CN115586169B - SERS (surface enhanced Raman Spectroscopy) determination method for content of benzotriazole in mineral insulating oil - Google Patents
SERS (surface enhanced Raman Spectroscopy) determination method for content of benzotriazole in mineral insulating oil Download PDFInfo
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Abstract
The invention discloses a SERS determination method for the content of benzotriazole in mineral insulating oil, which comprises the following steps of: (1) preparation of SERS substrate with hemispherical microcavity structure; (2) surface cleaning of the substrate; (3) pretreatment of the sample to be tested and the standard solution; (4) detection and quantification. The excitation light wavelength selected by the invention is relatively close to the ultraviolet absorption of the SERS substrate selected, the invention can play a good role in enhancing signals, and the portable Raman spectrometer with small volume and simple operation is conveniently selected, so that the use of large laboratory fixed instruments such as high-precision liquid chromatography and the like is avoided, and the on-site rapid detection of benzotriazole in mineral insulating oil can be realized.
Description
Technical Field
The invention belongs to the technical field of quality detection and analysis of mineral insulating oil samples, and particularly relates to a SERS (surface enhanced Raman scattering) determination method for the content of benzotriazole in mineral insulating oil.
Background
In oil-immersed power equipment such as transformers, mineral insulating oil plays a dual role of insulation and cooling. Transformer failure due to the presence of corrosive sulfur in mineral insulating oil is one of the more troublesome problems in recent years. The corrosive sulfur can react with copper materials such as coils in transformers, and finally cuprous sulfide with strong thermal stability and strong conductivity is generated. The existence of cuprous sulfide can change the electric field distribution inside the transformer, reduce the insulation strength of the coil in the winding and finally cause faults. To solve this problem, metal deactivators are often artificially added to mineral insulating oils containing corrosive sulfur to inhibit the corrosive effect of sulfur on metals. Benzotriazole (BTA) is one of the most common metal deactivators, and according to researches, 30mg/kg of benzotriazole can produce an obvious corrosion inhibition effect, the concentration of benzotriazole in mineral insulating oil is increased, and the effect of inhibiting sulfur corrosion can be further improved, but when the concentration of benzotriazole is more than 130mg/kg, the acid value, dielectric loss rate and moisture of the mineral insulating oil are increased compared with those of a sample without benzotriazole, so that the aging of insulating paper is accelerated. In actual operation of the transformer, benzotriazole in the mineral insulating oil is gradually consumed. Therefore, the content of benzotriazole in the mineral insulating oil is tracked and detected regularly, which is very important for ensuring the safe operation of the power transformer. The standard method for detecting the benzotriazole content in the mineral insulating oil is a high performance liquid chromatography method, such as the method recommended by the electric power industry standard DL/T1459-2015. The method has high accuracy, but needs to adopt methanol liquid-liquid extraction, oscillation, centrifugation and the like to carry out sample pretreatment, has long measurement time, can only be carried out in a professional analysis laboratory, and cannot carry out on-site detection. The units of Guangdong electric network limited responsibility company electric science research institute and the like improve the standard method by optimizing the detection conditions, for example, patent 201410193788.2 proposes a method for measuring furfural, antioxidant T501 and metal passivator in mineral insulating oil by one sample injection, but still high performance liquid chromatography is still necessary, and the method is a laboratory test method in essence.
As a rapid and accurate analysis method, the Surface Enhanced Raman Spectroscopy (SERS) has wide application in the fields of petrochemical industry, pesticide residue detection, biological medicine and the like. SERS has the advantages of high sensitivity, short detection time, less sample consumption, high efficiency, capability of utilizing a portable instrument to carry out field detection and the like, and is applied to the aspect of oil quality detection of mineral insulating oil, in particular to the aspect of furfural detection. However, high abundance, high viscosity mineral insulating oil in the sample can affect contact of low abundance target molecules with the enhanced substrate surface, and thus the sample is typically pre-treated. At present, only a few studies on SERS detection of benzotriazole in mineral insulating oil are performed, for example, patent 202110953500.7 uses a lignin nanosol to adsorb and extract benzotriazole from mineral insulating oil, and then drops the extract benzotriazole directly on a flat substrate for SERS detection. However, the preparation of the lignin nano sol provided by the invention takes a long time, and the lignin sol inevitably remains in the treated sample. From the practical detection operation point of view, the flat substrate has the defects in the aspects of positioning the target area, ensuring the detection repeatability and the like.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a SERS measuring method for the benzotriazole content in mineral insulating oil, which is simple and safe to operate and can adapt to the requirements of on-site rapid detection.
In order to achieve the above object, the present invention provides the following technical solutions: a SERS measurement method for the benzotriazole content in mineral insulating oil, comprising the steps of:
(1) Preparation of SERS substrate with hemispherical microcavity structure:
1.1 Processing a plurality of hemispheroidal microcavities on the quartz glass piece, cleaning and drying the processed quartz glass piece, vertically soaking the quartz glass piece in a 3-aminopropyl trimethoxy silane aqueous solution with the mass fraction of 0.1%, taking out the quartz glass piece, cleaning the quartz glass piece with deionized water, and drying the quartz glass piece with nitrogen to obtain a once soaked quartz glass piece;
1.2 Soaking the quartz glass sheet which is soaked once in a gold nanoparticle aqueous solution; taking out, cleaning with deionized water, drying with nitrogen, vertically placing into an EP tube, sequentially adding deionized water, 0.2% chloroauric acid aqueous solution and 0.04mol/L hydroxylamine hydrochloride aqueous solution, immediately oscillating for 13-17 min at 1500rpm oscillation speed, and completing a first growth cycle to obtain quartz glass sheets of one growth cycle; the addition amount of 0.2% chloroauric acid aqueous solution in every milliliter of deionized water is 140-160 mu L, and the addition amount of hydroxylamine hydrochloride aqueous solution of 0.04mol/L is 70-80 mu L;
1.3 Taking out quartz glass sheets of one-time growth cycle, washing with deionized water, drying with nitrogen, vertically putting into an EP tube, sequentially adding deionized water, 0.2% aqueous solution of chloroauric acid and 0.04mol/L aqueous solution of hydroxylamine hydrochloride, wherein the addition amount of the 0.2% aqueous solution of chloroauric acid in each milliliter of deionized water is 37-38 mu L, the addition amount of the 0.04mol/L aqueous solution of hydroxylamine hydrochloride is 18.5-19.0 mu L, and immediately oscillating for 13-17 min at 1500rpm to complete a second growth cycle; repeating the growth cycle continuously according to the parameters and conditions of the second growth cycle, and obtaining the SERS substrate with a hemispherical microcavity structure suitable for detecting benzotriazole in mineral insulating oil after finishing 5 growth cycles in total;
(2) Surface cleaning of the substrate: soaking the SERS substrate with the hemispherical microcavity structure prepared in the step 1.3) in a potassium iodide aqueous solution with the concentration of 0.001mol/L for 20min, taking out, washing with deionized water, and drying with nitrogen to finish surface cleaning of the substrate, thereby obtaining a clean SERS substrate;
(3) Pretreatment of a sample to be tested and a standard solution: carrying out pretreatment on a mineral insulating oil sample to be detected and a mineral insulating oil standard solution containing benzotriazole with different concentrations by adopting a solid-phase extraction mode; the standard solution of the mineral insulating oil containing the benzotriazole with different concentrations at least comprises 4 standard solutions of the benzotriazole mineral insulating oil with different concentrations, and the concentration coverage range of the benzotriazole in the standard solution is 10-1000 mg/kg;
(4) Detection and quantification: performing SERS detection on the eluent obtained in the pretreatment of the step (3) by using the clean SERS substrate in the step (2), wherein the excitation light wavelength is 785nm, establishing a correction curve by using the characteristic peak intensity of the eluent SERS spectrogram of the mineral insulating oil standard solution containing the benzotriazole with known concentration to the logarithm of the original concentration of the benzotriazole, and calculating the content of the benzotriazole in the sample to be detected according to the correction curve and the characteristic peak intensity of the eluent with known concentration at 783cm -1 in the SERS spectrogram of the sample to be detected.
Further, the method for cleaning and drying the processed quartz glass sheet in the step 1.1) comprises the following steps: the processed quartz glass sheet is washed by aqua regia, alkali liquor and deionized water in sequence, and then dried by nitrogen.
Further, the size of the quartz glass plate in the step 1.1) is 10 multiplied by 20mm, the diameter of the hemispherical microcavity is 0.8-1.2 mm, and the interval between the adjacent microcavities is 2.3-2.7 mm.
Further, the mass fraction of the gold nanoparticle aqueous solution in the step 1.2) is 1%, and the diameter of the gold nanoparticles is 5nm.
Further, in the step 1.2), the quartz glass sheet soaked once is soaked in the gold nanoparticle aqueous solution; taking out, cleaning with deionized water, drying with nitrogen, vertically placing into an EP tube, sequentially adding deionized water, 0.2% chloroauric acid aqueous solution and 0.04mol/L hydroxylamine hydrochloride aqueous solution, immediately oscillating for 15-17 min at 1500rpm oscillation speed, and completing a first growth cycle to obtain quartz glass sheets of one growth cycle; the addition amount of the aqueous solution of chloroauric acid with the concentration of 0.2 percent in each milliliter of deionized water is 150 to 160 mu L, and the addition amount of the aqueous solution of hydroxylamine hydrochloride with the concentration of 0.04mol/L is 75 to 80 mu L.
Further, taking out the quartz glass sheet of one growth cycle in the step 1.3), cleaning with deionized water, drying with nitrogen, vertically putting into an EP tube, sequentially adding deionized water, 0.2% chloroauric acid aqueous solution and 0.04mol/L hydroxylamine hydrochloride aqueous solution, wherein the addition amount of the 0.2% chloroauric acid aqueous solution in each milliliter of deionized water is 37.5-38 mu L, the addition amount of the 0.04mol/L hydroxylamine hydrochloride aqueous solution is 18.75-19.0 mu L, and immediately oscillating for 15-17 min at 1500rpm to finish the second growth cycle; and continuing to repeat the growth cycle according to the parameters and conditions of the second growth cycle, and after finishing 5 growth cycles in total, obtaining the SERS substrate with the hemispherical microcavity structure, which is suitable for detecting the benzotriazole in the mineral insulating oil.
Further, in the step (3), an activating solvent is firstly taken and injected into the solid-phase extraction column to fully wet the solid-phase extraction column; then fully mixing 1mL of mineral insulating oil to be tested sample or the mineral insulating oil standard solution containing benzotriazole with n-hexane according to the volume ratio of 1:1-1:3, and loading the sample; after the mixed solution completely flows through the column, leaching the extraction column by 0.5-1 mL of n-hexane, and then draining the residual liquid in the extraction column; and finally adding an eluting solvent to elute the benzotriazole adsorbed in the column, and reserving the eluent for sample measurement.
Further, the activating solvent is any one of deionized water, methanol and n-hexane, and the dosage of the activating solvent is 1-6 mL.
Further, the eluting solvent is any one of methanol, absolute ethyl alcohol and acetonitrile, and the dosage of the eluting solvent is 0.5-2 mL.
Further, in the step (3), the inner diameter of the solid phase extraction column body for solid phase extraction is 8-10 mm, dealkalized lignin is used as an adsorption filler, and the filling amount is 0.06-0.5 g.
The SERS determination method for the content of the benzotriazole in the mineral insulating oil has the following beneficial effects:
1. Compared with the national standard method for measuring the benzotriazole in the mineral insulating oil, the pretreatment method adopted in the invention does not need mechanical oscillation and centrifugal separation, is simple to operate and meets the requirement of on-site rapid detection; in addition, the wavelength of the excitation light selected by the invention is relatively close to the ultraviolet absorption of the SERS substrate selected, so that the invention has a good signal enhancement effect, and a portable Raman spectrometer with small volume and simple operation is conveniently selected, so that the use of large laboratory fixed instruments such as high-precision liquid chromatography and the like is avoided, and the on-site rapid detection of benzotriazole in mineral insulating oil can be realized;
2. Compared with the 202110953500.7 patent, the micro-cavity SERS enhancement device increases the contact area between the sample to be detected and the surface of the device, so that the object to be detected is enriched in the cavity, and the enhancement effect can be improved; the adopted microcavity structure SERS enhancement device also fixes a detection area, and is convenient and quick to focus, so that the Raman detection flow is simplified, and the detection time is shortened; compared with the 202110953500.7, the invention also adds a simple and effective substrate surface cleaning step, so that the baseline of the SERS spectrogram is smoother, and the subsequent data processing difficulty is reduced; in addition, the solid phase extraction column using dealkalized lignin as a filler replaces lignin nanosol in patent 202110953500.7 to pretreat the sample, and nanosol synthesis is not needed, so that the pretreatment flow is simplified; in the 202110953500.7 patent, lignin sol inevitably enters a sample to be detected, and by optimizing an elution solvent, the method not only ensures that benzotriazole can be effectively eluted, but also can prevent lignin from entering an eluent, simplifies components of the object to be detected, and has better detection effect.
Drawings
FIG. 1 is a flow chart of a SERS determination method for benzotriazole content in mineral insulating oil;
FIG. 2 is a SERS spectrum of a benzotriazole standard solution eluent and a calibration graph for quantification;
FIG. 3 is a final SERS spectrum of the same sample with different amounts of activating solvent;
FIG. 4 is a graph of the final SERS spectra at different sample/n-hexane mixing ratios;
FIG. 5 is a graph showing the effect of different excitation light wavelengths on the intensity of characteristic peaks at 783cm -1 in a SERS spectrum.
Detailed Description
The following examples will assist those skilled in the art in a more complete understanding of the invention, but are not intended to limit the invention in any way.
Example 1
(1) Processing 6 hemispheroidal microcavities with the diameter of 1mm on a quartz glass sheet with the size of 10 multiplied by 20mm, wherein the interval between every two adjacent microcavities is 2.5mm, cleaning the processed quartz glass sheet by aqua regia, alkali liquor and deionized water in sequence, drying by nitrogen, and vertically soaking in a 3-aminopropyl trimethoxysilane aqueous solution with the mass fraction of 0.1 percent for 20 minutes; taking out, cleaning with deionized water, drying with nitrogen, and soaking in gold nanoparticle aqueous solution with the diameter of 5nm for 10h; taking out, cleaning with deionized water, drying with nitrogen, vertically placing into an EP tube with a volume of 5mL, sequentially adding 2mL of deionized water, 300 mu L of 0.2% chloroauric acid aqueous solution and 150 mu L of 0.04mol/L hydroxylamine hydrochloride aqueous solution, immediately placing the EP tube into a constant temperature mixer, and oscillating for 15min at an oscillating speed of 1500rpm to complete a first growth cycle; taking out, cleaning with deionized water, drying with nitrogen, vertically placing into an EP tube with a volume of 5mL, sequentially adding 2mL of deionized water, 75 mu L of 0.2% chloroauric acid aqueous solution and 37.5 mu L of hydroxylamine hydrochloride aqueous solution with a concentration of 0.04mol/L, immediately placing the EP tube into a constant temperature mixer, and oscillating for 15min at an oscillating speed of 1500rpm to complete a second growth cycle; and continuing repeating the growth cycle for 3 times according to the parameters and conditions of the second growth cycle, and completing 5 growth cycles in total to obtain the SERS substrate which is applicable to detection of benzotriazole in mineral insulating oil and has a hemispherical microcavity structure.
(2) And (3) soaking the SERS substrate in a potassium iodide solution with the concentration of 0.001mol/L for 20min, taking out, cleaning with deionized water, and drying with nitrogen to finish surface cleaning of the substrate.
(3) The solid phase extraction column which adopts the dealkalized lignin as the adsorption filler is used for carrying out pretreatment on the mineral insulating oil sample to be detected and the mineral insulating oil standard solution with the concentration of benzotriazole of 10mg/kg, 50mg/kg, 100mg/kg, 500mg/kg and 1000 mg/kg. Firstly, 3mL of normal hexane is injected into a solid phase extraction column to fully wet the solid phase extraction column; then fully mixing 1mL of mineral insulating oil to be tested sample or the mineral insulating oil standard solution containing benzotriazole with 2mL of n-hexane, and loading the mixture; after the mixed liquid completely flows through the column, eluting the extraction column by using 1mL of normal hexane, and then draining residual liquid in the extraction column; and finally, adding 1mL of absolute ethyl alcohol into the extraction column to elute the benzotriazole adsorbed in the column, and reserving the eluent for sample detection.
(4) And carrying out SERS detection on the eluent by using the prepared SERS substrate with the hemispherical microcavity structure. During detection, transferring 0.6 mu L of eluent into a hemispherical microcavity of a substrate by using a pipetting gun, focusing excitation light of a Raman spectrometer with the center wavelength of 785nm to the center position of the bottom of the microcavity for spectrum acquisition after the solvent is naturally volatilized, and acquiring a spectrum range of 200-2000 cm -1. A correction curve is established by using the characteristic peak intensity at 783cm -1 in the SERS spectrum of the eluent of the standard solution to the concentration in the standard solution, as shown in fig. 2, a correction curve equation is obtained, wherein y= 871.04x-289.18, the determination coefficient R2 is 0.9714, x is the logarithm of the original concentration of benzotriazole in the mineral insulation oil sample, and y is the characteristic peak intensity of benzotriazole at 783cm -1 in the SERS spectrum.
In the SERS spectrogram of the eluent of the sample to be detected, the characteristic peak intensity at the position of 783cm -1 is 1325.73, and the original concentration of the benzotriazole in the sample to be detected is 71.45mg/kg according to the conversion of a correction curve equation. The same sample is tested by adopting a method in DL/T1459-2015, the concentration of the benzotriazole is 64.52mg/kg, the measured relative deviation is 10.7%, and the requirement of the DL/T1459-2015 on the reproducibility of the test result is met.
Example 2
In the pretreatment step of the sample to be tested and the standard solution, the excessive use of the activating solvent may cause insufficient activation of the extraction column, and the excessive use of the activating solvent may form a 'gully effect', so that the surface area of the adsorbent contacted with the sample is reduced, and the recovery rate is reduced. In order to select an appropriate amount of the activating solvent, in this example, 1mL,3mL and 6mL of n-hexane were used to activate the extraction column, and a standard solution of mineral spirits having a benzotriazole concentration of 1000mg/kg was subjected to pretreatment and SERS detection, and other steps and conditions were the same as in example 1, and the obtained SERS spectrum was shown in FIG. 3, and it was found that 3mL was the optimum amount based on the characteristic peak intensity at 783cm -1.
Example 3
In the pretreatment step of the sample to be tested and the standard solution, the mineral insulating oil has higher viscosity, which may cause the blocking of the sieve plate of the extraction column, so that the proper dilution of the oil sample is important, however, excessive dilution may affect the adsorption efficiency of the filling material on the benzotriazole in the oil sample. To select a proper mixing ratio of the sample and n-hexane, 1mL of a mineral insulating oil standard solution with a benzotriazole concentration of 1000mg/kg was taken and mixed with 1mL,2mL and 3mL of n-hexane, respectively, and then solid phase extraction and SERS detection were performed, and other steps and conditions were the same as in example 1, and the obtained SERS spectrum was shown in FIG. 4, and an optimal mixing ratio of 1:2 was found according to the characteristic peak intensity at 783cm -1.
Example 4
In order to study the influence of the excitation light wavelength on the detection result, in this example, excitation light wavelengths of 532nm, 633nm and 785nm are respectively selected, and other steps and conditions are the same as those in example 1, and the mineral insulating oil standard solution with the benzotriazole concentration of 800mg/kg is subjected to pretreatment and SERS detection, and SERS spectra obtained at different excitation light wavelengths are shown in FIG. 5. Since fluorescence interference is strong at the detection of short wavelength, characteristic peaks do not appear when the excitation light wavelength of 532nm is selected. When the excitation light wavelength of 633nm is selected, the characteristic peak intensity is weak. When the wavelength of the excitation light of 785nm is selected, the wavelength is relatively close to the wavelength corresponding to the solid ultraviolet absorption peak of the SERS active microcavity array, so that the detection effect is relatively good. From the characteristic peak intensity of benzotriazole at 783cm -1, the wavelength of 785nm, the most preferred excitation light, of the above three excitation light wavelengths, can be determined.
Compared with the national standard method for measuring the benzotriazole in the mineral insulating oil, the pretreatment method adopted in the invention does not need mechanical oscillation and centrifugal separation, is simple to operate and meets the requirement of on-site rapid detection; in addition, the wavelength of the excitation light selected by the invention is relatively close to the ultraviolet absorption of the SERS substrate selected, so that the invention has a good signal enhancement effect, and a portable Raman spectrometer with small volume and simple operation is conveniently selected, so that the use of large laboratory fixed instruments such as high-precision liquid chromatography and the like is avoided, and the on-site rapid detection of benzotriazole in mineral insulating oil can be realized; compared with the 202110953500.7 patent, the micro-cavity SERS enhancement device increases the contact area between the sample to be detected and the surface of the device, so that the object to be detected is enriched in the cavity, and the enhancement effect can be improved; the adopted microcavity structure SERS enhancement device also fixes a detection area, and is convenient and quick to focus, so that the Raman detection flow is simplified, and the detection time is shortened; compared with the 202110953500.7, the invention also adds a simple and effective substrate surface cleaning step, so that the baseline of the SERS spectrogram is smoother, and the subsequent data processing difficulty is reduced; in addition, the solid phase extraction column using dealkalized lignin as a filler replaces lignin nanosol in patent 202110953500.7 to pretreat the sample, and nanosol synthesis is not needed, so that the pretreatment flow is simplified; in the 202110953500.7 patent, lignin sol inevitably enters a sample to be detected, and by optimizing an elution solvent, the method not only ensures that benzotriazole can be effectively eluted, but also can prevent lignin from entering an eluent, simplifies components of the object to be detected, and has better detection effect.
While the invention has been described in detail in the foregoing general description and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that modifications and improvements can be made thereto. Accordingly, such modifications or improvements may be made without departing from the spirit of the invention and are intended to be within the scope of the invention as claimed.
Claims (10)
1. A SERS measurement method for the benzotriazole content in mineral insulating oil, comprising the steps of:
(1) Preparation of SERS substrate with hemispherical microcavity structure:
1.1 Processing a plurality of hemispheroidal microcavities on the quartz glass piece, cleaning and drying the processed quartz glass piece, vertically soaking the quartz glass piece in a 3-aminopropyl trimethoxy silane aqueous solution with the mass fraction of 0.1%, taking out the quartz glass piece, cleaning the quartz glass piece with deionized water, and drying the quartz glass piece with nitrogen to obtain a once soaked quartz glass piece;
1.2 Soaking the quartz glass sheet which is soaked once in a gold nanoparticle aqueous solution; taking out, cleaning with deionized water, drying with nitrogen, vertically placing into an EP tube, sequentially adding deionized water, 0.2% chloroauric acid aqueous solution and 0.04mol/L hydroxylamine hydrochloride aqueous solution, immediately oscillating for 13-17 min at 1500rpm oscillation speed, and completing a first growth cycle to obtain quartz glass sheets of one growth cycle; the addition amount of 0.2% chloroauric acid aqueous solution in every milliliter of deionized water is 140-160 mu L, and the addition amount of hydroxylamine hydrochloride aqueous solution of 0.04mol/L is 70-80 mu L;
1.3 Taking out quartz glass sheets of one-time growth cycle, washing with deionized water, drying with nitrogen, vertically putting into an EP tube, sequentially adding deionized water, 0.2% aqueous solution of chloroauric acid and 0.04mol/L aqueous solution of hydroxylamine hydrochloride, wherein the addition amount of the 0.2% aqueous solution of chloroauric acid in each milliliter of deionized water is 37-38 mu L, the addition amount of the 0.04mol/L aqueous solution of hydroxylamine hydrochloride is 18.5-19.0 mu L, and immediately oscillating for 13-17 min at 1500rpm to complete a second growth cycle; repeating the growth cycle continuously according to the parameters and conditions of the second growth cycle, and obtaining the SERS substrate with a hemispherical microcavity structure suitable for detecting benzotriazole in mineral insulating oil after finishing 5 growth cycles in total;
(2) Surface cleaning of the substrate: soaking the SERS substrate with the hemispherical microcavity structure prepared in the step 1.3) in a potassium iodide aqueous solution with the concentration of 0.001mol/L for 20min, taking out, washing with deionized water, and drying with nitrogen to finish surface cleaning of the substrate, thereby obtaining a clean SERS substrate;
(3) Pretreatment of a sample to be tested and a standard solution: carrying out pretreatment on a mineral insulating oil sample to be detected and a mineral insulating oil standard solution containing benzotriazole with different concentrations by adopting a solid-phase extraction mode; the standard solution of the mineral insulating oil containing the benzotriazole with different concentrations at least comprises 4 standard solutions of the benzotriazole mineral insulating oil with different concentrations, and the concentration coverage range of the benzotriazole in the standard solution is 10-1000 mg/kg;
(4) Detection and quantification: performing SERS detection on the eluent obtained in the pretreatment of the step (3) by using the clean SERS substrate in the step (2), wherein the excitation light wavelength is 785nm, establishing a correction curve by using the characteristic peak intensity of the eluent SERS spectrogram of the mineral insulating oil standard solution containing the benzotriazole with known concentration to the logarithm of the original concentration of the benzotriazole, and calculating the content of the benzotriazole in the sample to be detected according to the correction curve and the characteristic peak intensity of the eluent with known concentration at 783cm -1 in the SERS spectrogram of the sample to be detected.
2. The SERS measurement method for benzotriazole content in mineral insulating oil according to claim 1, wherein the method for cleaning and blow-drying the processed quartz glass sheet in step 1.1) comprises: the processed quartz glass sheet is washed by aqua regia, alkali liquor and deionized water in sequence, and then dried by nitrogen.
3. The SERS measurement method for benzotriazole content in mineral insulating oil according to claim 1, wherein the size of the quartz glass plate in the step 1.1) is 10 x 20mm, the diameter of the hemispheric microcavity is 0.8 to 1.2mm, and the interval between adjacent microcavities is 2.3 to 2.7mm.
4. The SERS measurement method for benzotriazole content in mineral insulating oil according to claim 1, wherein the mass fraction of the gold nanoparticle aqueous solution in the step 1.2) is 1%, and the diameter of the gold nanoparticles is 5nm.
5. The SERS measurement method for benzotriazole content in mineral insulating oil according to claim 1, wherein in step 1.2), the once-immersed quartz glass plate is immersed in an aqueous gold nanoparticle solution; taking out, cleaning with deionized water, drying with nitrogen, vertically placing into an EP tube, sequentially adding deionized water, 0.2% chloroauric acid aqueous solution and 0.04mol/L hydroxylamine hydrochloride aqueous solution, immediately oscillating for 15-17 min at 1500rpm oscillation speed, and completing a first growth cycle to obtain quartz glass sheets of one growth cycle; the addition amount of the aqueous solution of chloroauric acid with the concentration of 0.2 percent in each milliliter of deionized water is 150 to 160 mu L, and the addition amount of the aqueous solution of hydroxylamine hydrochloride with the concentration of 0.04mol/L is 75 to 80 mu L.
6. The SERS measurement method for benzotriazole content in mineral insulating oil according to claim 1, wherein in the step 1.3), a quartz glass piece of one growth cycle is taken out, washed with deionized water, dried with nitrogen, and then vertically placed in an EP tube, deionized water, aqueous solution of chloroauric acid with mass fraction of 0.2%, aqueous solution of hydroxylamine hydrochloride with mass fraction of 0.04mol/L, and aqueous solution of hydroxylamine hydrochloride with mass fraction of 0.2% in each ml of deionized water are sequentially added, the addition amount of aqueous solution of hydroxylamine hydrochloride with mass fraction of 0.04mol/L is 18.75 to 19.0 μl, and immediately oscillated at 1500rpm for 15 to 17min, completing a second growth cycle; and continuing to repeat the growth cycle according to the parameters and conditions of the second growth cycle, and after finishing 5 growth cycles in total, obtaining the SERS substrate with the hemispherical microcavity structure, which is suitable for detecting the benzotriazole in the mineral insulating oil.
7. The SERS measurement method for benzotriazole content in mineral insulating oil according to claim 1, wherein in step (3), an activating solvent is first injected into a solid phase extraction column to be sufficiently wetted; then fully mixing 1mL of mineral insulating oil to be tested sample or the mineral insulating oil standard solution containing benzotriazole with n-hexane according to the volume ratio of 1:1-1:3, and loading the sample; after the mixed solution completely flows through the column, leaching the extraction column by 0.5-1 mL of n-hexane, and then draining the residual liquid in the extraction column; and finally adding an eluting solvent to elute the benzotriazole adsorbed in the column, and reserving the eluent for sample measurement.
8. The SERS measurement method for benzotriazole content in mineral insulating oil according to claim 7, wherein the activating solvent is any one of deionized water, methanol and n-hexane, and the amount of the activating solvent is 1 to 6mL.
9. The SERS measurement method for benzotriazole content in mineral insulating oil according to claim 7, wherein the eluting solvent is any one of methanol, absolute ethanol and acetonitrile, and the amount of the eluting solvent is 0.5 to 2mL.
10. The SERS measurement method for benzotriazole content in mineral insulating oil according to claim 7, wherein in the step (3), the inner diameter of the solid phase extraction column tube for solid phase extraction is 8 to 10mm, dealkalized lignin is used as an adsorption filler, and the filling amount is 0.06 to 0.5g.
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