Method for detecting content of chloride ions in sand for concrete

Abstract

The invention relates to a method for detecting the content of chloride ions in sand for concrete, which indirectly determines the content of chloride ions in sand for concrete through ultraviolet-visible spectrophotometry, and has higher accuracy and higher analysis efficiency for large-batch samples compared with the existing titration method. Compared with an existing direct measurement ultraviolet spectrum method, the operation process is simpler and more convenient, and the light absorption value at the characteristic wavelength is stable and is not interfered by other halogens and organic matters.

Description

Technical Field

[0001] The invention relates to the technical field of chemical analysis, in particular to a method for detecting chloride ion content in concrete sand. Background Art

[0002] In the preparation process of concrete, the chloride ion content in sand is one of the important factors affecting the durability of concrete. Therefore, it is very important to accurately detect the chloride ion content in sand.

[0003] At present, the standard method for detecting chloride ions in concrete sand is mainly titration. This method uses potassium chromate as an indicator and uses a standard silver nitrate solution for titration. When the solution is titrated to the point where there is an excess of silver nitrate, the silver nitrate reacts with the potassium chromate indicator to produce brick-red silver chromate, marking the end point of the reaction. However, this method requires the use of a large amount of potassium chromate and silver nitrate reagents, which is costly and produces a large amount of waste liquid.

[0004] The existing titration method still has some obvious defects. Because the end point color is brick red, which is close to the color of sand, the end point judgment is not clear enough, and the subjective judgment of the test personnel will cause large errors. In addition, some researchers have tried other detection methods, such as ion chromatography, spectrophotometry and ultraviolet spectroscopy, hoping to improve the accuracy of detection and the convenience of operation.

[0005] Although patents have proposed ultraviolet spectroscopy as a method for directly measuring chloride ions, the absorption range of this method is easily interfered by impurities, which affects the accuracy of the detection. In addition, this method adds pretreatment steps such as grinding and burning on the basis of the standard detection process, which makes the operation complicated and further limits its practicality. Therefore, how to overcome the shortcomings of existing detection methods, simplify the operation process, and improve the stability and accuracy of the detection results is a problem that needs to be solved urgently in the current technical field. Summary of the invention

[0006] Based on this, it is necessary to provide a detection method that can accurately detect the chloride ion content in concrete sand.

[0007] To achieve the above object, the present invention provides a technical solution:

[0008] A method for detecting chloride ion content in concrete sand, characterized in that the detection method comprises the steps of:

[0009] S100, draw a standard curve of absorbance of solutions with different chloride ion concentrations:

[0010] S110, adding equal amounts of silver nitrate solutions of the same concentration to different volumes of sodium chloride solutions of the same concentration, respectively, to allow chloride ions and silver ions to fully react to obtain a suspension;

[0011] S120, adding an equal amount of the first buffer solution to the suspension, adjusting the pH value and then adding an equal amount of 3,3',5,5'-tetramethylbenzidine solution, making the volumes of the suspensions the same with the second buffer solution, mixing, centrifuging, and detecting the absorbance of the supernatant;

[0012] Specifically, the pH of the first buffer solution is ≤4;

[0013] The pH of the second buffer is ≤4.

[0014] The first buffer is at least one of acetic acid-sodium acetate, phosphate buffer, acetate buffer, carbonate buffer, borate buffer, citric acid buffer and maleic acid buffer;

[0015] The second buffer is at least one of acetic acid-sodium acetate, phosphate buffer, acetate buffer, carbonate buffer, borate buffer, citric acid buffer and maleic acid buffer.

[0016] The first buffer solution and the second buffer solution are the same buffer solution.

[0017] S130, drawing a standard curve diagram of solutions with different chloride ion concentrations and absorbance, and obtaining a linear equation about chloride ion concentration and absorbance;

[0018] S200, detection of chloride ion content in samples:

[0019] S210, soaking the sand sample to be tested in water, extracting and filtering to obtain a filtrate, adding an equal amount of the silver nitrate solution of the same concentration in step S100 to the filtrate to obtain a suspension;

[0020] S220, repeating the operation of step S120 with the suspension obtained in step S210, and detecting the absorbance of the supernatant;

[0021] S230, when the absorbance is within the range of the linear equation, substituting the absorbance into the linear equation to measure the chloride ion concentration in the filtrate;

[0022] S240. When the absorbance is higher than the range of the linear equation, dilute the filtrate obtained in step S210, repeat steps S210 to S220 until the absorbance is within the range of the linear equation, substitute the absorbance into the above linear equation, and measure the chloride ion concentration in the filtrate.

[0023] Furthermore, in step S120 and step S220, the absorbance of the supernatant is detected at a wavelength of 635 nm to 670 nm.

[0024] Further, in step S120 and step S220, the absorbance of the supernatant is detected at a wavelength of 650 nm.

[0025] Furthermore, the concentration of the silver nitrate solution is 0.01 mol / L to 0.1 mol / L.

[0026] Furthermore, the solvent in the 3,3',5,5'-tetramethylbenzidine solution is ethanol, and the concentration of the 3,3',5,5'-tetramethylbenzidine solution is 0.1 mmol / L to 1 mmol / L.

[0027] Furthermore, the concentration of the sodium chloride standard solution is 0.01 mol / L to 0.1 mol / L.

[0028] Furthermore, when the concentration of the sodium chloride standard solution is 0.01 mol / L, the volumes of the added sodium chloride standard solution are: 0 mL, 0.05 mL, 0.1 mL, 0.5 mL, 0.8 mL, and 1.0 mL, respectively.

[0029] Furthermore, in the standard curve, the chloride ion concentration range is 0 to 14.20 mg·L-1.

[0030] Silver ions preferentially combine with chloride ions, and excess silver ions react with the color developer 3,3',5,5'-tetramethylbenzidine. The blue product has UV-visible absorption. By drawing a standard curve of chloride ion concentration-blue product absorbance, the chloride ion content in the sand sample can be indirectly determined.

[0031] The method firstly dissolves the chloride ions in the sand into water by using deionized water, takes the filtrate after filtering the extract, adds a fixed volume of excess silver nitrate standard solution to the filtrate, makes the silver nitrate react fully with the chloride ions in the filtrate, and the remaining silver ions in the system react with excess color developer TMB (tetramethylbenzidine) to generate an oxidation product, and measures the content of the oxidation product by ultraviolet-visible spectrophotometry, so as to indirectly calculate the chloride ion content in the sand sample.

[0032] Since silver ions preferentially combine with chloride ions under acidic conditions to form acid-insoluble silver chloride precipitates, the remaining silver ions will react with tetramethylbenzidine (TMB). The blue oxidation product generated by the reaction is measured for its absorbance (the more blue oxidation products generated, the greater the absorbance). A standard curve of solutions with different chloride ion concentrations-absorbance is drawn. The absorbance is negatively correlated with the chloride ion concentration. The absorbance of the blue oxidation product generated by the reaction of the sand to be tested is then detected, and the chloride ion content in the sand sample can be obtained through the standard curve.

[0033] Beneficial effects of the present invention:

[0034] The present invention indirectly determines the chloride ion content in concrete sand by ultraviolet-visible spectrophotometry, which is more accurate than the existing titration method and more efficient for analyzing large quantities of samples.

[0035] Compared with the existing direct measurement ultraviolet spectroscopy method, the operation process is simpler, and the absorbance value at the characteristic wavelength is stable and will not be interfered by other halogens and organic matter. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is a graph of absorption intensity and wavelength in the embodiment;

[0037] Figure 2 It is the chloride ion concentration-absorbance curve diagram in the embodiment. DETAILED DESCRIPTION

[0038] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0039] In the examples, the test methods used are conventional methods unless otherwise specified, and the materials, reagents, etc. used are all commercially available unless otherwise specified.

[0040] A method for detecting chloride ion content in concrete sand, characterized in that the detection method comprises the steps of:

[0041] S100, draw a standard curve of absorbance of solutions with different chloride ion concentrations:

[0042] S110, adding equal amounts of silver nitrate solutions of the same concentration to different volumes of sodium chloride solutions of the same concentration, respectively, to allow chloride ions and silver ions to fully react to obtain a suspension;

[0043] S120, adding an equal amount of the first buffer solution to the suspension, adjusting the pH value and then adding an equal amount of 3,3',5,5'-tetramethylbenzidine solution, making the volumes of the suspensions the same with the second buffer solution, mixing, centrifuging, and detecting the absorbance of the supernatant;

[0044] Specifically, the pH of the first buffer solution is ≤4;

[0045] The pH of the second buffer is ≤4.

[0046] The first buffer is at least one of acetic acid-sodium acetate, phosphate buffer, acetate buffer, carbonate buffer, borate buffer, citric acid buffer and maleic acid buffer;

[0047] The second buffer is at least one of acetic acid-sodium acetate, phosphate buffer, acetate buffer, carbonate buffer, borate buffer, citric acid buffer and maleic acid buffer.

[0048] The first buffer solution and the second buffer solution are the same buffer solution.

[0049] S130, drawing a standard curve diagram of solutions with different chloride ion concentrations and absorbance, and obtaining a linear equation about chloride ion concentration and absorbance;

[0050] S200, detection of chloride ion content in samples:

[0051] S210, soaking the sand sample to be tested in water, extracting and filtering to obtain a filtrate, adding an equal amount of the silver nitrate solution of the same concentration in step S100 to the filtrate to obtain a suspension;

[0052] S220, repeating the operation of step S120 with the suspension obtained in step S210, and detecting the absorbance of the supernatant;

[0053] S230, when the absorbance is within the range of the linear equation, substituting the absorbance into the linear equation to measure the chloride ion concentration in the filtrate;

[0054] S240. When the absorbance is higher than the range of the linear equation, dilute the filtrate obtained in step S210, repeat steps S210 to S220 until the absorbance is within the range of the linear equation, substitute the absorbance into the above linear equation, and measure the chloride ion concentration in the filtrate.

[0055] In some embodiments, in step S120 and step S220, the absorbance of the supernatant is detected at a wavelength of 635 nm to 670 nm.

[0056] In some embodiments, in step S120 and step S220, the absorbance of the supernatant is detected at a wavelength of 650 nm.

[0057] In some embodiments, the concentration of the silver nitrate solution is 0.01 mol / L to 0.1 mol / L.

[0058] In some embodiments, the solvent in the 3,3',5,5'-tetramethylbenzidine solution is ethanol, and the concentration of the 3,3',5,5'-tetramethylbenzidine solution is 0.1 mmol / L to 1 mmol / L.

[0059] In some embodiments, the concentration of the sodium chloride standard solution is 0.01 mol / L to 0.1 mol / L.

[0060] In some embodiments, when the concentration of the sodium chloride standard solution is 0.01 mol / L, the volumes of the added sodium chloride standard solution are: 0 mL, 0.05 mL, 0.1 mL, 0.5 mL, 0.8 mL, and 1.0 mL, respectively.

[0061] In some embodiments, in the standard curve, the chloride ion concentration ranges from 0 to 14.20 mg·L-1.

[0062] Example 1

[0063] Take 2mL of 0.01mol / L silver nitrate solution, add 10mL of pH=4 buffer, and then add 10mL of TMB, shake well, the solution turns blue, use a UV-visible spectrophotometer to perform a full scan in the wavelength range of 250nm to 2500nm, and plot the absorption intensity and wavelength change to obtain Figure 1 Curves, such as Figure 1 As shown, when TMB reacts with silver ions under acidic conditions, a blue product is generated with a maximum absorption peak at 650 nm.

[0064] Take another 2mL of 0.01mol / L silver nitrate standard solution, add 2.5mL of 0.01mol / L sodium chloride standard solution, add 10mL of pH=4 buffer solution, and then add 10mL of TMB, shake well, the solution is colorless, and there is no absorption peak at 650nm.

[0065] Example 2

[0066] Different chloride ion concentration-absorbance standard curve

[0067] Take 5 25mL centrifuge tubes, add 0mL, 0.05mL, 0.1mL, 0.5mL, 0.8mL, and 1.0mL 0.01mol / L sodium chloride standard solution, add 1mL 0.01mol / L silver nitrate solution and 10mL pH=4 acetic acid-sodium acetate buffer solution to each tube, then add 10mL TMB, and then use acetic acid-sodium acetate buffer to make the volume to 25mL. After shaking, centrifuge for 2 minutes, take the supernatant, select 5mm and 10mm colorimetric dishes respectively, use UV-visible spectrophotometer to measure the absorbance of reaction solutions of different concentrations at 650nm, and draw the chloride ion concentration-absorbance curve. The test results are as follows: Figure 2 As shown, when the chloride ion concentration is between 0 and 14.20 mg·L-1, the absorbance and concentration show a good negative linear correlation. When using a 5 mm cuvette, the linear equation is y = -0.0644x + 0.9318, R 2 is 0.9981.

[0068] Example 3

[0069] Detection of chloride ion content in actual sand samples

[0070] The experiment was conducted on a sand sample with a chloride ion concentration of 0.0142% measured by titration in the standard method JGJ 52-2006. 100g of sand after shrinkage and drying was added with 100mL of deionized water, ultrasonically extracted at room temperature for 10 minutes, and filtered. Take 1mL of filtrate, add 1mL of silver nitrate, add about 10mL of pH=4 acetic acid-sodium acetate buffer, add 10mL of TMB, and then add acetic acid-sodium acetate buffer to 25mL, shake well, centrifuge for 2 minutes, take the supernatant and measure the absorbance at 650nm. Parallel determination, the absorbance values ​​of the sample determination are 0.593 and 0.562, substitute into the standard curve of y=-0.0644x+0.9318 for calculation, and find the average value, and the chloride ion content in the sample is 0.0137%, and the deviation of the relative standard method test result is 3.5%. It proves that this method has practical operability and accuracy.

[0071] Comparative Example 1

[0072] Compare with patent CN113552085A.

[0073] Patent CN113552085A directly measures chloride ions in a solution system at a wavelength of 190nm-200nm, and the chloride ion concentration is positively correlated with the absorbance value.

[0074] Patent CN113552085A is a direct measurement method, which is easily affected by impurities in the absorption range of 190-200nm. It also adds grinding, burning and other steps on the basis of the standard method, which makes the operation complicated.

[0075] It should be noted that the specific parameters or some reagents in the above embodiments are specific embodiments or preferred embodiments of the present invention, rather than limiting the present invention; those skilled in the art can make adaptive adjustments within the scope of the present invention.

Claims

1. A method for detecting chloride ion content in concrete sand, characterized in that: The detection method comprises the steps of: S100, draw a standard curve of absorbance of solutions with different chloride ion concentrations: S110, adding equal amounts of silver nitrate solutions of the same concentration to different volumes of sodium chloride solutions of the same concentration, respectively, to allow chloride ions and silver ions to fully react to obtain a suspension; S120, adding an equal amount of the first buffer solution to the suspension, adjusting the pH value and then adding an equal amount of 3,3',5,5'-tetramethylbenzidine solution, making the volumes of the suspensions the same with the second buffer solution, mixing, centrifuging, and detecting the absorbance of the supernatant; S130, drawing a standard curve diagram of solutions with different chloride ion concentrations and absorbance, and obtaining a linear equation about chloride ion concentration and absorbance; S200, detection of chloride ion content in samples: S210, soaking the sand sample to be tested in water, extracting and filtering to obtain a filtrate, adding an equal amount of the silver nitrate solution of the same concentration in step S100 to the filtrate to obtain a suspension; S220, repeating the operation of step S120 with the suspension obtained in step S210, and detecting the absorbance of the supernatant; S230, when the absorbance is within the range of the linear equation, substituting the absorbance into the linear equation to measure the chloride ion concentration in the filtrate; S240. When the absorbance is higher than the range of the linear equation, dilute the filtrate obtained in step S210, repeat steps S210 to S220 until the absorbance is within the range of the linear equation, substitute the absorbance into the above linear equation, and measure the chloride ion concentration in the filtrate.

2. The detection method according to claim 1, characterized in that: In step S120 and step S220, the absorbance of the supernatant is detected at a wavelength of 635 nm to 670 nm.

3. The detection method according to claim 2, characterized in that: In step S120 and step S220, the absorbance of the supernatant is detected at a wavelength of 650 nm.

4. The detection method according to claim 1, characterized in that: The concentration of the silver nitrate solution is 0.01 mol / L to 0.1 mol / L.

5. The detection method according to claim 1, characterized in that: The solvent in the 3,3',5,5'-tetramethylbenzidine solution is ethanol, and the concentration of the 3,3',5,5'-tetramethylbenzidine solution is 0.1 mmol / L to 1 mmol / L.

6. The detection method according to claim 1, characterized in that: The concentration of sodium chloride standard solution is 0.01mol / L~0.1mol / L.

7. The detection method according to claim 6, characterized in that: When the concentration of sodium chloride standard solution is 0.01 mol / L, the volumes of sodium chloride standard solution added are: 0 mL, 0.05 mL, 0.1 mL, 0.5 mL, 0.8 mL, and 1.0 mL, respectively.

8. The detection method according to claim 1, characterized in that: The first buffer is at least one of acetic acid-sodium acetate, phosphate buffer, acetate buffer, carbonate buffer, borate buffer, citric acid buffer and maleic acid buffer; The second buffer is at least one of acetic acid-sodium acetate, phosphate buffer, acetate buffer, carbonate buffer, borate buffer, citric acid buffer and maleic acid buffer.

9. The detection method according to claim 8, characterized in that: The pH of the first buffer solution is ≤4; The pH of the second buffer is ≤4.

10. The detection method according to claim 1, characterized in that: In the standard curve, the chloride ion concentration range is 0 mg·L-1 to 14.20 mg·L-1.

Images