 ml of isopropanol, stir until it is completely dissolved, and then use 10% isopropanol in mass fraction. Dilute with propanol until the solution volume is 100mL, and store in a brown bottle at room temperature;

Step (3), preparing the acid solution with thiosemicarbazide concentration of 15g/L; specifically: take 1.5g thiosemicarbazide, dissolve in mixed acid (mixed acid is made up of sulfuric acid: phosphoric acid volume ratio 9:1), add water to constant volume to 100mL, and stored in a brown bottle for later use;

Step (4), prepare a cadmium sulfate solution with a concentration of 8g/L, take by weighing 0.8g of cadmium sulfate and dissolve it in a concentration of 50vol.% sulfuric acid, add water to make the volume to 100mL, and store in a brown bottle for later use;

Step (5), digestion and color development: measure 25 mL of the concentrated water sample in step 1 and put it in a 50 mL brown colorimetric tube, and add 2 mL of diacetyl monooxime solution, 2 mL of thiosemiuric acid solution and 1 mL of cadmium sulfate to the colorimetric tube in turn. solution, and tie the nozzle tightly with raw tape and put it into a boiling water bath and heat for 30min, immediately take it out and cool it in flowing tap water (the purpose of cooling is: in the next measurement, it needs to be carried out at room temperature) for 2min;

Step (6), measure with an ultraviolet spectrophotometer, use a 5cm cuvette at a wavelength of 460nm, measure the absorbance of the reaction solution after the reaction and obtain the concentration of urea in the initial water sample according to the standard curve; when the urea concentration in the initial water sample 0.4ug/L; after vacuum freeze-drying, the absorbance value can still be detected when the urea concentration in the water sample is 4ug/L.

Establishment of standard curve: Measure 25mL with concentrations of 0.01mg/L, 0.02mg/L, 0.03mg/L, 0.04mg/L, 0.05mg/L, 0.06mg/L, 0.07mg/L, 0.08mg/L Put the urea standard solution in 50mL brown colorimetric tube, add 2mL diacetyl monooxime solution, 2mL thiosemiuric acid solution and 1mL cadmium sulfate solution to the colorimetric tube in turn, and carry out the above steps (5) and (6) , to obtain the urea standard solution curve. Using the curve diagram of the standard solution, the concentration of urea in the initial water sample can be quickly obtained after obtaining the absorbance value under the reaction reagent of the corresponding concentration.

Example 3

The quantitative detection method of low-concentration urea in ultrapure water of the present invention specifically comprises the following steps:

Step (1), take 250mL of the initial water sample and put it into a PTFE plastic bottle, tighten the bottle cap, then pre-freeze it in a -80°C freezer for 24 hours, take it out, unscrew the bottle cap, and put the PTFE plastic bottle. The bottle was placed in a vacuum freeze dryer and dried for 24 hours. After drying, the polytetrafluoroethylene plastic bottle was taken out and placed at room temperature until the ice cubes in it were completely dissolved; at this time, water was added to the liquid (same as the initial water sample) by constant volume. water with the same composition), until the liquid volume is 1/10 of the initial water sample volume (ie 25mL); the vacuum degree of the dryer is 0.05MPa, and the temperature is -50℃; the urea concentration in the initial water sample is 0.5ug/L; the vacuum After freeze-drying, the urea concentration in the water sample was 5ug/L;

Step (2), prepare a diacetyl monooxime solution with a concentration of 50 g/L; specifically: take 5 g of diacetyl mono oxime and dissolve it in 10 ml of isopropanol, stir until it is completely dissolved, and then use 10% isopropanol in mass fraction. Dilute with propanol until the solution volume is 100mL, and store in a brown bottle at room temperature;

Step (3), prepare an acid solution with an antipyrine concentration of 15 g/L; specifically: take 1.5 g of antipyrine, dissolve in mixed acid (mixed acid is composed of sulfuric acid: phosphoric acid volume ratio 9:1), add water Dilute to 100mL and store in a brown bottle for later use;

Step (4), prepare the ferric sulfate solution with a concentration of 10g/L, take by weighing 1.0g of ferric sulfate and dissolve it in a concentration of 50vol.% sulfuric acid, add water to dilute to 100mL, and store it in a brown bottle for later use;

Step (5), digestion and color development: measure 25 mL of the concentrated water sample in step 1 and put it in a 50 mL brown colorimetric tube, and add 2 mL of diacetylmonoxime solution, 2 mL of antipyrine acid solution and 1 mL of sulfuric acid to the colorimetric tube in turn. Iron solution, and tie the nozzle with raw tape and put it into a boiling water bath and heat for 50min, take it out immediately and cool it in flowing tap water (the purpose of cooling is: in the next measurement, it needs to be carried out at room temperature) 2min;

Step (6), use a 5cm cuvette at a wavelength of 460nm, measure the absorbance of the reaction solution after the reaction and obtain the concentration of urea in the initial water sample according to the standard curve; when the urea concentration in the initial water sample is 0.5ug/L; vacuum freezing After drying, the absorbance can still be detected when the concentration of urea in the water sample is 5ug/L.

Establishment of standard curve: Measure 25mL with concentrations of 0.01mg/L, 0.02mg/L, 0.03mg/L, 0.04mg/L, 0.05mg/L, 0.06mg/L, 0.07mg/L, 0.08mg/L The urea standard solution was placed in a 50mL brown colorimetric tube, followed by adding 2mL diacetyl monooxime solution (50g/L diacetyl monooxime solution), 2mL antipyrine acid solution (antipyrine concentration 15g/L acid solution) and 1mL ferric sulfate solution (10g/L silver sulfate solution), and carry out the above steps (5) and (6) to obtain a urea standard solution curve diagram. Using the curve diagram of the standard solution, the concentration of urea in the initial water sample can be quickly obtained after obtaining the absorbance value under the reaction reagent of the corresponding concentration.

Claims (10)

1. A quantitative detection method for low-concentration urea in ultrapure water is characterized by comprising the following steps: firstly, carrying out vacuum freeze drying treatment on a water sample; placing a water sample subjected to vacuum freeze drying in a reaction container, sequentially adding a diacetyl monoxime solution, a stabilizer and a catalyst into a tube, and placing the reaction container at a high temperature for reaction under the condition that a tube opening is closed; and (3) placing the reaction solution into a measuring container after reaction, measuring the absorbance of the reaction solution by using a spectrophotometer, and obtaining the concentration of the urea in the initial water sample according to a standard curve.

2. The method for quantitatively detecting low-concentration urea in ultrapure water as claimed in claim 1, wherein the vacuum freeze-drying treatment specifically comprises: placing an initial water sample in a closed container, and pre-freezing for 6-24 hours in a refrigerator at-80 ℃; and then, opening the container, putting the container into a vacuum freeze-drying instrument for drying for 12-24 hours, placing the container at normal temperature after drying until ice cubes in the container are completely dissolved, and supplementing water into the liquid in a constant volume mode until the volume of the liquid is 1/10 of the volume of the initial water sample.

3. The method for quantitatively detecting low-concentration urea in ultrapure water as claimed in claim 2, wherein: in the vacuum freeze drying process, the vacuum degree of a dryer is 0.05-0.06 MPa, and the temperature is-50 ℃.

4. The method for quantitatively detecting low-concentration urea in ultrapure water as claimed in claim 2, wherein: before the water sample is concentrated, the concentration of urea in the water sample is 0.5-4 ug/L, and after the water sample is subjected to vacuum freeze drying treatment, the concentration of urea in the water sample is 5-40 ug/L.

5. The method for quantitatively detecting low-concentration urea in ultrapure water as claimed in claim 1, wherein: the concentration of the diacetyl monoxime solution is 45 g/L-50 g/L.

6. The method for quantitatively detecting low-concentration urea in ultrapure water as claimed in claim 1, wherein: the stabilizer is antipyrine acid solution or thiourea acid solution; in the antipyrine acid solution, the concentration of antipyrine is 15 g/L-20 g/L; the concentration of the thiourea in the thiourea acid solution is 15 g/L-20 g/L.

7. The method for quantitatively detecting low-concentration urea in ultrapure water as claimed in claim 1, wherein: the catalyst is sulfate containing cadmium ions and/or iron ions and/or silver ions.

8. The method for quantitatively detecting low-concentration urea in ultrapure water as recited in claim 7, wherein: in the sulfate, the concentration of cadmium ions is 8 g/L; the concentration of iron ions is 10 g/L; the concentration of silver ions was 8 g/L.

9. The method for quantitatively detecting low-concentration urea in ultrapure water as claimed in claim 1, wherein: and heating the reaction container at 90-100 ℃ for 30-50 min under the condition of sealing the pipe orifice.

10. The method for quantitatively detecting low-concentration urea in ultrapure water as claimed in claim 1, wherein: the measuring container adopts a cuvette with the thickness of 5cm to measure.

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