Methods for detecting byproducts in cross-linked polyethylene cable insulation

Abstract

This invention belongs to the field of cable testing technology, specifically relating to a method for detecting by-products in the insulation layer of cross-linked polyethylene cables. Before dilution, a predetermined ratio of n-hexane and isopropanol is added, combined with ultrasonic elution and filtration separation under low-temperature conditions. The strong polarity of isopropanol dissolves small-molecule by-products, while n-hexane promotes polyethylene swelling. Simultaneously, low-temperature ultrasound synergistically reduces viscosity, achieving complete extraction of by-products such as cumyl alcohol at low temperatures, which improves the detection accuracy of the corresponding by-products. Furthermore, the use of ionic liquid injection enhances ionization, thereby increasing the charge on the supernatant and its activity, making the by-products more active during detection and thus improving detection sensitivity.

Description

Technical Field

[0001] This invention belongs to the field of cable testing technology, specifically relating to a method for detecting byproducts in the insulation layer of cross-linked polyethylene cables. Background Technology

[0002] Cross-linked polyethylene (XLPE) cables generate polar or small molecule compounds such as cumyl alcohol, acetophenone, and α-methylstyrene during production. Unlike AC cables, these residues continuously create charge traps and accumulate space charge during the operation of high-voltage DC cables, significantly affecting the cable's electrical performance and long-term operational safety. Therefore, their content needs to be controlled through a degassing process, and they must be tested after the degassing process is completed.

[0003] Traditional detection methods include the following:

[0004] 1. Gas chromatography-mass spectrometry (GC-MS) can achieve quantitative analysis, but substances such as cumyl alcohol, acetophenone, and α-methylstyrene have high boiling points and can destroy the original component system inside the sample during volatilization, leading to inaccurate test results.

[0005] 2. Fourier transform infrared spectroscopy: This method is simple to operate, but it can only measure the total content of by-products and cannot achieve accurate quantitative analysis of single components.

[0006] 3. Thermogravimetric analysis: This method can only estimate the total content by weight difference, and cannot meet the need for accurate quantitative detection of a single component;

[0007] 4. The conventional C18 column combined with an acetonitrile-water system liquid chromatograph and photodiode array detector method can avoid the disadvantages of the above three methods, but it is difficult to completely extract the target substance at a low temperature. In addition, due to the similarity in molecular structure and molecular weight between cumyl alcohol and acetophenone, traditional methods are difficult to separate the two and cannot accurately quantify all individual components.

[0008] Therefore, there is an urgent need for a new detection method that can overcome the shortcomings of existing technologies and perform highly sensitive and accurate quantitative analysis of byproducts such as cumyl alcohol, acetophenone, and α-methylstyrene in the insulation layer of cross-linked polyethylene cables, providing a basis for optimizing the cable degassing process.

[0009] It should be noted that this part of the present invention only provides background technology related to the present invention, and does not necessarily constitute prior art or known technology. Summary of the Invention

[0010] The purpose of this invention is to provide a method for detecting cross-linked polyethylene cable insulation byproducts that allows for more accurate and sensitive quantitative analysis.

[0011] To achieve the above objectives, the present invention provides a method for detecting by-products in the insulation layer of cross-linked polyethylene cables, comprising:

[0012] S100: Take a preset area of ​​the cross-linked polyethylene cable insulation layer to be tested as a sample;

[0013] S200: Using hexane and isopropanol in a ratio of (0.5~2):1 as solvent, the sample is ultrasonically eluted at 40~60℃ for a preset time, and the filtrate is obtained after filtering out solid impurities;

[0014] S300: Dilute the filtrate with a mixture of acetonitrile and water, and add 0.4~0.6 wt% of the diluted mixture. The solution was mixed, allowed to stand, and the supernatant was extracted.

[0015] S400: The extracted supernatant is eluted and separated by an attached electrostatic chromatographic column.

[0016] S500: Set the detection wavelength for different byproducts;

[0017] S600: Quantitative analysis yields the mass concentration of different byproducts.

[0018] In one possible embodiment, in S100, a predetermined area of ​​the cross-linked polyethylene cable insulation layer to be tested is taken as a sample, specifically including:

[0019] S110: Freeze the cross-linked polyethylene cable to be tested at -35~-45℃;

[0020] S120: After removing the conductor, cut the cross-linked polyethylene cable to be tested radially;

[0021] S130: Cut a layered rectangular section along the radial direction to obtain samples with different gradients of cross-linked byproducts at different positions within the insulation layer;

[0022] S140: After freezing the sample with liquid nitrogen for a preset time, place it in an ultracentrifuge grinder for grinding and sieving.

[0023] In one possible embodiment, in step S200, the ratio of n-hexane to isopropanol is 1:1, the ultrasonic elution temperature is 50°C, and the preset elution time is 50~70 min.

[0024] In one possible embodiment, in step S300, the ratio of acetonitrile to water in the mixture of acetonitrile and water is (1~4):2.

[0025] In one possible embodiment, in step S400, when the extracted supernatant is eluted with an attached gradient using a charged surface chromatographic column, multiple elution mixtures with different acetonitrile-water ratios are used for multi-gradient elution, so that the supernatant flows sequentially through multiple elution mixtures with different acetonitrile-water ratios to elute and separate different byproducts.

[0026] In one possible embodiment, the multi-gradient elution includes a first gradient elution and a second gradient elution, wherein the acetonitrile-water ratio of the first gradient elution is 35:65, and the acetonitrile content of the second gradient elution is 100%.

[0027] In one possible embodiment, the multigradient elution further includes a third gradient elution, wherein the acetonitrile-water ratio of the third gradient elution is 35:65.

[0028] In one possible embodiment, in step S400, the column temperature of the chromatographic column is 30~40°C.

[0029] In one possible embodiment, in step S400, the first mobile phase of the chromatographic column is an aqueous solution of 0.08% to 0.12% formic acid with a pH of 2.5 to 3; the second mobile phase of the chromatographic column is acetonitrile containing 0.08% to 0.12% formic acid.

[0030] In one possible embodiment, in step S500, the detection wavelength of cumyl alcohol in the byproducts is set to 210 nm, and the detection wavelength of acetophenone and α-methylstyrene is set to 245 nm.

[0031] The present invention has at least the following beneficial effects:

[0032] The present invention provides a method for detecting by-products in cross-linked polyethylene cable insulation. This method utilizes the strong polarity of isopropanol to dissolve small-molecule by-products and promotes polyethylene swelling with n-hexane. Simultaneously, low-temperature ultrasound is used to synergistically reduce viscosity, achieving complete extraction of by-products such as cumyl alcohol at low temperatures. This improves the detection accuracy of the corresponding by-products. Furthermore, the use of ionic liquid injection enhances ionization, thereby increasing the charge on the supernatant and its activity. This promotes greater activity of the by-products during detection, ultimately improving detection sensitivity.

[0033] Furthermore, this invention employs multi-gradient elution, which achieves complete separation of three types of byproducts by precisely controlling the elution intensity and avoiding cross-contamination. Combined with the gradient elution time window, it enables simultaneous and accurate quantification of different byproduct components.

[0034] Furthermore, by employing low-temperature freezing combined with liquid nitrogen rapid freezing, the volatilization of by-products can be significantly suppressed. And through radial layering and rectangular die stamping, the gradient distribution analysis of by-products within the insulation layer was achieved for the first time, providing spatial distribution data for optimizing the degassing process. Moreover, ultracentrifugal grinding and sieving after liquid nitrogen freezing better ensure the sufficiency and uniformity of sample grinding, avoiding uneven particle size due to the inherent toughness of the insulation layer. Subsequently, during the melting process, the uniformity of solute distribution after melting is better ensured, reducing errors in subsequent detection and guaranteeing accuracy.

[0035] Furthermore, by setting different detection wavelengths for different by-products, it is possible to achieve graded detection of different by-products, which is beneficial to improving the detection accuracy of different by-products. Attached Figure Description

[0036] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0037] Figure 1 This is a flowchart of a method for detecting byproducts in the insulation layer of cross-linked polyethylene cables provided in an embodiment of the present invention;

[0038] Figure 2 This is a schematic diagram of the specific process of step S100 provided in the embodiment of the present invention;

[0039] Figure 3 This is a chromatographic diagram of the detection of byproducts in the insulation layer of cross-linked polyethylene cables using the detection method of this invention.

[0040] Figure 4 This is a chromatographic diagram of the detection of byproducts in the insulation layer of cross-linked polyethylene cables using existing technical methods. Detailed Implementation

[0041] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless specifically defined as herein.

[0043] It should be further understood that the term "comprising" as used in this specification means the presence of the stated features, integers, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. The term "and / or" as used herein includes all or any unit and all combinations of one or more associated listed items.

[0044] like Figure 1 As shown, this embodiment of the invention provides a method for detecting by-products in the insulation layer of cross-linked polyethylene cables, comprising:

[0045] S100: Take a preset area of ​​the cross-linked polyethylene cable insulation layer to be tested as a sample.

[0046] Optionally, such as Figure 2 As shown, the specific steps involved in creating a sample image include:

[0047] S110: Freeze the cross-linked polyethylene cable to be tested at -35~-45℃.

[0048] Specifically, by using -40℃ freezing combined with liquid nitrogen quick-freezing, the volatilization of by-products can be significantly suppressed. It is necessary to use aluminum foil to wrap the sample to further reduce material loss.

[0049] S120: After removing the conductor, the cross-linked polyethylene cable to be tested is cut into radial slices, with a slice thickness of 2mm.

[0050] S130: Cut a layered rectangular section along the radial direction to obtain samples with different gradients of cross-linking byproducts at different positions within the insulation layer.

[0051] Specifically, rectangular molds are used to stamp and cut layered rectangular cross-section samples along the radial direction to obtain samples of cross-linking byproducts at different locations within the cable. Specifically, rectangular areas of the outer layer (near the metal shielding layer), middle layer, and inner layer (near the conductive layer) of the insulation layer are taken as samples for subsequent testing.

[0052] By using radial layering and rectangular die stamping, the gradient distribution analysis of by-products within the insulation layer was achieved for the first time, providing spatial distribution data for optimizing the degassing process.

[0053] S140: After freezing the sample with liquid nitrogen for a preset time, place it in an ultracentrifuge grinder for grinding and sieving.

[0054] Specifically, the sample was frozen with liquid nitrogen for 1 minute. After freezing, it was then placed in an ultracentrifuge for grinding and sieving to increase the surface area of ​​the sample and further improve the extraction recovery rate.

[0055] In this embodiment, ultracentrifugal grinding and sieving after liquid nitrogen freezing can better ensure the sufficiency and uniformity of sample grinding, avoiding the situation where the grinding particles are of different sizes due to the toughness of the insulation layer itself. Then, during the melting process of S200, the uniformity of solute distribution after melting can be better ensured, thereby reducing the error of subsequent detection and ensuring the accuracy of detection.

[0056] S200: Using hexane and isopropanol in a ratio of (0.5~2):1 as solvents, the sample is ultrasonically eluted at 40~60℃ for a preset time, and the filtrate is obtained after filtering out solid impurities.

[0057] The inventors discovered that by using a mixed solvent of n-hexane and isopropanol in a ratio of (0.5~2):1 as the elution solvent for the insulating layer, the strong polarity of isopropanol can dissolve small molecule byproducts, while n-hexane promotes the swelling of polyethylene. Simultaneously, combined with low-temperature ultrasound, viscosity is reduced, achieving complete extraction of byproducts such as cumyl alcohol at low temperatures. However, if the ratio is too high, the solubility of cumyl alcohol and acetophenone will be insufficient, potentially leading to stratification; if the ratio is too low, α-methylstyrene will be insufficiently extracted. The preferred ratio of n-hexane to isopropanol is 1:1.

[0058] Optionally, the ultrasonic elution temperature is 50°C, and the preset elution time is 50-70 min (preferably 60 min). However, excessively high ultrasonic elution temperatures can lead to further conversion of cumyl alcohol to α-methylstyrene, resulting in distorted results; excessively low temperatures can lead to incomplete elution; excessively long elution times can lead to the conversion of acetophenone to methane, resulting in distorted results and increasing the risk of headspace leakage; and excessively short elution times can lead to incomplete elution.

[0059] Specifically, a vacuum filtration device is used to filter the solution after ultrasonic elution (the ultrasonically eluted sample is ground particulate matter), mainly filtering out solid impurities after ultrasonic breakup, thereby obtaining a filtrate with higher purity, which is beneficial to improving the final detection results.

[0060] S300: Dilute the filtrate with a mixture of acetonitrile and water, and add 0.4~0.6 wt% of the diluted mixture. The solution was mixed, allowed to stand, and the supernatant was extracted.

[0061] The inventors discovered that the main material and byproducts of the insulating layer are both insulating materials, lacking conductivity, making it difficult to perform charged surface mixing technology using charge loading. This was addressed by injecting 0.4~0.6wt% of an ionic liquid (…). This can enhance the ionization of cumyl alcohol and acetophenone, increase the charge of the supernatant, and thus improve its activity, making the byproducts more active during detection and improving detection sensitivity. However, if the injected concentration is too high, it can lead to… The cations form strong ion pairs with the silanol groups (-SiOH) of the C18 bonded silica gel, which damage the hydrophobic layer of the chromatographic column and are difficult to clean. If the injection concentration is too low, the effect will be not obvious.

[0062] Optionally, the ratio of acetonitrile to water in the mixture of acetonitrile and water is (1~4):2, preferably 3:2. If the ratio is too high, it will lead to weakened polarity and precipitation of α-methylstyrene; if the ratio is too low, it will lead to excessive polarity and precipitation of cumyl alcohol. Preferably, The solution has a mass percentage of 0.5 wt%, and the mixing and standing time is 8-12 min, preferably 10 min.

[0063] S400: The extracted supernatant is eluted and separated by an attached electrostatic chromatographic column.

[0064] Specifically, when using a charged surface chromatographic column (the chromatographic column model used in this embodiment is CSH C18) to perform gradient elution separation of the extracted supernatant, multiple elution mixtures with different acetonitrile-water ratios are used for multi-gradient elution, so that the supernatant flows sequentially through multiple elution mixtures with different acetonitrile-water ratios to elute and separate different by-products.

[0065] The injection of ionic liquid into the extracted supernatant allows the anions and cations in the supernatant to form weak coordination bonds with the byproducts, enhancing molecular polarity. During chromatographic separation, the ionic liquid acts as a "charge carrier," amplifying the electrostatic difference between cumyl alcohol and acetophenone, further improving the separation and detection sensitivity.

[0066] Optionally, the multi-gradient elution includes a first gradient elution and a second gradient elution. The acetonitrile-water ratio in the first gradient elution is 35:65, and the acetonitrile ratio in the second gradient elution is 100%. Through this improvement, the acetonitrile-water ratio in the first gradient elution is set to achieve the elution separation of cumyl alcohol and acetophenone. If the ratio is too high, the separation degree between cumyl alcohol and acetophenone will decrease, and the quantitative accuracy will decrease. If the ratio is too low, the peak tailing phenomenon will be aggravated, and the quantitative accuracy will decrease. The acetonitrile-water ratio in the second gradient elution is set to achieve the elution separation of α-methylstyrene. If the ratio is too low, the efficiency will be low, and the peak time of α-methylstyrene will be severely delayed.

[0067] Optionally, in addition to the first and second gradient elutions, the multi-gradient elution also includes a third gradient elution, wherein the acetonitrile-water ratio in the first gradient elution is 35:65, the acetonitrile ratio in the second gradient elution is 100%, and the acetonitrile-water ratio in the third gradient elution is 35:65.

[0068] It should be noted that after eluting and separating cumyl alcohol, acetophenone, and α-methylstyrene, other byproducts will remain. To prevent these byproducts from depositing in the copper tubes used for elution, a third-gradient elution with an acetonitrile-water ratio is used to completely remove the remaining substances, thus avoiding any impact on the results of subsequent tests. However, if the third-gradient elution uses an acetonitrile-water ratio of 100:0, its versatility in removing substances is poor, and the remaining substances will not be completely removed. Therefore, an acetonitrile-water ratio of 35:65 is used. A ratio that is too high will reduce the cleaning efficiency, while a ratio that is too low will affect the baseline balance of the next sample.

[0069] This embodiment employs a three-stage gradient elution method. By precisely controlling the elution intensity, complete separation of three types of byproducts is achieved. Furthermore, the third gradient avoids cross-contamination. Combined with the gradient elution time window, simultaneous and accurate quantification of different byproduct components is realized. Table 1 below illustrates the parameters of the multi-gradient elution:

[0070] Table 1 Comparison of Multigradient Elution Parameters

[0071]

[0072] Optionally, the column temperature of the chromatographic column is 30~40℃, which is beneficial to optimize mass transfer, reduce peak tailing, and thus improve the detection accuracy of the chromatograph.

[0073] Optionally, the first mobile phase of the chromatographic column is an aqueous solution of 0.08%~0.12% formic acid (preferably 0.1% formic acid) with a pH of 2.5~3 (preferably pH 2.8) to protonate cumyl alcohol and enhance electrostatic repulsion. The pH is controlled at 2.5~3 to improve resolution. If the pH is too low, it will damage the chromatographic column, and if the pH is too high, it will significantly reduce the resolution. The second mobile phase of the chromatographic column is acetonitrile containing 0.08%~0.12% formic acid (preferably 0.1% formic acid), which helps maintain an acidic environment and avoid hydrophobic collapse. In addition, the acidic environment can inhibit the adsorption of silanol groups, and the gradient elution can shorten the mass transfer path, which is beneficial to improving peak symmetry.

[0074] Optionally, 0.1% formic acid can be added to various elution mixtures with different acetonitrile-water ratios. The addition of formic acid can alleviate the problem of peak tailing during detection and analysis, especially when the detection waveforms of cumyl alcohol and acetophenone are similar, as peak tailing can easily cause interference in the analysis and is beneficial to improving the detection accuracy of by-products.

[0075] S500: Set the detection wavelength corresponding to different by-products to detect a variety of by-products.

[0076] Optionally, in step S500, the detection wavelength of cumyl alcohol is set to 210 nm, and the detection wavelength of acetophenone and α-methylstyrene is set to 245 nm. That is, the contents of cumyl alcohol, acetophenone and α-methylstyrene can be detected at a detection wavelength of 210 nm, and the contents of acetophenone and α-methylstyrene can be detected at a detection wavelength of 245 nm. By setting different detection wavelengths for different by-products, it is beneficial to improve the detection accuracy of different by-products.

[0077] like Figure 3 As shown, under detection wavelengths of 210 nm and 245 nm, the black curve represents the detection curve at a detection wavelength of 210 nm, and the purple curve represents the detection curve at a detection wavelength of 245 nm. The horizontal axis represents time, and the vertical axis represents the output electrical signal of the detection device. As the multi-gradient elution process proceeds, cumyl alcohol, acetophenone, and α-methylstyrene are detected under a detection wavelength of 210 nm, and acetophenone and α-methylstyrene are detected under a detection wavelength of 245 nm. 2-Phenylacetol is cumyl alcohol. The peak area of ​​the detection wave of each curve represents the content of the analyte, and the content converted from the peak area of ​​different substances is independent. That is, the content of two analytes cannot be determined to be the same based on the fact that the peak areas of two analytes are the same.

[0078] S600: Quantitative analysis yields the mass concentration of different byproducts.

[0079] Specifically, the supernatant after elution and separation was analyzed by gas chromatography. The concentration of the corresponding byproducts was obtained by looking at the chromatogram. The amount of the three target substances was determined by the standard concentration curve determined by the external standard method. Finally, the contents of cumyl alcohol, acetophenone and α-methylstyrene in the insulating sample were calculated based on the mass of the solid sample taken.

[0080] The present invention provides a method for detecting by-products in cross-linked polyethylene cable insulation. This method utilizes the strong polarity of isopropanol to dissolve small-molecule by-products and promotes polyethylene swelling with n-hexane. Simultaneously, low-temperature ultrasound is used to synergistically reduce viscosity, achieving complete extraction of by-products such as cumyl alcohol at low temperatures. This improves the detection accuracy of the corresponding by-products. Furthermore, the use of ionic liquid injection enhances ionization, thereby increasing the charge on the supernatant and its activity. This promotes greater activity of the by-products during detection, ultimately improving detection sensitivity.

[0081] Furthermore, this invention employs multi-gradient elution, which achieves complete separation of three types of byproducts by precisely controlling the elution intensity and avoiding cross-contamination. Combined with the gradient elution time window, it enables simultaneous and accurate quantification of different byproduct components.

[0082] Furthermore, by employing low-temperature freezing combined with liquid nitrogen rapid freezing, the volatilization of by-products can be significantly suppressed. And through radial layering and rectangular die stamping, the gradient distribution analysis of by-products within the insulation layer was achieved for the first time, providing spatial distribution data for optimizing the degassing process. Moreover, ultracentrifugal grinding and sieving after liquid nitrogen freezing better ensure the sufficiency and uniformity of sample grinding, avoiding uneven particle size due to the inherent toughness of the insulation layer. Subsequently, during the melting process, the uniformity of solute distribution after melting is better ensured, reducing errors in subsequent detection and guaranteeing accuracy.

[0083] The embodiments of the present invention described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0084] Example 1

[0085] This embodiment uses two sets of samples (sample 1 and sample 2) for testing. Each set of samples includes an inner layer, a middle layer, and an outer layer. The specific method for detecting by-products in the cross-linked polyethylene cable insulation layer includes:

[0086] S100: Take a preset area of ​​the cross-linked polyethylene cable insulation layer to be tested as a sample.

[0087] Specifically:

[0088] S110: The cross-linked polyethylene cable to be tested was frozen at -40℃, then sliced ​​and centrifuged.

[0089] S120: After removing the conductor, cut the cross-linked polyethylene cable to be tested into a radial slice with a slice thickness of 2mm.

[0090] S130: Cut a layered rectangular section along the radial direction to obtain samples of the gradient of cross-linking byproducts at different positions within the insulating layer. Specifically, take rectangular areas of the outer layer (near the metal shielding layer), middle layer, and inner layer (near the conductive layer) of the insulating layer as samples for subsequent testing.

[0091] S140: After freezing the sample with liquid nitrogen for 1 minute, place it in an ultracentrifuge grinder for grinding and sieving.

[0092] S200: Using a 1:1 ratio of n-hexane and isopropanol as solvents, the sample was ultrasonically eluted at 50°C for 60 min, and the filtrate was obtained after filtering out solid impurities.

[0093] S300: Dilute the filtrate with a mixture of acetonitrile and water in a ratio of 3:2, and add 0.5 wt% of [unspecified ingredient] to the diluted mixture. The solution was mixed, allowed to stand, and the supernatant was extracted.

[0094] S400: The extracted supernatant is separated by electrostatic three-stage gradient elution using a charged surface chromatographic column. Specifically, the elution parameters are as follows: the temperature of the charged chromatographic column is 35℃; the first mobile phase of the column is a 0.1% formic acid aqueous solution with a pH of 2.8; the first gradient elution of the second mobile phase of the column uses an acetonitrile-water ratio of 35:65, the second gradient elution uses 100% acetonitrile; and the third gradient elution uses an acetonitrile-water ratio of 35:65.

[0095] S500: Set the detection wavelength corresponding to different by-products.

[0096] Specifically, the detection wavelength for cumyl alcohol in the byproducts was set to 210 nm, and the detection wavelength for acetophenone and α-methylstyrene was set to 245 nm.

[0097] S600: Quantitative analysis yields the mass concentration of different byproducts.

[0098] The byproduct detection results obtained using the scheme of Example 1 are shown in Table 2 below:

[0099] Table 2 shows the content of insulation layer by-products detected in Example 1.

[0100]

[0101] As shown in Table 2, the removal effect of polar substances in different regions of cross-linked polyethylene cables after degassing varies significantly. The overall effect shows a gradual decrease from the inner layer to the outer layer, which is presumably related to the degree of contact with air.

[0102] Example 2

[0103] The sample was the same as in Example 1, except that in step S110, the cross-linked polyethylene cable to be tested was frozen at -35°C during sample preparation; in step S200, hexane and isopropanol in a ratio of 0.5:1 were used as solvents, and the sample was ultrasonically eluted at 60°C for 60 min; in step S300, 0.6 wt% of [unspecified ingredient] was injected into the diluted mixture. Solution; in step S400, the temperature of the charged chromatographic column is 40℃; other process parameters are the same.

[0104] The test results are shown in Table 3 below:

[0105] Table 3. Detection content of insulation layer by-products in Example 2.

[0106]

[0107] As can be seen from Table 3, the experimental results did not change significantly under these conditions.

[0108] Example 3

[0109] The sample was the same as in Example 1, except that in step S110, the cross-linked polyethylene cable to be tested was frozen at -45°C during sample preparation; in step S200, hexane and isopropanol in a ratio of 2:1 were used as solvents, and the sample was ultrasonically eluted at 40°C for 60 minutes; in step S300, 0.4 wt% of [unspecified ingredient] was injected into the diluted mixture. Solution; in step S400, the temperature of the charged chromatographic column is 30℃; other process parameters are the same.

[0110] The test results are shown in Table 4 below:

[0111] Table 4 shows the content of insulation layer by-products detected in Example 3.

[0112]

[0113] As can be seen from Table 4, the experimental results did not change significantly under these conditions.

[0114] Example 4

[0115] The sample was the same as in Example 1, except that in step S140, liquid nitrogen freezing was not used after slicing; other process parameters were the same.

[0116] The test results are shown in Table 5 below:

[0117] Table 5. Detection content of insulation layer by-products in Example 4.

[0118]

[0119] As can be seen from Table 5, since liquid nitrogen freezing was not used after slicing, the content of each cross-linking byproduct in the test results decreased significantly, especially in the outer layer.

[0120] Comparative Example 1

[0121] The standard testing method involves extracting the sample using a 1:1 mixture of n-hexane and isopropanol at 60°C via ultrasonication, without freezing or grinding, and without injecting 0.4 wt% of [unspecified substance]. The solution, without the addition of formic acid, was prepared using a standard Bridge column.

[0122] like Figure 4As shown, this diagram illustrates a conventional detection method. The horizontal axis represents time, and the vertical axis represents the output electrical signal of the detection equipment. Detection is performed by boosting the output electrical signal. However, in the absence of charged surface mixing technology, 0.1% formic acid, and multi-gradient elution, problems arise such as overlapping peak curves of different analytes, numerous interfering peaks, and poor peak symmetry. This makes it difficult to convert the content of analytes, resulting in low accuracy and severely impacting the detection quality and the interpretation of the results. This is consistent with... Figure 3 The test results showed significant differences.

[0123] Comparative Example 2

[0124] The sample is the same as in Example 1, except that only isopropanol is used as the solvent in step S200, while other parameters are the same as in Example 1.

[0125] The test results are shown in Table 6 below:

[0126] Table 6 shows the content of insulation layer by-products in Comparative Example 2.

[0127]

[0128] As can be seen from Table 6, the α-methylstyrene content in the test results is significantly reduced due to the absence of n-hexane in the solvent, which does not conform to reality.

[0129] Comparative Example 3

[0130] The sample is the same as in Example 1, except that no injection was performed in step S300. Solution.

[0131] The test results are shown in Table 7 below:

[0132] Table 7 shows the content of insulation layer by-products in Comparative Example 3.

[0133]

[0134] As can be seen from Table 7, due to the lack of ionic liquid injection, the separation degree of substances decreased, the waveforms overlapped, resulting in a significantly low ratio of cumyl alcohol and acetophenone in each layer, leading to quantitative distortion.

[0135] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for detecting by-products in the insulation layer of cross-linked polyethylene cables, characterized in that, include: S100: Take a preset area of ​​the cross-linked polyethylene cable insulation layer to be tested as a sample; S200: Using hexane and isopropanol in a ratio of (0.5~2):1 as solvent, the sample is ultrasonically eluted at 40~60℃ for a preset time, and the filtrate is obtained after filtering out solid impurities; S300: Dilute the filtrate with a mixture of acetonitrile and water, and add 0.4~0.6 wt% of the diluted mixture. The solution was mixed, allowed to stand, and the supernatant was extracted. S400: The extracted supernatant is eluted and separated by an attached electrostatic chromatographic column. S500: Set the detection wavelength for different byproducts; S600: Quantitative analysis yields the mass concentration of different byproducts; In S100, a predetermined area of ​​the cross-linked polyethylene cable insulation layer to be tested is taken as a sample, specifically including: S110: Freeze the cross-linked polyethylene cable to be tested at -35~-45℃; S120: After removing the conductor, cut the cross-linked polyethylene cable to be tested radially; S130: Cut a layered rectangular section along the radial direction to obtain samples with different gradients of cross-linked byproducts at different positions within the insulation layer; S140: After freezing the sample with liquid nitrogen for a preset time, place it in an ultracentrifuge grinder for grinding and sieving; The cross-linked polyethylene cable insulation layer byproducts include cumyl alcohol, acetophenone, and α-methylstyrene.

2. The method for detecting by-products of cross-linked polyethylene cable insulation layer according to claim 1, characterized in that, In step S200, the ratio of n-hexane to isopropanol is 1:1, the ultrasonic elution temperature is 50°C, and the preset elution time is 50~70 min.

3. The method for detecting by-products of cross-linked polyethylene cable insulation layer according to claim 1, characterized in that, In step S300, the ratio of acetonitrile to water in the mixture of acetonitrile and water is (1~4):

2.

4. The method for detecting by-products of cross-linked polyethylene cable insulation layer according to claim 3, characterized in that, In step S400, when the extracted supernatant is eluted with an attached gradient using a charged surface chromatographic column, multiple elution mixtures with different acetonitrile-water ratios are used for multi-gradient elution, so that the supernatant flows sequentially through multiple elution mixtures with different acetonitrile-water ratios to elute and separate different by-products.

5. The method for detecting by-products of cross-linked polyethylene cable insulation layer according to claim 4, characterized in that, The multi-gradient elution includes a first gradient elution and a second gradient elution. The acetonitrile-water ratio in the first gradient elution is 35:65, and the acetonitrile content in the second gradient elution is 100%.

6. The method for detecting by-products of cross-linked polyethylene cable insulation layer according to claim 5, characterized in that, The multi-gradient elution also includes a third gradient elution, wherein the acetonitrile-water ratio of the third gradient elution is 35:

65.

7. The method for detecting by-products of cross-linked polyethylene cable insulation layer according to claim 1, characterized in that, In step S400, the column temperature of the chromatographic column is 30~40℃.

8. The method for detecting by-products of cross-linked polyethylene cable insulation layer according to claim 1, characterized in that, In step S400, the first mobile phase of the chromatographic column is a 0.08%~0.12% formic acid aqueous solution with a pH of 2.5~3; the second mobile phase of the chromatographic column is acetonitrile containing 0.08%~0.12% formic acid.

9. The method for detecting by-products of cross-linked polyethylene cable insulation layer according to claim 1, characterized in that, In step S500, the detection wavelength of cumyl alcohol in the byproducts is set to 210 nm, and the detection wavelength of acetophenone and α-methylstyrene is set to 245 nm.

Images