Method for measuring fluorine ions and total nitrogen by adopting low-content fluorine ion and total nitrogen mixed standard solution

Abstract

The invention belongs to the technical field of stoichiometry, and relates to a standard substance preparation technology, in particular to a method for measuring fluorine ions and total nitrogen by adopting a low-content fluorine ion and total nitrogen mixed standard solution. Firstly, a low-content fluorine ion and total nitrogen mixed solution standard substance preparation technology is provided, the storage condition of the standard substance is determined, and a method for rapidly measuring fluorine ions and total nitrogen by using the standard substance is provided. The preparation method adopts national standard substances for batching and subpackaging, and is simple in mode, low in cost and easy for large-scale preparation. In order to solve the problems that an existing standard substance lacks an effective and reasonable unified standard in the aspect of storage, part of reagents are easy to expire, measurement errors are large due to the fact that the ion content deviation of the expired reagents is too large during measurement, and the measurement requirements cannot be met, an optimized storage index is determined through short-term detection, and the measurement accuracy is improved. And through long-term storage and detection, the upper limit of the storage time of the standard solution can reach one year, and the measurement precision during use is ensured.

Description

Technical Field

[0001] The invention belongs to the technical field of chemometrics, relates to a standard substance preparation technology, and specifically relates to a method for measuring fluoride ions and total nitrogen by using a mixed standard solution of low-content fluoride ions and total nitrogen. Background Art

[0002] Water quality environmental monitoring plays an important role in protecting water resources and ensuring that water quality meets the needs of ecosystems and human health. Monitoring can detect pollutants in water bodies early to prevent long-term damage to the environment. At the same time, water quality monitoring helps ensure the safety of drinking water. By regularly monitoring various chemicals and microorganisms in water sources, timely measures can be taken to ensure that drinking water meets sanitary standards and protect public health. In addition, water quality monitoring is also an important part of environmental protection and sustainable development. Understanding the quality status of water bodies helps to formulate reasonable environmental policies and management measures, and encourages people to use and treat water resources more rationally.

[0003] Water quality environmental monitoring involves many aspects, including physical property indicators such as temperature, turbidity, and conductivity; chemical property indicators such as pH value, dissolved oxygen, nitrogen-containing compounds, and phosphorus-containing compounds; biological indicators such as aquatic community structure, aquatic organism quantity and diversity, and microbial indicators; indicator microbial indicators such as Escherichia coli; dissolved organic carbon (DOC), heavy metals and organic pollutants: such as organic matter and pollutant indicators such as lead, cadmium, and mercury.

[0004] Fluoride ions and total nitrogen are important indicators for water quality environmental monitoring. Understanding the fluoride ion content in water can help assess the health and suitability of water bodies. A moderate amount of fluoride ions is good for human health, but high concentrations of fluoride ions may cause dental and bone problems, and even cause fluoride poisoning. Therefore, fluoride ion monitoring is an important part of ensuring drinking water safety. Total nitrogen includes various forms of nitrogen in water, such as ammonia nitrogen, nitrite nitrogen, nitrate nitrogen, and organic nitrogen. Understanding the total nitrogen content in water is critical for assessing the eutrophication of water bodies, pollution conditions, and the impact on the ecosystem. Existing methods for fluoride ion detection include ion selective electrode method, ion chromatography, fluorescence method, inductively coupled plasma mass spectrometry (ICP-MS), ion chromatography mass spectrometry (IC-MS), etc. Methods for total nitrogen detection include nitrogen mass spectrometry (TN), ultraviolet-visible absorption spectroscopy (UV-Vis), nitrogen concentration meter, nitrogen evaporation method, etc. Among them, ion chromatography separates and detects fluoride ions in water through a chromatograph. This is a highly sensitive method suitable for detecting fluoride at lower concentrations.

[0005] However, the existing standard substances used for detection have high content and need to be diluted when used, which can easily cause measurement errors. In addition, there is a lack of effective and reasonable unified standards for the storage of low-content fluoride ions and total nitrogen solutions. Some reagents are prone to expire. When measuring, the ion content of expired reagents is too large to cause large measurement errors, which cannot meet the measurement requirements. In the prior art, ion chromatography measures different types of nitrogen separately when measuring nitrogen, such as nitrate nitrogen, ammonia nitrogen, etc. The measurement results may not be completely consistent with total nitrogen, and currently cannot be measured simultaneously with fluoride ions. Summary of the invention

[0006] In order to solve the above technical problems, the present invention provides a method for measuring fluoride ions and total nitrogen using a low-content fluoride ion and total nitrogen mixed standard solution. First, a preparation technology of a low-content fluoride ion and total nitrogen mixed solution standard substance is provided, and its storage conditions are determined, and a method for quickly measuring fluoride ions and total nitrogen is performed using the low-content fluoride ion and total nitrogen mixed solution standard substance.

[0007] The technical solution of the present invention includes:

[0008] Firstly, the present invention provides a method for preparing a low-content fluoride ion and total nitrogen mixed standard solution, comprising the following steps: according to the target value, weighing a certain mass of sodium fluoride national secondary purity standard material and a certain mass of ammonium dihydrogen phosphate purity standard material (national primary purity standard material), placing them in a volumetric flask, adding constant temperature pure water after dissolving, and fixing the volume to the graduation line to obtain a mixed low-content fluoride ion and total nitrogen mixed standard solution.

[0009] Furthermore, the fluoride ion content in the low-content fluoride ion and total nitrogen mixed standard solution is 10 mg / L.

[0010] Furthermore, the total nitrogen content in the low-content fluoride ion and total nitrogen mixed standard solution is 20 mg / L.

[0011] Furthermore, the constant temperature pure water is 20°C.

[0012] Furthermore, the volumetric flask is a 2000mL single-marked volumetric flask.

[0013] Furthermore, the low-content fluoride ion and total nitrogen mixed standard solution can also be tested for uniformity and stability.

[0014] Furthermore, the uniformity and stability test is carried out using ion chromatography.

[0015] Furthermore, the uniformity and stability test is based on the standard fluoride ion and total phosphorus as the standard, and the value is determined by the ratio of the peak area of ​​fluoride ion and total phosphorus in the mixed standard solution sample to the corresponding peak area in the standard. The total nitrogen content can be obtained by measuring the total phosphorus, and the anion can be measured in one injection, and the fluoride ion and total nitrogen detection can be completed at the same time.

[0016] Furthermore, the low-content fluoride ion and total nitrogen mixed standard solution can be packaged: a sealed packaging bottle is used, and after nitrogen blowing treatment, the low-content fluoride ion and total nitrogen mixed standard solution is added and quickly sealed.

[0017] Furthermore, the low-content fluoride ion and total nitrogen mixed standard solution is sealed and packaged in polyethylene bottles, and the maximum storage time is one year.

[0018] Furthermore, the storage conditions of the low-content fluoride ion and total nitrogen mixed standard solution are: storage temperature (4-8)°C, relative humidity (30-40)%, and avoid light.

[0019] Furthermore, the sealed packaging bottle is a 10 mL sealed packaging bottle.

[0020] Furthermore, during the packaging process of the low-content fluoride ion and total nitrogen mixed standard solution, the nitrogen blowing treatment conditions are: nitrogen blowing temperature: (90-120)°C, nitrogen flow rate: (2-5)L / min, and purge time: (30-60)min.

[0021] In a second aspect, the present invention provides a method for rapidly detecting the fluoride ion and total nitrogen content in water areas, using the above-mentioned low-content fluoride ion and total nitrogen mixed standard solution as a standard and using ion chromatography to detect the fluoride ion and total nitrogen content in water areas.

[0022] Compared with the prior art, the advantages of the present invention are:

[0023] The present invention adopts national standard substances for batching and packaging, which is simple in method, low in cost and easy to prepare on a large scale. In addition, in view of the lack of effective and reasonable unified standards for storage of existing standard substances, some reagents are easily expired, and the measurement error is large due to the excessive deviation of the ion content of expired reagents during measurement, which cannot meet the measurement requirements. The optimized storage index is determined by short-term detection, and the upper limit of the storage time of the standard solution is determined to be up to one year through long-term storage and detection, which ensures the measurement accuracy during use. In addition, diammonium dihydrogen phosphate is used in the preparation of this standard substance, and the type of nitrogen is single. Ion chromatography is not a direct measurement of nitrogen, so there is no need to distinguish and no pre-treatment is required. In summary, the preparation method of the low-content fluoride ion and total nitrogen mixed standard solution of the present invention is simple, low in cost, easy to prepare on a large scale, and the optimized storage condition index and deadline are determined, which ensures the measurement accuracy during use, and ion chromatography can be used to simultaneously detect fluoride ions and total nitrogen in water, and the method is simple and the results are accurate. DETAILED DESCRIPTION

[0024] The above contents of the present invention are further described in detail below by means of specific implementation methods in the form of embodiments, but this should not be understood as the scope of the above subject matter of the present invention being limited to the following examples. All technologies implemented based on the above contents of the present invention belong to the scope of the present invention. Unless otherwise specified, conventional technical operations are used in the following embodiments.

[0025] In the following embodiments:

[0026] The sealing equipment is an oxyhydrogen flame sealing machine with a flame temperature of (1800~2800)℃;

[0027] Sodium fluoride: National secondary purity standard material GBW(E)060323, National Defense Applied Chemistry Level 1 Metrology Station;

[0028] Ammonium dihydrogen phosphate: National first-level purity standard material GBW06502, China National Institute of Metrology.

[0029] Example 1 Mixed standard solution configuration

[0030] (1) According to the target value, weigh 0.04421 g of sodium fluoride national secondary purity standard material and 0.33112 g of ammonium dihydrogen phosphate purity standard material, place them in a 2000 mL single-line volumetric flask, add pure water after dissolving, keep the temperature at 20°C, and adjust the volume to the graduation line to obtain a mixed low-content fluoride ion and total nitrogen mixed standard solution.

[0031] (2) Packaging: Use 10 mL polyethylene sealed packaging bottles and nitrogen blow (nitrogen blowing temperature: 100 ° C,

[0032] Nitrogen flow rate: 3L / min, purge time: 50min), then add the mixed low-content fluoride ion and total nitrogen mixed standard solution and quickly seal.

[0033] Example 2: Homogeneity test of mixed standard solution

[0034] A total of 300 bottles of mixed standard solutions were prepared according to the above method, and 10 bottles of samples were randomly selected from them. The ion chromatography method was used for measurement (ion chromatography conditions: the eluent used was a mixed solution of Na2CO3-NaHCO3, flow rate: 1.0mL / min; the detector was CD20, and the chromatographic column was AS19). At the same time, the standard reference substances were measured (the standard reference substances were the national secondary fluoride ion solution standard substance GBW(E)080519; the national secondary phosphate standard substance GBW(E)083180). The fluoride ion content and total nitrogen content were determined by the ratio of the fluoride ion and phosphate peak areas in the samples to the fluoride ion and phosphate peak areas in the standard reference substances. The results of the measured fluoride ion and total nitrogen contents are shown in Table 1 below.

[0035] Table 1

[0036] Sample No. Fluoride ion content (mg / L) Total nitrogen content (mg / L) 1 10.01 20.00 2 10.02 19.98 3 9.98 19.99 4 10.04 20.04 5 10.03 20.06 6 10.02 19.97 7 10.00 20.00 8 10.05 20.00 9 9.99 19.96 10 10.04 19.98

[0037] It can be seen from the data in Table 1 that the content of the mixed standard solution obtained by the preparation method of the present invention is very stable, and no significant difference was found in the results, which indicates that the content characteristics of the mixed standard solution are uniform.

[0038] Example 3 Determination of storage conditions for mixed standard solution

[0039] As mentioned above, the currently configured standard solutions lack effective and reasonable unified standards in terms of storage, and some reagents are prone to expire, which can easily lead to low accuracy when used for actual measurements. Therefore, this embodiment tests and analyzes the storage conditions of the mixed standard solution and various parameters to determine the optimal storage method and storage date. Specifically, it includes:

[0040] (1) Short-term storage stability testing and index determination

[0041] A mixed standard solution was prepared according to the method of Example 1, with a total of 300 bottles of samples, and different storage conditions were selected as indicators, including environmental humidity, temperature, light conditions, and material of the volumetric flask.

[0042] The environmental temperatures are -20℃, 4℃, 20℃ and 50℃. The environmental humidity is 30%, 45%, 70% and 85%. The light conditions are 0.5, 500, 10000 and 50000 lux respectively, and the sealed packaging bottle materials are glass and polyethylene. Different parameters of each index are combined into different storage conditions. Ten samples are selected for storage under each condition, and samples are taken at 0 days (when the samples are initially stored), 3 days, 7 days, 15 days and 30 days respectively. The changes in the content of fluoride ions and total nitrogen in the mixed standard solution are detected by ion chromatography. The average value of the test results of the 10 samples stored under the same conditions is taken as the test result. The experimental data results of some polyethylene sealed packaging bottles are shown in Table 2.

[0043] Table 2

[0044]

[0045]

[0046] Short-term storage indicator selection, including:

[0047] 1) Compare all test results with the initial content and calculate their deviation:

[0048]

[0049] E iis the deviation value of the i-th result, C i is the detection value of the i-th result, and C0 is the initial concentration value.

[0050] 2) Perform the following operations on all deviation values ​​to obtain the standard deviation:

[0051]

[0052] is the standard deviation of the ith result, E max is the maximum value among all deviation values. A data set is established based on the storage conditions of each test result and the standard deviation of the test result.

[0053] 3) Taking environmental humidity, temperature, light conditions, and sealed packaging bottle material as independent variables, and the standard deviation of fluoride ion or total nitrogen content as dependent variables, multiple linear regression models were established for regression analysis, and the following results were obtained:

[0054]

[0055] Where y is the dependent variable, i.e., the standard deviation of fluoride ion or total nitrogen content, β i is the regression coefficient of the ith indicator, x i is the value of the ith indicator, β0 is the intercept, and ε is the error term.

[0056] 4) All regression coefficients are normalized to determine the weight ratio of each independent variable indicator; the independent variable indicators whose weight ratio is greater than the preset threshold are used as storage key indicators.

[0057] 5) Perform the above operations on the fluoride ion and total nitrogen contents respectively, and obtain their respective storage key indicators. Take the union of the storage key indicators of fluoride ion and total nitrogen contents to obtain the overall storage key indicator.

[0058] 6) According to the above analysis results, for the overall key indicators, select the indicator value with the smallest standard deviation for storage. In order to maintain the concentration stability of the mixed standard solution, other non-key indicators are not required. The short-term storage conditions are finally determined as follows: storage temperature (4-8) ° C, relative humidity (30-40)%, and avoid light.

[0059] (2) Determination of long-term storage stability time

[0060] 1) A mixed standard solution was prepared according to the method of Example 1, with a total of 250 bottles (polyethylene sealed bottles) of samples, which were divided into 5 groups and stored at a storage temperature of (4-8) ° C., a relative humidity of (30-40)%, and protected from light. The storage time was selected to be 0 month, 0.3 month, 1 month, 3 months and 6 months, respectively. Each storage time was 50 bottles, and samples were taken for detection. The obtained fluoride ion and total nitrogen content data are shown in Table 3 below.

[0061] Table 3

[0062] time Fluoride ion content (mg / L) Total nitrogen content (mg / L) 0 months 9.98 20.13 0.3 months 10.00 19.78 1 month 10.20 19.66 3 months 9.68 20.62 6 months 9.30 19.52

[0063] 2) For 50 bottles of samples at each storage time, the average concentration is calculated. The deviation value is obtained by comparing with the initial average value. The sample group with a deviation value higher than the preset value is judged as failed, and the shortest time of failure is recorded as the first failure time.

[0064] 3) For each group of samples, calculate:

[0065]

[0066] In the formula, x i is the concentration value of the i-th sample in the group. The sample group whose S is greater than the preset value is judged as failed, and the shortest failure time is recorded as the second failure time.

[0067] 4) The smaller of the two expiration times is used as the upper limit of the storage time.

[0068] After calculation, it is concluded that the preferred upper limit of the storage time of the mixed standard solution of the present invention is one year.

[0069] Example 4 Rapid Detection of Fluoride Ions and Total Nitrogen

[0070] 1) The same raw materials were prepared using standard substances to prepare high-concentration storage solutions with fluoride ion and total nitrogen contents of 1000 mg / L.

[0071] The mixed standard solution prepared in Example 1 (under the storage conditions of Examples 2 and 3) and the above-mentioned high-concentration storage solution were used as standards to measure the value of the national secondary ammonia nitrogen component solution standard substance GBW(E)080333.

[0072] Methods: Ion chromatography;

[0073] Detection conditions: The eluent used was a mixed solution of Na2CO3-NaHCO3, flow rate: 1.0 mL / min; the detector was CD20, and the chromatographic column was AS19.

[0074]

[0075] The measurement results show that the measurement accuracy is higher when the mixed solution standard substance of the present invention is used.

[0076] The above descriptions are merely embodiments of the present application and are not intended to limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification, or directly or indirectly applied in other related technical fields, are also included in the protection scope of the present application.

Claims

1. A method for preparing a low-content fluoride ion and total nitrogen mixed standard solution, characterized in that: The method comprises the following steps: according to the target value, weighing a certain mass of sodium fluoride national secondary purity standard material and a certain mass of ammonium dihydrogen phosphate purity standard material, placing them in a volumetric flask, adding constant temperature pure water after dissolving, and fixing the volume to the graduation line to obtain a uniformly mixed low-content fluoride ion and total nitrogen mixed standard solution; The fluoride ion content in the low-content fluoride ion and total nitrogen mixed standard solution is 10 mg / L; The total nitrogen content in the low-content fluoride ion and total nitrogen mixed standard solution is 20 mg / L.

2. The method for preparing a low-content fluoride ion and total nitrogen mixed standard solution according to claim 1, characterized in that: The constant temperature pure water is 20°C.

3. The method for preparing a low-content fluoride ion and total nitrogen mixed standard solution according to claim 1, characterized in that: The method also includes: packaging a mixed standard solution of low-content fluoride ions and total nitrogen: using a sealed packaging bottle, adding a mixed standard solution of low-content fluoride ions and total nitrogen after nitrogen blowing, and quickly sealing.

4. The method for preparing a low-content fluoride ion and total nitrogen mixed standard solution according to claim 3, characterized in that: The low-content fluoride ion and total nitrogen mixed standard solution is sealed and packaged in polyethylene bottles, and the maximum storage time is one year.

5. The method for preparing a low-content fluoride ion and total nitrogen mixed standard solution according to claim 3 or 4, characterized in that: The storage conditions of the low-content fluoride ion and total nitrogen mixed standard solution are: storage temperature (4-8)°C, relative humidity (30-40)%, and light-proof.

6. The method for preparing a low-content fluoride ion and total nitrogen mixed standard solution according to claim 3, characterized in that: The sealed packaging bottle is a 10mL sealed packaging bottle.

7. The method for preparing a low-content fluoride ion and total nitrogen mixed standard solution according to claim 3, characterized in that: During the packaging process of the low-content fluoride ion and total nitrogen mixed standard solution, the nitrogen blowing treatment conditions are: nitrogen blowing temperature: (90-120)°C, nitrogen flow rate: (2-5) L / min, and purge time: (30-60) min.

8. A low-content fluoride ion and total nitrogen mixed standard solution prepared according to any one of claims 1 to 7.

9. A method for rapid detection of fluoride ion and total nitrogen content in waters, characterized in that: Using the low-content fluoride ion and total nitrogen mixed standard solution described in claim 8 as a standard, ion chromatography is used to detect the fluoride ion and total nitrogen content in the water area.

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