A method for detecting low-concentration selenium in water

Abstract

The present application discloses a method for detecting low-concentration selenium in water, comprising: (1) taking a water sample, adding a first reagent and a second reagent in sequence, heating to boiling after fully dissolving, and maintaining a slight boil, and then cooling to room temperature; the first reagent is an acid solution; the second reagent is a mixed aqueous solution of a masking agent, a buffer, a stabilizer, and a color developer; (2) adding a third reagent to the cooled reaction solution, mixing it thoroughly, and then adding a fourth reagent, mixing it thoroughly, and then standing it for extraction; the third reagent is an alkaline buffer solution; the fourth reagent is an extractant, and the extractant is a 1:1 mixture of dichloromethane and cyclohexane; (3) taking the extract and filtering it through a membrane, and then detecting the absorbance value at 420nm, and substituting the obtained absorbance value into the standard curve to calculate the selenium concentration in the water sample. The present application can be used to detect water samples with a selenium concentration of 0.001-0.25mg / L and has high detection sensitivity.

Description

Technical Field

[0001] The invention relates to the technical field of water quality detection, and in particular to a method for detecting low-concentration selenium in water. Background Art

[0002] Selenium in people's daily diet includes inorganic selenium and organic selenium. Organic selenium, such as selenoprotein and selenoamino acid, can be converted into active substances beneficial to the human body in the body and absorbed and utilized by the human body. Inorganic selenium, especially hexavalent selenium, is highly toxic, and the limit between the poisoning amount and the required amount is very close. In addition, its absorption and utilization rate are poor, and its biological effectiveness is low. Therefore, its use is strictly limited. Therefore, when conducting ecological environment surveys and monitoring, it is of great significance to accurately detect the content of inorganic selenium in water quality.

[0003] Traditional detection methods include atomic spectrophotometry, absorption spectroscopy, mass spectrometry, electrochemical technology, chromatography, etc. Traditional spectrophotometry is widely used. Among them, the diaminobenzidine spectrophotometry method of the water quality industry standard HJ811-2016 is a relatively commonly used standard method. However, on the one hand, the reagents used in the standard need to be prepared and used immediately, and have a short shelf life; the extractant toluene is relatively toxic, the reagents are not environmentally friendly, and are not suitable for non-professionals to operate; the color development time is too long, affecting the detection efficiency; on the other hand, when detecting low-concentration selenium, the standard method has the need to synchronize the standard curve and the sample, and in the measurement process, there is a process of adjusting the pH to 1-3, and then a process of adjusting the pH back to 7-10, which causes the pH of the reaction solution to be offset and the repeatability is poor. Summary of the invention

[0004] The present application provides a new spectrophotometric detection method, the reagents used are environmentally friendly and non-toxic, suitable for non-professional operation, the reagents have a long shelf life and are simple to operate, the color development time is significantly shortened, and the detection efficiency is improved; and when detecting low-concentration water quality selenium, the sampling volume reaches 200 ml, and the colorimetric tube is 10mm, the detection limit of 2.0ug / L of the standard method 30mm can be reached, and the sampling volume reaches 200 ml, and the colorimetric dish adopts 30mm. When the minimum detection limit can reach 0.7ug / L, the sensitivity of HJ811 is increased by about 3 times. At the same time, by further increasing the volume of the sampled water sample, the detection limit can be further reduced. For example, if the sampling volume is 10L, the minimum detection limit is less than 0.01ug / L, which is better than any current national standard method.

[0005] A method for detecting low-concentration selenium in water, comprising:

[0006] (1) Take at least 200 mL of water sample, add the first reagent and the second reagent in sequence, heat to boiling after fully dissolving, and keep boiling for 5-6 minutes, then cool to room temperature; the selenium concentration in the water sample is 0.001-0.25 mg / L;

[0007] The first reagent is a 1-4 mol / L hydrochloric acid aqueous solution or a 1-2 mol / L sulfuric acid aqueous solution;

[0008] The second reagent is a mixed aqueous solution of a masking agent, a buffer, a stabilizer and a color developer, wherein the buffer is 1% to 10% by weight, the masking agent is 1% to 10% by weight, the stabilizer is 0.01% to 5% by weight, and the color developer is 1% to 10% by weight, and the solvent is water;

[0009] (2) Add 2 mL of the third reagent to the cooled reaction solution, mix thoroughly, then add 10 mL of the fourth reagent, mix thoroughly, and allow to stand for extraction;

[0010] The third reagent is an alkaline buffer solution, which contains 1%-20% sodium hydroxide, 1%-20% sodium carbonate, and 1-20% borax by weight, and the solvent is water;

[0011] The fourth reagent is an extractant, and the extractant is dichloromethane and cyclohexane in a volume ratio of 1:1;

[0012] (3) Take the extract and filter it through a membrane, then detect the absorbance at 420 nm. Substitute the obtained absorbance into the standard curve to calculate the selenium concentration in the water sample.

[0013] Several optional methods are also provided below, but they are not intended to be additional limitations on the above-mentioned overall solution, but are merely further supplements or preferences. Under the premise that there are no technical or logical contradictions, each optional method can be combined with the above-mentioned overall solution separately, and multiple optional methods can also be combined.

[0014] Optionally, based on 200 mL of water sample, the amount of the first reagent added is 1 mL, the amount of the second reagent added is 0.2 g, the amount of the third reagent added is 2 mL, and the amount of the fourth reagent added is 10 mL.

[0015] Optionally, when the amount of the water sample increases, the amounts of the first reagent, the second reagent and the third reagent are increased in equal proportions, and the amount of the fourth reagent remains unchanged. The detection limit can be further reduced by increasing the amount of the sampled water sample while keeping the amount of the extractant unchanged.

[0016] Optionally, in the second reagent: the buffer is citric acid or tartaric acid to maintain the pH of the first reagent between 1-3.

[0017] Optionally, in the second reagent: the stabilizer is a mixture of sodium sulfite and 2-hydroxy-4-methoxybenzophenone in a mass ratio of 1:1 or a mixture of sodium sulfite and 2-hydroxy-4-n-octyloxybenzophenone in a mass ratio of 1:1.

[0018] Optionally, in the second reagent: the masking agent is one or a combination of ethylenediaminetetraacetic acid and EDTA sodium salt thereof; the color developer is 4,5-diaminophthalonitrile or its salts. The color developer is non-hazardous chemical as checked on the Sinopharm website (https: / / www.reagent.com.cn / ).

[0019] Optionally, the membrane filtration is: filtration through a 0.45 μm organic filter membrane.

[0020] Optionally, the selenium is inorganic selenium in water.

[0021] Optionally, the standard curve is: y = 0.2448x - 0.0041, R 2 =0.9999, where y is the selenium concentration in mg / L and x is the absorbance.

[0022] Optionally, the first reagent is a 2 mol / L hydrochloric acid solution;

[0023] In the second reagent: the masking agent is ethylenediaminetetraacetic acid and its weight percentage concentration in the mixed aqueous solution is 5%; the buffer is citric acid and its weight percentage concentration in the mixed aqueous solution is 5%; the stabilizer is sodium sulfite and 2-hydroxy-4-methoxybenzophenone mixed in a mass ratio of 1:1 and its weight percentage concentration in the mixed aqueous solution is 1%; the color developer is 4,5-diaminophthalonitrile and its weight percentage concentration in the mixed aqueous solution is 5%; the solvent is water;

[0024] The third reagent comprises 20% sodium hydroxide, 5% sodium carbonate and 5% borax; the solvent is water;

[0025] The fourth reagent is dichloromethane and cyclohexane in a volume ratio of 1:1.

[0026] Compared with the standard method, the present invention has at least one of the following beneficial effects:

[0027] (1) The HJ811-2016 standard method requires 200 ml of water sample and 30 mm cuvette to achieve a detection limit of 2.0 ug / L; while the present application can achieve the detection limit of 2.0 ug / L described in the standard method with 200 ml of water sample and 10 mm cuvette; and can achieve a detection limit of 0.7 ug / L with 200 ml of water sample and 30 mm cuvette. Therefore, when detecting low concentration of selenium in water, the sensitivity of the present application method is better than that of the HJ811-2016 standard method.

[0028] (2) The color development time of the color developer used in the method of this application is shortened. The reaction is complete after heating for 5 minutes, and then the measurement can be performed after cooling with cold water for 5 minutes. Compared with the spectrophotometric method of HJ811-2016, it is significantly shorter and the detection efficiency is improved.

[0029] (3) Compared with toluene used in HJ811-2016, the extraction agent is more environmentally friendly and convenient for non-professionals to operate.

[0030] (4) The precision and accuracy are not inferior to the standard method. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is the curve test chart of Example 1. DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0034] The detection method of the present application is a new spectrophotometric method.

[0035] About First Reagent:

[0036] The acid solution used in the first reagent is related to the sampling volume of the water sample. If the amount of water sample increases, the amount of acid needs to be increased in the same proportion to maintain the reaction under suitable acidic conditions.

[0037] About the second reagent:

[0038] The detection reaction of the present method requires an acidity of about pH 2, and citric acid can provide a reaction environment of about pH 2. At the same time, citric acid has a certain reducing property, which can reduce the high-valent selenium in the water sample to tetravalent selenium that can react, thereby promoting the detection accuracy. Since the reaction may be interfered by some metal ions, a masking agent is added to the first reagent to mask some common metal ions, thereby promoting the detection accuracy. The color developer contained in the first reagent will be degraded by light and oxygen, and the detection reaction will also be affected by light and oxides. The present application adds a stabilizer, which includes an ultraviolet absorber such as 2-hydroxy-4-methoxybenzophenone, and a reducing agent with strong reducing property, sodium sulfite. The stabilizer ensures the stability of the color developer during the shelf life and avoids interference from light and water sample oxides during the reaction.

[0039] About the third reagent:

[0040] The present application adopts a buffer solution to stabilize the acid-base environment of the reaction during different reaction steps, thereby promoting the reaction to proceed stably and rapidly.

[0041] About the fourth reagent:

[0042] This application uses a mixture of dichloromethane and cyclohexane in a ratio of 1:1 (volume ratio) as an extractant, which can extract the reactants from the water sample into the organic phase. The selection of the extractant needs to be strictly screened and tested, and a standard curve is required to be established according to the concentration of selenium. During the screening process, this application tested mixed extractants of n-butanol: cyclopentane = 1:1 (volume ratio), ethyl acetate: dichloromethane = 1:1 (volume ratio) and dichloromethane: cyclohexane = 1:1 (volume ratio). The absorbance value comparison results of different extractants are shown in Table 1. With the absorbance value as the horizontal axis and the selenium concentration value as the vertical axis, a standard curve was established and it was found that the use of a mixed extractant of n-butanol and cyclopentane and a mixed extractant of ethyl acetate and dichloromethane can extract the reactants, but the required dosage is large, the extraction volume is unstable, the linearity is poor, and the absorbance value is low, so it is impossible to make a standard curve, while the linearity of the mixed extractant of dichloromethane: cyclohexane = 1:1 (volume ratio) is very good ( Figure 1 ).

[0043] Table 1. Comparison of absorbance values ​​of different extractants

[0044]

[0045] The following is a description of specific examples, and the reagents used in the examples can be purchased commercially:

[0046] Example 1

[0047] Detection reagents:

[0048] The first reagent: 2 mol / L hydrochloric acid solution.

[0049] The second reagent, calculated by weight percentage concentration: buffer citric acid 5%, masking agent ethylenediaminetetraacetic acid 5%, stabilizer (sodium sulfite and 2-hydroxy-4-methoxybenzophenone mixed in a ratio of 1:1) 1%, color developer (4,5-diaminophthalonitrile) 5%, and solvent is water.

[0050] The third reagent, by weight percentage concentration: sodium hydroxide 20%, sodium carbonate: 5%, borax: 5%, the solvent is water.

[0051] The fourth reagent: a mixed extractant of dichloromethane: cyclohexane = 1:1 (volume ratio).

[0052] The process of making the song:

[0053] Purchase Aladdin selenium standard solution (100 mg / L in 1% HCl) S115455-80mL, take 5 mL of the standard solution and dilute to a 100 mL volumetric flask to obtain a selenium standard working solution (5 mg / L). 0.025, 0.05, 0.1, and 0.25 mg / L concentrations are obtained by diluting the 5 mg / L selenium standard solution, and 0.01 mg / L concentration is obtained by diluting the 0.1 mg / L selenium standard solution, see Table 2.

[0054] Table 2

[0055]

[0056] The detection operation was carried out according to the following detection process. The detection results were taken as the absorbance value as the horizontal axis and the selenium concentration value as the vertical axis. The standard curve was established: y = 0.2448x - 0.0041, R 2 = 0.9999, where y is the selenium concentration in mg / L, and x is the absorbance. Figure 1 shown.

[0057] Testing process:

[0058] (1) Turn on the water quality detector (e.g. ZY-360 Multi-parameter Water Quality Analyzer, Zhejiang Luheng Environmental Technology Co., Ltd.), select the selenium measurement position or 420 nm wavelength, and add an appropriate amount of the fourth reagent into the colorimetric tube for zero adjustment.

[0059] (2) Add 200 ml of water sample to a 250 ml iodine volumetric flask, first add 1 ml of the first reagent, then add 0.2 g of the second reagent, shake to fully dissolve, place on an electric stove, heat to boiling, keep it at a slight boil for 5 minutes, allow the color reaction to develop, remove and cool to 25 °C. The reaction liquid is yellow.

[0060] (3) Add 2 mL of the third reagent to the iodine volumetric flask, cover and shake for 10 seconds to mix thoroughly, add 10 mL of the fourth reagent to the iodine volumetric flask, and stir magnetically at 2000 rpm for 1 min.

[0061] (4) After standing for 5 minutes, use a pipette to draw an appropriate amount of extract into a transition bottle. Use a disposable syringe to draw the extractant and filter it through a 0.45 μm organic filter membrane. Inject it into a 10 mm colorimetric tube and place it in the detection tank of the water quality detector. After timing for 1 minute, read its absorbance value.

[0062] (5) After the test, long press the power button to turn off the instrument.

[0063] Precision test results

[0064] The relative standard deviations of inorganic selenium concentrations determined by three laboratories using this method are shown in Table 3:

[0065] Table 3

[0066]

[0067] From the results in Table 3, it can be seen that the relative standard deviations within the laboratory are -0.85%~4.78%, -3.91%~0.43%, and -1.83%~0.98%, respectively, and the precision error is less than 5%.

[0068] Accuracy test results:

[0069] Four water samples were taken for spike recovery experiments, and the recovery rates were shown in Table 4:

[0070] Table 4

[0071]

[0072] From the results in Table 4, we can see that the recovery rate of tap water spiked is 90%~101.10%, the recovery rate of river water spiked is 106.5%~95.3%, the recovery rate of seawater spiked is 104.3%~93.8%, the recovery rate of wastewater spiked is 105.3%~97.1%, and the spiked recovery rates of natural water samples and wastewater samples are ≤10%. Compared with the HJ811 sewage sample spiked recovery rate of more than 10%, it has certain advantages.

[0073] Water samples with different selenium concentrations were taken for testing, and the results are shown in Table 5:

[0074] Table 5

[0075]

[0076] It can be seen from the results in Table 5 that the method of the present application has good detection results for water samples with selenium concentrations of 0.001-0.25 mg / L.

[0077] The present invention can achieve the detection limit of 2.0ug / L when the standard method uses a 30mm colorimetric tube with 200ml water sample and 10mm colorimetric tube. Further experimental verification shows that when taking 200ml water sample and using a 30mm colorimetric dish, the detection limit can reach 0.7ug / L. Therefore, when detecting low-concentration selenium in water quality, the sensitivity of the present invention method is significantly better than the HJ811-2016 standard method.

[0078] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. A method for detecting low-concentration selenium in water, characterized in that: include: (1) Take at least 200 mL of water sample, add the first reagent and the second reagent in sequence, heat to boiling after fully dissolving, and keep boiling for 5 to 6 minutes, and then cool to room temperature; the selenium concentration in the water sample is 0.001-0.25 mg / L; The first reagent is a 1-4 mol / L hydrochloric acid aqueous solution or a 1-2 mol / L sulfuric acid aqueous solution; The second reagent is a mixed aqueous solution of a masking agent, a buffer, a stabilizer and a developer, and the concentration by weight percentage is 1% to 10% for the buffer; 1% to 10% for the masking agent; 0.01% to 5% for the stabilizer, and 1% to 10% for the developer, and the solvent is water; the stabilizer is a mixture of sodium sulfite and 2-hydroxy-4-methoxybenzophenone in a mass ratio of 1:1 or a mixture of sodium sulfite and 2-hydroxy-4-n-octyloxybenzophenone in a mass ratio of 1:1; the developer is 4,5-diaminophthalonitrile or its salts; (2) adding the third reagent to the cooled reaction solution, mixing thoroughly, then adding the fourth reagent, mixing thoroughly, and then standing for extraction; The third reagent is an alkaline buffer solution, which contains 1%-20% sodium hydroxide, 1%-20% sodium carbonate, and 1-20% borax by weight, and the solvent is water; The fourth reagent is an extractant, and the extractant is dichloromethane and cyclohexane in a volume ratio of 1:1; (3) Take the extract and filter it through a 0.45 μm organic filter membrane, then measure the absorbance at 420 nm. Substitute the obtained absorbance into the standard curve to calculate the selenium concentration in the water sample. Based on 200 mL of water sample, the amount of the first reagent added is 1 mL, the amount of the second reagent added is 0.2 g, the amount of the third reagent added is 2 mL, and the amount of the fourth reagent added is 10 mL; When the amount of the water sample increases, the amounts of the first reagent, the second reagent and the third reagent increase in equal proportions, and the amount of the fourth reagent remains unchanged.

2. The detection method according to claim 1, characterized in that: In the second reagent: the buffer is citric acid or tartaric acid to maintain the pH of the first reagent between 1-3.

3. The detection method according to claim 1, characterized in that: In the second reagent: the masking agent is one or a combination of ethylenediaminetetraacetic acid and EDTA sodium salt.

4. The detection method according to claim 1, characterized in that: The selenium is inorganic selenium in water.

5. The detection method according to claim 1, characterized in that: The standard curve is: y=0.2448x-0.0041, R 2 =0.9999where y is the selenium concentration in mg / L and x is the absorbance.

6. The detection method according to claim 1, characterized in that: The first reagent is a 2 mol / L hydrochloric acid solution; In the second reagent: the masking agent is ethylenediaminetetraacetic acid and its weight percentage concentration in the mixed aqueous solution is 5%; the buffer is citric acid and its weight percentage concentration in the mixed aqueous solution is 5%; the stabilizer is sodium sulfite and 2-hydroxy-4-methoxybenzophenone mixed in a mass ratio of 1:1 and its weight percentage concentration in the mixed aqueous solution is 1%; the color developer is 4,5-diaminophthalonitrile or its salts and its weight percentage concentration in the mixed aqueous solution is 5%; The third reagent includes 20% sodium hydroxide, 5% sodium carbonate and 5% borax; The fourth reagent is dichloromethane and cyclohexane in a volume ratio of 1:1.

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