Method for measuring moisture content of anticorrosive paint based on gas chromatography

Abstract

The invention provides a method for measuring the moisture content of an anticorrosive coating based on gas chromatography, which comprises the following steps: carrying out gradient dilution and constant volume on water by using a diluting solvent to prepare a plurality of standard solutions; carrying out gradient dilution and constant volume on the internal standard substance by using a diluting solvent to prepare an internal standard solution; placing the standard solutions with different volumes in a volumetric flask, adding a quantitative internal standard solution, and supplementing a diluting solvent to a target volume to obtain a plurality of groups of working solutions; performing gas chromatography detection on each group of working solutions by adopting a single-point relative response factor test method to obtain the peak area of water, the peak area of the internal standard substance and the relative response factor of water; taking the peak area ratio as an abscissa and the relative response factor as an ordinate, constructing a plurality of candidate functions based on a preset function, and obtaining a fitting curve expression; calculating goodness of fit of each candidate function, and selecting the candidate function with the highest goodness of fit as a target function; measuring a to-be-measured sample to obtain target data, and substituting the target data into the target function to obtain the moisture content. The determination method improves the accuracy of the moisture content test result.

Description

Technical Field

[0001] This application relates to the field of moisture measurement technology, and in particular to a method for determining the moisture content of anti-corrosion coatings based on gas chromatography. Background Technology

[0002] Anti-corrosion coatings, as an economical and efficient protective measure, form a continuous and dense protective film on the substrate surface to block contact between corrosive media and the substrate, or exert a protective effect through mechanisms such as cathodic protection and corrosion inhibition. They have become a core material for extending the service life of substrates and ensuring the safe and stable operation of engineering projects. Based on the film-forming substances, anti-corrosion mechanisms, and application scenarios, anti-corrosion coatings can be divided into several categories, forming composite protective systems. Among them, epoxy resin coatings, due to their strong adhesion and excellent chemical corrosion resistance, account for more than 40% of the global anti-corrosion coating market share and are widely used in ship cabins, oil and gas storage tanks, pipelines, and other scenarios. Subtypes include epoxy coal tar pitch and epoxy zinc powder. Polyurethane coatings possess good flexibility and weather resistance and are often used on ship decks, the outer layer of offshore platforms, and other areas requiring both aesthetics and protection. Zinc-based coatings (typically containing >80% zinc powder) achieve long-term protection through cathodic protection mechanisms and are suitable for harsh scenarios such as marine steel structures and nuclear power plants. Fluorocarbon coatings, silane / siloxane coatings, and emerging graphene-modified coatings are gradually being promoted in high-end anti-corrosion fields due to their ultra-weather resistance, low VOC, and self-healing properties. In practical applications, a multi-layer composite system of "primer-intermediate layer-topcoat" is often used, such as the combination of zinc base paint + epoxy intermediate layer + polyurethane topcoat in the marine field, with a design life of 15-20 years.

[0003] With social development, water-based and solvent-free low-VOC anti-corrosion coatings have become a trend. However, regardless of whether it is a traditional solvent-based coating or a new environmentally friendly coating, moisture is a key negative factor affecting its application performance, film quality, and protective durability. Moisture sources are diverse, including high humidity in the application environment, condensation on the substrate surface (such as "sweating" on offshore platforms or morning condensation on bridges), residual moisture inside the substrate, moisture introduced during the coating production process, moisture intrusion during storage and transportation, and infiltration from rainwater, seawater, and industrial wastewater in the service environment. Although this moisture may only exist in the form of a micron-sized water film, it can damage the protective efficacy of anti-corrosion coatings from multiple physical and chemical perspectives, leading to a series of coating defects and failures. Therefore, it is necessary to accurately calculate the moisture content of anti-corrosion coatings.

[0004] Currently, the main methods for measuring the moisture content of anti-corrosion coatings in the industrial field fall into two categories: Karl Fischer titration and gas chromatography. Karl Fischer titration, as a traditional method for moisture determination, detects moisture content based on the quantitative reaction between iodine and water. However, this method is highly selective for sample types; organic solvents and corrosion inhibitors in anti-corrosion coatings can easily contaminate the detection electrode, leading to increased errors in determining the titration endpoint. Furthermore, the method itself has poor parallelism, with relative errors typically exceeding 5%, making it difficult to meet the demands of high-precision detection. Gas chromatography, with its advantages of low instrument requirements, ease of operation, and strong sample compatibility, has become the mainstream technology for moisture detection in anti-corrosion coatings. Its core principle is to calculate the moisture content by separating and detecting the peak areas of water and other components, combined with the response factor. However, existing gas chromatography methods still have significant technical limitations in practical applications. Firstly, commonly used diluents in anti-corrosion coatings (such as esters and hydrocarbons) readily absorb moisture from the air, causing background moisture content to interfere with detection results. Existing methods lack robust logic for subtracting blank interference, making it difficult to accurately offset systematic errors introduced by reagents. Secondly, the instrument's signal response is not strictly linear under different moisture contents. Existing techniques determine a fixed response factor using a single concentration standard solution, which cannot adapt to the wide range of moisture content fluctuations in anti-corrosion coatings (e.g., 0.1%–50%). For samples with low moisture content (<1%) or high moisture content (>30%), the mismatch between the response factor and the actual concentration can significantly increase calculation errors. Furthermore, existing methods rely on operator experience to estimate sample moisture content and determine the amount of internal standard to add, leading to significant subjective errors that further affect the accuracy and repeatability of the detection results. Therefore, when using the industry standard of approximately equal masses of distilled water and internal standard to calculate moisture content, it may cause significant errors in the calculation results for anti-corrosion coatings with low or high moisture content. Summary of the Invention

[0005] This application provides a method for determining the moisture content of anti-corrosion coatings based on gas chromatography, in order to solve the problem that the existing technology of measuring the moisture content in anti-corrosion coatings using gas chromatography is prone to errors, resulting in inaccurate moisture content of the obtained anti-corrosion coatings.

[0006] This application provides a method for determining the moisture content of anti-corrosion coatings based on gas chromatography, the method comprising:

[0007] Water was serially diluted with diluents and brought to a set volume to obtain multiple standard solutions.

[0008] The internal standard was serially diluted with diluent and brought to a set volume to obtain the internal standard solution;

[0009] Take different volumes of each standard solution and place them in volumetric flasks. Add a corresponding amount of the internal standard solution and add the dilution solvent to the target volume according to the preset requirements. After mixing, multiple sets of working solutions are obtained.

[0010] The single-point relative response factor test method was used to perform gas chromatography detection on multiple groups of working solutions to obtain the peak area of ​​water in each group of working solutions. Peak area of ​​internal standard , and the relative response factor R of water;

[0011] Using the peak area ratio of water to internal standard corresponding to each working solution as the abscissa and the corresponding relative response factor R of water as the ordinate, multiple candidate functions are constructed based on a preset function to obtain the fitting curve expression of each candidate function.

[0012] Based on the abscissa data of each working solution, the goodness of fit of the fitting curve expression of each candidate function is calculated, and the candidate function corresponding to the highest goodness of fit is determined as the target function.

[0013] The target data is obtained by measuring the sample to be tested, and the moisture content of the sample to be tested is obtained by substituting the target data into the objective function.

[0014] In some possible implementations, the preset function form includes quadratic functions and logarithmic functions.

[0015] In some possible implementations, the internal standard is isopropanol, and the diluent is N,N-dimethylformamide.

[0016] In some possible implementations, when the objective function is a quadratic function, the function expression is R = a(peak area of ​​water / peak area of ​​isopropanol). 2 +b (peak area of ​​water / peak area of ​​isopropanol) + c;

[0017] When the objective function is a logarithmic function, the function expression is R = aln(peak area of ​​water / peak area of ​​isopropanol) + b; where a, b, and c are all constants.

[0018] In some possible implementations, measuring the sample to be tested to obtain target data, and substituting the target data into the objective function to obtain the moisture content of the sample to be tested, includes:

[0019] The target data is obtained by measuring the sample to be tested, and the target data includes the peak areas of water and isopropanol;

[0020] Substitute the target data into the objective function to determine the first relative response factor;

[0021] The moisture content of the sample to be tested is calculated based on the first formula; the first formula is:

[0022] ;

[0023] This represents the moisture content in the sample. , The mass of isopropanol and the mass of the sample to be tested. , , R× represents the peak area of ​​isopropanol, the peak area of ​​water in the test sample, and the peak area of ​​water in the blank sample, respectively, and R× is the first relative response factor.

[0024] In some possible implementations, determining the candidate function corresponding to the highest goodness-of-fit value as the objective function includes:

[0025] The highest value of the goodness of fit is compared with the preset goodness of fit value;

[0026] When the highest value of the goodness of fit is greater than or equal to the preset goodness of fit value, the candidate function corresponding to the highest value of the goodness of fit is determined as the objective function;

[0027] When the highest value of the goodness of fit is less than the preset goodness of fit value, the sampling amount of water in the standard solution is adjusted, and the relative response factor of water in the standard solution is re-measured.

[0028] Among the possible implementations, the following are also included:

[0029] After substituting the target data into the objective function to obtain the first relative response factor R×, the first relative response factor is then corrected.

[0030] Where the objective function is a quadratic function, after calculating R×, verify ( - ) / Whether the ratio is within the range of the abscissa when fitting the standard solution (i.e., 0.01~0.4, corresponding to the peak area ratio range of water sample amount 0.0100g~0.2000g).

[0031] If it exceeds the range of the horizontal axis, when ( - ) / When >0.4, the corrected first relative response factor value is R××0.98; when ( - ) / When <0.01, the corrected first relative response factor value is adjusted to R××1.02;

[0032] The corrected R× is used for the first formula to calculate the moisture content to compensate for the systematic error in the edge region of the fitting curve.

[0033] In some possible implementation manners, it further includes:

[0034] Calculate the corrected ratio Y of the peak area of water to the internal standard substance of the sample to be measured, where Y = ( - ) / ;

[0035] If Y ≤ 0, it is determined that the blank deduction is abnormal or the moisture content of the sample is lower than the detection lower limit, and the blank sample and the sample to be measured are re-prepared and re-detected;

[0036] If 0 < Y < 0.02 (lower than the minimum abscissa range during the fitting of the standard solution, corresponding to the lower limit of the peak area ratio of the water sampling amount of 0.0100 g), since the absolute value of the slope of the logarithmic function is large and the fitting error is significant when X approaches 0, R is corrected to R×(1 + 0.03×ln(0.02 / X)), where ln(0.02 / X) is the domain compensation coefficient, and the correction amplitude is linearly adjusted with the deviation of X from the fitting lower limit, and the maximum correction amplitude does not exceed 15%, and X is the peak area of water / the peak area of isopropanol.

[0037] In some possible implementation manners, it further includes:

[0038] When the peak area of water in the sample to be measured <2× , it is determined that the moisture content is lower than the detection lower limit, where the detection lower limit is 0.1%;

[0039] When the deviation of the peak area of isopropanol from the average value of the peak area of isopropanol during the detection of the standard solution exceeds ±10%, it is determined that the instrument response is abnormal, and the injection port temperature and carrier gas flow rate of the gas chromatograph are re-calibrated and then detected again;

[0040] When ( - ) is negative, it is determined that the blank deduction is abnormal, and the blank sample and the sample to be measured are re-prepared and then detected.

[0041] In some possible implementation manners,

[0042] If the goodness of fit R 2 ≥0.96 of multiple candidate functions exists, through comparing the sum of squared residuals and combining with the function complexity for screening, the selection principle of the target function is that the priority of the quadratic polynomial function is higher than that of the logarithmic function.

[0043] In some possible implementations, water, internal standard, and dilution solvent are weighed, and solutions are prepared by adjusting the water sampling amount to obtain multiple sets of standard solutions, including:

[0044] The moisture content of the internal standard and diluent is tested to determine whether it is an anhydrous reagent;

[0045] When the internal standard and the diluting solvent are anhydrous reagents, the internal standard and water are weighed in the same sample preparation bottle, wherein the water sampling amount is set with multiple gradients, and the sampling amount ranges from 0.0100g to 0.2000g.

[0046] Record the mass m of water w and the quality of internal standard Add diluent to obtain a mixture, seal the sample bottle and shake well;

[0047] Inject 1 μL of the mixture from the sample vial into the chromatograph and record the chromatogram;

[0048] Calculate the relative response factor R of water for different water sampling amounts using the second formula, where R is the relative response factor of water. , The mass of isopropanol and water, , The peak areas are for isopropanol and water, respectively.

[0049] The second formula is: .

[0050] In some possible implementations, the method of weighing water, internal standard, and dilution solvent, and preparing multiple sets of standard solutions by adjusting the water sampling amount, also includes:

[0051] When the internal standard and the diluent are not anhydrous reagents, weigh the internal standard and water in the same sample preparation bottle, wherein the water sampling amount is set with multiple gradients, and the sampling amount ranges from 0.0100g to 0.2000g.

[0052] Weigh the internal standard and diluent to prepare a blank sample, and record the peak area of ​​water in the blank sample. The blank sample was prepared without water.

[0053] The relative response factor R of water is calculated using the third formula, where R is the relative response factor of water. , For the mass of isopropanol and the mass of water, , These represent the peak areas of isopropanol and water, respectively.

[0054] The third formula is ;

[0055] The test was conducted in parallel twice, and the average of the two test results was taken as the water relative response factor R.

[0056] In some possible implementations, the test conditions for measuring the sample to obtain the target data are as follows:

[0057] The gas chromatograph has an injection port temperature of 160℃ and a detector temperature of 250℃. The chromatographic column is a packed column with an inner diameter of 3mm and a length of 2m. The temperature program is used: the initial column temperature is 70℃, held for 5 min, then increased to 160℃ at a rate of 25℃ / min, held for 5 min, then increased to 200℃ at a rate of 10℃ / min, and held for 10 min. The carrier gas used in the gas chromatography is nitrogen with a purity of ≥99.995%, and a splitless injection method is used with an injection volume of 1.2μL.

[0058] As described above, this application provides a method for determining the moisture content of anti-corrosion coatings based on gas chromatography. Water is serially diluted with a diluent and brought to volume to prepare multiple standard solutions. An internal standard is serially diluted with a diluent and brought to volume to prepare an internal standard solution. Different volumes of each standard solution are placed in volumetric flasks, a quantitative internal standard solution is added, and diluent is added to the target volume and mixed thoroughly to obtain multiple working solutions. The single-point relative response factor test method is used to perform gas chromatography detection on each working solution to obtain the peak area of ​​water, the peak area of ​​the internal standard, and the relative response factor of water. Multiple candidate functions are constructed based on a preset function, with the peak area ratio as the abscissa and the relative response factor as the ordinate, and a fitting curve expression is obtained. The goodness of fit of each candidate function is calculated, and the function with the highest goodness of fit is selected as the objective function. The target data of the sample is measured, and the moisture content is obtained by substituting the data into the objective function. This application optimizes and improves the single-point response factor method in the standard. Through function fitting and calculation methods, the relative response factor that should be used to calculate the moisture content of different test samples can be obtained quickly, thus obtaining accurate sample moisture content and improving the accuracy and reliability of the moisture content test results of anti-corrosion coatings. Detailed Implementation

[0059] With social development, water-based and solvent-free low-VOC anti-corrosion coatings have become a trend. However, regardless of whether it is a traditional solvent-based coating or a new environmentally friendly coating, moisture is a key negative factor affecting its application performance, film quality, and protective durability. Moisture sources are diverse, including high humidity in the application environment, condensation on the substrate surface (such as "sweating" on offshore platforms or morning condensation on bridges), residual moisture inside the substrate, moisture introduced during the coating production process, moisture intrusion during storage and transportation, and infiltration from rainwater, seawater, and industrial wastewater in the service environment. Although this moisture may only exist in the form of a micron-sized water film, it can damage the protective efficacy of anti-corrosion coatings from multiple physical and chemical perspectives, leading to a series of coating defects and failures. Therefore, it is necessary to accurately calculate the moisture content of anti-corrosion coatings.

[0060] Currently, the main methods for measuring the moisture content of anti-corrosion coatings in the industrial field fall into two categories: Karl Fischer titration and gas chromatography. Karl Fischer titration, as a traditional method for moisture determination, detects moisture content based on the quantitative reaction between iodine and water. However, this method is highly selective for sample types; organic solvents and corrosion inhibitors in anti-corrosion coatings can easily contaminate the detection electrode, leading to increased errors in determining the titration endpoint. Furthermore, the method itself has poor parallelism, with relative errors typically exceeding 5%, making it difficult to meet the demands of high-precision detection. Gas chromatography, with its advantages of low instrument requirements, ease of operation, and strong sample compatibility, has become the mainstream technology for moisture detection in anti-corrosion coatings. Its core principle is to calculate the moisture content by separating and detecting the peak areas of water and other components, combined with the response factor. However, existing gas chromatography methods still have significant technical limitations in practical applications. Firstly, commonly used diluents in anti-corrosion coatings (such as esters and hydrocarbons) readily absorb moisture from the air, causing background moisture content to interfere with detection results. Existing methods lack robust logic for subtracting blank interference, making it difficult to accurately offset systematic errors introduced by reagents. Secondly, the instrument's signal response is not strictly linear under different moisture contents. Existing techniques determine a fixed response factor using a single concentration standard solution, which cannot adapt to the wide range of moisture content fluctuations in anti-corrosion coatings (e.g., 0.1%–50%). For samples with low moisture content (<1%) or high moisture content (>30%), the mismatch between the response factor and the actual concentration can significantly increase calculation errors. Furthermore, existing methods rely on operator experience to estimate sample moisture content and determine the amount of internal standard to add, leading to significant subjective errors that further affect the accuracy and repeatability of the detection results. Therefore, when using the industry standard of approximately equal masses of distilled water and internal standard to calculate moisture content, it may cause significant errors in the calculation results for anti-corrosion coatings with low or high moisture content.

[0061] This application provides a method for determining the moisture content of anti-corrosion coatings based on gas chromatography, in order to solve the problem that the existing technology of measuring the moisture content in anti-corrosion coatings using gas chromatography is prone to errors, resulting in inaccurate moisture content of the obtained anti-corrosion coatings.

[0062] Accurate moisture content determination can prevent many problems, such as coating defects, product stability, user experience, and the durability and corrosion resistance of the paint film. The moisture content determination method provided in this application greatly improves the accuracy of moisture content test results, thereby increasing the product's factory qualification rate and avoiding related problems, thus preventing unnecessary losses for users.

[0063] This application provides a method for determining the moisture content of anti-corrosion coatings based on gas chromatography, the method comprising:

[0064] Water was serially diluted with diluents and brought to a set volume to obtain multiple standard solutions.

[0065] The internal standard was serially diluted with diluent and brought to a set volume to obtain the internal standard solution;

[0066] Take different volumes of each standard solution and place them in volumetric flasks. Add a corresponding amount of the internal standard solution and add the dilution solvent to the target volume according to the preset requirements. After mixing, multiple sets of working solutions are obtained.

[0067] The single-point relative response factor test method was used to perform gas chromatography detection on multiple groups of working solutions to obtain the peak area of ​​water in each group of working solutions. Peak area of ​​internal standard , and the relative response factor R of water;

[0068] Using the peak area ratio of water to internal standard corresponding to each working solution as the abscissa and the corresponding relative response factor R of water as the ordinate, multiple candidate functions are constructed based on a preset function to obtain the fitting curve expression of each candidate function.

[0069] Based on the abscissa data of each working solution, the goodness of fit of the fitting curve expression of each candidate function is calculated, and the candidate function corresponding to the highest goodness of fit is determined as the target function.

[0070] The target data is obtained by measuring the sample to be tested, and the moisture content of the sample to be tested is obtained by substituting the target data into the objective function.

[0071] In some embodiments, the preset function form includes quadratic functions and logarithmic functions.

[0072] In some embodiments, the internal standard is isopropanol, and the diluent is N,N-dimethylformamide.

[0073] In some embodiments, when the objective function is a quadratic function, the function expression is R = a (peak area of ​​water / peak area of ​​isopropanol). 2 +b (peak area of ​​water / peak area of ​​isopropanol) + c;

[0074] When the objective function is a logarithmic function, the function expression is R = aln(peak area of ​​water / peak area of ​​isopropanol) + b; where a, b, and c are all constants.

[0075] In some embodiments, measuring the sample to be tested to obtain target data, and substituting the target data into the objective function to obtain the moisture content of the sample to be tested, includes:

[0076] The target data is obtained by measuring the sample to be tested, and the target data includes the peak areas of water and isopropanol;

[0077] Substitute the target data into the objective function to determine the first relative response factor;

[0078] The moisture content of the sample to be tested is calculated based on the first formula; the first formula is:

[0079] ;

[0080] This represents the moisture content in the sample. , The mass of isopropanol and the mass of the sample to be tested. , , R× represents the peak area of ​​isopropanol, the peak area of ​​water in the test sample, and the peak area of ​​water in the blank sample, respectively, and R× is the first relative response factor.

[0081] In some embodiments, determining the candidate function corresponding to the highest goodness-of-fit value as the objective function includes:

[0082] The highest value of the goodness of fit is compared with the preset goodness of fit value;

[0083] When the highest value of the goodness of fit is greater than or equal to the preset goodness of fit value, the candidate function corresponding to the highest value of the goodness of fit is determined as the objective function;

[0084] When the highest value of the goodness of fit is less than the preset goodness of fit value, the sampling amount of water in the standard solution is adjusted, and the relative response factor of water in the standard solution is re-measured.

[0085] In some embodiments, it also includes:

[0086] After substituting the target data into the objective function to obtain the first relative response factor R×, the first relative response factor is then corrected.

[0087] Where the objective function is a quadratic function, after calculating R×, verify ( - ) / Whether the ratio is within the range of the abscissa when fitting the standard solution (i.e., 0.01~0.4, corresponding to the peak area ratio range of water sample amount 0.0100g~0.2000g).

[0088] If it exceeds the range of the horizontal axis, when ( - ) / When >0.4, the corrected first relative response factor value is R××0.98; when ( - ) / When <0.01, the corrected first relative response factor value is adjusted to R××1.02;

[0089] The corrected R× is used in the first formula to calculate the moisture content in order to compensate for systematic errors in the edge region of the fitted curve.

[0090] For example, the mass m of the sample to be tested s =0.2050g, internal standard (isopropanol) mass m i =0.1992g, water peak area of ​​blank sample =9230, the peak area of ​​the water in the sample to be tested, S w =586420, isopropanol peak area S i =628500.

[0091] The calculated peak area correction ratio X≈0.918 (outside the range of 0.01~0.4, and X>0.4).

[0092] Substitute into the quadratic function to find the original relative response factor R ∗ =0.4143×(0.918) 2 -1.9669×0.918+3.12≈0.4143×0.843−1.805+3.12≈0.349−1.805+3.12≈1.664;

[0093] Rcorrected = 1.664 × 0.98 ≈ 1.631; ω w ≈54.92%

[0094] In some embodiments, it also includes:

[0095] Calculate the peak area correction ratio Y of water and internal standard in the sample to be tested, where Y = ( - ) / ;

[0096] If Y ≤ 0, it is determined as blank deduction anomaly or the moisture content of the sample is lower than the detection lower limit. After re-preparing the blank sample and the sample to be measured, re-detection is carried out;

[0097] If 0 < Y < 0.02 (lower than the minimum abscissa range during the fitting of the standard solution, corresponding to the lower limit of the peak area ratio of the water sampling amount of 0.0100 g), since the absolute value of the slope of the logarithmic function is large and the fitting error is significant when X approaches 0, R is corrected to R×(1 + 0.03×ln(0.02 / X)), where ln(0.02 / X) is the domain compensation coefficient, and the correction amplitude is linearly adjusted with the deviation of X from the fitting lower limit, and the maximum correction amplitude does not exceed 15%, and X is the peak area of water / the peak area of isopropanol.

[0098] In some embodiments, it further includes:

[0099] When the peak area of water in the sample to be measured <2× , it is determined that the moisture content is lower than the detection lower limit, where the detection lower limit is 0.1%;

[0100] When the deviation of the peak area of isopropanol from the average value of the peak area of isopropanol during the detection of the standard solution exceeds ±10%, it is determined as instrument response anomaly. After re-calibrating the injection port temperature and carrier gas flow rate of the gas chromatograph, re-detection is carried out;

[0101] When ( - ) is negative, it is determined as blank deduction anomaly. After re-preparing the blank sample and the sample to be measured, detection is carried out.

[0102] In some embodiments,

[0103] If the goodness of fit R of multiple candidate functions 2 ≥0.96, through screening by comparing the sum of squared residuals and combining with the function complexity, the principle for selecting the target function is that the priority of the quadratic polynomial function is higher than that of the logarithmic function.

[0104] In some embodiments, water, internal standard substance and dilution solvent are weighed, and solutions are prepared by adjusting the water sampling amount, and multiple groups of standard solutions are obtained, including:

[0105] Detect the moisture content of the internal standard substance and the dilution solvent to determine whether they are anhydrous reagents;

[0106] When the internal standard and the diluting solvent are anhydrous reagents, the internal standard and water are weighed in the same sample preparation bottle, wherein the water sampling amount is set with multiple gradients, and the sampling amount ranges from 0.0100g to 0.2000g.

[0107] Record water quality and the quality of internal standard Add diluent to obtain a mixture, seal the sample bottle and shake well;

[0108] Inject 1 μL of the mixture from the sample vial into the chromatograph and record the chromatogram;

[0109] Calculate the relative response factor R of water for different water sampling amounts using the second formula, where R is the relative response factor of water. , The mass of isopropanol and water, , The peak areas are for isopropanol and water, respectively.

[0110] The second formula is: .

[0111] In some embodiments, the process of weighing water, internal standard, and dilution solvent, and preparing solutions by adjusting the water sampling amount to obtain multiple sets of standard solutions, further includes:

[0112] When the internal standard and the diluent are not anhydrous reagents, weigh the internal standard and water in the same sample preparation bottle, wherein the water sampling amount is set with multiple gradients, and the sampling amount ranges from 0.0100g to 0.2000g.

[0113] Weigh the internal standard and dilution solution to prepare a blank sample, and record the peak area of ​​water in the blank sample. In this blank sample, no water was added;

[0114] The relative response factor R of water is calculated using the third formula, where R is the relative response factor of water. , For the mass of isopropanol and the mass of water, , These represent the peak areas of isopropanol and water, respectively.

[0115] The third formula is ;

[0116] The test was conducted in parallel twice, and the average of the two test results was taken as the water relative response factor R.

[0117] In some embodiments, the test conditions for obtaining target data by measuring the sample to be tested are as follows:

[0118] The gas chromatograph has an injection port temperature of 160℃ and a detector temperature of 250℃. The chromatographic column is a packed column with an inner diameter of 3mm and a length of 2m. The temperature program is used: the initial column temperature is 70℃, held for 5 min, then increased to 160℃ at a rate of 25℃ / min, held for 5 min, then increased to 200℃ at a rate of 10℃ / min, and held for 10 min. The carrier gas used in the gas chromatography is nitrogen with a purity of ≥99.995%, and a splitless injection method is used with an injection volume of 1.2μL.

[0119] The steps for re-measuring the relative response factors of water under multiple gradients are as follows:

[0120] (1) Check the instrument status and adjust the instrument parameters. Ensure that the instrument's sensitivity, baseline stability and other indicators are normal. Check whether the chromatographic column is aging, and replace the chromatographic column if necessary.

[0121] (2) Increase the number of repeated measurements. Perform multiple measurements (e.g., 3 or more) for each concentration gradient solution and take the average value to reduce random error.

[0122] (3) Prepare multiple standard solutions. Prepare a series of standard solutions with different concentrations, usually 10-15 concentration gradients, to cover different concentration ranges of moisture content in the anti-corrosion coating.

[0123] In some embodiments, the goodness of fit is a preset value, which is greater than or equal to 0.96.

[0124] According to Appendix A of GB 18582-2020, the gas chromatography method for determining moisture content requires testing the relative response factor R of water with only 0.2 g of water and approximately 0.2 g of internal standard. This relative response factor can be obtained using a calculation function, correcting the point-to-point response factor calculated by the single-point method. Furthermore, in the gas chromatography method for determining moisture content in GB 18582-2020, the mass of the internal standard needs to be close to the mass of moisture in the sample, requiring extensive experience to ensure minimal deviation from visual estimation results. However, the optimized gas chromatography method for determining the moisture content of anti-corrosion coatings provided in this application eliminates the need for visual estimation of sample moisture content, thus avoiding errors caused by insufficient experience in visual estimation.

[0125] This application optimizes and improves the single-point response factor method in the standard. Through function fitting and calculation methods, the relative response factor that should be used to calculate the moisture content of different anti-corrosion coating samples can be obtained quickly, thus obtaining accurate sample moisture content and improving the accuracy and reliability of anti-corrosion coating test results. Example

[0126] In this embodiment, the water used is distilled water from the laboratory. The anti-corrosion coating in this embodiment is an epoxy resin coating.

[0127] In this embodiment, the gas chromatography conditions were as follows: gas chromatograph injection port temperature was 160℃, detector temperature was 250℃, and the chromatographic column was a packed column with an inner diameter of 3mm and a length of 2m. A programmed temperature ramp was used: initial column temperature was 70℃, held for 5 min, then increased to 160℃ at a rate of 25℃ / min, held for 5 min, then increased to 200℃ at a rate of 10℃ / min, and held for 10 min. The carrier gas used in the gas chromatography was nitrogen with a purity ≥99.995%. A splitless injection method was used, with an injection volume of 1.2 μL.

[0128] 1. Test the relative response factor R of water under different gradients.

[0129] Weigh approximately 0.2 g of the internal standard and different masses of distilled water into the same sample bottle. Set up a series of gradients for the distilled water mass (no fewer than 10 groups). The sample size ranges from 0.0100 g to 0.2100 g, accurate to 0.1 mg. Record the mass m of the water. w and the mass m of the internal standard i Add 5 mL of diluent, seal the sample vial, and shake well. Use a microsyringe to inject 1 μL of the mixture from the sample vial into the chromatograph and record the chromatogram. Calculate the relative response factor R of water for different distilled water sample volumes using the second formula, where... , The mass of isopropanol and water, , The peak areas are for isopropanol and water.

[0130] The second formula is: ;

[0131] If the internal standard and diluent are not anhydrous reagents, use the same amount of internal standard and diluent (mixture) but without water as a blank sample, and record the peak area of ​​water in the blank sample. The relative response factor R of water is calculated using the third formula, where R is the relative response factor of water. , The mass of isopropanol and water, , The peak areas are for isopropanol and water.

[0132] The third formula is: ;

[0133] Perform two parallel tests and take the average of the two results; the relative deviation should be less than 5%. Record the peak areas of distilled water and isopropanol for different sample sizes. , And the corresponding water relative response factor R.

[0134] In this embodiment, 13 sets of experiments were set up according to a certain gradient. The relative response factors of water under different gradients were calculated according to the single-point relative response factor test method, as shown in Table 1. Table 1 is calculated based on the second formula in the anhydrous reagent scenario.

[0135] Table 1. Multi-point relative response factors

[0136]

[0137] 2. Data Fitting Relative Response Factor Calculation Function

[0138] Based on 13 sets of peak areas and their corresponding relative response factors for distilled water and isopropanol, the peak area ratio of distilled water to isopropanol (peak area of ​​water / peak area of ​​isopropanol) was plotted on the x-axis, and the relative response factor (R) was plotted on the y-axis. Two functional forms were determined: a quadratic function and a logarithmic function. Substituting these values ​​into the 13 sets of data, the corresponding fitted curve expressions were solved. The two fitted curve expressions and their corresponding goodness-of-fit r are presented. 2 As shown in Table 2. Based on the function's variation pattern and the goodness-of-fit r... 2 A quadratic function was chosen as the best-fit curve.

[0139] Table 2. Expressions of the fitted curves and their goodness of fit

[0140]

[0141] 3. Analysis of the sample to be tested

[0142] Weigh approximately 0.2 g of the thoroughly mixed sample and 0.2 g of the internal standard into a sample preparation bottle, accurate to 0.1 mg, and record the mass m of the sample. s The mass m of the internal standard i Seal the sample vial and shake well. Prepare an internal standard without the sample as a blank. Vigorously shake or sonicate the sample vial containing the sample for 15 minutes, then let it stand for 5 minutes to allow precipitation. To expedite precipitation, a few small glass beads can be added to the sample vial before vigorous shaking; alternatively, a low-speed centrifuge can be used to induce precipitation. Using a microsyringe, aspirate 1 μL of the supernatant from the sample vial and inject it into the chromatograph. Record the chromatogram.

[0143] 4. Determining the moisture content of the sample to be tested.

[0144] By substituting the peak areas of distilled water and isopropanol obtained from the instrumental analysis using the quadratic function R=f(peak area of ​​water / peak area of ​​isopropanol),... , This allows us to determine the relative response factor R to be used when calculating the moisture content of the sample. Then, we calculate the moisture content of the sample using the first formula. ,in This represents the moisture content in the sample. , The mass of isopropanol and the sample. , , denoted as , where is the peak area of ​​isopropanol, water in the sample, and water in the blank sample, and R is the relative response factor of water.

[0145] The first formula is: .

[0146] For example: Take 0.2018g of anti-corrosion coating sample and 0.1988g of internal standard isopropanol. After chromatographic analysis, the water peak area in the reagent blank is 8870, the water peak area in the sample is 317430, subtracting the reagent blank (308560), the isopropanol peak area is 385700. Substituting these values ​​into a quadratic function fitting curve, the relative response factor R is obtained as 1.81. Calculated using the first formula, the moisture content is 43.55%.

[0147] Meanwhile, to verify that the optimized gas chromatography method for determining the moisture content of anticorrosive coatings provided in this application is more accurate than the existing single-point correction factor method for testing moisture content, the moisture content calculated by the optimized gas chromatography method for determining the moisture content of anticorrosive coatings provided in this application is compared with that calculated by the single-point correction factor method. In the optimized gas chromatography method for determining the moisture content of anticorrosive coatings, the objective function is a quadratic function, which will be referred to as the quadratic function calculation method below.

[0148] The moisture content of 20 anti-corrosion coating samples was calculated using the quadratic function method and the single-point correction factor method, and compared with the actual moisture content of the samples, as shown in Table 3. The absolute error between the moisture content calculated by the quadratic function method and the actual moisture content of the samples was -2.88% to -0.44%, indicating that the moisture content calculated by this method was lower than the actual value of the samples. The absolute error between the moisture content calculated by the single-point relative response factor method and the true value was 0.80% to 4.26%, with 95% of the samples having calculated moisture content values ​​higher than the actual values. Among these, the relative error between the calculated and actual values ​​for 20 samples ranged from 2.52% to 19.00%, with 11 samples having a relative error between 0.4% and 8.9%, 1 sample having a relative error between 8.9% and 10%, and 8 samples having a relative error exceeding 10%.

[0149] Table 3 Comparison of actual moisture content values ​​with those calculated using the quadratic function method and the single-point correction factor method

[0150]

[0151] The test methods provided in the above embodiments are applicable to anti-corrosion coating samples from different manufacturers and batches. However, due to factors such as instrument stability, it is necessary to periodically test and correct the multi-point response factor to calibrate the objective function. The objective function needs to be recalibrated in the following situations:

[0152] (1) If the objective function has been used for too long, the multi-point response factors should be tested regularly, the relative response factors corresponding to a certain moisture content should be re-measured, and their values ​​should be checked to see if they have changed significantly.

[0153] (2) Changes in instrument conditions, such as changing the chromatographic column or temperature program. The instrument status should be checked regularly to ensure consistency of instrument conditions.

[0154] (3) The analytical range exceeds the objective function range. It is necessary to prepare a new standard solution to test the response factor at multiple points and expand the objective function range. Alternatively, the sample size can be increased or decreased to ensure that the ratio of the water content to the internal standard peak area is within the objective function range.

[0155] In summary, compared with the single-point correction factor method, the quadratic function method can more accurately and quickly reflect the VOC content in anti-corrosion coatings, which helps to reduce the negative environmental impact of anti-corrosion coatings during production and use.

[0156] As described in the above embodiments, this application provides a method for determining the moisture content of anti-corrosion coatings based on gas chromatography. Water is serially diluted with a diluent and brought to volume to prepare multiple standard solutions. An internal standard is serially diluted with a diluent and brought to volume to prepare an internal standard solution. Different volumes of each standard solution are placed in volumetric flasks, a quantitative internal standard solution is added, and diluent is added to the target volume to obtain multiple working solutions. The single-point relative response factor test method is used to perform gas chromatography detection on each working solution to obtain the peak area of ​​water, the peak area of ​​the internal standard, and the relative response factor of water. Multiple candidate functions are constructed based on a preset function, with the peak area ratio as the abscissa and the relative response factor as the ordinate, and a fitting curve expression is obtained. The goodness of fit of each candidate function is calculated, and the function with the highest goodness of fit is selected as the objective function. The target data of the sample is measured, and the moisture content is obtained by substituting it into the objective function. This application improves the accuracy of moisture content testing results.

[0157] Similar parts between the embodiments provided in this application can be referred to mutually. The specific implementation methods provided above are only a few examples under the overall concept of this application and do not constitute a limitation on the scope of protection of this application. For those skilled in the art, any other implementation methods extended from the solution of this application without creative effort shall fall within the scope of protection of this application.

Claims

1. A method for determining the moisture content of anti-corrosion coatings based on gas chromatography, characterized in that, The method includes: Water was serially diluted with diluents and brought to a set volume to obtain multiple standard solutions. The internal standard was serially diluted with diluent and brought to a set volume to obtain the internal standard solution; Take different volumes of each standard solution and place them in volumetric flasks. Add a corresponding amount of the internal standard solution and add the dilution solvent to the target volume according to the preset requirements. After mixing, multiple sets of working solutions are obtained. The single-point relative response factor test method was used to perform gas chromatography detection on multiple groups of working solutions to obtain the peak area of ​​water in each group of working solutions. Peak area of ​​internal standard , and the relative response factor R of water; Using the peak area ratio of water to internal standard corresponding to each working solution as the abscissa and the corresponding relative response factor R of water as the ordinate, multiple candidate functions are constructed based on a preset function to obtain the fitting curve expression of each candidate function. Based on the abscissa data of each working solution, the goodness of fit of the fitting curve expression of each candidate function is calculated, and the candidate function corresponding to the highest goodness of fit is determined as the target function. The target data is obtained by measuring the sample to be tested, and the moisture content of the sample to be tested is obtained by substituting the target data into the objective function.

2. The method for determining the moisture content of anti-corrosion coatings based on gas chromatography according to claim 1, characterized in that, The preset function forms include quadratic functions and logarithmic functions.

3. The method for determining the moisture content of anti-corrosion coatings based on gas chromatography according to claim 2, characterized in that, The internal standard is isopropanol, and the diluent is N,N-dimethylformamide.

4. The method for determining the moisture content of anti-corrosion coatings based on gas chromatography according to claim 3, characterized in that, When the objective function is a quadratic function, the function expression is R = a (peak area of ​​water / peak area of ​​isopropanol). 2 +b (peak area of ​​water / peak area of ​​isopropanol) + c; When the objective function is a logarithmic function, the function expression is R = aln(peak area of ​​water / peak area of ​​isopropanol) + b; where a, b, and c are all constants.

5. The method for determining the moisture content of anti-corrosion coatings based on gas chromatography according to claim 4, characterized in that, The process of measuring the sample to be tested to obtain target data, and substituting the target data into the objective function to obtain the moisture content of the sample to be tested, includes: The target data is obtained by measuring the sample to be tested, and the target data includes the peak areas of water and isopropanol; Substitute the target data into the objective function to determine the first relative response factor; The moisture content of the sample to be tested is calculated based on the first formula; the first formula is: ； This represents the moisture content in the sample. , The mass of isopropanol and the mass of the sample to be tested. , , R× represents the peak area of ​​isopropanol, the peak area of ​​water in the test sample, and the peak area of ​​water in the blank sample, respectively, and R× is the first relative response factor.

6. The method for determining the moisture content of anti-corrosion coatings based on gas chromatography according to claim 5, characterized in that, Determining the candidate function corresponding to the highest goodness-of-fit value as the objective function includes: The highest value of the goodness of fit is compared with the preset goodness of fit value; When the highest value of the goodness of fit is greater than or equal to the preset goodness of fit value, the candidate function corresponding to the highest value of the goodness of fit is determined as the objective function; When the highest value of the goodness of fit is less than the preset goodness of fit value, the sampling amount of water in the standard solution is adjusted, and the relative response factor of water in the standard solution is re-measured.

7. The method for determining the moisture content of anti-corrosion coatings based on gas chromatography according to claim 6, characterized in that, Also includes: After substituting the target data into the objective function to obtain the first relative response factor R×, the first relative response factor is then corrected. Where the objective function is a quadratic function, after calculating R×, verify ( - ) / Is the ratio between 0.01 and 0.4? If it exceeds the range of the horizontal axis, when ( - ) / When >0.4, the corrected first relative response factor value is R××0.98; when ( - ) / When <0.01, the corrected first relative response factor value is adjusted to R××1.02; The corrected R× is used in the first formula to calculate the moisture content in order to compensate for systematic errors in the edge region of the fitted curve.

8. The method for determining the moisture content of anti-corrosion coatings based on gas chromatography according to claim 7, characterized in that, Also includes: Calculate the peak area correction ratio Y of water and internal standard in the sample to be tested, where Y = ( - ) / ; If Y ≤ 0, it is determined to be an abnormal blank subtraction or the sample moisture content is lower than the detection limit. The blank sample and the sample to be tested are prepared again and tested again. If 0 < Y < 0.02, correct R to R×(1 + 0.03×ln (0.02 / X)), where X is the peak area of ​​water / peak area of ​​isopropanol.

9. The method for determining the moisture content of anti-corrosion coatings based on gas chromatography according to claim 1, characterized in that, Also includes: When the peak area of ​​water in the sample to be tested <2× When the moisture content is below the detection limit, it is determined to be 0.1%; When the peak area of ​​isopropanol If the deviation of the average peak area of ​​isopropanol from that of the standard solution exceeds ±10%, it is determined to be an abnormal instrument response. The gas chromatograph should be recalibrated for the injection port temperature and carrier gas flow rate before detection. when( - When the value is negative, it is determined to be an abnormal blank subtraction, and the blank sample and the sample to be tested are re-prepared and then tested.

10. The method for determining the moisture content of anti-corrosion coatings based on gas chromatography according to claim 1, characterized in that, If there are multiple candidate functions, the goodness-of-fit R 2 ≥0.96, by comparing the sum of squared residuals and the function complexity, the objective function selection principle is that quadratic polynomial functions have higher priority than logarithmic functions.

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