A method for determining total alkalinity in different base water bodies

Abstract

The application relates to a method for measuring total alkalinity of different base water bodies, and belongs to the field of total alkalinity measurement of water bodies, which can measure wide-range alkalinity of different base water bodies. The steps of the application are as follows: filtering a water sample to be measured, adding the water sample into a colorimetric cup, adding an indicator and hydrochloric acid in sequence, discharging air for a certain time after fully mixing the water sample, reading the absorbance of the water sample at a corresponding characteristic wavelength by using a spectrophotometer, substituting the absorbance into an alkalinity algorithm to obtain algorithmic alkalinity, and bringing the algorithmic alkalinity into a correction equation to obtain the total alkalinity of the water sample to be measured. The application has the advantages of simple operation, low requirement on instruments, easy availability of test materials, small required sample volume, and the like, and can be used for measuring total alkalinity of different base water bodies.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of water total alkalinity determination, in particular to a method for determining wide range total alkalinity of water bodies suitable for different substrates. BACKGROUND

[0002] Total alkalinity (TA) is one of the four basic parameters of carbonate system, which is defined as the number of moles of hydrogen ions equivalent to the excess of proton acceptors (bases formed from weak acids with dissociation constant K≤10 -4.5 over proton donors (acids with K>10 -4.5 ) in 1 kg of sample and zero ionic strength”. According to this definition, TA can be expressed as follows:

[0003] TA = [HCO3 - ] + 2[CO3 2- ] + [B(OH)4 - ] + [OH - ] + [HPO4 2- ] + 2[PO4 3- ] + [SiO(OH)3 - ] + [NH3] + [HS - ] + … - [H + ] F - [HSO4 - ] - [HF] - [H3PO4] - …

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

[0005] TA is an important indicator of water body buffering capacity, and is a means of measuring water body acid resistance. TA is also an important parameter in the environment and industrial processes (water quality control, wastewater treatment, water ecological system 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 greatly, ranging from 1 to 10000 μmol / kg.

[0006] The current multi-step titration method for TA includes multi-step titration-electrode potential method and multi-step titration-spectrophotometric method. The multi-step titration-electrode potential method is the most commonly used method for TA determination, but this method has the disadvantages of large sample consumption, long determination time, frequent calibration, and complex operation steps. The present application aims to establish a small volume, wide range, and simple operation method for determining water total alkalinity, which can be applied to the determination of total alkalinity in different substrate water bodies. SUMMARY

[0007] The present application aims at solving the above problems in the prior art, and provides a method for determining 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] To achieve the above object, the present application adopts the following technical scheme:

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

[0010] 1) filtering a water sample to be measured to obtain a filtered water sample, and measuring the temperature and salinity of the filtered water sample by using a thermometer and a salinity meter;

[0011] 2) taking 2-5 mL of the filtered water sample obtained in step 1) and adding it into a cuvette, and sequentially adding an indicator stock solution and hydrochloric acid into the water sample;

[0012] 3) after the solution is uniformly mixed, discharging carbon dioxide gas;

[0013] 4) after the carbon dioxide is discharged, placing the cuvette in a spectrophotometer to read the absorbance of the cuvette at a characteristic wavelength;

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

[0015] 6) substituting the algorithmic alkalinity into a correction formula to obtain the final total alkalinity of the sample;

[0016] The algorithm is as follows:

[0017]

[0018] wherein TA is the total alkalinity of the sample; ρ s , ρ a , and ρ i are the densities of the water sample, the hydrochloric acid, and the indicator stock solution, respectively; V s , V a , and V i are the volumes of the water sample, the hydrochloric acid, and the indicator stock solution, respectively; C a , C i are the concentration of the hydrochloric acid and the total concentration of the indicator in the indicator stock solution, respectively; 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; and φ1(HI) and φ2(HI) are the proportions of the acid-state indicator in the total indicator in the indicator stock solution and the solution after the reaction, respectively.

[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 selected indicator species; if the indicator is bromocresol green, the characteristic wavelength is 444 nm, 616 nm; if the indicator is bromocresol purple, the characteristic wavelength is 432 nm, 589 nm.

[0023] The correction formula in step 6) is that the known alkalinity standard is determined by the method, the obtained data is processed by the algorithm to obtain an algorithmic alkalinity, and the algorithmic alkalinity is plotted with the theoretical standard value thereof to obtain.

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

[0025] 1. The single-point titration method is used in the present application. Compared with the multi-point titration method, the single-point titration method is simpler to operate, and only one addition of acid is needed.

[0026] 2. The spectrophotometer commonly used in laboratories is used to determine the absorbance, and then a specific algorithm and correction formula are used to determine the total alkalinity in water, without the need for complex instruments and equipment.

[0027] 3. Compared with the existing total alkalinity determination method, the sample volume required by the present application is small. The sample volume required by most alkalinity determination methods is 50-100 mL, and the present application can complete one determination with only a few milliliters.

[0028] 4. The method of the present application has good precision, simple operation process and easy operation, and there is no significant difference in determination results of different operators and different spectrophotometers, and it has universality.

[0029] 5. The present application can be used for the determination of total alkalinity of different substrates such as freshwater and seawater, is not disturbed by the substrate, and can realize on-site determination.

[0030] 6. The present application can be used for the determination of a wide range of alkalinity, 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 DRAWINGS

[0031] Figure 1 The operation flowchart of the present application.

[0032] Figure 2 The seawater correction curve of the present application.

[0033] Figure 3 The freshwater correction curve of the present application. DETAILED DESCRIPTION

[0034] In order to make the technical problems, technical solutions and beneficial effects of the present application clearer and more understandable, the present application will be further described in detail below in combination with the drawings and examples.

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

[0036] (1) The water sample to be measured is filtered through a 0.45 μm filter membrane to obtain a filtered water sample, and the temperature and salinity of the filtered water sample are measured by a thermometer and a salinometer;

[0037] (2) 2-5 mL of the filtered water sample obtained in step (1) is taken into a cuvette, and an indicator stock solution and hydrochloric acid are sequentially added into the water sample;

[0038] (3) The solution is uniformly mixed, and the carbon dioxide gas in the solution is discharged within a certain time;

[0039] (4) After the carbon dioxide is discharged, the cuvette is placed in a spectrophotometer, and the absorbance of the cuvette at a characteristic wavelength is read;

[0040] (5) The temperature, salinity, absorbance and the like are brought into an algorithm to obtain an algorithmic alkalinity;

[0041] (6) The algorithmic alkalinity is substituted into a correction formula to obtain the final total alkalinity of the sample.

[0042] In the present application, 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 application, 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 application, the exhaust time is 2 min-24 h.

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

[0046] In the present application, the algorithm principle is as follows:

[0047]

[0048] Wherein, TA is the total alkalinity of the sample; ρ s , ρ a , ρi Density of water sample, hydrochloric acid and indicator stock solution, respectively; V s , V a , V i Volume of water sample, hydrochloric acid and indicator stock solution, respectively; C a , C i Concentration of hydrochloric acid and total concentration of indicator in indicator stock solution, respectively; C i Total concentration of indicator in solution after reaction; A1, A2 are absorbance read by spectrophotometer (if the indicator is bromocresol green, A1, A2 are absorbance at wavelength 444 nm, 616 nm, respectively; if the indicator is bromocresol purple, A1, A2 are absorbance at wavelength 432 nm, 589 nm, respectively); t is reaction temperature; S is salinity of sample; φ1(HI), φ2(HI) are the proportion of acid indicator in total indicator in indicator stock solution and solution after reaction, respectively.

[0049] In the present application, the correction formula in step (6) is that the known alkalinity standard is determined by the method, the obtained data is processed by algorithm to obtain algorithmic alkalinity, and the algorithmic alkalinity is plotted with the theoretical standard value to obtain.

[0050] The seawater correction curve is established by using the present application.

[0051] The aged seawater with known total alkalinity and salinity of 35 is selected as a total alkalinity standard solution. The seawater solution with salinity of 35 is prepared by using pure water and sodium chloride, the total alkalinity standard solution is mixed with the seawater solution at different proportions to obtain a series of alkalinity solutions.

[0052] The series of solutions are determined by using the present application, and the specific steps are as shown in Figure 1 The solution is filtered through a 0.45 μm filter membrane, and the temperature and salinity of the solution are determined by using a thermometer and a salinity meter; 2 mL of the filtrate is taken into a cuvette, 50 μL of bromocresol green (concentration of 2 mmol / L) and 90-120 μL of hydrochloric acid (the addition volume is not equal, which is determined according to the alkalinity of the sample; the concentration of hydrochloric acid is 0.048 mol / L) are added in turn; the upper end of the cuvette is covered with a sealing film, and the cuvette is inverted and turned over for 5 times, then the sealing film is discarded, and the solution is naturally aerated at room temperature for 5 min to discharge the carbon dioxide gas in the solution; the cuvette is placed in a spectrophotometer to read the absorbance at characteristic wavelengths 444 nm and 616 nm.

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

[0054] Table 1 Correction curve of seawater base

[0055]

[0056] The fresh water correction curve is established by using the application.

[0057] A total alkalinity solution standard substance is selected from the China Institute of Metrology, and the true alkalinity is known. Pure water is mixed with the total alkalinity solution standard substance in different proportions to obtain a series of alkalinity solutions.

[0058] The series of solutions are determined by using the application, and the specific steps are as shown in Figure 1 The solution is filtered through a 0.45 μm filter membrane, and the temperature and salinity are measured by a thermometer and a salinity meter. 2 mL of the filtrate is placed in a cuvette, 50 μL of bromocresol green (concentration of 2 mmol / L) and 25-500 μL of hydrochloric acid (the addition volume is different, depending on the alkalinity of the sample; the concentration of the hydrochloric acid is 0.048 mol / L) are added in turn. The upper end of the cuvette is covered with a sealing film, and it is inverted and turned over for 5 times, then the sealing film is discarded, and it is naturally aerated at room temperature for 5 min to discharge the carbon dioxide gas in the solution. The cuvette is placed in a spectrophotometer to read the absorbance at the characteristic wavelengths of 444 nm and 616 nm.

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

[0060] Table 2 Fresh water base correction curve

[0061]

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

Claims

1. A method for determining total alkalinity in different base water bodies, characterized by, The method comprises the following steps: 1) filtering the water sample to be tested to obtain a filtered water sample, and measuring the temperature and salinity of the filtered water sample by using a thermometer and a salinity meter; 2) taking 2-5 mL of the filtered water sample obtained in step 1) and adding the water sample into a cuvette, and then sequentially adding an indicator stock solution and hydrochloric acid into the water sample; 3) after the solution is uniformly mixed, discharging carbon dioxide gas; 4) after the carbon dioxide is discharged, placing the cuvette in a spectrophotometer to read the absorbance of the cuvette at a characteristic wavelength; 5) inputting the temperature, salinity and absorbance into an algorithm to obtain an algorithmic alkalinity; 6) substituting the algorithmic alkalinity into a correction formula to obtain the final total alkalinity of the sample; The algorithm is as follows: p a V a C a + p i V i C i φ1(HI) = TAρ s V s + (p s V s + p i V i + p 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 + p i V i + p a V a )C i 'φ2(HI) Wherein, TA is the total alkalinity of the sample; p s , p a , p i are the densities of the water sample, hydrochloric acid and the indicator stock solution, respectively; V s , V a , V i are the volumes of the water sample, hydrochloric acid and the indicator stock solution, respectively; C a , C i are the concentration of hydrochloric acid and the total concentration of the indicator in the indicator stock solution, respectively; C i ' is the total concentration of the indicator in the solution after the reaction; A1, A2 are the absorbance readings of the spectrophotometer; t is the reaction temperature; S is the salinity of the sample; φ1(HI), φ2(HI) are the proportions of the acid-state indicator in the total indicator in the indicator stock solution and the solution after the reaction, respectively; The indicator stock solution is one of bromocresol green or bromocresol purple; the characteristic wavelength is related to the type of the selected indicator; if the indicator is bromocresol green, the characteristic wavelength is 444 nm and 616 nm, and A1 and A2 are the absorbances at the wavelengths of 444 nm and 616 nm, respectively; if the indicator is bromocresol purple, the characteristic wavelength is 432 nm and 589 nm, and A1 and A2 are the absorbances at the wavelengths of 432 nm and 589 nm, respectively.

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

3. The method for determining total alkalinity in different base water bodies according to claim 1, characterized in that: The concentration of the hydrochloric acid is 0.02-1 mol / L.

4. The method for determining total alkalinity in different base water bodies according to claim 1, characterized in that: The correction formula in step 6) is obtained by measuring a known alkalinity standard by using the method, processing the obtained data by using the algorithm to obtain an algorithmic alkalinity, and plotting the algorithmic alkalinity and the theoretical standard value thereof.

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