Sintered red clay coating solid-phase extraction fiber and preparation method thereof
By preparing porous sintered red clay coated fibers, the stability and sensitivity issues of existing SPME fibers in the determination of moisture in mineral oil were solved, achieving efficient and reliable moisture detection, suitable for rapid detection of mineral oil.
Patent Information
- Application Number
- CN202511682532.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-17
- Publication Date
- 2025-12-30
AI Technical Summary
Existing SPME fiber coatings suffer from poor stability, low sensitivity to trace moisture, and susceptibility to interference from the mineral oil matrix in the determination of moisture in mineral oils. Furthermore, traditional methods are not suitable for rapid, on-site, or environmentally friendly applications.
Solid-phase extraction fibers coated with sintered red clay were used to prepare a porous coating through traditional brick and tile sintering processes. The coating was then extracted and analyzed using GC/TCD, and the high hydrophilicity of the clay was utilized to achieve specific adsorption of water.
It achieves solvent stability, thermal stability, and mechanical durability. The fiber can be reused more than 150 times and can efficiently extract water from mineral oil, providing a rapid and sensitive detection method as an alternative to traditional methods.
Smart Images
Figure CN121228408A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of analytical chemistry, specifically to a method for preparing a solid-phase extraction fiber coated with sintered red clay and its application in the determination of moisture sensitivity in mineral oil. Background Technology
[0002] Since its introduction into analytical practice by Pawliszyn's team in the early 1990s, solid-phase microextraction (SPME) has attracted widespread attention due to its ease of operation, high separation efficiency, environmental friendliness, and compatibility with analytical instruments. In SPME, extraction, enrichment, and sample introduction are integrated into a single step. The sensitivity of this analytical method depends primarily on the enrichment efficiency of the SPME, which is mainly determined by the properties of the fiber coating material. Although various commercial SPME fiber coatings have been developed, they are mainly limited to materials such as polyacrylate (PA), polydimethylsiloxane / divinylbenzene (PDMS / DVB), divinylbenzene (DVB), and polydimethylsiloxane (PDMS), or combinations thereof. However, these commercial coatings suffer from drawbacks such as high cost, mechanical brittleness, limited thermal and solvent stability, and insufficient adsorption selectivity, limiting their widespread application. To address these issues, various novel materials have been investigated as alternative SPME coatings, including carbon nanomaterials, graphene, covalent organic frameworks, ionic liquids, molecularly imprinted polymers, aerogels, metal oxides, and metal-organic frameworks. An ideal SPME fiber should possess excellent selectivity, high extraction capacity, and strong robustness. It is worth noting that, since SPME fibers produced in the same batch are not interchangeable, ensuring robustness in practical applications is crucial. This challenge may stem from inconsistencies in preparation techniques and gradual physicochemical changes during reuse.
[0003] In western China, especially in Gansu Province, clay has long been used to produce red bricks and blue tiles. The general preparation process includes: (1) collecting raw clay from the field, crushing it into fine particles and removing impurities such as grass roots and small stones; (2) soaking the purified clay in an appropriate amount of water for 4-6 hours, mixing and kneading it thoroughly until smooth and not sticky; (3) shaping the clay into brick and tile bases and air-drying it; (4) firing the dried product at about 800°C in an air atmosphere to obtain red bricks and tiles, and blue bricks and tiles in an oxygen-deficient environment. After calcination, the sintered clay products become thermally stable and solid, while retaining the inherent hydrophilicity of raw clay.
[0004] In recent decades, clay has been used in analytical processes. Saraji et al. first prepared organically modified clay by exchanging Na⁺ ions in the clay structure with hexadecyltrimethylammonium bromide (CTAB). Subsequently, they developed PDMS / nanoclay composite materials as SPME coatings using sol-gel technology and determined four organophosphorus pesticides in water samples using gas chromatography-corona discharge ion mobility spectrometry. Pelit et al. modified the surface of clay with polythiophene-ionic liquid and coated the surface-modified clay onto stainless steel wire (SSW) to prepare fibers. They determined five pesticides in fruit juice using GC / ECD. Erdem et al. prepared a bio-nanocomposite coating by intercalating montmorillonite (MMT) clay with carboxymethyl cellulose and dicationic imidazole ionic liquid (Im-DIL). Utilizing hydrogen bonding, π-π stacking, hydrophobic-hydrophobic interactions, and electrostatic interactions, they determined six phthalates in mineral water and carbonated lemon juice using GC / MS. The above studies demonstrate the application potential of clay in sample pretreatment, but the advantages of unmodified clay and more efficient methods for preparing clay-coated SPME fibers still need to be explored.
[0005] Water contamination in mineral oil products such as gasoline, transformer oil, and diesel can severely impair their performance, stability, and safety. Trace amounts of water can also accelerate oxidation, reduce dielectric strength, and cause corrosion or mechanical failure in sensitive systems such as power transformers and internal combustion engines. Traditional moisture determination methods, such as Karl Fischer titration and infrared spectroscopy, while widely used, have significant limitations: they often require complex instruments, large sample preparation, long analysis times, or toxic reagents, making them unsuitable for rapid, on-site, or environmentally friendly applications. Therefore, there is an urgent need to develop sensitive and practical methods for detecting trace moisture in mineral oils. Notably, to our knowledge, SPME coatings specifically targeting water molecules are rarely reported.
[0006] Inspired by the unique properties of sintered clay, especially its strong affinity for water, this invention uses sintered red clay to design an SPME fiber coating to achieve solvent stability for extracting and enriching water from mineral oil, and couples a gas chromatograph (GC / TCD) equipped with a thermal conductivity detector as a sensitive analytical platform. Summary of the Invention
[0007] The purpose of this invention is to improve the problems of poor stability, low sensitivity to trace moisture, and susceptibility to interference from mineral oil matrix in existing pure clay coatings, and to provide a sintered red clay coating solid phase extraction fiber, its preparation method, and its application in the determination of moisture sensitivity in mineral oil.
[0008] According to a first aspect of the present invention, a method for preparing sintered red clay coated solid-phase extraction fibers is provided, comprising the following steps: Step 1: After drying the red clay, pass it through a 20-100 mesh sieve to obtain clay powder; Step 2: Mix clay powder and deionized water at a mass ratio of 3-5:1. After mixing, let it stand for the first time to obtain clay. Knead the clay evenly, then wrap it in plastic wrap and let it stand for the second time to obtain a settled clay ball. Step 3: Take a portion of the settled clay, mix the settled clay with deionized water and knead it thoroughly again to obtain clay mud. Insert a stainless steel wire vertically into the clay mud and pull it out. Repeat this 2-4 times to form a uniform coating on the surface of the stainless steel wire. Step 4: Air-dry the stainless steel wire with a uniform coating obtained in Step 3 at room temperature, retaining two centimeters of clay material starting from the insertion end of the stainless steel wire, and scraping off the excess clay material with a blade to obtain the clay-coated fiber precursor. Step 5: Calcine the clay-coated fiber precursor obtained in Step 4 at 400-600℃ in air for 30-60 minutes, cool it to room temperature and remove it to obtain sintered red clay-coated solid-phase extraction fiber.
[0009] Furthermore, in step 2, the first settling time is 8-12 hours, and the second settling time is 8-12 hours.
[0010] 3. The method for preparing solid-phase extraction fiber with sintered red clay coating according to claim 2, characterized in that the mass ratio of the settled mud clump to deionized water in step 3 is 10-15:1.
[0011] Furthermore, in step 3, the length of the stainless steel wire is 5cm, the stainless steel wire is cleaned with filter paper before being inserted into the clay, and the depth of the stainless steel wire inserted into the clay is greater than 2cm.
[0012] Furthermore, in step 3, the position of the stainless steel wire inserted into the clay remains unchanged each time.
[0013] Furthermore, in step 3, the stainless steel wire is inserted into the clay at different positions each time, and the insertion position of the next insertion is different from the previous insertion position.
[0014] According to a second aspect of the present invention, a sintered red clay coated solid-phase extraction fiber is provided, the fiber being prepared using the sintered red clay coated solid-phase extraction fiber preparation method described in this invention.
[0015] According to a third aspect of the present invention, a method for detecting the water content in mineral oil is provided. The method employs the sintered red clay-coated solid-phase extraction fiber of the present invention to perform solid-phase extraction on actual samples or standards, and utilizes GC / TCD for desorption and quantitative analysis. Specifically, the method includes the following steps: Step 1: Extraction was performed using an SPME platform with a temperature-controlled magnetic stirrer. The mineral oil sample to be tested was loaded into a headspace vial and sealed with a PTFE-coated silicone septum. Before starting the extraction, nitrogen was purged for 10 minutes to remove moisture from the headspace. Step 2: Place the headspace vial containing the sample into an oil bath and heat at 60-80℃ for 5 minutes. Step 3: Install the sintered red clay coated solid phase extraction fiber on the SPME handle, and pass the sintered red clay coated solid phase extraction fiber through the handle to expose the sintered red clay coated solid phase extraction fiber to the headspace of the mineral oil sample for water extraction. The extraction time is 10-30 minutes, and the mixture is stirred at a speed of 200-700 rpm. Step 4: After extraction, the sintered red clay-coated solid-phase extraction fiber is subjected to GC-TCD analysis after thermal desorption.
[0016] Furthermore, the extraction conditions in step 3 are an extraction time of 30 minutes and stirring at a speed of 500 rpm.
[0017] Furthermore, in step 4, the sintered red clay-coated solid-phase extraction fiber is retracted into the handle and immediately inserted into the GC injection port for desorption for 5 minutes at a desorption temperature of 300°C.
[0018] The beneficial effects of this invention are as follows: 1. Material Innovation: For the first time, a pure inorganic coating is constructed using unmodified natural red clay, breaking through the limitations of traditional organic / composite coatings. Through traditional Chinese brick and tile sintering techniques, the coating forms a porous structure, fully preserving the hydrophilic groups of the clay and achieving specific adsorption of water molecules.
[0019] 2. Technological Innovation: Adopting the traditional "soaking-kneading-air drying-calcination" process. Key steps include: 1) Fine processing of clay: 40-mesh sieve / 12-hour hydration / repeated kneading to enhance adhesion; 2) Unique "insert-pull-out" coating technology precisely controls coating thickness; 3) Optimize sintering parameters to balance mechanical strength and water resistance at 600℃; 3. Performance Breakthrough: The fiber exhibits triple stability: 1) Solvent stable: Withstands immersion in 6 solvents for 2 hours; 2) Thermal stability: Withstands high-temperature operation up to 330℃; 3) Mechanical durability: The extraction efficiency remains at 91% after 150 repeated uses. Attached Figure Description
[0020] Figure 1SEM images of the sintered red clay-coated solid-phase extraction fibers prepared in Example 1: (a) side view (250x magnification), (b) side view (1,000x magnification), (c) cross-section (250x magnification), (d) cross-section (5,000x magnification). Figure 2 An overview of the elemental distribution of the sintered red clay-coated solid-phase extraction fiber prepared in Example 1; Figure 3 FT-IR spectra of solid-phase extraction fibers for clay mud coating and sintered red clay coating prepared in Example 1; Figure 4 XRD spectra of the sintered red clay coating of the solid phase extraction fiber and the sintered red clay coating prepared in Example 1. Figure 5 The effect of the experimental conditions in Example 1 on the extraction efficiency of 100 ng / L water by clay-coated fibers; Figure 6 Chromatograms of (a) gasoline 98, (b) gasoline 95, (c) gasoline 90, (d) diesel, and (e) transformer oil. Detailed Implementation
[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.
[0022] Example 1 A method for preparing solid-phase extraction fibers with sintered red clay coatings specifically includes the following steps: Step 1: Collect red clay blocks. In this embodiment, the blocks were collected in Longxi County, Dingxi City. Impurities such as grass roots, leaves, and sand were removed, and the clay was dried and then crushed through a 40-mesh sieve to obtain clay powder.
[0023] Step 2: Weigh 10g of clay powder into a beaker, add 2.5g of deionized water, mix evenly with a glass rod, and let stand for 12 hours to soften the clay particles and obtain mud. Place the resulting mud on a plastic board and knead repeatedly until smooth and no longer sticky. Wrap it in plastic wrap and let it stand for another 12 hours to obtain a settled mud ball. During this process, the clay particles become finer, and the mixed components generate stronger adhesive force within the mud ball, effectively enhancing the adhesion of the mud to the stainless steel wire during the insertion-extraction process and preventing coating cracking during subsequent drying and calcination pretreatment. Step 3: Take 2.5g of the settled clay and add 0.2g of deionized water, kneading thoroughly again. Cut the stainless steel wire into 5cm sections, clean the filter paper, insert it vertically into the kneaded clay, and then pull it out. The insertion and withdrawal holes should be the same. Repeat the insertion and withdrawal process three times to achieve the desired coating thickness, obtaining the clay coating fiber precursor.
[0024] Step 4: Let the clay-coated fiber precursor air dry overnight at room temperature. To accurately control the thickness, the length of the stainless steel wire inserted into the clay should be greater than 2cm. Trim the excess clay on the stainless steel wire with a razor blade, leaving only the first 2cm of coating at the insertion end of the stainless steel wire, so that the coating thickness of the last 2cm is consistent, thus obtaining the clay-coated fiber precursor.
[0025] Step 5: Place the clay-coated fiber precursor into an open tube furnace and calcine it at 600°C for 30 minutes in an air atmosphere. After cooling to room temperature, remove it to obtain sintered red clay-coated solid-phase extraction fiber.
[0026] Example 2 Based on the solid-phase extraction fiber preparation method of sintered red clay coating shown in Example 1, the difference is that in step 3, stainless steel wire is cut into 5cm segments, and after cleaning the filter paper, it is vertically inserted into the kneaded clay mud and then pulled out. Three different points are selected to insert the stainless steel wire, and the insertion-pulling is repeated three times to achieve the required coating thickness, so as to obtain the clay mud coating fiber precursor.
[0027] Example 3 The preparation of the sintered red clay-coated solid-phase extraction fiber prepared in Example 2 was characterized.
[0028] Depend on Figure 1-4 As can be seen, the surface morphology of the SPME fiber coating was observed using a scanning electron microscope at an accelerating voltage of 20.0 kV. Figure 1 Low-magnification surface SEM shows that the clay coating is distributed around the SSW, forming fibers with a rough and uneven surface, which increases the surface area of the coating and provides more adsorption sites, effectively improving the extraction efficiency. Figure 1 b. High-magnification surface SEM further revealed the typical morphology of the clay coating—rough with no visible cracks, confirming the effectiveness of the preparation method. Figure 1 c is a low-magnification cross-sectional view showing that the sintered clay coating tightly wraps the SSW, with a thickness of approximately 10 μm. Figure 1 Image d, a high-magnification cross-sectional view, shows that the coating has a relatively loose and porous structure. The BET specific surface areas of the clay and sintered clay coatings, measured by N2 adsorption experiments, were 42.3 and 3.3 m²•g⁻¹, respectively, indicating that the clay particles were effectively transformed into a monolithic coating during the preparation process, while retaining a certain surface area. This structure is beneficial for the water extraction performance of the sintered coating.
[0029] Energy dispersive spectroscopy (EDS) analysis was performed on the elemental composition of the sintered red clay coating. Figure 2 and Figure 3 The results show that carbon (C) and oxygen (O) are the main elements (97 at%), followed by silicon (Si), aluminum (Al), and calcium (Ca) (2.7 at%), with trace amounts of potassium (K) and magnesium (Mg) (only 0.3% of total). All elements are evenly distributed along the fibers, attributed to thorough soaking, mixing, and kneading during the processing. See details... Figure 2 i: The outermost layer of the coating mainly contains oxygen and silicon.
[0030] Table 1 Oxide content of clay mud coating and sintered red clay coating Further XRF analysis of the coating elemental composition yielded results shown in Table 1. The clay mud coating and sintered red clay coating on the clay mud coating fiber precursor obtained in step 4 mainly contained SiO2, Al2O3, CaO, Fe2O3, and MgO. The percentages of oxides in the uncalcined clay mud coating were 56.4%, 17.1%, 11.1%, 6.2%, and 3.8%, respectively, while those in the sintered red clay were 55.1%, 17.4%, 12.4%, 5.7%, and 4.3%. The high silica and aluminum content indicates the presence of silicate minerals, particularly quartz and kaolinite; the high CaO and Fe2O3 content suggests calcite and hematite; and MgO may indicate minor components such as dolomite or chlorite. These results indicate that the chemical composition of the coating remained essentially unchanged before and after sintering, with the calcination process primarily involving physical changes. This demonstrates that the sintered red clay coating prepared by this method retains the high water affinity of the raw materials.
[0031] The sintered red clay coating was characterized by FT-IR and XRD. Figure 3 The FT-IR spectrum of the α-raw clay shows: Si-O-Si bending vibration peaks at 476 cm⁻¹ and 533 cm⁻¹, characteristic of quartz and kaolinite; Si-O stretching vibrations at 1021 cm⁻¹ and 1055 cm⁻¹, a common feature of silicate minerals; HOH bending at 1638 cm⁻¹, indicating adsorption of water or hydroxyl groups; and a broad OH stretching band at 3433 cm⁻¹, a typical feature of hydroxyl groups in clay minerals such as kaolinite. These spectral characteristics are consistent with those of quartz, kaolinite, and hydroxyl-containing minerals. Figure 3 b shows that after calcination, the intensity of some peaks, namely 478, 533 and 1052 cm⁻¹, decreased sharply, while the hydroxyl peaks at 1638 and 3444 cm⁻¹ remained strong, indicating that the sintered clay coating structure still retains abundant hydroxyl groups, which is beneficial to its high water affinity. Figure 4 Demonstrating raw clay Figure 4 a and sintered coating Figure 4The crystal spectrum of b shows peaks at 20.8° and 26.7° corresponding to quartz, peaks at 29.5° and 28.2° attributable to calcite, and peaks at 36.7°, 39.5°, 42.6°, 43.6°, 54.8°, 59.9°, 67.6°, and 68.4° corresponding to hematite and other minor phases. These results confirm the presence of quartz, calcite, and hematite in both the raw clay and the sintered coating. Finally, the water affinity of the raw clay and the sintered coating was evaluated using the water contact angle. Figure 5 In the study, the water contact angle was measured using a Kruss contact angle meter (DSA30). The results showed that the contact angle of the raw clay was 37.3°, which decreased to 21.4° after being prepared into a clay coating. This indicates that the raw clay has inherent hydrophilicity, and the preparation process further enhances its hydrophilicity, which is beneficial for the coating to absorb the target analyte, namely water.
[0032] Example 3 A sintered red clay-coated solid-phase extraction fiber prepared by the method in Example 2 was used to verify its solvent stability and thermal stability.
[0033] Solvent stability: Most extractions were completed within 2 hours. Multiple fibers were immersed in different solvents for 2 hours each, including 0.1M HCl solution, 0.1M NaOH solution, methanol, n-hexane, acetone, and acetonitrile. After immersion, the fibers were immediately rinsed with deionized water and dried at 110°C for 30 minutes.
[0034] Thermal stability: The fibers were aged at 300°C and 330°C for 1 hour respectively.
[0035] The fibers were then immersed in different solvents and subjected to heat aging for extraction applications, and the changes in extraction performance and stability were tested.
[0036] Table 2. Ratio of fiber extraction efficiency before and after treatment (r) Table 2 lists the fiber extraction efficiency ratio (r) before and after treatment. The extraction efficiency before the stability test was set to 100%. According to the r value, the extraction efficiency was 94% after solvent treatment and 97% after heat treatment. The fiber extraction efficiency was almost unchanged after solvent and heat treatment, indicating that the clay-coated fiber has excellent physicochemical stability.
[0037] It is worth noting that the fiber's thermal stability far exceeds the test temperature, as it was calcined at 600°C during preparation. Furthermore, the extraction efficiency of the same fiber was examined after 150 extractions: Table 2 shows an r-value of 91% after 150 cycles, indicating no significant change in extraction efficiency, highlighting the excellent mechanical stability of the clay-coated fiber. This robustness is attributed to the high mechanical strength of both the sintered clay coating and the SSW carrier material, which together ensure the fiber life exceeds 150 extraction cycles.
[0038] Example 4 This embodiment provides a method for detecting moisture in gasoline 90, gasoline 95, gasoline 98, diesel, and transformer oil using sintered red clay coated solid-phase extraction fibers prepared based on those described in Example 2. The method utilizes GC / TCD for desorption and quantitative analysis. The detection steps include: Step 1: Extraction was performed using the SPME platform with a temperature-controlled magnetic stirrer. 5 mL of the sample to be tested was loaded into a headspace vial with a headspace volume of 10 mL. The vial was sealed with a PTFE-coated silicone septum. Before extraction, nitrogen was purged for 10 minutes to remove moisture from the headspace. The headspace vial is a commonly used device in the prior art. Step 2: Place the headspace vial containing the sample into an oil bath and heat at 80°C for 5 minutes. Step 3: Place the sintered red clay coated solid phase extraction fiber into a headspace vial containing the sample and extract for 30 minutes with a stirring speed of 500 rpm. Step 4: After extraction, retract the fiber handle and immediately insert it into the GC injection port. Perform GC-TCD analysis after thermal desorption at 300°C for 5 min.
[0039] The moisture concentration, regression equation, correlation coefficient, repeatability, and reproducibility detected in this embodiment are shown in Table 3.
[0040] Table 3. Moisture concentration in mineral oil samples The prepared fibers exhibited excellent solvent stability: after being sequentially immersed in 0.1M HCl, 0.1M NaOH, methanol, n-hexane, acetone, and acetonitrile for at least 2 hours, their function remained unaffected; thermal stability: they remained stable after aging at 330°C for 1 hour and calcining at 600°C; and high mechanical strength: they could be reused more than 150 times. A standard addition analytical method for determining moisture in five mineral oil samples was established by coupling with GC / TCD, achieving good linearity, acceptable repeatability, and reproducibility.
[0041] This invention overcomes the industry challenges of fragile and difficult-to-fix pure clay coatings by using a sintering process to firmly bond the inorganic coating to a stainless steel wire substrate. It also breaks through the bottleneck of weak water molecule adsorption in commercial coatings, utilizing the intrinsic hydrophilicity of clay to achieve efficient extraction of trace water. Furthermore, it eliminates interference from the mineral oil matrix, establishing a headspace extraction-GC / TCD coupled method to replace the traditional Karl Fischer titration method. This method has been successfully applied to the detection of moisture in gasoline, diesel, and transformer oil, providing a new tool for mineral oil quality monitoring and serving as a model for the transformation of traditional processes in modern analytical chemistry.
Claims
1. A method of preparing a sintered red clay coating solid phase extraction fiber, characterized by, The method comprises the following steps: Step 1: Dry the red clay and sieve it through a 20-100 mesh screen to obtain clay powder; Step 2: Mix the clay powder with deionized water at a mass ratio of 3-5:1, and after mixing, first stand to obtain mud, knead the mud uniformly, then wrap the mud with plastic wrap and second stand to obtain a standing mud group; Step 3: Take part of the standing mud group, mix the standing mud group with deionized water and knead again to obtain clay mud, insert a stainless steel wire vertically into the clay mud and pull it out, repeat 2-4 times to form a uniform coating on the surface of the stainless steel wire; Step 4: Dry the stainless steel wire with a uniform coating on the surface obtained in step 3 at room temperature, retain the mud from the end of the stainless steel wire insertion for two centimeters, remove the excess mud with a blade to obtain a clay mud coating fiber precursor; Step 5: Calcine the clay mud coating fiber precursor obtained in step 4 at 400-600 DEG C for 30-60 minutes in an air atmosphere, take it out after cooling to room temperature, and obtain a sintered red clay coating solid-phase extraction fiber.
2. A method of preparing a sintered red clay coating solid phase extraction fiber according to claim 1, wherein, The standing time of the first standing in step 2 is 8-12 hours, and the standing time of the second standing is 8-12 hours.
3. A method of preparing a sintered red clay coating solid phase extraction fiber according to claim 2, wherein, The mass ratio of the standing mud group to deionized water in step 3 is 10-15:
1.
4. The method of claim 3, wherein the sintered red clay coating solid phase extraction fiber is prepared by the steps of: The length of the stainless steel wire in step 3 is 5 cm, the stainless steel wire is wiped clean with filter paper before being inserted into the clay mud, and the depth of the stainless steel wire inserted into the clay mud is greater than 2 cm.
5. A method of preparing a sintered red clay coating solid phase extraction fiber according to claim 4, wherein, The position of the stainless steel wire inserted into the clay mud is unchanged in step 3.
6. A method of preparing a sintered red clay coating solid phase extraction fiber according to claim 4, wherein, The position of the stainless steel wire inserted into the clay mud is different each time in step 3, and the insertion hole position of the next time is different from that of the last time.
7. A sintered red clay coating solid phase extraction fiber, characterized by, The sintered red clay coating solid-phase extraction fiber is prepared by the preparation method of any one of claims 1-6.
8. A method for detecting the moisture content of mineral oil, characterized by, The detection method uses the sintered red clay coating solid-phase extraction fiber of claim 7 for solid-phase extraction of actual samples or standard samples, and uses GC / TCD for desorption and quantitative analysis, and specifically comprises the following steps: Step 1: Extraction is performed using a SPME platform combined with a temperature-controlled magnetic stirrer, the mineral oil sample to be tested is placed in a headspace bottle, and a polytetrafluoroethylene-coated silica gel septum is used for sealing, before starting the extraction, nitrogen is blown for 10 minutes to remove water in the headspace; Step 2: Place the sample-containing headspace bottle in an oil bath and heat at 60-80 DEG C for 5 minutes; Step 3: Install the sintered red clay coating solid-phase extraction fiber on the SPME handle, pass the sintered red clay coating solid-phase extraction fiber through the septum by the handle, so that the sintered red clay coating solid-phase extraction fiber is exposed to the mineral oil sample headspace for moisture extraction, the extraction time is 10-30 minutes, and the stirring speed is 200-700 rpm; Step 4: After the extraction is completed, the sintered red clay coating solid-phase extraction fiber is desorbed and then analyzed by GC-TCD.
9. Use of a sintered red clay coating solid phase extraction fibre according to claim 8, characterised in that, The extraction conditions in step 3 are that the extraction time is 30 minutes, and the stirring speed is 500 rpm.
10. Use of a sintered red clay coating solid phase extraction fiber according to claim 8, characterized in that, In step 4, the sintered red clay coating solid-phase extraction fiber is retracted into the handle and immediately inserted into the GC injection port, desorbed for 5 minutes, and the desorption temperature is 300 DEG C.