Method suitable for measuring total alkalinity in different base water bodies

Abstract

The invention discloses a method suitable for measuring total alkalinity in different substrate water bodies, relates to the field of water body total alkalinity measurement, and can be used for measuring wide-range alkalinity of different substrate water bodies. The method comprises the following steps: filtering a water sample to be detected, adding the filtered water sample into a cuvette, sequentially adding an indicator and hydrochloric acid, fully and uniformly mixing, and exhausting for a certain time; and reading the absorbance under the corresponding characteristic wavelength by using a spectrophotometer, and substituting the absorbance into an alkalinity algorithm to obtain the algorithm alkalinity. And substituting the algorithm alkalinity into the correction equation to obtain the actual total alkalinity of the water sample to be detected. The method has the advantages of simple operation, low requirements on instruments, easily available test materials and small volume of required samples, and can be used for determining the total alkalinity in different substrate water bodies.

Description

Technical Field

[0001] The invention relates to the field of total alkalinity determination of water bodies, and in particular to a method for determining total alkalinity in a wide range applicable to water bodies with different bases. Background Art

[0002] Total Alkalinity (TA) is one of the four basic parameters of carbonate systems and is defined as “the total amount of proton acceptors (with dissociation constants K≤10 -4.5 The base formed by the weak acid with zero ionic strength) exceeds the proton donor (K>10 -4.5 According to this definition, TA can be expressed as follows:

[0003] TA=[HCO 3 - ]+2[CO 3 2- ]+[B(OH) 4 - ]+[OH - ]+[HPO 4 2- ]+2[PO 4 3- ]+[SiO(OH) 3 - ]+[NH 3 ]+[HS - ]+…-[H + ] F -[HSO 4 - ]-[HF]-[H 3 PO 4 ]-…

[0004] TA is expressed in weight units, indicating that it is not affected by the temperature and pressure within the system.

[0005] TA is an important indicator of the buffering capacity of water bodies and a means of measuring the ability of water bodies to resist acidification. TA is also an important parameter in environmental and industrial processes (water quality control, wastewater treatment, aquatic ecosystem management and industrial process control), which affects the availability of nutrients and the toxicity of different chemicals to aquatic organisms in natural water systems. The alkalinity of natural water bodies varies widely, ranging from 1 to 10,000 μmol / kg.

[0006] At present, the multi-step titration method of TA includes multi-step titration-electrode potential method and multi-step titration-spectrophotometry. Among them, the multi-step titration-electrode potential method is the most commonly used method for TA determination, but this method has large sample consumption, long determination time, frequent calibration, and complicated operation steps. The present invention aims to establish a method for determining the total alkalinity of water bodies with small volume, wide range, and simple operation, which can be applied to the determination of total alkalinity in different base water bodies. Summary of the invention

[0007] The purpose of the present invention is to solve the above problems in the prior art and provide a method for determining the total alkalinity in different base water bodies, which has the advantages of small volume, wide range, simple operation, and no need for complex instruments and equipment.

[0008] In order to achieve the above object, the present invention adopts the following technical scheme:

[0009] A method for determining total alkalinity in water bodies with different bases, comprising the following steps:

[0010] 1) Filter the water sample to be tested through a membrane to obtain the filtered water sample, and measure its temperature and salinity with a thermometer and a salinometer;

[0011] 2) Take 2-5 mL of the filtered water sample obtained in step 1) and add it to a cuvette. Then add the indicator stock solution and hydrochloric acid to the water sample in sequence.

[0012] 3) After the solution is mixed evenly, the carbon dioxide gas is discharged;

[0013] 4) After the carbon dioxide is expelled, place the cuvette in a spectrophotometer and read its absorbance at the characteristic wavelength;

[0014] 5) Bring temperature, salinity, and absorbance into the algorithm to obtain algorithm alkalinity;

[0015] 6) Substitute the algorithm alkalinity into the correction formula to obtain the final total alkalinity of the sample;

[0016] The algorithm is as follows:

[0017]

[0018] Where TA is the total alkalinity of the sample; ρ s , a , i are the densities of water sample, hydrochloric acid and indicator stock solution respectively; V s 、V a 、V i are the volumes of water sample, hydrochloric acid and indicator stock solution respectively; C a , C i are the concentration of hydrochloric acid and the total concentration of indicator in the indicator stock solution; C i' is the total concentration of indicator in the solution after the reaction; A 1 , A 2 is the absorbance read by the spectrophotometer; t is the reaction temperature; S is the salinity of the sample; φ 1 (HI), φ 2 (HI) is the ratio of acidic indicator to total indicator in the indicator stock solution and the solution after reaction.

[0019] The indicator stock solution is one of bromocresol green or bromocresol purple.

[0020] The concentration of the indicator stock solution is 2-10 mmol / L.

[0021] The concentration of the hydrochloric acid is 0.02~1 mol / L.

[0022] The characteristic wavelength is related to the type of indicator selected; if the indicator is bromocresol green, the characteristic wavelength is 444 nm and 616 nm; if the indicator is bromocresol purple, the characteristic wavelength is 432 nm and 589 nm.

[0023] The correction formula in step 6) is obtained by measuring a known alkalinity standard using this method, processing the obtained data with the algorithm to obtain the algorithmic alkalinity, and plotting the algorithmic alkalinity against its theoretical standard value.

[0024] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0025] 1. The present invention uses a single-point titration method. Compared with the multi-point titration method, the single-point titration method is simpler to operate and only requires adding acid once.

[0026] 2. The present invention uses a common spectrophotometer in the laboratory to measure the absorbance and then uses a specific algorithm and correction formula to measure the total alkalinity in the water body without the need for complex instruments and equipment.

[0027] 3. Compared with the existing total alkalinity determination method, the present invention requires a smaller sample volume. Currently, most alkalinity determination methods require a sample volume of 50-100 mL, while the present invention only requires a few milliliters to complete a determination.

[0028] 4. The method of the present invention has good precision, simple operation process, and is easy to use. There is no obvious difference in the measurement results between different operators and different spectrophotometers, and it has universal applicability.

[0029] 5. The present invention can be used to determine the total alkalinity of different substrates such as fresh water and sea water, is not affected by the substrate, and can achieve on-site determination.

[0030] 6. The present invention can be used to measure alkalinity in a wide range, and can measure the alkalinity of freshwater samples in the range of 500-10000 μmol / kg, and can also measure the alkalinity in the normal seawater range (1800-2200 μmol / kg). BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is an operation flow chart of the present invention.

[0032] Figure 2 This is the seawater calibration curve of the present invention.

[0033] Figure 3 It is the fresh water calibration curve of the present invention. DETAILED DESCRIPTION

[0034] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer and more understandable, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0035] A method for determining total alkalinity in water bodies with different bases, the specific steps are as follows:

[0036] (1) Pass the water sample to be tested through a 0.45 μm filter membrane to obtain the filtered water sample, and measure its temperature and salinity using a thermometer and a salinometer;

[0037] (2) Take 2-5 mL of the filtered water sample obtained in step (1) and add it to a cuvette. Then, add the indicator stock solution and hydrochloric acid to the water sample in sequence.

[0038] (3) Mix the solution evenly and discharge the carbon dioxide gas in the solution within a certain period of time;

[0039] (4) After the carbon dioxide is expelled, place the cuvette in a spectrophotometer and read its absorbance at the characteristic wavelength;

[0040] (5) Bring temperature, salinity, absorbance, etc. into the algorithm to obtain the algorithm alkalinity;

[0041] (6) Substitute the algorithm alkalinity into the correction formula to obtain the final total alkalinity of the sample.

[0042] In the present invention, the indicator stock solution is one of bromocresol green or bromocresol purple, and the concentration is 2-10 mmol / L; the solvent of the indicator stock solution is a mixture of water and ethanol in a weight ratio of (2-10):1; the concentration of hydrochloric acid is 0.02-1 mol / L.

[0043] In the present invention, the volume ratio of the sample to the indicator stock solution is (10-120):1, and the volume ratio of the sample to hydrochloric acid is (4-80):1.

[0044] In the present invention, the exhaust time is 2 min to 24 h.

[0045] In the present invention, the characteristic wavelength is related to the type of indicator selected. If the indicator is bromocresol green, the characteristic wavelength is 444 nm and 616 nm; if the indicator is bromocresol purple, the characteristic wavelength is 432 nm and 589 nm.

[0046] In the present invention, the algorithm principles are as follows:

[0047]

[0048] Where TA is the total alkalinity of the sample; ρ s , a , i are the densities of water sample, hydrochloric acid and indicator stock solution respectively; V s 、V a 、V i are the volumes of water sample, hydrochloric acid and indicator stock solution respectively; C a , C i are the concentration of hydrochloric acid and the total concentration of indicator in the indicator stock solution; C i ' is the total concentration of indicator in the solution after the reaction; A 1 , A 2 is the absorbance read by the spectrophotometer (if the indicator is bromocresol green, A 1 , A 2 are the absorbances at wavelengths of 444 nm and 616 nm respectively; if the indicator is bromocresol purple, A 1 , A 2 are the absorbance at wavelengths of 432 nm and 589 nm respectively); t is the reaction temperature; S is the salinity of the sample; φ 1 (HI), φ 2 (HI) is the ratio of acidic indicator to total indicator in the indicator stock solution and the solution after reaction.

[0049] In the present invention, the correction formula in step (6) is obtained by measuring a known alkalinity standard using the method, processing the obtained data using an algorithm to obtain an algorithmic alkalinity, and plotting the algorithmic alkalinity against its theoretical standard value.

[0050] The present invention is used to establish a seawater calibration curve.

[0051] Aged seawater with known total alkalinity and salinity of 35 was selected as the total alkalinity standard solution. A saline solution with a salinity of 35 was prepared using pure water and sodium chloride, and the total alkalinity standard solution and the saline solution were mixed in different proportions to obtain a series of alkalinity solutions.

[0052] The present invention is used to measure a series of solutions, and the specific steps are as follows: Figure 1As shown, the solution was filtered through a 0.45 μm filter membrane, and its temperature and salinity were measured with a thermometer and a salinity meter; 2 mL of the filtrate was placed in a cuvette, and 50 μL of bromocresol green (concentration was 2 mmol / L) and 90-120 μL of hydrochloric acid (the added volume varied, depending on the alkalinity of the sample; the concentration of hydrochloric acid was 0.048 mol / L) were added in sequence; the upper end of the cuvette was covered with a sealing film, and after turning it upside down 5 times, the sealing film was discarded, and it was allowed to aerate naturally at room temperature for 5 min to discharge the carbon dioxide gas in the solution; the cuvette was placed in a spectrophotometer to read its absorbance at characteristic wavelengths of 444 nm and 616 nm.

[0053] Substitute the absorbance into the algorithm to obtain the algorithm alkalinity. The results are shown in Table 1. With the algorithm alkalinity as the x-axis and the theoretical alkalinity value of aged seawater as the y-axis, a calibration curve is drawn, as shown in Table 1. Figure 2 As shown, the correction formula under the seawater base is obtained.

[0054] Table 1 Seawater base correction curve

[0055]

[0056] The present invention is used to establish a fresh water calibration curve.

[0057] A total alkalinity solution standard material purchased from the National Institute of Metrology of China was selected, and its true alkalinity was known. Pure water and the total alkalinity solution standard material were mixed in different proportions to obtain a series of alkalinity solutions.

[0058] The present invention is used to measure a series of solutions, and the specific steps are as follows: Figure 1 As shown, the solution was filtered through a 0.45 μm filter membrane, and its temperature and salinity were measured with a thermometer and a salinity meter; 2 mL of the filtrate was placed in a cuvette, and 50 μL of bromocresol green (concentration was 2 mmol / L) and 25-500 μL of hydrochloric acid (the added volume varied, depending on the alkalinity of the sample; the concentration of hydrochloric acid was 0.048 mol / L) were added in sequence; the upper end of the cuvette was covered with a sealing film, and after turning it upside down 5 times, the sealing film was discarded, and it was allowed to aerate naturally at room temperature for 5 min to discharge the carbon dioxide gas in the solution; the cuvette was placed in a spectrophotometer to read its absorbance at characteristic wavelengths of 444 nm and 616 nm.

[0059] Substitute the absorbance into the algorithm to obtain the algorithm alkalinity. The results are shown in Table 2. With the algorithm alkalinity as the x-axis and the theoretical alkalinity of the standard substance as the y-axis, a calibration curve is drawn, as shown in Table 2. Figure 3 As shown, the correction formula under fresh water base is obtained.

[0060] Table 2 Freshwater base calibration curve

[0061]

[0062] The above is a typical embodiment of the present invention, but the present invention should not be limited to the contents disclosed in the embodiment. Therefore, any equivalent or modification completed without departing from the spirit disclosed in the present invention shall fall within the scope of protection of the present invention.

Claims

1. A method for determining total alkalinity in water bodies with different bases, characterized in that: The following steps are involved: 1) Filter the water sample to be tested through a membrane to obtain the filtered water sample, and measure its temperature and salinity with a thermometer and a salinometer; 2) Take 2-5 mL of the filtered water sample obtained in step 1) and add it to a cuvette. Then add the indicator stock solution and hydrochloric acid to the water sample in sequence. 3) After the solution is mixed evenly, the carbon dioxide gas is discharged; 4) After the carbon dioxide is expelled, place the cuvette in a spectrophotometer and read its absorbance at the characteristic wavelength; 5) Bring temperature, salinity, and absorbance into the algorithm to obtain algorithm alkalinity; 6) Substitute the algorithm alkalinity into the correction formula to obtain the final total alkalinity of the sample; The algorithm is as follows: r a V a C a +r i V i C i φ1(HI)=TAρ s V s +(r s V s +r i V i +r a V a )(10^(-(4.2699+0.002578(35-S)+lg(((A2 / A1)(1+0.00909(25-t))-0.00131) / (2.3148-0.1299((A2 / A1)(1+0.00909(25-t)))))-lg(1-0.001005S))))+(p s V s +r i V i +r a V a )C i 'φ2(HI); Where TA is the total alkalinity of the sample; ρ s , a , i are the densities of water sample, hydrochloric acid and indicator stock solution respectively; V s 、V a 、V i are the volumes of water sample, hydrochloric acid and indicator stock solution respectively; C a , C i are the concentration of hydrochloric acid and the total concentration of indicator in the indicator stock solution; C i ' is the total concentration of the indicator in the solution after the reaction; A1 and A2 are the absorbances read by the spectrophotometer; t is the reaction temperature; S is the salinity of the sample; φ1(HI) and φ2(HI) are the proportions of the acidic indicator in the total indicator in the indicator stock solution and the solution after the reaction, respectively.

2. A method for determining total alkalinity in water bodies of different bases as claimed in claim 1, characterized in that: The indicator stock solution is one of bromocresol green or bromocresol purple.

3. A method for determining total alkalinity in water bodies of different bases as claimed in claim 1, characterized in that: The concentration of the indicator stock solution is 2-10 mmol / L.

4. A method for determining total alkalinity in water bodies of different bases as claimed in claim 1, characterized in that: The concentration of the hydrochloric acid is 0.02~1 mol / L.

5. A method for determining total alkalinity in water bodies of different bases as claimed in claim 1, characterized in that: The characteristic wavelength is related to the type of indicator selected; if the indicator is bromocresol green, the characteristic wavelength is 444 nm and 616 nm; if the indicator is bromocresol purple, the characteristic wavelength is 432 nm and 589 nm.

6. A method for determining total alkalinity in water bodies of different bases as claimed in claim 1, characterized in that: The correction formula in step 6) is obtained by measuring a known alkalinity standard using this method, processing the obtained data with the algorithm to obtain the algorithmic alkalinity, and plotting the algorithmic alkalinity against its theoretical standard value.

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