Seawater chemical oxygen demand solution standard substance and preparation method thereof

Abstract

The embodiment of the invention discloses a seawater chemical oxygen demand solution standard substance and a preparation method thereof, and belongs to the technical field of standard substances. The method comprises the following steps: dissolving phenol in a proper amount of simulated seawater, transferring into a 1000mL volumetric flask, fixing the volume to a scale by using the simulated seawater, and uniformly shaking to prepare the seawater chemical oxygen demand solution standard substance with the concentration range of 5-500mg / L. According to the invention, high-purity phenol is taken as a solute, simulated seawater is taken as a solvent, and the seawater chemical oxygen demand solution standard substance with good stability is prepared. The validity period of the seawater chemical oxygen demand solution standard substance provided by the invention is as long as 2 years. The value setting mode of the seawater chemical oxygen demand solution standard substance provided by the invention is accurate and reliable, and is not influenced by experimental conditions and the like.

Description

Technical Field

[0001] The embodiments of the present invention relate to the technical field of reference materials, and particularly to a seawater chemical oxygen demand solution reference material and a preparation method thereof. Background Art

[0002] Chemical oxygen demand (COD) refers to the amount of chemical oxygen required to completely oxidize organic matter in a water sample under certain conditions, which reflects the degree of pollution of water by reducing substances, especially organic matter. As an important indicator for evaluating water quality, the larger the COD, the more serious the pollution of the water body by organic matter.

[0003] With the acceleration of industrialization and urbanization, the problem of marine environmental pollution is becoming increasingly serious. A large amount of industrial wastewater, domestic sewage, and agricultural non-point source pollution are continuously discharged into the ocean, resulting in an increasing content of organic matter in seawater. These organic matters not only consume the oxygen in seawater, causing water body hypoxia, but also cause serious damage to the marine ecosystem. Therefore, timely and accurate monitoring and grasping of the content of seawater COD is of great significance for the safety of the marine ecological environment, comprehensive pollution prevention and control, and early warning and forecasting of ecological disasters.

[0004] In China, the research on reference materials for seawater started relatively late, and the reference materials for monitoring seawater quality are still relatively scarce. At present, although there is a seawater chemical oxygen demand solution reference material, the raw material used is glucose. Due to the large difference in the oxidation-reduction characteristics between glucose and organic pollutants in seawater (such as petroleum hydrocarbons and phenolic compounds), and glucose is easily decomposed by microorganisms, resulting in extremely unstable data, the validity period of seawater chemical oxygen demand solution reference materials on the market is less than 1 year. Therefore, it is of great significance to develop a seawater chemical oxygen demand solution reference material with low cost, long validity period, and accurate and reliable value determination method. Summary of the Invention

[0005] For this reason, the embodiments of the present invention provide a seawater chemical oxygen demand solution reference material and a preparation method thereof. The reaction equation of phenol and potassium permanganate under acidic conditions is:

[0006] 5C6H5OH + 4KMnO4 + 6H2SO4 → 5C6H4O2 + 4MnSO4 + 2K2SO4 + 11H2O

[0007] The chemical reaction equation of phenol oxygen consumption is:

[0008] 2C6H5OH + O2 → 2C6H4O2 + 2H2O

[0009] From the above reaction equation, it can be obtained that every 2 moles of phenol will consume 1 mole of oxygen to produce 2 moles of benzoquinone. The mass concentration coefficient of phenol and oxygen is 5.875, that is, a phenol solution with a concentration of 1 mg / L corresponds to a seawater chemical oxygen demand solution standard substance with a concentration of 0.170 mg / L. Compared with the standard substance prepared from glucose, the seawater chemical oxygen demand solution standard substance prepared by the present invention has a validity period of up to 2 years, and the value determination method is accurate and reliable, and is not affected by reaction conditions.

[0010] In order to achieve the above object, the embodiments of the present invention provide the following technical solutions:

[0011] According to the first aspect of the embodiments of the present invention, the present invention provides a preparation method of a seawater chemical oxygen demand solution standard substance, the method comprising:

[0012] Dissolve phenol in an appropriate amount of simulated seawater, transfer it to a 1000 mL volumetric flask, make up to the mark with simulated seawater, and shake well to prepare a seawater chemical oxygen demand solution standard substance with a concentration range of 5 mg / L to 500 mg / L.

[0013] Further, the amount of phenol used is 0.02937 g to 2.93752 g.

[0014] Further, the purity of the phenol is 98.5% to 100%.

[0015] Further, the seawater is simulated seawater, and its composition is: 24.5 g to 28.5 g of sodium chloride, 3.21 g to 3.41 g of magnesium sulfate, 2.3 g to 2.7 g of magnesium chloride, 1.04 g to 1.24 g of calcium chloride, 0.705 g to 0.745 g of potassium chloride, 0.182 g to 0.222 g of sodium bicarbonate, and 0.073 g to 0.093 g of sodium bromide in every 1000 mL of water.

[0016] According to the second aspect of the embodiments of the present invention, the present invention provides a seawater chemical oxygen demand solution standard substance prepared by the preparation method described in any one of the above.

[0017] According to the third aspect of the embodiments of the present invention, the present invention provides the application of the seawater chemical oxygen demand solution standard substance described above for monitoring the quality of seawater.

[0018] Further, the seawater chemical oxygen demand is detected by the acid potassium permanganate titration method for oxygen consumption 44.1 in GB 8538 "National Food Safety Standard - Inspection Methods for Drinking Natural Mineral Water".

[0019] The embodiments of the present invention have the following advantages:

[0020] (1)The present invention uses high-purity phenol as the solute and simulated seawater as the solvent to prepare a seawater chemical oxygen demand solution reference material with good stability.

[0021] (2)The validity period of the seawater chemical oxygen demand solution reference material provided by the present invention is up to 2 years.

[0022] (3)The value determination method of the seawater chemical oxygen demand solution reference material provided by the present invention is accurate and reliable, and is not affected by experimental conditions, etc.

[0023] (4)The simulated seawater formula provided by the present invention is closer to the composition of natural seawater, reproducing the interaction between organic matter and ions in real seawater, making the chemical oxygen demand measurement results closer to the actual environmental data. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only exemplary, and for those of ordinary skill in the art, without creative efforts, other implementation drawings can also be obtained according to the provided drawings.

[0025] Figure 1 It is a flowchart for preparing the seawater chemical oxygen demand solution reference material provided by the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] The following specific embodiments illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the protection scope of the present invention.

[0027] Example 1 Seawater Chemical Oxygen Demand Solution Reference Material with a Concentration of 5 mg / L

[0028] This example provides a preparation method, value verification, and stability test for a seawater chemical oxygen demand solution reference material with a concentration of 5 mg / L.

[0029] 1. Preparation Method

[0030] The preparation method of the above seawater chemical oxygen demand solution reference material includes the following steps:

[0031] (1)Prepare simulated seawater containing 26.5 g of sodium chloride, 3.31 g of magnesium sulfate, 2.5 g of magnesium chloride, 1.14 g of calcium chloride, 0.725 g of potassium chloride, 0.202 g of sodium bicarbonate, and 0.083 g of sodium bromide in every 1000 mL of water.

[0032] (2)Accurately weigh 0.02937 g of phenol (converted to 100% pure phenol according to purity), dissolve it with simulated seawater, transfer it to a 1000 mL volumetric flask, and make up the volume to the mark with simulated seawater. Shake well to prepare a phenol solution with a concentration of 29.37 mg / L, corresponding to a seawater chemical oxygen demand of 5 mg / L.

[0033] (3)Seal the solution in clean 20 mL ampoules and store it refrigerated and protected from light.

[0034] (4)Verify the quantity value of the seawater chemical oxygen demand solution reference material according to the acid potassium permanganate titration method for the determination of oxygen consumption in GB 8538 "National Food Safety Standard - Methods for Inspection of Drinking Natural Mineral Water", and conduct stability tests.

[0035] 2. Quantity value verification

[0036] Randomly select 3 bottles of reference materials, repeat the determination 2 times for each bottle by the acid potassium permanganate titration method, compare the measured data with the values obtained by theoretical calculation, and calculate the relative deviation. The results are shown in Table 1. From the results in Table 1, it can be seen that the relative difference between the quantity value calculated from the reaction equation of phenol and potassium permanganate and the quantity value measured by the acid potassium permanganate titration method is 0.1%, indicating that this value determination method is accurate and reliable.

[0037]

[0038] 3. Stability test

[0039] The stability study of reference materials usually includes short-term stability study and long-term stability study. Short-term stability refers to the stability of the characteristic quantity value of the reference material during transportation under specified transportation conditions, which is related to the additional effects caused by the transportation of the reference material and the packaging. Long-term stability refers to the stability of the characteristic quantity value of the reference material under the specific storage conditions required in the reference material certificate, which is related to its production, development, use, and storage conditions.

[0040] Place the reference materials in storage at 60 °C. Take 1 sample at each time point of 0 day, 1 day, 2 days, 3 days, 5 days, 9 days, and 14 days, and conduct parallel determinations 3 times to investigate the short-term stability. The results are shown in Table 2, indicating that the short-term stability of this reference material is good.

[0041]

[0042] The reference material was stored under refrigeration and away from light. One sample was taken at each time point of 0 month, 1 month, 2 months, 3 months, 6 months, 9 months, 12 months, 18 months, and 24 months, and measured in parallel 3 times (taking the average value) to investigate the long-term stability. As shown in Table 3, the results indicate that the reference material can be stably stored for 2 years.

[0043]

[0044] Example 2 Reference Material of Seawater Chemical Oxygen Demand Solution with a Concentration of 100 mg / L

[0045] This example provides a preparation method, value verification, and stability test for a reference material of seawater chemical oxygen demand solution with a concentration of 100 mg / L.

[0046] 1. Preparation Method

[0047] The preparation method of the above-mentioned reference material of seawater chemical oxygen demand solution includes the following steps:

[0048] (1) Prepare simulated seawater containing 26.5 g of sodium chloride, 3.31 g of magnesium sulfate, 2.5 g of magnesium chloride, 1.14 g of calcium chloride, 0.725 g of potassium chloride, 0.202 g of sodium bicarbonate, and 0.083 g of sodium bromide in every 1000 mL of water.

[0049] (2) Accurately weigh 0.58751 g of phenol (phenol with a purity converted to 100%), dissolve it with simulated seawater, transfer it to a 1000 mL volumetric flask, and make up to the mark with simulated seawater and shake well to prepare a phenol solution with a concentration of 587.51 mg / L, corresponding to a seawater chemical oxygen demand of 100 mg / L.

[0050] (3) Seal the solution into clean 20 mL ampoules and store under refrigeration and away from light.

[0051] (4) According to the acidic potassium permanganate titration method for oxygen consumption in GB 8538 "National Food Safety Standard - Methods for Inspection of Drinking Natural Mineral Water", verify the value of the reference material of seawater chemical oxygen demand solution (the reference material needs to be diluted 20 times with simulated seawater before detection), and conduct a stability test.

[0052] 2. Value Verification

[0053] Randomly select 3 bottles of reference materials, repeat the measurement 2 times for each bottle by the acidic potassium permanganate titration method, compare the measured data with the calculated values, and calculate the relative deviation. The result is 0.2%, indicating that this value determination method is accurate and reliable.

[0054] 3. Stability Test

[0055] The standard substance of seawater chemical oxygen demand solution with a concentration of 100 mg / L was subjected to short-term and long-term stability tests according to the stability test method in Example 1. As shown in Table 4, the results indicate that the short-term stability of this standard substance meets the requirements and it can be stored for 2 years under refrigeration and in the dark.

[0056]

[0057] Example 3 Standard Substance of Seawater Chemical Oxygen Demand Solution with a Concentration of 500 mg / L

[0058] This example provides a standard substance of seawater chemical oxygen demand solution with a concentration of 500 mg / L.

[0059] 1. Preparation Method

[0060] The preparation method of the above-mentioned standard substance of seawater chemical oxygen demand solution includes the following steps:

[0061] (1) Prepare simulated seawater, containing 26.5 g of sodium chloride, 3.31 g of magnesium sulfate, 2.5 g of magnesium chloride, 1.14 g of calcium chloride, 0.725 g of potassium chloride, 0.202 g of sodium bicarbonate, and 0.083 g of sodium bromide in every 1000 mL of water.

[0062] (2) Accurately weigh 2.93752 g of phenol (phenol with a purity converted to 100%), dissolve it with simulated seawater, transfer it to a 1000 mL volumetric flask, and make up to the mark with simulated seawater, then shake well to prepare a phenol solution with a concentration of 2937.52 mg / L, corresponding to a seawater chemical oxygen demand of 500 mg / L.

[0063] (3) Seal the solution into clean 20 mL ampoules and store it under refrigeration and in the dark.

[0064] (4) According to the acidic potassium permanganate titration method for oxygen consumption in GB 8538 "National Food Safety Standard - Inspection Methods for Drinking Natural Mineral Water", conduct value verification on the standard substance of seawater chemical oxygen demand solution (the standard substance needs to be diluted 100 times with simulated seawater before detection), and conduct stability tests.

[0065] 2. Value Verification

[0066] Randomly select 3 bottles of standard substances, repeat the determination 2 times for each bottle by the acidic potassium permanganate titration method, compare the measured data with the calculated values, and calculate the relative deviation. The result is 0.1%, indicating that this value determination method is accurate and reliable.

[0067] 3. Stability Test

[0068] The seawater chemical oxygen demand solution reference material with a concentration of 500 mg / L was subjected to short-term and long-term stability tests according to the stability test method in Example 1. As shown in Table 5, the results indicate that the short-term stability of this reference material meets the requirements and it can be stored for 2 years under refrigeration and light protection conditions.

[0069]

[0070] Comparative Example 1 Seawater chemical oxygen demand solution reference material with a concentration of 100 mg / L

[0071] This comparative example provides a seawater chemical oxygen demand solution reference material with a concentration of 100 mg / L, which is prepared with glucose as the solute and simulated seawater as the solvent.

[0072] 1. Preparation method

[0073] The preparation method of the above seawater chemical oxygen demand solution reference material includes the following steps:

[0074] (1) Prepare simulated seawater, which contains 26.5 g of sodium chloride, 3.31 g of magnesium sulfate, 2.5 g of magnesium chloride, 1.14 g of calcium chloride, 0.725 g of potassium chloride, 0.202 g of sodium bicarbonate, and 0.083 g of sodium bromide in every 1000 mL of water.

[0075] (2) Accurately weigh 0.09375 g of glucose (calculated as 100% pure glucose), dissolve it with simulated seawater, transfer it to a 1000 mL volumetric flask, and make up to the mark with simulated seawater, then shake well to prepare a glucose solution with a concentration of 93.75 mg / L, corresponding to a seawater chemical oxygen demand of 100 mg / L.

[0076] (3) Seal the solution into clean 20 mL ampoules and store them under refrigeration and light protection.

[0077] (4) Conduct a stability test on the seawater chemical oxygen demand solution reference material according to the acid potassium permanganate titration method for oxygen consumption 44.1 in GB 8538 "National Food Safety Standard - Inspection Methods for Drinking Natural Mineral Water" (the reference material needs to be diluted 20 times with simulated seawater before detection). The stability test results are shown in Table 6. It can be seen from Table 6 that the seawater chemical oxygen demand solution reference material prepared with glucose has poor stability and begins to degrade after 6 months, while the seawater chemical oxygen demand solution reference material prepared with phenol remains stable after 24 months of storage.

[0078]

[0079] Comparative Example 2 Seawater chemical oxygen demand solution reference material with a concentration of 100 mg / L

[0080] This comparative example provides a seawater chemical oxygen demand solution reference material with a concentration of 100 mg / L, prepared with potassium hydrogen phthalate as the solute and simulated seawater as the solvent.

[0081] 1. Preparation method

[0082] The preparation method of the above seawater chemical oxygen demand solution reference material includes the following steps:

[0083] (1) Prepare simulated seawater, containing 26.5 g of sodium chloride, 3.31 g of magnesium sulfate, 2.5 g of magnesium chloride, 1.14 g of calcium chloride, 0.725 g of potassium chloride, 0.202 g of sodium bicarbonate, and 0.083 g of sodium bromide in every 1000 mL of water.

[0084] (2) Accurately weigh 0.08519 g of potassium hydrogen phthalate (potassium hydrogen phthalate with a purity converted to 100%). After dissolving it with simulated seawater, transfer it to a 1000 mL volumetric flask, and make up the volume to the mark with simulated seawater, then shake well to prepare a glucose solution with a concentration of 85.19 mg / L, corresponding to a seawater chemical oxygen demand of 100 mg / L.

[0085] (3) Seal the solution into clean 20 mL ampoules and store it refrigerated and protected from light.

[0086] (4) According to the acid potassium permanganate titration method for oxygen consumption in GB 8538 "National Food Safety Standard - Methods for Inspection of Drinking Natural Mineral Water", the value of the seawater chemical oxygen demand solution reference material is verified (the reference material needs to be diluted 20 times with simulated seawater before detection). The verification results are shown in Table 7. It can be seen from Table 7 that the detection results of the seawater chemical oxygen demand solution reference material prepared with potassium hydrogen phthalate are quite different from the prepared values. The possible reason for the analysis is that there are a large number of ions in the simulated seawater that will affect the solubility of potassium hydrogen phthalate, resulting in a lower detection result.

[0087]

[0088] Test Example 1 Uncertainty Evaluation

[0089] Taking Example 2 as an example, the uncertainty evaluation is carried out. The main sources of uncertainty in the concentration of the solution reference material are as follows: the uncertainty caused by the purity of the raw materials; the uncertainty caused by the solution preparation process; the uncertainty caused by the inhomogeneity and instability of the sample.

[0090] 1. Uncertainty introduced by the purity of raw materials

[0091] The uncertainty introduced by the purity of raw materials is 0.0037%.

[0092] 2. Uncertainty caused by the solution preparation process

[0093] The uncertainty in the solution preparation process is introduced by the balance and volume fixing during the solution preparation process.

[0094] 2.1 Relative uncertainty of the balance, \(u_{balance,rel}\)

[0095] (1) Repeatability error of balance weighing: According to the balance verification certificate, for a sample weighing 0.58751 g, the maximum allowable repeatability error is 0.15 mg. The net weight of the sample is obtained from 2 weighing operations, and each is an independent observation result. Its relative standard uncertainty is

[0096]

[0097] (2) Indication error of balance: According to the balance verification certificate, for a sample weighing 0.58751 g, the maximum allowable indication error is 0.05 mg. The net weight of the sample is obtained from 2 weighing operations, and each is an independent observation result. Then the relative standard uncertainty is

[0098]

[0099] (3) Buoyancy effect: Weighing is carried out under normal pressure, and the weighing volume is small, so this item can be ignored.

[0100] Therefore, the relative standard uncertainty introduced by the balance, \(u_{balance,rel}\), is 0.022%.

[0101] 2.2 Relative uncertainty of the fixed volume, \(u_{volume,rel}\)

[0102] There are mainly three factors affecting the fixed volume: the maximum allowable difference in the volumetric flask volume, the repeatability of volume fixing, and temperature.

[0103] The volumetric flask used in the solution preparation process is 1000 mL.

[0104] (1) Maximum allowable tolerance of volumetric flask volume: From the volumetric flask verification certificate, the maximum allowable tolerance of a 1000 mL volumetric flask is 0.4 mL. Assuming a uniform distribution, its relative standard uncertainty is

[0105]

[0106] (2) Repeatability of volume fixing: For a 5000 mL volumetric flask filled and weighed 10 times, the standard deviation is obtained as 0.2 mL. Then its relative uncertainty is 0.2 / 1000×100% = 0.02%.

[0107] (3) Temperature effect: The temperature during the preparation of the solution standard substance in this experiment varies between ±3 °C. The volume expansion coefficient of water is 2.5×10 -4 mL•°C -1 , assuming a uniform distribution, the relative standard uncertainty is

[0108]

[0109] Combining the components of the above three factors, the relative standard uncertainty u_volume_rel introduced by the constant-volume is 0.050%.

[0110] 3. Uncertainty caused by the inhomogeneity and instability of the sample

[0111] The uncertainty caused by the inhomogeneity and instability of the sample is 0.43%.

[0112] Combining each relative uncertainty component, the relative combined standard uncertainty u_rel of the reference material is obtained as 0.44%. Taking the coverage factor k = 2, U_rel = 0.44% × 2 ≈ 0.9%.

[0113] Although the present invention has been described in detail with general descriptions and specific embodiments above, based on the present invention, some modifications or improvements can be made, which are obvious to those skilled in the art. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection required by the present invention.

Claims

1. A preparation method of a seawater chemical oxygen demand solution reference material, characterized in that, The method includes: Dissolve phenol in an appropriate amount of simulated seawater, transfer it to a 1000 mL volumetric flask, make up to the mark with simulated seawater, shake well, and prepare a standard substance of seawater chemical oxygen demand solution with a concentration range of 5 mg / L to 500 mg / L.

2. The preparation method of the seawater chemical oxygen demand solution reference material according to claim 1, characterized in that, The dosage of the phenol is 0.02937 g to 2.93752 g.

3. The preparation method of the seawater chemical oxygen demand solution reference material according to claim 1, characterized in that, The purity of the phenol is 98.5% to 100%.

4. The preparation method of the seawater chemical oxygen demand solution reference material according to claim 1, characterized in that, The seawater is simulated seawater, and its composition is: 24.5 g to 28.5 g of sodium chloride, 3.21 g to 3.41 g of magnesium sulfate, 2.3 g to 2.7 g of magnesium chloride, 1.04 g to 1.24 g of calcium chloride, 0.705 g to 0.745 g of potassium chloride, 0.182 g to 0.222 g of sodium bicarbonate, and 0.073 g to 0.093 g of sodium bromide per 1000 mL of water.

5. A seawater chemical oxygen demand solution reference material, characterized in that, It is made by the preparation method described in any one of claims 1-4.

6. Use of the seawater chemical oxygen demand solution reference material according to claim 5, characterized in that, For the monitoring of seawater quality.

7. The application according to claim 6, wherein The seawater chemical oxygen demand is detected by the acid potassium permanganate titration method for oxygen consumption 44.1 in GB 8538 "National Food Safety Standard - Inspection Methods for Drinking Natural Mineral Water".

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