Method for determining content of sulfate radicals in water sample

Abstract

The invention discloses a method for determining the content of sulfate radicals in a water sample. According to the method, a calcium ion selective electrode is selected as an indicator electrode through a full-automatic potentiometric titration method, the amount of EDTA consumed by Ca < 2 + > and Mg < 2 + > in a to-be-detected water sample and the amount of EDTA consumed by Ba < 2 + > in a blank solution are respectively measured by using an EDTA standard solution, and then the previously titrated blank solution containing Ba < 2 + > which is excessive relative to the content of SO4 < 2-> in the to-be-detected water sample is added into the to-be-detected water sample; and measuring the content of excessive Ba < 2 + > by using an EDTA standard solution, and calculating to obtain the content of SO4 < 2-> in the water sample to be measured. The method is suitable for measuring the content of sulfate radicals in a water sample with high content of calcium, magnesium ions and sulfate radicals, and has the advantages of simple detection method, low cost and high practical value.

Description

Technical Field

[0001] The invention belongs to the field of analytical technology, and in particular relates to a method for measuring the sulfate content in a water sample, in particular in production wastewater with high calcium and magnesium contents. Background Art

[0002] The current literature on sulfate (SO4 2 -) content is determined by gravimetric method, volumetric method, spectrophotometry, potentiometric titration, ion chromatography, etc. However, there are a large number of organic matter and heavy metal ions in water samples. During the detection of water environment, it is impossible to accurately determine the sulfate content in such water samples due to the limitation of organic matter or heavy metal ions, or based on the limitations of the method itself.

[0003] The existing national standard GB / T 6911-2017 describes a potentiometric titration method for determining sulfate content. This method uses a barium ion selective electrode, which relies on specific ion carriers (such as crown ether compounds) to achieve Ba 2+ However, the synthesis process of such materials is complex and their stability is poor, which makes the production of electrodes difficult and costly, and therefore their practical value is not high in actual production. At the same time, barium chloride standard solution is required for titration, and the calibration process of barium chloride standard solution is more complicated than that of disodium ethylenediaminetetraacetic acid (EDTA) standard solution, and the price is much more expensive than EDTA. Furthermore, the calcium and magnesium content in production wastewater is generally high and the sulfate content is variable. When using a barium ion selective electrode to analyze samples with high calcium and magnesium content, since calcium and magnesium ions have similar charges and ionic radii to barium ions, they will form competitive adsorption on the electrode membrane surface, interfering with the potential detection of barium ions, which has a greater impact on data measurement and cannot accurately determine the sulfate content in the sample. Summary of the Invention

[0004] In view of the above problems, the present invention aims to provide a method for determining the sulfate content in water samples, especially in industrial wastewater with high calcium and magnesium content. The method uses a fully automatic potentiometric titration method, selects a calcium ion selective electrode as an indicator electrode, and uses an EDTA standard solution for determination. Specifically, the Ca in the water sample to be tested is determined using an EDTA standard solution. 2+ Mg 2+ The amount of EDTA consumed and the Ba content in the blank solution (barium chloride solution) 2+ The amount of EDTA consumed is then titrated to the amount of SO4 in the water sample to be tested. 2- Excessive content 2+ The blank solution is added to the water sample to be tested, and after the sulfate radical and barium chloride react completely, the excess Ba is determined with EDTA standard solution. 2+ The content of SO4 in the water sample to be tested is calculated using formula (I)2- content.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A method for determining sulfate content in a water sample, characterized in that the method adopts a potentiometric titration method with a calcium ion selective electrode as an indicator electrode, and comprises the following steps:

[0007] (1) Determination of blank reagent: take pure water of the same volume as the water sample to be tested, add BaCl2 solution, add buffer solution, and add water until the electrode is covered, as a blank reagent; titrate with EDTA standard solution, and record the amount of EDTA standard solution V2 at the potential jump point; wherein, Ba in the BaCl2 solution is 2+ The content is in excess relative to the ions that react with it in the water sample to be tested in step (2);

[0008] (2) Ca in the water sample to be tested 2+ Mg 2+ Determination: Accurately measure the water sample to be tested, add buffer solution, add water until the electrode is covered, titrate the water sample to be tested with EDTA standard solution, and record the amount of EDTA standard solution V3 at the second potential jump point;

[0009] (3) SO4 in the water sample to be tested 2- Determination: Accurately measure the water sample to be tested in an amount equal to that in step (2), add the BaCl2 solution in an amount equal to that in step (1), add buffer, add water until the electrode is covered, titrate the water sample to be tested with EDTA standard solution, and record the amount of EDTA standard solution V1 at the last potential jump point;

[0010] (4) SO4 in the water sample to be tested 2- The content C is calculated according to the following formula (I):

[0011] C=c(V2+V3-V1)M(I)

[0012] In formula (I):

[0013] C: SO4 in the water sample to be tested 2- Content, unit: mg;

[0014] c: EDTA concentration in EDTA standard titration solution, unit: mol / L;

[0015] The unit of V1, V2, and V3 is mL;

[0016] M:SO4 2- The molar mass of 2,96.06 g / mol.

[0017] The potentiometric titration method described in the present invention uses a potentiometric titrator to collect potential information during the titration process. In addition to using a calcium ion selective electrode as an indicator electrode, the reference electrode can be selected from a double salt bridge reference electrode, a ceramic reference electrode, etc., preferably a double salt bridge reference electrode.

[0018] In a specific embodiment, the concentration of the EDTA standard solution used in steps (1) to (3) is 0.02 to 0.10 mol / L, preferably 0.05 mol / L.

[0019] In step (1), the Ba in the blank reagent is titrated with EDTA standard solution. 2+ The potential jump point is EDTA and Ba 2+ The titration reaction end point is reached, at which point the molar amount of EDTA consumed is equal to the Ba in the blank reagent. 2+ The molar amount of .

[0020] In a specific embodiment, in step (1), the BaCl2 concentration in the BaCl2 solution is 10.5 to 35.0 g / L, preferably 12.5 g / L. 2+ The molar content is the SO4 2- 3 to 10 times, preferably 6 times the molar content.

[0021] In step (2), the water sample to be tested may contain other substances that may affect the subsequent EDTA and Ba 2+ Interfering ions in the titration reaction, resulting in inaccurate titration results, such as Ca 2+ Mg 2+ Therefore, it is necessary to first calculate the amount of EDTA consumed by these interfering ions in order to deduct their influence.

[0022] When the water sample to be tested contains Ca 2+ Mg 2+ , the water sample to be tested is titrated with EDTA standard solution, and there are two potential jump points. The second potential jump point is the potential jump point between EDTA and Ca 2+ Mg 2+ The titration reaction end point of the two is when the molar amount of EDTA consumed is equal to the Ca content in the water sample to be tested. 2+ Mg 2+ The molar amount of .

[0023] In some embodiments, in steps (2) and (3), the Ca in the titration system is 2+ Mg 2The content range is 0-1200 mg / L, for example, 50-1200 mg / L, 0-600 mg / L, 50-600 mg / L, 100-600 mg / L, 0-300 mg / L, 100-300 mg / L or 200 mg / L.

[0024] In some embodiments, in steps (2) and (3), the SO4 2- The content range is 0-3000 mg / L, preferably 800-2700 mg / L.

[0025] In step (3), the BaCl2 introduced into the BaCl2 solution is first reacted with SO4 2- Reaction, excess Ba 2+ Then react with EDTA, and the interfering ions (such as Ca 2+ Mg 2+ ) also reacts with EDTA, so there are multiple potential jump points in the titration process, and the last potential jump point is the titration endpoint of the above reactions.

[0026] In a specific embodiment, the buffer solution is an ammonia-ammonium chloride buffer solution. EDTA exists in different forms under different pH conditions, and the stability of the complexes it forms with metal ions will also vary. In order to ensure that EDTA can effectively complex with barium, calcium, and magnesium ions, and to maintain the conditional stability constant of the complex reaction within an appropriate range, it is necessary to add a buffer solution to maintain a relatively stable pH value of the solution. The ammonia-ammonium chloride buffer solution is added to adjust the pH to 10.

[0027] In a specific embodiment, in order to facilitate operation and ensure the accuracy of the test results, the volume of the water sample to be tested can be controlled at 10-25 mL, and adjusted as appropriate according to the content of sulfate in the water sample.

[0028] Beneficial effects of the technical solution of the present invention:

[0029] (1) The present invention selects a calcium ion selective electrode as the indicator electrode for the potentiometric titration method for determining sulfate in water samples. Compared with the method using a barium ion selective electrode as the indicator electrode, the method of the present invention utilizes the selective response of the calcium ion selective electrode to calcium and magnesium ions and amplifies the signal, thereby accurately determining the concentrations of calcium and magnesium ions. The method is suitable for determining the sulfate content in water samples with high calcium and magnesium ion contents and high sulfate content. Even if the calcium and magnesium contents in the test sample are as high as about 1200 mg / L and the sulfate content is as high as 3000 mg / L, satisfactory measurement results can be obtained.

[0030] (2) The method of the present invention uses a calcium ion selective electrode with low preparation cost and high marketability, and the detection method is simple, low cost and high practical value. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is the titration curve in Example 1, wherein (a) is the titration curve in step (2), and (b) is the titration curve in step

[0032] (3) is the titration curve, and (c) is the titration curve in step (4). DETAILED DESCRIPTION

[0033] In order to better understand the technical solution provided by the present invention, the present invention is described in detail below through specific implementation methods, but the claims of the present invention are not limited to these embodiments. The embodiments only provide some experimental conditions for achieving the purpose of this technical invention.

[0034] Unless otherwise specified, the raw materials, reagents, methods, etc. used in the examples are conventional raw materials, reagents, and methods in the art.

[0035] instrument:

[0036] Fully automatic potentiometric titrator: KEM Kyoto Electronics automatic potentiometric titrator, AT-710; indicator electrodes: calcium ion electrode (I-171); barium ion electrode (51107674); reference electrode: double salt bridge reference electrode (R-173).

[0037] Reagents and sources:

[0038] Anhydrous sodium sulfate: CAS: 7757-82-6, PT (reference reagent), Tianjin Guangfu Technology Development Co., Ltd.;

[0039] Anhydrous calcium chloride: CAS: 10043-52-4, PT (reference reagent), Tianjin Guangfu Technology Development Co., Ltd.

[0040] Magnesium oxide: CAS: 1309-48-4, PT (reference reagent), Tianjin Guangfu Technology Development Co., Ltd.

[0041] Ammonium chloride: CAS: 12125-02-9, AR (analytical grade), Sinopharm Chemical Reagent Co., Ltd.

[0042] Concentrated ammonia: CAS: 1336-21-6, AR (analytical grade), Sinopharm Chemical Reagent Co., Ltd.

[0043] Barium chloride: CAS: 10361-37-2, AR (analytical grade), Sinopharm Chemical Reagent Co., Ltd.

[0044] Disodium ethylenediaminetetraacetic acid: CAS: 6381-92-6, AR (analytical grade), Sinopharm Chemical Reagent Co., Ltd.

[0045] Lithium acetate dihydrate: CAS: 6108-17-4, AR (analytical grade), Sinopharm Chemical Reagent Co., Ltd.

[0046] Glacial acetic acid: CAS: 64-19-7, AR (analytical grade), Sinopharm Chemical Reagent Co., Ltd.

[0047] Isopropyl alcohol: CAS: 67-63-0, AR (analytical grade), Sinopharm Chemical Reagent Co., Ltd.

[0048] Example 1

[0049] Solutions of different concentrations were prepared using anhydrous sodium sulfate (142.04 g / mol), anhydrous calcium chloride (110.98 g / mol), and magnesium oxide (40.30 g / mol) reagents and measured using a calcium ion selective electrode and a barium ion selective electrode, respectively.

[0050] Note: SO4 2- (96.06 g / mol), Ca 2+ (40.08g / mol), mg 2+ (24.30 g / mol).

[0051] Reagent pretreatment: Dry anhydrous sodium sulfate and anhydrous calcium chloride in an oven at 105℃~110℃ to constant weight, and place them in a desiccator for later use; burn magnesium oxide in a muffle furnace at 800℃±50℃ to constant weight, and place them in a desiccator for later use.

[0052] Water sample 1: Weigh 2.2180g of anhydrous sodium sulfate and 0.2775g of anhydrous calcium chloride and dissolve them in water. Weigh 0.1659g of magnesium oxide and dissolve them in 2.5mL of hydrochloric acid and a small amount of water. Transfer them to a 500mL volumetric flask and dilute to the mark for later use (SO4 2- The concentration is 3000.02 mg / L, Ca 2+ The concentration is 200.44 mg / L, Mg 2+ The concentration is 200.07 mg / L).

[0053] Water sample 2: Weigh 1.3308g of anhydrous sodium sulfate and 0.2777g of anhydrous calcium chloride and dissolve them in water. Weigh 0.1658g of magnesium oxide and dissolve them in 2.5mL of hydrochloric acid and a small amount of water. Transfer them to a 500mL volumetric flask and dilute to the mark for later use (SO4 in the solution 2- The concentration is 1800.01 mg / L, Ca 2+ The concentration is 200.58 mg / L, Mg2+ The concentration is 199.95 mg / L).

[0054] Water sample 3: Weigh 0.5915g of anhydrous sodium sulfate and 0.2776g of anhydrous calcium chloride and dissolve them in water. Weigh 0.1660g of magnesium oxide and dissolve them in 2.5mL of hydrochloric acid and a small amount of water. Transfer them to a 500mL volumetric flask and dilute to the mark for later use (SO4 in the solution 2- The concentration is 800.05 mg / L, Ca 2+ The concentration is 200.51 mg / L, Mg 2+ The concentration is 200.19 mg / L).

[0055] A fully automatic potentiometric titrator was used to measure the above-mentioned test solution using a calcium ion selective electrode and a barium ion selective electrode respectively.

[0056] I. Measurement using calcium ion selective electrodes:

[0057] (1) Experimental process:

[0058] (1) Prepare reagents:

[0059] Ammonia-ammonium chloride buffer solution: Weigh 54 g of ammonium chloride and dissolve it in 500 mL of water. Add 350 mL of concentrated aqueous ammonia and dilute to 1 L with water.

[0060] EDTA standard titration solution: c(EDTA) = 0.05 mol / L;

[0061] Barium chloride solution (12.5 g / L): Weigh 14.7 g of BaCl2·2H2O solid and dissolve it in 1 L of water.

[0062] (2) Blank reagent determination:

[0063] Use a pipette to transfer 25.00 mL of pure water into a 100 mL measuring cup. Use a pipette to accurately add 10.00 mL of barium chloride solution, add 10 mL of ammonia-ammonium chloride buffer solution, and add water until the electrode is covered (total volume is approximately 80 mL). Place the measuring cup containing the sample on the titration table and use a fully automatic potentiometric titrator to titrate with 0.05 mol / L EDTA standard titrant. Stop the titration when a complete jump curve appears. Record the titration volume of the EDTA standard titrant at the potential jump point as V2.

[0064] (3) Determination of calcium and magnesium in samples:

[0065] Use a pipette to transfer 25.00 mL of water sample into a 100 mL measuring cup, add 10 mL of ammonia-ammonium chloride buffer solution, and add water until the electrode is covered (total volume is approximately 80 mL). Place the measuring cup containing the sample on the titration table and use a fully automatic potentiometric titrator to titrate with 0.05 mol / L EDTA standard titrant. Stop the titration when a complete jump curve of calcium and magnesium appears. Record the volume of EDTA standard titrant titrated at the second potential jump point as V3.

[0066] (4) Determination of sulfate, calcium and magnesium content in samples:

[0067] Use a pipette to transfer 25.00 mL of water sample into a 100 mL measuring cup. Use a pipette to accurately add 10.00 mL of barium chloride solution, add 10 mL of ammonia-ammonium chloride buffer solution, and add water until the electrode is covered (total volume is approximately 80 mL). Place the measuring cup containing the sample on the titration table and use a fully automatic potentiometric titrator to titrate with 0.05 mol / L EDTA standard titration solution. Stop the titration when a complete jump curve appears. Record the titration volume of the EDTA standard solution at the last potential jump point as V1.

[0068] (5) The sulfate content C in the sample is calculated according to the following formula:

[0069] C=c(V2+V3-V1)M(I)

[0070] In formula (I):

[0071] C: S04 in the water sample to be tested 2- Content, unit: mg;

[0072] c: EDTA concentration in EDTA standard titration solution, unit: mol / L;

[0073] The unit of V1, V2, and V3 is mL;

[0074] M:SO4 2- Molar mass, 96.06 g / mol;

[0075] Furthermore, the sulfate concentration ρ of the sample is calculated according to the following formula (II):

[0076]

[0077] Where:

[0078] ρ-SO4 in water samples 2- Concentration, unit: mg / L;

[0079] V-volume of the water sample taken, unit: mL.

[0080] (2) Experimental results

[0081] The above method was used for analysis 5 times to calculate the concentration of sulfate ions in the water sample, and the relative error and relative standard deviation were calculated. Table 1 shows the experimental results of relative error and relative standard deviation. It can be seen from Table 1 that the relative error and relative standard deviation of the water sample to be tested are good. The accuracy of this experiment is good and it is worth recommending.

[0082] Table 1: Relative error and relative standard deviation of water samples to be tested

[0083]

[0084] II. Determination using a barium ion selective electrode:

[0085] (1) Experimental process:

[0086] (1) Prepare reagents:

[0087] 1. Isopropyl alcohol

[0088] 2. Lithium Acetate Buffer Solution: Weigh 10.2 g of lithium acetate dihydrate and dissolve it in 500 mL of water. Add 5.7 mL of glacial acetic acid while stirring. Stir thoroughly and transfer the solution to a 1 L volumetric flask. Rinse the beaker several times with water, transfer the wash solution to the volumetric flask, and dilute to the mark with water.

[0089] 3. Barium chloride standard titration solution: c(BaCl2) = 0.05 mol / L;

[0090] (2) Water sample determination:

[0091] 1. Use a pipette to measure 20.00 mL of water sample into a 100 mL titration cup. Add 8 mL of isopropyl alcohol and 2 mL of lithium acetate buffer solution. Titrate with barium chloride standard solution until a complete potential jump curve appears. Stop the titration and record the titration volume of barium chloride standard solution at the potential jump point as V1.

[0092] (3) Data processing:

[0093] The sulfate content in the sample is expressed as SO4 2- Calculate according to the following formula:

[0094]

[0095] Where:

[0096] ρ: SO4 in water sample 2- Concentration, unit: mg / L;

[0097] c: concentration of barium chloride standard titration solution, unit: mol / L;

[0098] V1 unit: mL;

[0099] M:SO4 2- The molar mass is 96.06 g / mol;

[0100] V: Volume of the water sample taken, unit: mL.

[0101] (2) Experimental results

[0102] The above method was used for analysis 5 times to calculate the concentration of sulfate ions in the water sample and calculate the relative error and relative standard deviation. Table 2 shows the experimental results of relative error and relative standard deviation. It can be seen from Table 2 that the relative error deviation is large, which shows that high calcium and magnesium contents have a greater impact on it, and it is not recommended.

[0103] Table 2: Relative error and relative standard deviation of water samples to be tested

[0104]

[0105]

[0106] Example 2

[0107] There are three industrial wastewater samples with unknown sulfate content, and the sulfate content needs to be measured. The method for determining the sulfate content in industrial wastewater in this embodiment is to use a fully automatic potentiometric titrator, and the specific steps are as follows:

[0108] (1) Experimental process:

[0109] (1) Prepare reagents:

[0110] Ammonia-ammonium chloride buffer solution: Weigh 54 g of ammonium chloride and dissolve it in 500 mL of water. Add 350 mL of concentrated aqueous ammonia and dilute to 1 L with water.

[0111] EDTA standard titration solution: c(EDTA) = 0.05 mol / L;

[0112] Barium chloride solution (12.5 g / L): Weigh 14.7 g of BaCl2·2H2O solid and dissolve it in 1 L of water.

[0113] (2) Blank reagent determination:

[0114] Use a pipette to transfer 25.00 mL of pure water into a 100 mL measuring cup, and accurately add 10.00 mL of barium chloride solution with a pipette, add 10 mL of ammonia-ammonium chloride buffer solution, and add water until the electrode is covered (total volume is about 80 mL); place the measuring cup containing the sample on the titration table, and use a fully automatic potentiometric titrator to titrate with 0.05 mol / L EDTA standard titration solution. When the titration reaches a complete jump curve (the titration curve of water sample 1 is shown in Figure 1), the sample is titrated to a peak value of 0.05 mol / L. Figure 1 Stop the titration after (a) and record the titration volume of EDTA standard titration solution at the potential jump point as V2.

[0115] (3) Determination of calcium and magnesium in samples:

[0116] Use a pipette to transfer 25.00 mL of water sample into a 100 mL measuring cup, add 10 mL of ammonia-ammonium chloride buffer solution, and add water until the electrode is covered (total volume is about 80 mL); place the measuring cup containing the sample on the titration table and use a fully automatic potentiometric titrator to titrate with 0.05 mol / L EDTA standard titration solution. Stop the titration when the complete jump curve of calcium and magnesium appears (the titration curve of water sample 1 is shown in Figure 1). Figure 1 In (b), the volume of EDTA standard titrant solution titrated when the second potential jump point is recorded is V3.

[0117] (4) Determination of sulfate, calcium and magnesium content in samples:

[0118] Use a pipette to transfer 25.00 mL of water sample into a 100 mL measuring cup. Use a pipette to accurately add 10.00 mL of barium chloride solution, add 10 mL of ammonia-ammonium chloride buffer solution, and add water until the electrode is covered (total volume is about 80 mL). Place the measuring cup containing the sample on the titration table and use a fully automatic potentiometric titrator to titrate with 0.05 mol / L EDTA standard titrant. Stop the titration when a complete jump curve appears (see the titration curve of water sample 1). Figure 1 In (c), the titration volume of the EDTA standard solution at the last potential jump point is recorded as V1.

[0119] (5) The sulfate content C in the sample is calculated according to the following formula:

[0120] C=c(V2+V3-V1)M(I)

[0121] In formula (I):

[0122] C: SO4 in the water sample to be tested 2- Content, unit: mg;

[0123] c: EDTA concentration in EDTA standard titration solution, unit: mol / L;

[0124] The unit of V1, V2, and V3 is mL;

[0125] M:SO4 2- Molar mass, 96.06 g / mol;

[0126] Furthermore, the sulfate concentration ρ of the sample is calculated according to the following formula (II):

[0127]

[0128] Where:

[0129] ρ-SO4 in water samples 2- Concentration, unit: mg / L;

[0130] V-volume of the water sample taken, unit: mL.

[0131] (2) Experimental results

[0132] The water sample in (1) was taken as the investigation object and analyzed 5 times using the above method to calculate the concentration of sulfate ions in the water sample. Table 3 is the precision experiment results, and RSD (%) is the relative standard deviation. It can be seen from Table 3 that RSD (%) is less than 0.3%, and the precision of this experiment is good.

[0133] Table 3: Precision test results

[0134]

[0135]

[0136] Example 3

[0137] Weigh 0.0740 g, 0.1479 g, and 0.0740 g of anhydrous sodium sulfate, respectively, and dissolve them in water sample 1, water sample 2, and water sample 3 of Example 2, transfer them to a 500 mL volumetric flask, and dilute them to the scale with the corresponding water sample of Example 2 for later use. Use a fully automatic potentiometric titrator with a calcium ion selective electrode as the indicator electrode to measure the sulfate content, and calculate the sample recovery rate. The specific steps are as follows:

[0138] (1) Experimental process:

[0139] (1) Prepare reagents:

[0140] Ammonia-ammonium chloride buffer solution: Weigh 54 g of ammonium chloride and dissolve it in 500 mL of water. Add 350 mL of concentrated aqueous ammonia and dilute to 1 L with water.

[0141] EDTA standard titration solution: c(EDTA) = 0.05 mol / L;

[0142] Barium chloride solution (12.5 g / L): Weigh 14.7 g of BaCl2·2H2O solid and dissolve it in 1 L of water.

[0143] (2) Blank reagent determination:

[0144] Use a pipette to transfer 25.00 mL of pure water into a 100 mL measuring cup. Use a pipette to accurately add 10.00 mL of barium chloride solution, add 10 mL of ammonia-ammonium chloride buffer solution, and add water until the electrode is covered (total volume is approximately 80 mL). Place the measuring cup containing the sample on the titration table and use a fully automatic potentiometric titrator to titrate with 0.05 mol / L EDTA standard titrant. Stop the titration when a complete jump curve appears. Record the titration volume of the EDTA standard titrant at the potential jump as V2.

[0145] (3) Determination of calcium and magnesium in samples:

[0146] Use a pipette to transfer 25.00 mL of water sample into a 100 mL measuring cup, add 10 mL of ammonia-ammonium chloride buffer solution, and add water until the electrode is covered (total volume is approximately 80 mL). Place the measuring cup containing the sample on the titration table and use a fully automatic potentiometric titrator to titrate with 0.05 mol / L EDTA standard titrant. Stop the titration when a complete jump curve of calcium and magnesium appears. Record the titration volume of the EDTA standard titrant at the second potential jump as V3.

[0147] (4) Determination of sulfate, calcium and magnesium content in samples:

[0148] Use a pipette to transfer 25.00 mL of water sample into a 100 mL measuring cup. Use a pipette to accurately add 10.00 mL of barium chloride solution, add 10 mL of ammonia-ammonium chloride buffer solution, and add water until the electrode is covered (total volume is approximately 80 mL). Place the measuring cup containing the sample on the titration table and use a fully automatic potentiometric titrator to titrate with 0.05 mol / L EDTA standard titration solution. Stop the titration when a complete jump curve appears. Record the titration volume of the EDTA standard solution at the last potential jump point as V1.

[0149] (5) The sulfate content in the sample is expressed as SO4 2- Calculate according to the following formula:

[0150]

[0151] Where:

[0152] ρ: SO4 in water sample 2- Concentration, unit: mg / L;

[0153] c: EDTA concentration in EDTA standard titration solution, unit: mol / L;

[0154] The unit of V1, V2, and V3 is mL;

[0155] M:SO4 2-The molar mass is 96.06 g / mol;

[0156] V: Volume of the water sample taken, unit: mL.

[0157] (2) Experimental results

[0158] The above method was used to analyze the water sample 5 times, and the concentration of sulfate ions in the water sample was calculated, and the sample recovery rate was calculated. Table 4 shows the accuracy test results. It can be seen from Table 4 that the sample recovery rate is between 98% and 102%, and the accuracy of this experiment is good.

[0159] Table 4 Sample recovery experimental results

[0160]

[0161]

[0162] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for determining sulfate content in a water sample, characterized in that: The method adopts a potentiometric titration method with a calcium ion selective electrode as an indicator electrode, and comprises the following steps: (1) Determination of blank reagent: take pure water of the same volume as the water sample to be tested, add BaCl2 solution, add buffer solution, and add water until the electrode is covered, as a blank reagent; titrate with EDTA standard solution, and record the amount of EDTA standard solution V2 at the potential jump point; wherein, Ba in the BaCl2 solution is 2+ The content is in excess relative to the ions that react with it in the water sample to be tested in step (2); (2) Ca in the water sample to be tested 2+ Mg 2+ Determination: Accurately measure the water sample to be tested, add buffer solution, add water until the electrode is covered, titrate the water sample to be tested with EDTA standard solution, and record the amount of EDTA standard solution V3 at the second potential jump point; (3) SO4 in the water sample to be tested 2- Determination: Accurately measure the water sample to be tested in an amount equal to that in step (2), add the BaCl2 solution in an amount equal to that in step (1), add buffer, add water until the electrode is covered, titrate the water sample to be tested with EDTA standard solution, and record the amount of EDTA standard solution V1 at the last potential jump point; (4) SO4 in the water sample to be tested 2- The content C is calculated according to the following formula (I): C=c(V2+V3-V1)M (I) In formula (I): C: SO4 in the water sample to be tested 2- Content, unit: mg; c: EDTA concentration in EDTA standard titration solution, unit: mol / L; The unit of V1, V2, and V3 is mL; M:SO4 2- The molar mass of 2,96.06 g / mol.

2. The method according to claim 1, characterized in that In the potentiometric titration method, the reference electrode is selected from a double salt bridge reference electrode and a ceramic reference electrode, preferably a double salt bridge reference electrode.

3. The method according to claim 1, characterized in that In steps (1)-(3), the concentration of the EDTA standard solution is 0.02-0.10 mol / L, preferably 0.05 mol / L.

4. The method according to claim 1, wherein In step (1), the BaCl2 concentration in the BaCl2 solution is 10.5 to 35.0 g / L, preferably 12.5 g / L.

5. The method according to claim 1, wherein In step (1), the BaCl2 solution contains Ba 2+ The molar content is the SO4 2- 3 to 10 times, preferably 6 times the molar content.

6. The method according to claim 1, characterized in that In steps (2) and (3), the Ca in the titration system 2+ Mg 2 The content range is 0-1200 mg / L, preferably 50-600 mg / L.

7. The method according to claim 1, characterized in that In steps (2) and (3), the SO4 in the titration system 2 -The content range is 0~3000mg / L.

8. The method according to claim 7, characterized in that In steps (2) and (3), the SO4 in the titration system 2 -The content range is 0~2700mg / L.

9. The method according to claim 1, characterized in that In steps (1)-(3), the buffer solution is an ammonia-ammonium chloride buffer solution, and the ammonia-ammonium chloride buffer solution is added to make the pH of the titration system = 10.

10. The method according to claim 1, characterized in that The volume of the water sample to be tested is 10 to 25 mL.

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