A quantitative detection method for low concentration urea in ultrapure water

Abstract

The invention discloses a quantitative detection method for low-concentration urea in ultrapure water, specifically: firstly subject a water sample to vacuum freeze drying treatment; placing the vacuum freeze-dried water sample in a reaction vessel, sequentially adding diacetyl monoxime solution, stabilizer and catalyst into the tube, placing the reaction vessel at high temperature under the condition of a closed tube mouth for reaction; placing the reaction solution after the reaction in a measuring container, measuring the absorbance of the reaction solution with a spectrophotometer and obtaining the concentration of urea in the initial water sample according to a standard curve. The quantitative detection method of the present invention can accurately detect urea with a concentration of 0.5 to 80ug / L in the water body; the method of the present invention first subject a water sample containing low-concentration urea to vacuum freeze drying treatment, and then increasing the concentration of diacetyl monoxime, antipyrine / thiocarbamide to increase the color of the solution after the reaction, thereby effectively reducing the detection lower limit of urea concentration in the water body; at the same time, the method of the present invention accelerates the reaction and increases the stability of color development by adding metal ions, so that the reaction solution after the reaction is placed for a period of time, and the absorbance is almost not reduced compared with the absorbance at 0.

Description

Technical Field

[0001] The invention relates to a quantitative detection method for low-concentration urea in ultrapure water. Background Art

[0002] Urea is considered to be an important pollutant in the production of ultrapure water (UPW) in the electronics industry. After actual water body testing and literature research, it was found that the content of urea in tap water is 10-30ug / L, and the content in recycled water is 40-100ug / L. After tap water is treated by a conventional ultrapure water treatment system, the total organic carbon (TOC) of the terminal effluent is less than 1ug / L, which meets the effluent standard. If recycled water is used, the terminal effluent often does not meet the standard, and urea has been confirmed to be one of the main reasons for non-compliance. In addition, urea releases ammonium when heated, which has a negative impact on the photolithography process. Therefore, it is necessary to develop a urea treatment process for recycled water and embed the process into the end of recycled water treatment to reduce the urea concentration in the effluent and make the effluent of the treatment terminal meet the standard. In the process of new process development, quantitative detection of urea is particularly important.

[0003] The national standard method (GB / T18204.2-2014) uses the diacetyl monoxime-antipyrine spectrophotometer method to detect urea. However, even after changing the concentration and optical path of the color developer, this method still cannot accurately and quantitatively detect urea below a concentration of 5ug / L. This method obviously cannot meet the urea detection requirements for recycled water in the electronics industry. Summary of the invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a method for quantitatively detecting low concentration urea in ultrapure water.

[0005] Technical solution: The quantitative detection method of low-concentration urea in ultrapure water described in the present invention is specifically as follows: firstly subjecting the water sample to vacuum freeze-drying treatment; placing the vacuum freeze-dried water sample in a reaction container, sequentially adding diacetyl monoxime solution, stabilizer and catalyst into the tube, placing the reaction container at high temperature for reaction with the tube mouth sealed; placing the reaction liquid in a measuring container, measuring the absorbance of the reaction liquid with a spectrophotometer and obtaining the concentration of urea in the initial water sample according to the standard curve.

[0006] The concentration of urea in the initial water sample is positively correlated with the concentration of the reaction product (diazine derivative). The higher the urea concentration, the more reaction products there are.

[0007] Among them, before the water sample was concentrated, the urea concentration in the water sample was 0.3~0.5ug / L, and after vacuum freeze-drying treatment, the urea concentration in the water sample was 3~5ug / L.

[0008] Among them, the vacuum freeze-drying treatment is specifically as follows: take the initial water sample and place it in a sealed container, and 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 24 hours. After drying, place the container at room temperature until the ice in the container is completely dissolved. At this time, water (water with the same composition as the initial water sample) is added to the liquid by a constant volume method until the volume of the liquid is 1 / 10 of the volume of the initial water sample.

[0009] Among them, during the vacuum freeze-drying process, the vacuum degree of the dryer is 0.05-0.06MPa and the temperature is -50°C.

[0010] Wherein, the concentration of the diacetyl monoxime solution is 45g / L to 50g / L.

[0011] Wherein, the stabilizer is antipyrine acid solution or thiocarbamide solution; in the antipyrine acid solution, the concentration of antipyrine is 15g / L to 20g / L; in the thiocarbamide solution, the concentration of thiocarbamide is 15g / L to 20g / L.

[0012] The reaction of urea and diacetyl monoxime needs to be carried out under acidic conditions. A large amount of sulfuric acid is added when preparing antipyrine. The addition of sulfate ions can make more hydrogen ions in the water when the dissociation equilibrium is reached, thus strengthening the acidic environment.

[0013] Wherein, the catalyst is a sulfate containing cadmium ions and / or iron ions and / or silver ions.

[0014] Among them, in sulfate, the concentration of cadmium ions is 8g / L; the concentration of iron ions is 10g / L; and the concentration of silver ions is 8g / L.

[0015] The reaction vessel is placed in a boiling water bath and heated for 30 to 50 minutes under the condition that the pipe mouth is sealed. The effect of heating on the reaction is to accelerate the reaction.

[0016] The measuring container is a 5 cm thick cuvette for measurement. The 5 cm thick cuvette is used to increase the optical path and thus increase the absorbance.

[0017] The saturated vapor pressure of urea is lower than that of water. Water sublimates first due to its higher saturated vapor pressure. Urea has fewer hydrogen bonds with water due to its lower concentration (in an environment with a high content of water molecules, water molecules tend to self-aggregate and rarely combine with other substances. Therefore, in an extremely low concentration of urea aqueous solution, there are few hydrogen bonds between urea and water molecules, and most of them are self-aggregated clusters between water molecules), and then sublimates. Therefore, the use of vacuum freeze-drying can achieve the concentration of water samples on the one hand, and will not cause the loss of urea during the vacuum freeze-drying process, thereby ensuring accurate measurement.

[0018] The detection principle of the present invention is that urea and diacetyl monoxime are condensed under acidic conditions through the catalysis of cadmium ions, trivalent iron ions or silver ions to generate red diazine derivatives, which are unstable to light (diazine derivatives are prone to decomposition reactions under light and will also decompose after being left for a long time), so the reaction needs to be carried out in a brown reaction container; cadmium ions, trivalent iron ions and silver ions can not only play a catalytic role but also improve the color stability of diazine derivatives, that is, after metal ions and stabilizers are added to the reaction system, the diazine derivatives after the reaction will not decompose even if they are left for 24 hours.

[0019] The reaction equation of urea and diacetyl monoxime is:

[0020]

[0021]

[0022] 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 to 80 ug / L in water; the method of the present invention first performs vacuum freeze-drying treatment on a water sample containing low-concentration urea, and then increases the concentration of diacetyl monoxime and antipyrine / thiocarbamide to increase the color of the solution after the reaction, thereby effectively reducing the detection lower limit of the urea concentration in the water; at the same time, the method of the present invention accelerates the reaction and increases the stability of the color development by adding metal ions, so that the absorbance of the reaction solution after the reaction is almost unchanged after being placed for a period of time compared with the absorbance at 0. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a curve diagram of the urea standard solution in the embodiment. DETAILED DESCRIPTION

[0024] Example 1

[0025] The quantitative detection method of low-concentration urea in ultrapure water of the present invention specifically comprises the following steps:

[0026] Step (1), taking 250mL of the initial water sample and putting it into a polytetrafluoroethylene plastic bottle, tightening the bottle cap, and then pre-freezing it in a -80°C freezer for 24 hours and then taking it out, unscrewing the bottle cap, and putting the polytetrafluoroethylene plastic bottle into a vacuum freeze dryer, drying it for 24 hours, and after drying, taking out the polytetrafluoroethylene plastic bottle and placing it at room temperature until the ice cubes therein are completely dissolved; at this time, water (water with the same composition as the initial water sample) is added to the liquid by a constant volume method until the volume of the liquid is 1 / 10 of the volume of the initial water sample (i.e., 25mL); the vacuum degree of the dryer is 0.05MPa, and the temperature is -50°C; the urea concentration in the initial water sample is 0.3ug / L; after vacuum freeze drying, the urea concentration in the water sample is 3ug / L;

[0027] Step (2), preparing a diacetyl monoxime solution with a concentration of 50 g / L; specifically, weighing 5 g of diacetyl monoxime and dissolving it in 10 ml of isopropanol, stirring until completely dissolved, then diluting the solution with 10% isopropanol by mass to a volume of 100 mL, and storing it in a brown bottle at room temperature;

[0028] Step (3), preparing an acid solution with an antipyrine concentration of 15 g / L; specifically, weighing 1.5 g of antipyrine, dissolving it in a mixed acid (the mixed acid consists of sulfuric acid:phosphoric acid in a volume ratio of 9:1), adding water to make the volume to 100 mL, and storing it in a brown bottle for later use;

[0029] Step (4), preparing a silver sulfate solution with a concentration of 8 g / L: weighing 0.8 g of silver sulfate and dissolving it in 50 vol.% sulfuric acid, adding water to make the volume to 100 mL, and storing it in a brown bottle for later use;

[0030] Step (5), digestion and color development: 25 mL of the concentrated water sample in step 1 is measured and placed in a 50 mL brown colorimetric tube, 2 mL of diacetyl monoxime solution, 2 mL of antipyrine acid solution and 1 mL of silver sulfate solution are added to the colorimetric tube in sequence, and the tube mouth is tied with raw tape and placed in a boiling water bath and heated for 50 min, and then taken out immediately and cooled in running tap water (the purpose of cooling is: in the next step of measurement, it needs to be carried out at room temperature) for 2 min;

[0031] Step (6), using a 5 cm cuvette at a wavelength of 460 nm, measuring the absorbance of the reaction solution after the reaction and obtaining the concentration of urea in the initial water sample according to the standard curve; when the urea concentration in the initial water sample is 0.3 ug / L; after vacuum freeze-drying, the absorbance value can still be detected when the urea concentration in the water sample is 3 ug / L.

[0032] The establishment of the standard curve: 25 mL of urea standard solution with a concentration of 0.01 mg / L, 0.02 mg / L, 0.03 mg / L, 0.04 mg / L, 0.05 mg / L, 0.06 mg / L, 0.07 mg / L, and 0.08 mg / L is measured in a 50 mL brown colorimetric tube, and 2 mL of diacetyl monoxime solution (50 g / L diacetyl monoxime solution), 2 mL of antipyrine acid solution (acid solution with an antipyrine concentration of 15 g / L) and 1 mL of silver sulfate solution (8 g / L silver sulfate solution) are added to the colorimetric tube in sequence, and the above steps (5) and (6) are performed to obtain a urea standard solution curve. Using the standard solution curve, the concentration of urea in the initial water sample is quickly obtained after obtaining the absorbance value under the same concentration of the reaction reagent.

[0033] like Figure 1As shown, the relationship between urea concentration and absorbance in the range of 0 to 80 ug / 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.

[0034] Comparative Example 1

[0035] A quantitative detection method for urea specifically comprises the following steps:

[0036] Step (1), taking 250mL of the initial water sample and putting it into a polytetrafluoroethylene plastic bottle, tightening the bottle cap, and then pre-freezing it in a -80°C freezer for 24 hours and then taking it out, unscrewing the bottle cap, and putting the polytetrafluoroethylene plastic bottle into a vacuum freeze dryer, drying it for 24 hours, and after drying, taking out the polytetrafluoroethylene plastic bottle and placing it at room temperature until the ice cubes therein are completely dissolved; at this time, water (water with the same composition as the initial water sample) is added to the liquid by a constant volume method until the volume of the liquid is 1 / 10 of the volume of the initial water sample (i.e., 25mL); the vacuum degree of the dryer is 0.05MPa, and the temperature is -50°C; the urea concentration in the initial water sample is 0.3ug / L; after vacuum freeze drying, the urea concentration in the water sample is 3ug / L;

[0037] Step (2), preparing a diacetyl monoxime solution with a concentration of 50 g / L; specifically, weighing 5 g of diacetyl monoxime and dissolving it in 10 ml of isopropanol, stirring until completely dissolved, then diluting the solution with 10% isopropanol by mass to a volume of 100 mL, and storing it in a brown bottle at room temperature;

[0038] Step (3), preparing an acid solution with an antipyrine concentration of 15 g / L; specifically, weighing 1.5 g of antipyrine, dissolving it in a mixed acid (the mixed acid consists of sulfuric acid:phosphoric acid in a volume ratio of 9:1), adding water to make the volume to 100 mL, and storing it in a brown bottle for later use;

[0039] Step (4), preparing a silver sulfate solution with a concentration of 8 g / L, weighing 0.8 g of silver sulfate and dissolving it in 50 vol.% sulfuric acid, adding water to make the volume to 100 mL, and storing it in a brown bottle for later use;

[0040] Step (5), digestion and color development: 25 mL of the concentrated water sample in step 1 is measured and placed in a 50 mL brown colorimetric tube, 2 mL of diacetyl monoxime solution and 2 mL of antipyrine acid solution are added to the colorimetric tube in sequence, and the tube mouth is tied with raw tape and placed in a boiling water bath and heated for 80 min, and then immediately taken out and cooled in running tap water (the purpose of cooling is: in the next step of measurement, it needs to be carried out at room temperature) for 2 min;

[0041] Step (6), measuring with an ultraviolet spectrophotometer, using a 5 cm cuvette at a wavelength of 460 nm, determining the absorbance of the reaction solution after the reaction and obtaining the concentration of urea in the initial water sample according to the standard curve.

[0042] After 24 hours, the absorbance of the reaction solution of Example 1 and Comparative Example 1 was measured again. The absorbance of Comparative Example 1 without adding metal ions decreased by 12.15% (this absorbance is compared with time 0), while the absorbance of Example 1 with adding metal ions decreased by only 3%. At the same time, the heating time of Comparative Example 1 without adding metal ions also increased significantly.

[0043] Comparative Example 2

[0044] A quantitative detection method for urea specifically comprises the following steps:

[0045] Step (1), preparing a diacetyl monoxime solution with a concentration of 50 g / L; specifically, weighing 5 g of diacetyl monoxime and dissolving it in 10 ml of isopropanol, stirring until completely dissolved, then diluting the solution with 10% isopropanol by mass to a volume of 100 mL, and storing it in a brown bottle at room temperature;

[0046] Step (2), preparing an acid solution with an antipyrine concentration of 15 g / L; specifically, weighing 1.5 g of antipyrine, dissolving it in a mixed acid (the mixed acid is composed of sulfuric acid:phosphoric acid in a volume ratio of 9:1), adding water to make the volume to 100 mL, and storing it in a brown bottle for later use;

[0047] Step (3), preparing a silver sulfate solution with a concentration of 8 g / L, weighing 0.8 g of silver sulfate and dissolving it in 50 vol.% sulfuric acid, adding water to make the volume to 100 mL, and storing it in a brown bottle for later use;

[0048] Step (4), digestion and color development: 25 mL of water sample was measured and placed in a 50 mL brown colorimetric tube, 4 mL of diacetyl monoxime solution, 4 mL of antipyrine acid solution and 1 mL of silver sulfate solution were added to the colorimetric tube in sequence, and the tube was tied with raw tape and placed in a boiling water bath and heated for 50 min, then immediately taken out and cooled in running tap water (the purpose of cooling is: in the next step of measurement, it needs to be carried out at room temperature) for 2 min;

[0049] Step (5), measuring with an ultraviolet spectrophotometer, using a 5 cm cuvette at a wavelength of 460 nm, determining the absorbance of the reaction solution after the reaction and obtaining the concentration of urea in the initial water sample according to the standard curve.

[0050] The establishment of the standard curve: 25 mL of urea standard solution with a concentration of 0.01 mg / L, 0.02 mg / L, 0.03 mg / L, 0.04 mg / L, 0.05 mg / L, 0.06 mg / L, 0.07 mg / L, and 0.08 mg / L is measured in a 50 mL brown colorimetric tube, and 4 mL of diacetyl monoxime solution (50 g / L diacetyl monoxime solution), 4 mL of antipyrine acid solution (acid solution with an antipyrine concentration of 15 g / L) and 1 mL of silver sulfate solution (8 g / L silver sulfate solution) are added to the colorimetric tube in sequence, and the above steps (5) and (6) are performed to obtain a urea standard solution curve. Using the standard solution curve, the concentration of urea in the initial water sample is quickly obtained after obtaining the absorbance value under the same concentration of the reaction reagent.

[0051] The detection limit 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, which means that even if the reaction concentration of the reaction reagent is increased in Comparative Example 2, it is still impossible to quantitatively detect water samples with a urea concentration below 5ug / L.

[0052] Comparative Example 3

[0053] A quantitative detection method for urea specifically comprises the following steps:

[0054] Step (1), taking 250mL of the initial water sample and putting it into a polytetrafluoroethylene plastic bottle, tightening the bottle cap, and then pre-freezing it in a -80°C freezer for 24 hours and then taking it out, unscrewing the bottle cap, and putting the polytetrafluoroethylene plastic bottle into a vacuum freeze dryer, drying it for 24 hours, and after drying, taking out the polytetrafluoroethylene plastic bottle and placing it at room temperature until the ice cubes therein are completely dissolved; at this time, water (water with the same composition as the initial water sample) is added to the liquid by a constant volume method until the volume of the liquid is 1 / 10 of the volume of the initial water sample (i.e., 25mL); the vacuum degree of the dryer is 0.05MPa, and the temperature is -50°C; the urea concentration in the initial water sample is 0.3ug / L; after vacuum freeze drying, the urea concentration in the water sample is 3ug / L;

[0055] Step (2), preparing a diacetyl monoxime solution with a concentration of 50 g / L; specifically, weighing 5 g of diacetyl monoxime and dissolving it in 10 ml of isopropanol, stirring until completely dissolved, then diluting the solution with 10% isopropanol by mass to a volume of 100 mL, and storing it in a brown bottle at room temperature;

[0056] Step (3), preparing an acid solution with an antipyrine concentration of 15 g / L; specifically, weighing 1.5 g of antipyrine, dissolving it in a mixed acid (the mixed acid consists of sulfuric acid:phosphoric acid in a volume ratio of 9:1), adding water to make the volume to 100 mL, and storing it in a brown bottle for later use;

[0057] Step (4), preparing a silver sulfate solution with a concentration of 8 g / L, weighing 0.8 g of silver sulfate and dissolving it in 50 vol.% sulfuric acid, adding water to make the volume to 100 mL, and storing it in a brown bottle for later use;

[0058] Step (5), digestion and color development: 25 mL of the concentrated water sample in step 1 is measured and placed in a 50 mL colorless colorimetric tube, 2 mL of diacetyl monoxime solution, 2 mL of antipyrine acid solution and 1 mL of silver sulfate solution are added to the colorimetric tube in sequence, and the tube mouth is tied with raw tape and placed in a boiling water bath and heated for 50 min, and then taken out immediately and cooled in running tap water (the purpose of cooling is: in the next step of measurement, it needs to be carried out at room temperature) for 2 min;

[0059] Step (6), measuring with an ultraviolet spectrophotometer, using a 5 cm cuvette at a wavelength of 460 nm, determining the absorbance of the reaction solution after the reaction and obtaining the concentration of urea in the initial water sample according to the standard curve.

[0060] By comparing the absorbance of the reaction solution of Example 1 and Comparative Example 3, it can be found that the measured value of the reaction using the colorless colorimetric tube is 3.15% lower than that of the reaction using the brown colorimetric tube, which is within the error range specified by the standard. This shows that the color stability of the reaction product is increased after the addition of metal ions, and a transparent colorimetric tube can be used instead of a brown colorimetric tube.

[0061] Comparative Example 4

[0062] A quantitative detection method for urea specifically comprises the following steps:

[0063] Step (1), taking 250mL of the initial water sample and putting it into a polytetrafluoroethylene plastic bottle, tightening the bottle cap, and then pre-freezing it in a -80°C freezer for 24 hours and then taking it out, unscrewing the bottle cap, and putting the polytetrafluoroethylene plastic bottle into a vacuum freeze dryer, drying it for 24 hours, and after drying, taking out the polytetrafluoroethylene plastic bottle and placing it at room temperature until the ice cubes therein are completely dissolved; at this time, water (water with the same composition as the initial water sample) is added to the liquid by a constant volume method until the volume of the liquid is 1 / 10 of the volume of the initial water sample (i.e., 25mL); the vacuum degree of the dryer is 0.05MPa, and the temperature is -50°C; the urea concentration in the initial water sample is 0.3ug / L; after vacuum freeze drying, the urea concentration in the water sample is 3ug / L;

[0064] Step (2), preparing a diacetyl monoxime solution with a concentration of 50 g / L; specifically, weighing 5 g of diacetyl monoxime and dissolving it in 10 ml of isopropanol, stirring until completely dissolved, then diluting the solution with 10% isopropanol by mass to a volume of 100 mL, and storing it in a brown bottle at room temperature;

[0065] Step (3), preparing an acid solution with an antipyrine concentration of 15 g / L; specifically, weighing 1.5 g of antipyrine, dissolving it in a mixed acid (the mixed acid consists of sulfuric acid:phosphoric acid in a volume ratio of 9:1), adding water to make the volume to 100 mL, and storing it in a brown bottle for later use;

[0066] Step (4), preparing a silver sulfate solution with a concentration of 8 g / L, weighing 0.8 g of silver sulfate and dissolving it in 50 vol.% sulfuric acid, adding water to make the volume to 100 mL, and storing it in a brown bottle for later use;

[0067] Step (5), digestion and color development: 25 mL of the concentrated water sample in step 1 is measured and placed in a 50 mL brown colorimetric tube, 2 mL of diacetyl monoxime solution, 2 mL of antipyrine acid solution and 1 mL of silver sulfate solution are added to the colorimetric tube in sequence, and the tube mouth is tied with raw tape and placed in a boiling water bath and heated for 30 min, and then taken out immediately and cooled in running tap water (the purpose of cooling is: in the next step of measurement, it needs to be carried out at room temperature) for 2 min;

[0068] Step (6), measuring with an ultraviolet spectrophotometer, using a 5 cm cuvette at a wavelength of 460 nm, determining the absorbance of the reaction solution after the reaction and obtaining the concentration of urea in the initial water sample according to the standard curve.

[0069] By comparing the absorbance of the reaction solution of Example 1 and Comparative Example 4, it can be found that the measured value of the reaction for 30 minutes after adding metal ions is 2.89% lower than that of the reaction for 50 minutes, which is within the error range specified by the standard. This shows that the reaction is accelerated after adding metal ions, and the reaction time is shortened by 20 minutes.

[0070] Example 2

[0071] The quantitative detection method of low-concentration urea in ultrapure water of the present invention specifically comprises the following steps:

[0072] Step (1), taking 250mL of the initial water sample and putting it into a polytetrafluoroethylene plastic bottle, tightening the bottle cap, and then pre-freezing it in a -80°C freezer for 24 hours and then taking it out, unscrewing the bottle cap, and putting the polytetrafluoroethylene plastic bottle into a vacuum freeze dryer, drying it for 24 hours, and then taking out the polytetrafluoroethylene plastic bottle after drying and placing it at room temperature until the ice cubes therein are completely dissolved; at this time, water (water with the same composition as the initial water sample) is added to the liquid by a constant volume method until the volume of the liquid is 1 / 10 of the volume of the initial water sample (i.e., 25mL); the vacuum degree of the dryer is 0.05MPa, and the temperature is -50°C; the urea concentration in the initial water sample is 0.4ug / L; after vacuum freeze drying, the urea concentration in the water sample is 4ug / L;

[0073] Step (2), preparing a diacetyl monoxime solution with a concentration of 50 g / L; specifically, weighing 5 g of diacetyl monoxime and dissolving it in 10 ml of isopropanol, stirring until completely dissolved, then diluting the solution with 10% isopropanol by mass to a volume of 100 mL, and storing it in a brown bottle at room temperature;

[0074] Step (3), preparing an acid solution with a thiocarbazide concentration of 15 g / L; specifically, weighing 1.5 g of thiocarbazide, dissolving it in mixed acid (the mixed acid is composed of sulfuric acid: phosphoric acid in a volume ratio of 9:1), adding water to make the volume to 100 mL, and storing it in a brown bottle for later use;

[0075] Step (4), preparing a cadmium sulfate solution with a concentration of 8 g / L, weighing 0.8 g of cadmium sulfate and dissolving it in 50 vol.% sulfuric acid, adding water to make the volume to 100 mL, and storing it in a brown bottle for later use;

[0076] Step (5), digestion and color development: Measure 25 mL of the concentrated water sample in step 1 and put it into a 50 mL brown colorimetric tube, add 2 mL of diacetyl monoxime solution, 2 mL of thiosuccinic acid solution and 1 mL of cadmium sulfate solution into the colorimetric tube in sequence, and tie the tube mouth with raw tape and put it into a boiling water bath and heat for 30 minutes, then take it out immediately and cool it in running tap water (the purpose of cooling is: in the next step of measurement, it needs to be carried out at room temperature) for 2 minutes;

[0077] Step (6), measuring with an ultraviolet spectrophotometer, using a 5 cm cuvette at a wavelength of 460 nm, determining the absorbance of the reaction solution after the reaction and obtaining the concentration of urea in the initial water sample according to the standard curve; when the urea concentration in the initial water sample is 0.4 ug / L; after vacuum freeze-drying, the absorbance value can still be detected when the urea concentration in the water sample is 4 ug / L.

[0078] Establishment of standard curve: 25 mL of urea standard solution with concentrations of 0.01 mg / L, 0.02 mg / L, 0.03 mg / L, 0.04 mg / L, 0.05 mg / L, 0.06 mg / L, 0.07 mg / L, and 0.08 mg / L are respectively measured in 50 mL brown colorimetric tubes, 2 mL of diacetyl monoxime solution, 2 mL of thiosuccinic acid solution, and 1 mL of cadmium sulfate solution are added to the colorimetric tubes in sequence, and the above steps (5) and (6) are performed to obtain a urea standard solution curve. Using the standard solution curve, the concentration of urea in the initial water sample can be quickly obtained after obtaining the absorbance value under the corresponding concentration of the reaction reagent.

[0079] Example 3

[0080] The quantitative detection method of low-concentration urea in ultrapure water of the present invention specifically comprises the following steps:

[0081] Step (1), taking 250mL of the initial water sample and putting it into a polytetrafluoroethylene plastic bottle, tightening the bottle cap, and then pre-freezing it in a -80°C freezer for 24 hours and then taking it out, unscrewing the bottle cap, putting the polytetrafluoroethylene plastic bottle into a vacuum freeze dryer, and drying it for 24 hours. After drying, taking out the polytetrafluoroethylene plastic bottle and placing it at room temperature until the ice cubes therein are completely dissolved; at this time, water (water with the same composition as the initial water sample) is added to the liquid by a constant volume method until the volume of the liquid is 1 / 10 of the volume of the initial water sample (i.e., 25mL); the vacuum degree of the dryer is 0.05MPa, and the temperature is -50°C; the urea concentration in the initial water sample is 0.5ug / L; after vacuum freeze drying, the urea concentration in the water sample is 5ug / L;

[0082] Step (2), preparing a diacetyl monoxime solution with a concentration of 50 g / L; specifically, weighing 5 g of diacetyl monoxime and dissolving it in 10 ml of isopropanol, stirring until completely dissolved, then diluting the solution with 10% isopropanol by mass to a volume of 100 mL, and storing it in a brown bottle at room temperature;

[0083] Step (3), preparing an acid solution with an antipyrine concentration of 15 g / L; specifically, weighing 1.5 g of antipyrine, dissolving it in a mixed acid (the mixed acid consists of sulfuric acid:phosphoric acid in a volume ratio of 9:1), adding water to make the volume to 100 mL, and storing it in a brown bottle for later use;

[0084] Step (4), preparing a 10 g / L ferric sulfate solution, weighing 1.0 g of ferric sulfate and dissolving it in 50 vol.% sulfuric acid, adding water to make the volume to 100 mL, and storing it in a brown bottle for later use;

[0085] Step (5), digestion and color development: 25 mL of the concentrated water sample in step 1 is measured and placed in a 50 mL brown colorimetric tube, 2 mL of diacetyl monoxime solution, 2 mL of antipyrine acid solution and 1 mL of ferric sulfate solution are added to the colorimetric tube in sequence, and the tube mouth is tied with raw tape and placed in a boiling water bath and heated for 50 min, and then taken out immediately and cooled in running tap water (the purpose of cooling is: in the next step of measurement, it needs to be carried out at room temperature) for 2 min;

[0086] Step (6), using a 5 cm cuvette at a wavelength of 460 nm, measuring the absorbance of the reaction solution after the reaction and obtaining the concentration of urea in the initial water sample according to the standard curve; when the urea concentration in the initial water sample is 0.5 ug / L; after vacuum freeze-drying, the absorbance value can still be detected when the urea concentration in the water sample is 5 ug / L.

[0087] The establishment of the standard curve: 25 mL of urea standard solution with a concentration of 0.01 mg / L, 0.02 mg / L, 0.03 mg / L, 0.04 mg / L, 0.05 mg / L, 0.06 mg / L, 0.07 mg / L, and 0.08 mg / L is measured in a 50 mL brown colorimetric tube, and 2 mL of diacetyl monoxime solution (50 g / L diacetyl monoxime solution), 2 mL of antipyrine acid solution (acid solution with an antipyrine concentration of 15 g / L) and 1 mL of ferric sulfate solution (10 g / L silver sulfate solution) are added to the colorimetric tube in sequence, and the above steps (5) and (6) are performed to obtain a urea standard solution curve. Using the standard solution curve, the concentration of urea in the initial water sample is quickly obtained after obtaining the absorbance value under the corresponding concentration of the reaction reagent.

Claims

1. A quantitative detection method for low concentration urea in ultrapure water, characterized in that: The specific steps include: Step (1), taking 250mL of the initial water sample and putting it into a polytetrafluoroethylene plastic bottle, tightening the bottle cap, and then pre-freezing it in a -80°C freezer for 24 hours before taking it out, unscrewing the bottle cap, and putting the polytetrafluoroethylene plastic bottle into a vacuum freeze dryer for drying for 24 hours. After drying, taking out the polytetrafluoroethylene plastic bottle and placing it at room temperature until the ice cubes therein are completely dissolved; at this time, water with the same composition as the initial water sample is added to the liquid by a constant volume method until the volume of the liquid is 1 / 10 of the volume of the initial water sample; the vacuum degree of the dryer is 0.05MPa, and the temperature is -50°C; the urea concentration in the initial water sample is 0.3μg / L, and after vacuum freeze drying, the urea concentration in the water sample is 3μg / L; Step (2), preparing a diacetyl monoxime solution with a concentration of 50 g / L; specifically, weighing 5 g of diacetyl monoxime and dissolving it in 10 mL of isopropanol, stirring until completely dissolved, then diluting the solution with 10% isopropanol by mass to a volume of 100 mL, and storing it in a brown bottle at room temperature; Step (3), preparing an acid solution with an antipyrine concentration of 15 g / L; specifically, weighing 1.5 g of antipyrine, dissolving it in mixed acid, adding water to make the volume to 100 mL, and storing it in a brown bottle for later use; the mixed acid is composed of sulfuric acid: phosphoric acid in a volume ratio of 9:1; Step (4), prepare a silver sulfate solution with a concentration of 8 g / L: weigh 0.8 g of silver sulfate and dissolve it in 50 vol.% sulfuric acid, add water to make up to 100 mL, 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 into a 50 mL brown colorimetric tube, add 2 mL of diacetyl monoxime solution, 2 mL of antipyrine acid solution and 1 mL of silver sulfate solution into the colorimetric tube in sequence, tie the tube mouth with raw tape, put it into a boiling water bath and heat it for 50 minutes, then take it out immediately and cool it in running tap water for 2 minutes; Step (6), using a 5 cm cuvette at a wavelength of 460 nm, measure the absorbance of the reaction solution after the reaction and obtain the concentration of urea in the initial water sample based on the standard curve.

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