Method for detecting content of dimeticone in silicone oil cream

Abstract

The invention discloses a method for detecting the content of dimeticone in silicone oil cream, and relates to the technical field of component detection. The method comprises the following steps: dispersing a sample by using an n-hexane saturated dispersing agent, then carrying out liquid-liquid extraction by using n-hexane, combining extracting solutions and fixing the volume to obtain a test solution; dissolving a dimeticone reference substance in n-hexane to prepare a reference substance solution; carrying out infrared spectrum detection on the dehydrated test sample and the reference substance solution, and determining the absorbance at a characteristic absorption peak; and calculating the content of dimeticone in the sample. By optimizing the preparation method of the test sample, the technical problems of incomplete extraction and unstable determination of dimeticone in a complex matrix are effectively solved. The dispersing agent saturated by the normal hexane ensures clear two-phase separation, and the extraction efficiency is remarkably improved by combining quantitative extraction of the normal hexane; the method is high in specificity, high in accuracy and good in reproducibility, and a reliable technical means is provided for quality control of the silicone oil cream.

Description

Technical Field

[0001] This invention relates to the field of component detection technology, and in particular to a method for detecting the content of dimethicone in silicone oil cream. Background Technology

[0002] Silicone cream is a commonly used preparation for preventing and treating chapped skin on the hands and feet, as well as dermatitis caused by acidic substances. Its main active ingredient is dimethicone (polydimethylsiloxane), supplemented with base ingredients such as stearic acid, lanolin, petrolatum, ethylparaben, triethanolamine, and glycerin. Dimethicone, as a colorless, odorless, non-toxic, and non-irritating transparent oily liquid, has good chemical stability and can quickly form a protective film on the skin surface while allowing water vapor to penetrate. Therefore, it provides suitable occlusion without affecting normal skin respiration and sweat evaporation, and is thus widely used in moisturizing preparations and skin care products.

[0003] Regarding content determination, the Chinese Pharmacopoeia, Part II, currently uses gravimetric methods for the determination of dimethicone aerosols and tablets. This method requires multiple extractions with chloroform, filtration, washing, and drying to constant weight, making the process quite cumbersome. Furthermore, the Chinese Pharmacopoeia, Part IV, uses attenuated total reflectance infrared spectroscopy for the determination of dimethicone excipient content. While dimethicone lacks characteristic ultraviolet absorption peaks, its infrared absorption is significant and highly specific; some literature reports the use of infrared spectrophotometry (liquid cell method) for determination. However, the presence of various matrix excipients in silicone oil creams makes this method difficult to directly apply to the determination of dimethicone content in cream formulations. Currently, there is a lack of technology for detecting dimethicone content in oil-in-water creams.

[0004] Existing technologies, such as the invention patent "A Method for Determining the Content of Dimethicone Emulsion" (Liu Chunyan), provide a method for determining the content of dimethicone emulsion, which involves extraction with hydrochloric acid solution and n-heptane, combined with infrared spectrophotometry at 1260 cm⁻¹. -1 The method, which measures absorbance, demonstrates good accuracy, repeatability, and recovery. The invention patent "A Method for Determining the Content of Dimethicone in Simethicone Emulsions" (by Yu Xiaoyan) discloses a method for determining the content of dimethicone in simethicone emulsions. This method, targeting simethicone emulsions, uses a mixture of toluene and dilute hydrochloric acid for extraction and achieves highly specific and precise content determination through infrared detection. The invention patent "A Method for Determining the Content of Dimethicone Powders" (by Liu Ping) provides a method for determining the content of dimethicone powders, using carbon tetrachloride as the extraction solvent and also based on infrared spectrophotometry. While these methods perform well in specific dosage forms, the reagents used, such as toluene and carbon tetrachloride, have shortcomings in terms of safety and environmental friendliness.

[0005] Therefore, the aforementioned existing technologies are not effectively applicable to the content determination of silicone oil creams. This cream is an oil-in-water formulation with a complex matrix containing various excipients such as stearic acid, lanolin, and petrolatum. Its unique preparation process leads to two key problems in sample pretreatment: First, the cream sample is difficult to disperse uniformly in the solvent, resulting in incomplete extraction of dimethicone and deviations in the measured content. Second, existing methods often use volatile organic solvents (such as n-heptane, toluene, or carbon tetrachloride) for precise extraction, but these solvents are prone to evaporation during operation, introducing significant errors and leading to higher measured content. Therefore, developing a method suitable for the content determination of silicone oil creams that overcomes matrix interference, ensures complete extraction, reduces solvent errors, and is applicable to this field has become a pressing technical challenge. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to address at least one of the defects mentioned in the background art, and to provide a highly accurate method for detecting the dimethicone content in silicone oil creams.

[0007] To address the above problems, the present invention proposes the following technical solution: This invention provides a method for detecting the dimethicone content in silicone oil creams, comprising the following steps: (1) Preparation of test solution: Take a silicone oil cream sample, weigh it accurately, add a dispersant saturated with n-hexane to disperse the sample evenly, and then perform at least one liquid-liquid extraction with n-hexane. Combine the n-hexane extracts and dilute to volume with n-hexane to obtain the test solution. (2) Preparation of reference solution: Accurately weigh dimethicone reference standard, dissolve and dilute it with n-hexane to prepare reference solution; (3) Determination: Take the test solution and the reference solution respectively, add anhydrous sodium sulfate to dehydrate them, take the supernatant, and determine the absorbance at the characteristic absorption peak of dimethicone by infrared spectrophotometry. (4) Content calculation: Calculate the content of dimethicone in silicone oil cream based on the absorbance of the test solution and the reference solution.

[0008] The further technical solution is that, in step (1), the dispersant is methanol or acetonitrile, and the dispersant needs to be saturated with n-hexane.

[0009] The further technical solution is that, in step (1), the sample amount of the silicone oil cream is 0.2~0.8g, the amount of the dispersant saturated with n-hexane added is about 10~20mL, the volume of n-hexane used for extraction each time is 10~20mL, and the volumetric flask is a glass volumetric flask with a specification of 20~100mL.

[0010] A further technical solution is that, in step (2), the concentration of the reference solution is 1.0~4.0 mg / mL.

[0011] The further technical solution is that, in step (3), the dehydration treatment is to add 1.5~3.0g of anhydrous sodium sulfate to every 10 mL of solution, shake and centrifuge to take the supernatant.

[0012] A further technical solution is that, in step (3), the determination conditions for the infrared spectrophotometry are: using a potassium bromide liquid cell, scanning 25-40 times, and a wavenumber range of 1100 cm⁻¹. -1 ~1400 cm -1 Resolution 2~8 cm -1 .

[0013] A further technical solution is that, in step (3), the characteristic absorption peak of the dimethicone oil is 1260 cm⁻¹. -1 ~1263cm -1 The absorption peak of the wavenumber, wherein the absorbance is expressed as peak height.

[0014] The further technical solution is that, in step (4), the content of dimethicone is calculated using the following formula: Dimethicone content (%) = 100 × (W) S ×P×A U ×V U ) / (A S ×V S ×W U ×M) In the formula, W S The sample weight of the reference standard is in mg. P represents the content of the reference standard, % A U The absorbance of the test solution; A S The absorbance of the reference solution; V U This refers to the volume of the sample dissolved and the dilution factor. V S This refers to the volume of the reference standard dissolved and the dilution factor. W U The sample weight is in grams. M represents the labeled amount of dimethicone, in mg / g.

[0015] A further technical solution is that all containers that come into contact with the sample or reagent during the entire testing process are glass containers.

[0016] A further technical solution is that the silicone oil cream is an oil-in-water type cream.

[0017] Compared with the prior art, the technical effects achieved by the present invention include: The present invention provides a method for detecting dimethyl silicone oil content in silicone oil creams. During the preparation of the sample solution, a hexane-saturated dispersant is used to disperse the sample, enabling efficient dispersion of water-in-oil silicone oil creams with complex matrices. This minimizes the miscibility of the two solvent phases during subsequent liquid-liquid extraction, ensuring system stability. Further, multiple liquid-liquid extractions with hexane thoroughly disrupt the structure of the water-in-oil cream and efficiently and completely transfer the dimethyl silicone oil to the hexane phase, fundamentally overcoming the problems of incomplete sample extraction and low results. The combined hexane extract is then diluted to volume with hexane to eliminate the influence of volatile solvent volume changes. Finally, during determination, dehydration with anhydrous sodium sulfate is performed, followed by infrared spectrophotometry at the characteristic absorption peak. The detection method of this invention is highly specific, effectively eliminating interference from complex matrices. All operations together achieve a convenient, accurate, and reliable quantitative detection method for water-in-oil silicone oil creams with complex matrices. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 Infrared (IR) spectrum of a placebo solution without dimethicone.

[0020] Figure 2 The image shows the IR spectrum of the dimethicone reference solution.

[0021] Figure 3 The image shows the IR spectrum of the test solution.

[0022] Figure 4 This is a standard curve plot used in methodology verification experiments. Detailed Implementation

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0024] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0025] It should also be understood that the terminology used in this specification of embodiments of the invention is for the purpose of describing particular embodiments only and is not intended to limit the embodiments of the invention. As used in this specification of embodiments of the invention and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0026] It should be noted that in this invention, "precise weighing" means that the weight should be accurate to one-thousandth of the weight taken.

[0027] This invention provides a method for detecting the dimethicone content in silicone oil cream, comprising the following steps: (1) Preparation of test solution: Take a silicone oil cream sample, weigh it accurately, add a dispersant saturated with n-hexane to disperse the sample evenly, and then perform at least one liquid-liquid extraction with n-hexane. Combine the n-hexane extracts and dilute to volume with n-hexane to obtain the test solution. (2) Preparation of reference solution: Accurately weigh dimethicone reference standard, dissolve and dilute it with n-hexane to prepare reference solution; (3) Determination: Take the test solution and the reference solution respectively, add anhydrous sodium sulfate to dehydrate them, take the supernatant, and determine the absorbance at the characteristic absorption peak of dimethicone by infrared spectrophotometry. (4) Content calculation: Calculate the content of dimethicone in silicone oil cream based on the absorbance of the test solution and the reference solution.

[0028] In some embodiments, the sample size of the silicone oil cream is 0.2–0.8 g, for example, 0.3 g, 0.5 g, or 0.8 g. The amount of the hexane-saturated dispersant added is 10–20 mL, for example, 10 mL, 15 mL, or 20 mL. The volume of hexane used for extraction each time is 10–20 mL, for example, 10 mL, 15 mL, or 20 mL. The volumetric flask is a 20–100 mL glass volumetric flask, for example, 20 mL, 50 mL, or 100 mL.

[0029] In some embodiments, in step (2), the concentration of the reference solution is 1.0 to 4.0 mg of dimethicone per 1 mL, for example, 1.0 mg, 2.0 mg, 3.0 mg, or 4.0 mg.

[0030] In some embodiments, in step (3), the dehydration process involves adding 1.5 to 3.0 g (e.g., 1.5 g, 2.0 g, 2.5 g, 3.0 g) of anhydrous sodium sulfate to every 10 mL of solution, shaking, and then centrifuging to collect the supernatant.

[0031] In some embodiments, in step (3), the determination conditions for the infrared spectrophotometry are: using a potassium bromide liquid cell, scanning 25-40 times, and a wavenumber range of 1100 cm⁻¹. -1 ~1400 cm -1 Resolution 2~8 cm -1 .

[0032] In some embodiments, in step (3), the characteristic absorption peak of the dimethicone oil is 1260 cm⁻¹. -1 ~1263cm -1 The absorption peak of the wavenumber, wherein the absorbance is expressed as peak height.

[0033] In a specific embodiment, the present invention screened different extraction solvents and extraction methods in the preparation step of the test sample solution, as detailed below: 1) Direct extraction test: Approximately 0.5 g of silicone oil cream sample was accurately weighed and directly extracted with n-hexane. The results showed that n-hexane could not effectively disperse the silicone oil cream matrix, and the dimethyl silicone oil was not completely extracted, indicating that n-hexane alone is not suitable for this sample.

[0034] 2) Acid dispersion extraction test: Approximately 0.5 g of silicone oil cream sample was accurately weighed and added to 10 mL of dilute hydrochloric acid solution (mass fraction of 9.5%–10.5%, 10.0% dilute hydrochloric acid was used in this example). The sample was sonicated for 10 minutes to disperse the matrix, and then hexane was added for extraction. The results showed that the sample was still not evenly dispersed, and the measured content was about 10% lower than the actual amount added, proving that the extraction method was incomplete.

[0035] 3) Methanol dispersion and precise addition extraction test: Approximately 0.5 g of silicone oil cream sample was accurately weighed, 10 mL of methanol was added, and the mixture was sonicated for 10 minutes to disperse the matrix. Then, 20 mL of n-hexane was precisely added for ultrasonic extraction. Clearly, methanol effectively disperses the matrix and releases the encapsulated dimethyl silicone oil. However, this method has two problems: First, the measured content is about 10% higher than the actual amount added. The reason is that methanol and n-hexane are miscible during sonication, and n-hexane is highly volatile, resulting in a reduction in the actual volume of precisely added n-hexane and thus a falsely high concentration. Second, the absorbance of the same test solution fluctuated in two consecutive measurements, while the control solution did not exhibit this phenomenon. This is because a small amount of methanol dissolved in the n-hexane affected the stability of the measurement.

[0036] 4) Saturated Methanol Dispersion and Quantitative Extraction Experiment: To address the issues mentioned in 3), this example uses hexane-saturated methanol as the dispersant, building upon the method described in 3). The effects of adding 5 mL, 10 mL, 15 mL, and 20 mL of saturated methanol on the dispersion and content determination were investigated. The results showed that adding 5 mL resulted in incomplete dispersion and a lower content; adding 10 mL, 15 mL, and 20 mL resulted in complete dispersion and accurate determination results with no significant differences between the additions.

[0037] Based on ease of operation and reagent dosage, the final determined amount of methanol (saturated with n-hexane) added in step 4) was 15 mL. Furthermore, since methanol and n-hexane are only partially miscible, the n-hexane extracts can be combined using liquid-liquid extraction with n-hexane and quantitatively transferred to a 50 mL volumetric flask, then diluted to volume with n-hexane. This completely eliminates volume errors introduced by solvent evaporation and miscibility, eliminating the need for precise addition of n-hexane.

[0038] It should be noted that in this invention, the dispersant methanol can penetrate and disrupt the structure of the oil-in-water emulsion, ensuring uniform dispersion and releasing the encapsulated dimethyl silicone oil. Simultaneously, methanol is partially miscible with n-hexane, forming a temporary emulsion or two-phase system. Shaking provides a large contact surface area, allowing the dimethyl silicone oil to be efficiently distributed (extracted) into the n-hexane layer. Subsequently, rapid stratification facilitates separation. Therefore, this invention effectively extracts dimethyl silicone oil from silicone oil emulsion samples using hexane-saturated methanol. In other embodiments, acetonitrile can be used instead of methanol as the dispersant, both satisfying the characteristics of being miscible with water, penetrating and disrupting the structure of the oil-in-water emulsion, and being partially miscible with n-hexane, thus enabling liquid-liquid extraction by n-hexane. The dispersant must be saturated with n-hexane to reduce volume changes caused by the mutual dissolution of the dispersant and n-hexane during liquid-liquid extraction, thereby ensuring the precision and accuracy of the measurement results.

[0039] Based on the above experiments, the optimal method for preparing the test sample solution finally established by this invention is as follows: Accurately weigh approximately 0.5 g of silicone oil cream sample and place it in a stoppered conical flask. Add approximately 15 mL of methanol (saturated with n-hexane), seal tightly, and sonicate with occasional shaking until the sample is evenly dispersed. Transfer the mixture to a separatory funnel. Wash the conical flask with 15 mL of n-hexane, adding the washings to the separatory funnel. Shake thoroughly and allow to stand for separation. Separate the lower methanol layer and place it back into the original conical flask. Transfer the upper n-hexane layer to a 50 mL volumetric flask. Transfer the methanol layer from the conical flask back to the same separatory funnel, wash the conical flask with 15 mL of n-hexane, adding the washings to the separatory funnel. Shake thoroughly and allow to stand for separation. Separate the n-hexane layer from this step and combine it with the previous 50 mL volumetric flask. Dilute to the mark with n-hexane and shake well.

[0040] In specific embodiments, the present invention has screened different sample concentrations and injection methods in the preparation step of the reference solution, as detailed below: Dimethicone n-hexane reference solutions with concentrations of 1.0 mg / mL, 2.0 mg / mL, 3.0 mg / mL, and 4.0 mg / mL were prepared, and their spectra were scanned by infrared spectrophotometry. The results showed that the peak shape was optimal at a concentration of 2 mg / mL, and the response value was within the linear range. Therefore, the optimal concentration of dimethicone in the test solution was determined to be 2 mg / mL.

[0041] In the initial precision test, the sample solution was injected using a 1 mL plastic syringe. The relative standard deviation (RSD) of the instrument precision was greater than 3%, which did not meet the requirements. Analysis suggested that hexane has a dissolving effect on the plastic syringe material (such as polystyrene) and its additives, potentially introducing interfering substances. Therefore, the injection tool was replaced with a glass syringe, and the instrument precision RSD was tested again. This time, the RSD met the requirements (typically ≤2.0%). Therefore, in the detection method of this invention, all containers in contact with the sample or solvent are determined to be glass containers.

[0042] In summary, the method for detecting the dimethicone content in silicone oil cream provided by the preferred embodiment of the present invention includes the following steps: (1) Preparation of reference solution: Accurately weigh an appropriate amount of dimethicone reference standard, dissolve it in n-hexane and dilute quantitatively to prepare a solution containing 2.0 mg of dimethicone per 1 mL. The solution is stable for 5 days when stored at 2–8 °C.

[0043] (2) Preparation of the test solution: Accurately weigh approximately 0.5 g of silicone oil cream sample and place it in a stoppered conical flask. Accurately add 15 mL of methanol saturated with n-hexane, stopper tightly, sonicate, and shake frequently to ensure uniform sample dispersion. Transfer the solution to a separatory funnel, and wash the conical flask several times with 15 mL of n-hexane, adding the washings to the separatory funnel. After thorough shaking, allow the layers to separate. Separate the lower methanol layer into the original conical flask, and transfer the upper n-hexane layer to a 50 mL volumetric flask. Pour the methanol layer from the conical flask back into the separatory funnel, wash the conical flask with 15 mL of n-hexane, adding the washings to the separatory funnel, and repeat the extraction once. Combine the two n-hexane extracts in the same 50 mL volumetric flask, dilute to the mark with n-hexane, and shake well. This solution is stable for 1 day when stored at 2–8 °C.

[0044] (3) Determination: Accurately measure 10 mL each of the test solution and the reference solution, and place them separately in stoppered glass centrifuge tubes. Add 2.0 g of anhydrous sodium sulfate, shake, and centrifuge at 3000 rpm for 5 minutes. Take the supernatant, pour it into a 0.5 mm potassium bromide liquid cell and fill it completely (be careful to avoid introducing air bubbles). After sealing, wipe the window clean and place it in the infrared light path to collect the spectrum. Scanning conditions: 32 scans, wavenumber range 1400 cm⁻¹ -1 ~1100cm -1 4cm resolution -1 At 1261 cm -1 Absorbance was measured at wavenumber (expressed as peak height).

[0045] (4) Content Calculation: The content of polydimethylsiloxane in the sample is calculated using the following formula: Dimethicone content (%) = 100 × (W) S ×P×A U ×V U ) / (A S ×V S ×W U ×M) In the formula, W S The sample weight of the reference standard is in mg. P represents the content of the reference standard, % A U The absorbance of the test solution; A S The absorbance of the reference solution; V U This refers to the volume of the sample dissolved and the dilution factor. V S This refers to the volume of the reference standard dissolved and the dilution factor. W U The sample weight is in grams. M represents the labeled amount of dimethicone, in mg / g.

[0046] The detection method of the above preferred embodiment was validated methodologically: I. Exclusivity Prepare blank solution: Take 10 mL of n-hexane, add 2 g of anhydrous sodium sulfate, shake, centrifuge at 3000 rpm for 5 minutes, and take the supernatant.

[0047] Preparation of a placebo solution without dimethicone: Accurately weigh approximately 0.4 g of the dimethicone-free cream sample and place it in a stoppered conical flask. Add approximately 15 mL of methanol (saturated with n-hexane), stopper tightly, sonicate and shake intermittently until the sample is evenly dispersed. Transfer the solution to a separatory funnel. Wash the conical flask with 15 mL of n-hexane, adding the washings to the separatory funnel. Shake thoroughly and allow to stand to separate the layers. Separate the methanol layer and place it in the conical flask. Separate the n-hexane layer and place it in a 50 mL volumetric flask. Transfer the methanol layer to the separatory funnel and wash the conical flask with 15 mL of n-hexane, adding the washings to the separatory funnel. Shake thoroughly and allow to stand to separate the layers. Separate the n-hexane layer and place it in the volumetric flask. Dilute to the mark with n-hexane and shake well. Take 10 mL of the solution and place it in a stoppered glass centrifuge tube. Add 2 g of anhydrous sodium sulfate, shake, and centrifuge at 3000 rpm for 5 minutes. Collect the supernatant.

[0048] Using the blank solution as background subtraction, placebo solution, control solution, and test solution were taken respectively, and spectra were acquired by scanning under the spectral conditions of step (3) in the best embodiment. The results are shown in […]. Figures 1-3 The experimental results showed that both the reference solution and the test solution were within 1261 cm⁻¹. -1 The wavenumber showed a characteristic peak; the placebo solution without dimethicone showed a peak at 1261 cm⁻¹. -1 The absence of an absorption peak in the wavenumber indicates that the detection method provided by this invention has good specificity for dimethicone.

[0049] II. Instrument Precision Weigh approximately 40 mg of dimethicone reference standard (content: 100%) accurately, place it in a 20 mL volumetric flask, add n-hexane to dissolve and dilute to the mark, and shake well (actual concentration: 2.2340 mg / mL).

[0050] Take 10 mL (2 portions) of the above reference solution and place them in stoppered glass centrifuge tubes. Add 2 g of anhydrous sodium sulfate, shake, and centrifuge at 3000 rpm for 5 minutes. Take the supernatant and scan and collect the spectrum according to the spectral conditions of step (3) in the best embodiment. Measure the 1261 cm⁻¹ spectrum. -1 The absorbance near the wavenumber (expressed as peak height) was measured 6 times, with each measurement performed by re-injecting the sample. The reference solution was injected 6 times consecutively. The results are shown in Table 1.

[0051] Table 1. Results of instrument precision test (n=6) The precision RSD value of the dimethicone peak height measured in this embodiment is 1.4%, indicating that the detection method provided by the present invention has good precision.

[0052] III. Linearity and Detection Range Preparation of dimethicone reference standard stock solution: Weigh approximately 200 mg of dimethicone reference standard (content: 100%) accurately, place it in a 50 mL volumetric flask, add n-hexane to dissolve and dilute to the mark, and shake well (actual concentration: 4.2164 mg / mL).

[0053] Preparation of linear solutions: Accurately measure 5 mL, 4 mL, 5 mL, 6 mL, and 8 mL of the above dimethicone reference standard stock solution and place them into 20 mL, 10 mL, 10 mL, 10 mL, and 10 mL volumetric flasks, respectively. Dilute to the mark with n-hexane to obtain linear solutions containing 1.0541 mg, 1.6866 mg, 2.1082 mg, 2.5298 mg, and 3.3731 mg of dimethicone per mL, respectively.

[0054] Take 10 mL of each of the above linear solutions and place them in different stoppered glass centrifuge tubes. Add 2 g of anhydrous sodium sulfate, shake, and centrifuge at 3000 rpm for 5 minutes. Take the supernatant and scan and collect the spectrum according to the spectral conditions of step (3) in the best embodiment. Measure the 1261 cm⁻¹ spectrum. -1 Absorbance near wavenumber (expressed as peak height). The results were plotted with dimethicone concentration on the x-axis and dimethicone absorbance on the y-axis to create a standard curve. The regression equation and correlation coefficient were then determined. The results are shown in Table 2. Figure 4 .

[0055] Table 2. Linear equations, linear ranges, and correlation coefficients of dimethicone. The results showed that dimethicone exhibited a good linear relationship with absorbance within the concentration range of 1.0541 mg / mL to 3.373 mg / mL, with correlation coefficients all greater than 0.999. These results indicate that the detection method provided by this invention demonstrates good linearity within the aforementioned range and meets the requirements for quantitative analysis.

[0056] IV. Precision (1) Repeatability test Two reference solutions and six test solutions were prepared from the same batch of samples according to steps (1) and (2) in the best embodiment. The content of dimethicone was determined by sampling according to step (3). The results are shown in Table 3. The RSD of the content determination results of the six test solutions was 1.0%, indicating that the test method provided by the present invention has good repeatability.

[0057] Table 3 Repeatability test results (batch number: 20250126, n=6) (2) Intermediate precision test Two analysts performed measurements on different dates using the same batch of samples. Two reference solutions and six test solutions were prepared according to steps (1) and (2) of the preferred embodiment. The dimethicone content was determined by sampling according to step (3), and the results are shown in Table 4. The RSD of the dimethicone content determination results in the six test solutions was 0.5%, and the RSD of the dimethicone content determination results in the 12 test solutions of repeatability was 0.7%, indicating that the intermediate precision of the test method provided by the present invention is good. V. Accuracy Reference solution: prepared according to step (1) in the best embodiment.

[0058] Preparation of the test solution for recovery rate: Accurately weigh 6 portions of silicone oil cream sample, each approximately 0.25 g, and place them in stoppered conical flasks. Accurately add approximately 50 mg of dimethicone reference standard to each portion, and add approximately 15 mL of methanol (saturated with n-hexane). Stopper tightly, sonicate, and shake intermittently until the sample is evenly dispersed. Transfer the solution to a separatory funnel. Wash the conical flask with 15 mL of n-hexane, adding the washings to the separatory funnel. Shake thoroughly, allow to stand to separate the layers, and separate the methanol layer into the same conical flask. Separate the hexane layer into a 50 mL volumetric flask. (The process is repeated in the original text.)

[0059] Take 10 mL of each of the above reference solution and recovery test solution and place them in stoppered glass centrifuge tubes. Add 2 g of anhydrous sodium sulfate, shake, and centrifuge at 3000 rpm for 5 minutes. Collect the supernatant. Scan and collect the spectrum according to the spectral conditions in step (3) and measure the 1261 cm⁻¹ spectrum. -1 The absorbance near the wavenumber (expressed as peak height) was measured, and the recovery rate was calculated. The results are shown in Table 5. The recovery rates of the six samples and the average recovery rate were all within the range of 97.1% to 101.5%, and the RSD of the six recovery rates was 1.8%, indicating that the detection method of the present invention has good accuracy.

[0060] Table 5. Accuracy test results (batch number: 20250126, n=6) Note: The amount of dimethicone oil in the sample (mg) refers to the theoretical value calculated based on the sample weight and the labeled content.

[0061] VI. Solution Stability (1) Stability of the reference solution Prepare the reference solution according to step (1) in the preferred embodiment and store it under refrigeration (2~8℃) and room temperature conditions. At different times (0 days, 1 day, 2 days, 5 days and 7 days), take about 10 mL and place it in a stoppered glass centrifuge tube, add 2 g of anhydrous sodium sulfate, shake, and centrifuge at 3000 rpm for 5 minutes. Take the supernatant and determine the reference solution at 1261 cm⁻¹ according to step (3). -1 The absorbance near the wavenumber was measured, and the percentage ratio of the absorbance of dimethicone oil at day 0 to that at each time point was calculated. Three parallel samples were used, and the average value of the results was taken. The experimental results are shown in Table 6.

[0062] Table 6 Results of stability test of reference solution Under refrigerated conditions (2–8 °C), the percentages of the ratios of the average absorbance of dimethicone in the reference solution on day 0 to the average absorbance on days 1, 2, and 5 were all within the range of 98%–102%, while the percentage for day 7 exceeded this range. This indicates that the reference solution was stable after 5 days of refrigerated storage (2–8 °C). At room temperature, the percentages of the ratios of the average absorbance of dimethicone in the reference solution on day 0 to the average absorbance on day 1 were also within the range of 98%–102%, while the percentages for days 2, 5, and 7 all exceeded this range. This indicates that the reference solution was stable after 1 day of storage at room temperature.

[0063] (2) Stability of the test solution Prepare the test solution according to step (2) in the preferred embodiment and store it under refrigeration (2~8℃) and room temperature conditions. At different times (0 days, 1 day, 2 days, 5 days and 7 days), take about 10 mL and place it in a stoppered glass centrifuge tube, add 2 g of anhydrous sodium sulfate, shake, centrifuge at 3000 rpm for 5 minutes, take the supernatant and measure 1261 cm⁻¹ according to step (3). -1 The absorbance near the wavenumber was calculated, and the percentage of the dimethicone absorbance ratio at day 0 to each time point was calculated. The test results are shown in Table 7. Three parallel samples were used, and the average value of the results was taken.

[0064] Table 7 Results of the stability test of the test sample solution Under refrigerated conditions (2~8 ℃), the percentage of the average absorbance of the test solution at day 0 divided by the average absorbance of the test solution at day 1 was within the range of 98%~102%. The percentages of the ratios at days 2, 5, and 7 exceeded the range of 98%~102%. This indicates that the test solution is stable after 1 day of storage under refrigerated conditions (2~8 ℃). At room temperature, the percentages of the average absorbance of the test solution at day 0 divided by the average absorbance of the test solution at days 1, 2, and 5 were all within the range of 98%~102%. The percentage of the ratio at day 7 exceeded the range of 98%~102%. This indicates that the test solution is stable for 5 days at room temperature.

[0065] VII. Durability Test Prepare the reference solution and the test solution according to steps (1) and (2) in the preferred embodiment. Adjust the number of scans and resolution appropriately for the spectral conditions in step (3) to conduct the experiment and examine the changes in the sample content determination results after the spectral conditions change.

[0066] (1) Effect of the number of scans on the content determination results The number of scans was reduced by 4 and increased by 4, i.e., the number of scans was adjusted from 32 to 28 and 36 respectively, while other conditions remained unchanged. The changes in the sample content determination results were observed. The experimental results are shown in Table 8. Appropriate changes in the number of scans (±4 times) did not affect the sample content determination results.

[0067] Table 8. Durability Test 1 Results (Variable: Number of Scans) (2) Effect of resolution on content determination results Reduce resolution by 2 cm -1 and increase by 4 cm -1 That is, 4 cm -1 The resolution was adjusted to 2 cm. -1 With 8 cm -1 With all other conditions unchanged, the changes in sample content determination results were examined. The experimental results are shown in Table 9. The resolution was appropriately varied (+4 cm). -1 or -2 cm -1 This does not affect the sample content determination results.

[0068] Table 9. Durability Test 2 (Variable: Resolution) Results In summary, the detection method of this invention, through optimized pretreatment (preparation of the test solution), effectively solves the technical problems of incomplete extraction and unstable determination of dimethicone in complex matrices. The hexane-saturated dispersant ensures clear separation of the two phases, and combined with quantitative extraction with hexane, significantly improves extraction efficiency. Finally, quantification is performed by infrared spectroscopy. The method is highly specific, accurate, and reproducible, providing a reliable technical means for the quality control of silicone oil creams.

[0069] VIII. Determination of content in actual samples Different batches of samples were taken to prepare reference solutions and test solutions according to steps (1) and (2) in the best embodiment, and the dimethicone content in the silicone oil cream samples was determined and calculated according to steps (3) and (4). The results are shown in Table 10.

[0070] Table 10 Results of Sample Content Determination In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0071] The above description describes specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for detecting the dimethicone content in silicone oil cream, characterized in that, Includes the following steps: (1) Preparation of test solution: Take a silicone oil cream sample, weigh it accurately, add a dispersant saturated with n-hexane to disperse the sample evenly, and then perform at least one liquid-liquid extraction with n-hexane. Combine the n-hexane extracts and dilute to volume with n-hexane to obtain the test solution. (2) Preparation of reference solution: Accurately weigh dimethicone reference standard, dissolve and dilute it with n-hexane to prepare reference solution; (3) Determination: Take the test solution and the reference solution respectively, add anhydrous sodium sulfate to dehydrate them, take the supernatant, and determine the absorbance at the characteristic absorption peak of dimethicone by infrared spectrophotometry. (4) Content calculation: Calculate the content of dimethicone in silicone oil cream based on the absorbance of the test solution and the reference solution.

2. The detection method according to claim 1, characterized in that, In step (1), the dispersant is methanol or acetonitrile, and the dispersant needs to be saturated with n-hexane.

3. The detection method according to claim 1, characterized in that, In step (1), the sample amount of the silicone oil cream is 0.2~0.8g, the amount of the dispersant saturated with n-hexane added is 10~20mL, the volume of n-hexane used for extraction each time is 10~20mL, and the volumetric flask is a glass volumetric flask with a specification of 20~100mL.

4. The detection method according to claim 1, characterized in that, In step (2), the concentration of the reference solution is 1.0~4.0 mg / mL.

5. The detection method according to claim 1, characterized in that, In step (3), the dehydration process involves adding 1.5 to 3.0 g of anhydrous sodium sulfate to every 10 mL of solution, shaking, and then centrifuging to collect the supernatant.

6. The detection method according to claim 1, characterized in that, In step (3), the determination conditions for the infrared spectrophotometry are as follows: using a potassium bromide liquid cell, scanning 25-40 times, and a wavenumber range of 1100 cm⁻¹. -1 ~1400 cm -1 Resolution 2~8 cm -1 .

7. The detection method according to claim 1, characterized in that, In step (3), the characteristic absorption peak of the dimethicone oil is 1260 cm⁻¹. -1 ~1263cm -1 The absorption peak of the wavenumber, wherein the absorbance is expressed as peak height.

8. The detection method according to claim 1, characterized in that, In step (4), the content of dimethicone is calculated using the following formula: Dimethicone content (%) = 100 × (W) S ×P×A U ×V U ) / (A S ×V S ×W U ×M) In the formula, W S The sample weight of the reference standard is in mg. P represents the content of the reference standard, % . A U The absorbance of the test solution; A S The absorbance of the reference solution; V U This refers to the volume of the sample dissolved and the dilution factor. V S This refers to the volume of the reference standard dissolved and the dilution factor. W U The sample weight is in grams. M represents the labeled amount of dimethicone, in mg / g.

9. The detection method according to claim 1, characterized in that, Throughout the entire testing process, all containers that come into contact with the sample or reagent are glassware.

10. The detection method according to claim 1, characterized in that, The silicone oil cream is an oil-in-water emulsion.

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