A method for detecting alkalinity of a water sample

Abstract

The application provides a method for detecting the alkalinity of water sample, comprising the following steps: S1. constructing a mathematical model of the alkalinity of water body and the change value of the electric signal of water body; S2. contacting the water sample with acidic material to change the electric signal value of the water sample, collecting the electric signal value of the water sample before and after the water sample is contacted with the acidic material, and then constructing the change value of the electric signal of the water sample; and S3. substituting the change value of the electric signal of the water sample into the change value of the electric signal of the water body in the mathematical model to calculate the alkalinity of the water sample. The above method does not need to involve the use of titrant and the pre-calibration operation, and has low requirement on the hardware equipment, so that the complicated and tedious daily maintenance of the instrument can be saved, and the method has the advantages of simple operation, high reliability and green environmental protection.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of water quality detection, and particularly relates to a method for detecting alkalinity of a water sample. BACKGROUND

[0002] Water is the source of life, and human beings cannot live and work without water. The quality of drinking water is closely related to human health. With the development of social economy, scientific progress and the improvement of people's living standards, people's requirements for the quality of drinking water are increasing, and the standards for the quality of drinking water are also continuously developed and improved. Water alkalinity is a comprehensive characteristic index of water, and is an important index for judging water quality and water treatment control. Alkalinity is also commonly used to evaluate the buffering capacity of water bodies and the solubility and toxicity of metals in them.

[0003] The existing water alkalinity detection methods mainly include the following: acid-base titration, potentiometric titration, spectrophotometry, etc. These methods are complicated and complex, generally involve the use of auxiliary detection chemical titrants, pre-calibration steps before formal detection, and the need for constant maintenance of the instrument. However, the accuracy of the above-mentioned test methods is difficult to control, and individual operational differences of the test personnel, equipment contamination or aging, etc. can all cause the test results to deviate significantly. Based on the problems existing in the current water alkalinity detection methods, the popularization and application of water alkalinity detection technology in life and production are promoted. SUMMARY

[0004] The purpose of the present application is to provide a method for detecting the alkalinity of a water sample, so as to realize accurate detection of water alkalinity through simple operation steps.

[0005] According to one aspect of the present application, a method for detecting the alkalinity of a water sample is provided, comprising the following steps: S1. constructing a mathematical model relating the alkalinity of a water body to the change in the electrical signal of the water body, the change in the electrical signal of the water body including at least one of the change in the conductivity or a function constructed from the change in the conductivity; S2. contacting the water sample with an acidic material to cause a change in the electrical signal of the water sample, collecting the electrical signal of the water sample before and after the contact with the acidic material, and then constructing the change in the electrical signal of the water sample; and S3. substituting the change in the electrical signal of the water sample into the change in the electrical signal of the water body in the mathematical model to calculate the alkalinity of the water sample. The alkalinity of a water body is contributed by carbonate ions, bicarbonate ions, hydroxide ions and other alkaline ions in the water body. In the present application, the alkalinity of a water body or a water sample refers to the total amount of alkaline substances in the water that can consume the acidic material. The consumption of the alkalinity-contributing ions in the water body will result in a decrease in the ion concentration of the water body and a change in the conductivity of the water body. In the present application, the acidic material is introduced to cause the alkalinity-contributing ions in the water sample to be consumed through a neutralization reaction with the acidic material, thereby causing a change in the electrical signal of the water sample. The change in the electrical signal resulting from the neutralization reaction can directly reflect the content of the alkalinity-contributing ions. By constructing the calculation relationship between the alkalinity of a water body and the electrical signal of the water body, the alkalinity of a water sample can be quickly and accurately obtained. The above method does not require the use of titrants and pre-calibration operations, and has low requirements for hardware devices, thereby saving the complex and tedious daily maintenance of instruments, and having the advantages of simple operation, high reliability and green environmental protection. The electrical signal of a water body includes electrical performance parameters of the water body, such as conductivity, resistivity, voltage, current, potential and other parameters directly representing the electrical signal of the water body, as well as parameters and functions constructed from the electrical performance parameters of the water body. It should be noted that the acidic material used in the present application is a material that is not easily soluble in water. The change in the electrical signal of the water body is constructed in the above manner as a variable for calculating the alkalinity of the water body. The above variable has a strong linear correlation with the alkalinity of the water body, and the linear correlation number of the constructed linear relationship can be as high as 0.99 or more. The linear relationship fitted from the above variable and the alkalinity of the water body can accurately calculate the alkalinity of the water body.

[0006] Preferably, the function includes the total amount of dissolved solids.

[0007] Preferably, the dissociation constant pKa of the acidic material satisfies pKa>2.

[0008] Preferably, the dissociation constant pKa of the acidic material satisfies pKa>3.

[0009] Preferably, the dissociation constant pKa of the acidic material satisfies pKa>4.

[0010] Taking the dissociation constant as one of the indicators for selecting the acidic material is conducive to ensuring the sensitivity of the reaction between the acidic material and the water body, thereby improving the detection efficiency of the alkalinity of the water body.

[0011] Preferably, the acidic material satisfies that the change of the electric signal contributed by the dissolved substance of the acidic material in the test solution is less than 50% of the change of the electric signal caused by the alkalinity. The dissolved substance of the acidic material in water can affect the conductivity of the water, thus causing errors in the detection of the alkalinity of the water body based on the change of the electric signal. In the selection of the acidic material, the conductivity contribution ability of the acidic material in water is taken as one of the indicators, which is beneficial to improve the accuracy of the detection of the alkalinity of the water body.

[0012] Preferably, the acidic material comprises an acidic resin, and the acidic resin is selected from at least one of sulfonic acid resin, carboxylic acid resin, phosphoric acid resin, boric acid resin and silicic acid resin.

[0013] Preferably, the acidic resin comprises a carboxylic acid resin.

[0014] Preferably, the acidic material comprises a non-ionic material and an anionic substance, the non-ionic material is used to provide a non-ionic group in an acidic state, the non-ionic group is represented as A-H, and the anionic substance is represented as A － , wherein A represents the anionic substance; and the amount ratio of A － to A-H is 0 to 99% in terms of molar ratio.

[0015] Preferably, the content of R-A-H in the acidic resin is 0.01 mmol / g to 50 mmol / g.

[0016] Preferably, the content of R-A-H in the acidic resin is 0.5 mmol / g to 5 mmol / g.

[0017] Preferably, the content of R-A-H in the acidic resin is 2 mmol / g to 4 mmol / g.

[0018] Preferably, the amount ratio of A － to A-H is 0.001 to 1% in terms of molar ratio.

[0019] The anionic resin and the non-ionic resin are compounded, so as to reduce the conductivity contribution rate of the acidic resin to the water body, which is beneficial to improve the accuracy of the detection of the alkalinity of the water body.

[0020] Preferably, the acidic material contains metal ions in an amount of 50 ppm to 50,000 ppm. Optionally, the metal ions are selected from at least one of alkali metal ions, alkaline earth metal ions and transition metal ions. The content of the metal ions in the acidic material is in the above range, which can ensure a faster response speed of the detection of the alkalinity.

[0021] Preferably, in S2, the volume ratio of the water sample to the acidic material is 0.1 to 10. Within the above ratio range, the water sample and the acidic material can sufficiently react in a short time, and the conductivity of the water sample can be obviously changed, so that the alkalinity detection has a faster response speed.

[0022] Preferably, in S2, a water temperature detection operation is further included, a temperature correction is performed on the measured electric signal based on the water temperature of the water sample to obtain a corrected electric signal, and the water sample electric signal change value is calculated by using the corrected electric signal instead of the electric signal; and the temperature correction rule is that, compared with 25℃, when the water temperature increases by 1℃, the corrected electric signal is increased by 1-5%, and when the water temperature decreases by 1℃, the corrected electric signal is reduced by 1-5%.

[0023] Preferably, the electric signal is the conductivity; and the temperature correction rule is that, compared with 25℃, when the water temperature increases by 1℃, the corrected electric signal is increased by 2%, and when the water temperature decreases by 1℃, the corrected electric signal is reduced by 2%.

[0024] Based on the electric conductivity of the alkalinity contribution ions, the alkalinity detection method of the present application is proposed by calculating the alkalinity of the water sample based on the electric signal change of the water sample, so that, in the reaction of consuming the alkalinity contribution ions, the selection of the ion types participating in the reaction, the selection of the electric signal parameters, and the correction of the error factors can positively affect the accuracy of the water sample alkalinity value obtained by using the above method. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 The linear relationship fitting graph about the electric conductivity change value and the alkalinity value of the water sample is constructed by using the weak acid hydrogen resin in Example 2.

[0026] Figure 2 The linear relationship fitting graph about the TDS change value and the alkalinity value of the water sample is constructed by using the weak acid hydrogen resin in Example 3. DETAILED DESCRIPTION

[0027] In order for those skilled in the art to better understand the technical scheme of the present application, the technical scheme in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present application, but not all the embodiments.

[0028] In the following examples, the gradient alkalinity value water samples are tap water samples taken from all over the country, the alkalinity of the water body is tested by Guangzhou Microorganism Research Institute, and is the total alkalinity (i.e. methyl orange alkalinity), the electric conductivity change value is measured by the electric conductivity meter of the American Millon Company, and the TDS value is measured by the TDS pen of Xiaomi.

[0029] Example 1

[0030] (1) Verify the contribution of different types of resin to the conductivity of water samples

[0031] The conductivity of pure water and tap water samples was measured after soaking with different types of resin for 24 hours. The experimental results are shown in Table 1. The data provided in Table 1 show that the strong acid hydrogen resin (sulfonic acid resin) exchanges cations in water to form strong acid, resulting in a sharp rise in solution conductivity; the weak acid potassium resin (carboxylic acid resin) dissolves more ions in pure water. However, the strong acid sodium resin (sulfonic acid sodium resin) and the weak acid hydrogen resin (carboxylic acid resin) do not cause significant fluctuations in the conductivity of pure water samples, indicating that the strong acid sodium resin and the weak acid hydrogen resin have little contribution to the conductivity of water samples. Further, the above four types of test resins were immersed in tap water and the conductivity of the water samples was observed. The data in Table 1 show that the strong acid sodium resin and the weak acid potassium resin do not cause significant changes in the conductivity of tap water, while the strong acid hydrogen resin and the weak acid hydrogen resin cause significant changes in the conductivity of tap water before and after immersion. In summary, among the four resins provided in this embodiment, only the weak acid hydrogen resin meets the following two conditions: it does not contribute to the conductivity of the water body (the change in the conductivity of pure water before and after immersion of the weak acid hydrogen resin is almost zero); it can fully react with the water sample to cause significant changes in the conductivity of the water sample. Based on this, the weak acid hydrogen resin is suitable for water quality monitoring based on conductivity changes. The weak acid resin cleaned with pure water has almost no dissolved substances, and its conductivity is most sensitive to water samples, even for low TDS water samples.

[0032] Table 1 Contribution of different types of resin to the conductivity change of water samples

[0033] Resin type Change in pure water conductivity on soaking Change in tap water conductivity on soaking Strong acid H type 230 uS >200％ Strong acid Na type <10uS 1.0％ Weak acid H type <10uS 43.1％ Weak acid K type 110 uS 0.6％

[0034] (2) Verify that the weak acid hydrogen resin only causes conductivity changes in water samples with alkalinity

[0035] Based on the above experimental results, the weak acid hydrogen resin has more advantages than other test resins in water quality monitoring based on conductivity changes. The weak acid hydrogen resin was mixed with a sodium chloride or calcium chloride solution prepared with pure water overnight (alkalinity of only 20 ppm). The hardness, alkalinity and conductivity of the water sample were tested before and after soaking the weak acid hydrogen resin, and the relevant data were recorded in Table 2. The test results show that the hardness of the water sample did not change, but the alkalinity of the water sample changed significantly, indicating that the weak acid resin only reacts with substances that contribute to the alkalinity of the water sample, and does not exchange or adsorb other cations, thereby accurately reflecting the alkalinity value of the water sample.

[0036] Table 2 Results of solution immersion experiment of weak acid hydrogen type resin

[0037]

[0038] Example 2

[0039] The mathematical model for the method for detecting water sample alkalinity according to the present example is constructed as follows:

[0040] S1. Using water samples with gradient alkalinity values (as shown in Table 3) as gradient standards, the conductivities of the gradient standards are measured respectively;

[0041] S2. Then the gradient standards are mixed with acidic materials and stirred for about 1 h respectively;

[0042] S3. Then the conductivities of the gradient standards are measured;

[0043] S4. For the same standard, the first measured conductivity is C1 and the second measured conductivity is C2. The data of the conductivity change value (i.e. C2-C1) of the gradient standards before and after the reaction with acidic materials are arranged. The conductivity change value is taken as the abscissa and the alkalinity value of the water sample is taken as the ordinate. The linear relationship curve is fitted to obtain the mathematical model for correlating the conductivity change value and the alkalinity value of the water sample.

[0044] Table 3 Gradient standards and their corresponding alkalinity values

[0045] Standard source Alkalinity value (mg / L) A site tap water 95.1 B site tap water 102.0 C site tap water 35.0 D site tap water 25.0 E site tap water 112.0 F site tap water 49.0 G site tap water 110.0 H site tap water 270.0 I site tap water 114.0 J site tap water 260.0 K site tap water 118.0

[0046] According to the present example, a mathematical model for correlating the conductivity change value and the alkalinity value of the water sample is constructed by using different types of acidic resins as acidic materials for constructing the mathematical model. The acidic resins used in the present example are commercially available acidic resins, and the tested resins are as follows: weak acid hydrogen type resin I (Purolite C107E, carboxylic acid type resin), weak acid hydrogen type resin II (Dupont Amberlite IRP-64, carboxylic acid type resin), and weak acid Na type resin (ZGC152, carboxylic acid type resin). Before use, the acidic resins are pretreated as follows: a certain amount of acidic resin is immersed in deionized water to remove the leachables in the acidic resin. The immersion and stirring are continued for about 12 h. Then the acidic resin is taken out and washed with a large amount of deionized water and taken out for standby. In the above pretreatment step, the contribution rate of the leachables to the conductivity of the water body is reduced, which is beneficial to improving the accuracy of the detection of the alkalinity of the water body.

[0047] Among the above-mentioned tested resins, the R 2The data involved in constructing the linear model is shown in Table 4, and the linear relationship obtained by fitting is shown in Figure 1 2 The R 2 of the linear relationship is 0.9985, indicating that the alkalinity of the water sample and the change in the conductivity of the water sample are in a strong linear relationship.

[0048] Table 4 Data involved in constructing the linear relationship using weak acid hydrogen type resin

[0049]

[0050] The weak acid hydrogen type resin of the present embodiment and Figure 1 linear relationship shown in the figure to test the alkalinity of the water sample, the specific operation is as follows:

[0051] S1. Before testing the water sample, use the conductivity meter to measure the conductivity of the test water, record it as C1, then mix the acidic material with the test water and stir for about 1 h, the mass of the test water is 80 g, the drained acidic material is 15 g, measure the conductivity of the water after stirring for 1 h, record it as C2.

[0052] S2. Calculate the change in conductivity before and after the reaction of the water sample and the acidic material (i.e. C2-C1), and bring the calculated conductivity change value into Figure 1 linear relationship shown in the figure to calculate the alkalinity value of the water sample.

[0053] The calculation results are shown in Table 5, and the absolute value of the deviation between the calculated alkalinity value and the measured alkalinity value is not more than 10%.

[0054] Table 5 Calculate the alkalinity value of the water sample using Figure 1 linear relationship shown in the figure

[0055]

[0056] Example 3

[0057] The weak acid sodium resin and the weak acid hydrogen resin are mixed in different proportions, and then soaked in tap water. When the soaking time reaches 60 min, the TDS value of the water sample is tested. Before use, the weak acid hydrogen resin and the weak acid sodium resin are pretreated as follows: a certain mass of the acid resin and the sodium resin are soaked in deionized water to remove the eluate in the resin. After about 12 h of continuous soaking and stirring, the acid resin is taken out and washed with a large amount of deionized water, and then taken out for standby. In the above pretreatment step, the contribution rate of the eluate to the conductivity of the water body is reduced, which is beneficial to improve the accuracy of the alkalinity detection of the water body. Before soaking the resin, the TDS value of the raw water sample used in this embodiment is 140 ppm, as shown in Table 6. After soaking in tap water for 60 min, the conductivity of the water sample corresponding to 100% sodium resin does not change, while the TDS corresponding to the mixed resin composed of sodium resin and hydrogen resin decreases to 81-88 ppm due to the removal of alkalinity.

[0058] Table 6 Contribution of the proportion of sodium type weak acid resin and hydrogen type weak acid resin to the change of TDS of water sample

[0059]

[0060]

[0061] Example 4

[0062] Based on the experimental results of Example 2 and Example 3, the weak acid hydrogen resin I and the weak acid Na resin (Ningbo Zhengguang ZGC152, carboxylic acid type resin) are mixed to form a mixed resin (weight ratio of 10:1) which reacts with the water sample, so that the conductivity change value of the water sample and the alkalinity of the water sample have a strong linear relationship. This embodiment uses the weak acid hydrogen resin used in Example 2, and establishes a mathematical model relating the change of TDS of the water sample and the alkalinity value of the water sample by referring to the method provided in Example 2 for constructing a mathematical model for detecting the alkalinity of the water sample. The specific operation is as follows:

[0063] S1. The water sample with gradient alkalinity value (as shown in Table 3) is used as a gradient standard, and the conductivity of each gradient standard is measured respectively;

[0064] S2. Then each gradient standard is mixed with the mixed resin and stirred for about 1 h;

[0065] S3. Then the TDS value of each gradient standard is tested;

[0066] S4. For the same standard, the first measured TDS value is T1, and the second measured TDS value is T2. The TDS change value (i.e. T2-T1) of each gradient standard before and after the reaction with the mixed resin is calculated. The TDS change value is taken as the abscissa, and the alkalinity value of the water sample is taken as the ordinate. The linear relationship curve is fitted to obtain the mathematical model of the correlation between the alkalinity of the water body and the TDS change value.

[0067] The data involved in the construction of the above linear model is shown in Table 7. The linear relationship fitted is shown in Figure 2 2 The R 2 of the linear relationship reaches 0.9986, indicating that the alkalinity of the water sample has a strong linear relationship with the TDS change value of the water sample.

[0068] Table 7 Relationship between TDS drop and alkalinity value of water sample

[0069]

[0070]

[0071] The weak acid hydrogen type and Na type mixed resin of the present embodiment and the linear relationship shown in Figure 2 are used to test the alkalinity of the water sample. The specific operation is as follows:

[0072] S1. Before testing the water sample, the TDS value of the test water is measured with a TDS pen and recorded as T1. Then the acidic material is mixed with the test water and stirred for about 1 h. The mass of the test water is 80 g, and the drained acidic material is 15 g. The TDS value of the water after stirring for 1 h is measured and recorded as T2.

[0073] S2. The TDS change value (i.e. T2-T1) before and after the reaction of the water sample with the acidic material is calculated. The TDS change value calculated is brought into the linear relationship shown in Figure 2 to calculate the alkalinity value of the water sample.

[0074] The calculation results are shown in Table 8. The absolute value of the deviation between the calculated alkalinity value and the measured alkalinity value is not more than 5%.

[0075] Table 8 Calculation of the alkalinity value of the water sample using the linear relationship shown in Figure 2

[0076]

[0077] The above examples are only used to illustrate the technical solutions of the present application and not to limit the protection scope of the present application. Although the present application is described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A method for detecting alkalinity in a water sample, characterized in that, Includes the following steps: S1. Construct a mathematical model relating water alkalinity to changes in water electrical signals, wherein the changes in water electrical signals include at least one of the changes in water conductivity or a function constructed from the changes in water conductivity; S2. Contact the water sample with an acidic material to change the electrical signal value of the water body, collect the electrical signal of the water body before and after contact with the acidic material, and then construct the change value of the electrical signal of the water body. The acidic material includes an acidic resin, and the acidic resin is a weak acid hydrogen type resin. S3. Substitute the change value of the water body electrical signal into the mathematical model to calculate the alkalinity of the water sample.

2. The method for detecting alkalinity in a water sample as described in claim 1, characterized in that: The function includes the total amount of dissolved solids.

3. The method for detecting alkalinity in a water sample as described in claim 1, characterized in that: The dissociation constant pKa of the acidic material satisfies pKa>2.

4. The method for detecting alkalinity in a water sample as described in claim 3, characterized in that: The dissociation constant pKa of the acidic material satisfies pKa>4.

5. The method for detecting alkalinity in a water sample as described in claim 4, characterized in that: The acidic material is such that the contribution of the dissolved substances from the acidic material to the change in electrical signal in the test solution is less than 50% of the change in electrical signal caused by alkalinity.

6. The method for detecting alkalinity in a water sample as described in claim 1, characterized in that: The acidic resin includes carboxylic acid resin.

7. The method for detecting alkalinity in a water sample as described in claim 1, characterized in that: The acidic material includes nonionic materials and anionic substances. The nonionic material is used to provide acidic nonionic groups, denoted by A-H, and the anionic substance is denoted by A-. Based on molar ratio calculations, the proportion of A- to A-H is 0% to 99%.

8. The method for detecting alkalinity in a water sample as described in claim 1, characterized in that: The acidic material contains 50 ppm to 50,000 ppm of metal ions.

9. The method for detecting alkalinity in a water sample as described in claim 8, characterized in that: In S2, the reaction volume ratio of the water sample to the acidic material is 0.1 to 10.

10. The method for detecting alkalinity in a water sample as described in claim 1, characterized in that: In S2, the method further includes performing a water temperature detection operation on the water sample, performing temperature correction on the measured water body electrical signal based on the water temperature of the water sample to obtain a correction electrical signal, and using the correction electrical signal to replace the water body electrical signal to calculate the change value of the water body electrical signal. The temperature correction rule is as follows: for every 1°C increase in water temperature compared to 25°C, the water body electrical signal is increased by 1 to 5% as the correction electrical signal; for every 1°C decrease in water temperature, the water body electrical signal is reduced by 1 to 5% as the correction electrical signal value.

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