A method for rapid identification of white vaseline from different manufacturers based on silver salt-assisted laser desorption ionization-time of flight mass spectrometry

Abstract

The present invention relates to a method for quickly identifying white vaseline from different manufacturers based on silver salt-assisted laser desorption ionization-time of flight mass spectrometry, and belongs to the field of detection. Specifically comprising the following steps: S1, exploring and optimizing metal salt ion conditions, matrix conditions, and sampling methods, and using the optimized experimental conditions for sample preparation; S2, measuring the sample; S3, using eMSTAT Solution software for data analysis to achieve identification of white vaseline from different manufacturers. The method of the present invention replaces traditional organic matrices with silver salts, eliminates background interference, and improves the mass spectrometry signal-to-noise ratio; combines a direct smearing method to avoid complex solvent preparation and extraction, and is easy to operate; applies a mass spectrometer for mass spectrometry acquisition, has accurate molecular weight, reduces the detection time of each sample to 6 seconds, has high analytical throughput, and is low in cost, thereby achieving high-throughput, accurate, and rapid identification of large quantities of white vaseline from different sources.

Description

Technical Field

[0004] , ,

[0005] , ,

[0001] The present invention belongs to the field of detection, and relates to a method for rapidly identifying white petrolatum from different manufacturers based on silver salt assisted laser desorption ionization-time of flight mass spectrometry (Ag-LDI-TOF MS). Background Art

[0002] White petrolatum is a semi-solid mixture of various hydrocarbons obtained from petroleum and subjected to decolorization treatment. It appears as a uniform ointment-like substance from white to slightly yellowish, and is a commonly used excipient in current pharmaceutical products, widely used as the matrix for pharmaceutical preparations such as ointments, creams, ointments, and lotions. To ensure the safety and effectiveness of the use of pharmaceutical-grade white petrolatum, the 2020 edition of the Chinese Pharmacopoeia has clearly defined the quality standards for pharmaceutical-grade white petrolatum, such as requirements in terms of impurities, solvent residues, etc.

[0003] Due to differences in raw material sources and processing technologies, there are differences in the composition and proportion of white petrolatum produced by different manufacturers, and there are differences in the molecular weight composition, which greatly affects the stability of the properties of ointments. White petrolatum is composed of a complex mixture, and it is difficult for gas chromatography-mass spectrometry (GC-MS) to analyze substances with relatively large molecular weights and low volatility. When analyzing by liquid chromatography-mass spectrometry (LC-MS), complex pretreatment of samples is required and the data is complex. Although gel permeation chromatography (GPC) or size exclusion chromatography (SEC) can be used to measure the molecular weight distribution of polymers and high molecular weight substances, it depends on standard substances and is not suitable for precise analysis of small molecular weights. Therefore, the prior art lacks a rapid and accurate analysis method for the molecular composition of white petrolatum.

[0004] In terms of molecular weight detection, matrix-assisted laser desorption-ionization time-of-flight mass spectrometry (MALDI-TOF) has advantages such as soft ionization and fast analysis speed. However, traditional MALDI-TOF requires the use of organic matrices (such as DHB, CHCA), resulting in background interference peaks in the low mass range (<m / z 500), which limits its application in the analysis of small hydrocarbon molecules. In recent years, surface-assisted laser desorption ionization mass spectrometry (SALDI-MS) technology has received attention because it does not require the use of traditional organic matrices. Nanomaterials (such as graphene, metal nanoparticles) are widely used in SALDI-MS, but the synthesis of nanomaterials is complex and impurities are easily introduced. Summary of the Invention

[0005] Metal-assisted laser desorption ionization (SALDI), a subclass of SALDI, achieves ionization by forming adducts (e.g., [hydrocarbon + Ag]⁺) between metal ions (e.g., Ag⁺) and the sample, effectively circumventing matrix interference. However, existing studies have not systematically optimized the complex compositional characteristics of white vaseline. Conventional sample pretreatment generally requires dissolution or dilution (e.g., using chloroform or toluene), which is cumbersome and easily alters the original composition. Application of non-optimized metal salt types or concentrations can lead to uneven sample crystallization and poor signal reproducibility. Therefore, the development of an Ag-LDI-TOF MS method based on matrix-free and solvent-free extraction to achieve rapid in situ identification of the molecular composition of white vaseline is of great significance for improving the efficiency of pharmaceutical excipient quality control.

[0006] The present invention provides a method for rapidly identifying white vaseline from different manufacturers based on silver-assisted laser desorption ionization-time of flight mass spectrometry (Ag-LDI-TOF MS). By replacing the traditional matrix with Ag salt, background interference is eliminated and the signal-to-noise ratio is improved. The method employs a direct smearing method for spotting, which is simple to operate and avoids the effects of traditional solvent extraction on the sample, while also reducing the cost of related detection reagents. Analysis using a time-of-flight mass spectrometer can complete the testing of 100 white vaseline samples within 10 minutes, enabling rapid manufacturer tracing based on differences in molecular composition. This method is simple to operate and requires minimal technical expertise, providing a highly efficient solution for the quality control of white vaseline.

[0007] Specifically, the present invention establishes a method for rapidly identifying white vaseline from different manufacturers based on silver-assisted laser desorption ionization-time of flight mass spectrometry, which includes preparation of the test sample, Ag-LDI-TOF MS determination, data processing and PCA analysis;

[0008] S1, preparation of the sample to be tested: exploring and optimizing the metal salt ion conditions, matrix conditions, and spotting method for the sample to be tested; spotting using the optimized experimental conditions, namely: applying a white vaseline sample evenly on a target plate; spotting an Ag salt solution on the target plate and allowing it to dry naturally;

[0009] S2, Ag-LDI-TOF MS determination: The target plate obtained by S1 was placed in a MALDI-TOF mass spectrometer, and the following mass spectrometry conditions were applied for mass spectrometry acquisition: the tuning mode was positive ion linear mode, the laser type was a 355 nm solid-state laser, the scan range was set to m / z 1-2000, the pulse delay extraction was set to 1500 Da, the laser energy was set to 40%-50%, and the laser scanning frequency was 100 Hz;

[0010] S3, data processing and PCA analysis: perform data analysis on the collected mass spectra and export the mass spectrometry data into ASCII format files; perform PCA analysis using the data statistics software eMSTAT Solution.

[0011] In an embodiment of the present invention, in S1, the white vaseline sample is directly applied to the target plate for spotting, the sample volume is within 0.5 μL, and a new cotton swab is used to wipe.

[0012] In an embodiment of the present invention, in S1, the white vaseline sample is directly applied to the target plate for spotting, and the sample sampling volume is preferably within 0.1 μL, and is wiped with a new cotton swab.

[0013] In an embodiment of the present invention, in S1, the white vaseline sample is dissolved in dichloromethane and then spotted, and the sample concentration is 0.1-10 mg / mL.

[0014] In an embodiment of the present invention, in S1, the white vaseline sample is dissolved in dichloromethane and then spotted, and the sample concentration is 0.1-0.5 mg / mL.

[0015] In an embodiment of the present invention, in S1, the Ag salt solution is an AgTFA solution, which is dissolved in tetrahydrofuran or water.

[0016] In an embodiment of the present invention, in S1, the Ag salt solution is an AgTFA solution, which is dissolved in tetrahydrofuran.

[0017] In an embodiment of the present invention, in said S1, the concentration of the Ag salt solution is 2-20 mg / mL, preferably 2 mg / mL.

[0018] In an embodiment of the present invention, in S1, the spotting volume of the Ag salt solution is 0.5-1 μL.

[0019] In an embodiment of the present invention, the spotting volume of the Ag salt solution is 0.5 μL.

[0020] In an embodiment of the present invention, the method is specifically:

[0021] S1. Preparation of the sample to be tested: Exploration of a) metal salt ion type and matrix conditions, b) metal salt solvent and concentration, and c) spotting method for the sample to be tested was conducted to confirm that Ag salts replacing traditional matrices (without matrix addition) are more effective in assisting sample ionization than adding conventional matrices or other types of metal salts, and to confirm the final sample preparation conditions. Samples were spotted using the optimized experimental conditions. The specific method was as follows: a small amount of white vaseline sample (within 0.1 µL) visible to the naked eye was picked up with a pipette tip and smeared on a stainless steel target plate. The sample was evenly spread with a cotton swab and wiped with a new cotton swab to ensure that no visible solids were left on the target. The dark mark produced by the sample wiping was evenly distributed and covered the entire target. 0.5 µL AgTFA tetrahydrofuran solution (2 mg / mL) was applied to the target and allowed to dry naturally. 12 target spots were prepared for each sample.

[0022] S2, Ag-LDI-TOF MS determination: The target plate was placed in the mass spectrometer, and the following mass spectrometry conditions were applied for mass spectrometry acquisition: the tuning mode was positive ion linear mode, the laser type was a 355 nm solid-state laser, the scan range was set to m / z 1-2000, the pulse delay extraction was set to 1500 Da, the laser energy was set to 40%-50%, the laser scanning frequency was 100 Hz, 150 profile images were collected for each sample, and 4 shots were collected for each image. The analysis time for a single sample was approximately 6 seconds;

[0023] S3, Data processing and principal component analysis (PCA) analysis: The collected mass spectra were preprocessed (including baseline subtraction and smoothing), and the mass spectrometry data were exported as ASCII format files. PCA analysis was performed using the data statistics software eMSTAT Solution to obtain the PCA analysis score graph.

[0024] In an embodiment of the present invention, the metal salts examined in substep S1a) include four conditions: no salt added, sodium salt (NaTFA), potassium salt (KI), and silver salt (Ag TFA). NaTFA, KI, and silver TFA powders were weighed and dissolved in water to prepare a 2 mg / mL aqueous solution. Upon use, 1 µL of the metal salt solution was applied to the target and allowed to dry naturally. The metal salt was preferably silver salt. Five matrix conditions were examined: no matrix added, 2,5-dihydroxybenzoic acid (DHB), α-cyano-4-hydroxycinnamic acid (CHCA), anthracenetriol, and trans-2-[3-(4-tert-butylphenyl)-2-methyl-2-propenylidene]malononitrile (DCTB). The matrix was prepared by dissolving solid 2,5-dihydroxybenzoic acid (DHB) and α-cyano-4-hydroxycinnamic acid (CHCA) in a 1:1:0.01 volume ratio of ACN / H₂O / TFA to form a 10 mg / mL matrix solution. Anthracenetriol was dissolved in tetrahydrofuran to form a 10 mg / mL matrix solution. Trans-2-[3-(4-tert-butylphenyl)-2-methyl-2-propenylidene]malononitrile (DCTB) was dissolved in dichloromethane to form a 10 mg / mL matrix solution. Matrix conditions were evaluated in conjunction with the type of metal salt. The optimal matrix conditions, i.e., no matrix addition, were preferred for optimal detection results when the sample was ionized with Ag salt as an auxiliary.

[0025] In an embodiment of the present invention, the AgTFA solvents examined in sub-step S1 b) are tetrahydrofuran and water, and the AgTFA concentrations examined are 2 mg / mL, 5 mg / mL, 10 mg / mL, and 20 mg / mL. The metal salt solvent is preferably tetrahydrofuran, and the concentration is preferably 2 mg / mL.

[0026] In an embodiment of the present invention, the sample spotting methods examined in sub-step S1 c) are dichloromethane dissolution and direct smearing. The sample concentrations used for dichloromethane dissolution are 0.1 mg / mL, 0.5 mg / mL, 1 mg / mL, 5 mg / mL, and 10 mg / mL. For water, the AgTFA concentrations examined are 2 mg / mL, 5 mg / mL, 10 mg / mL, and 20 mg / mL. The direct smearing method includes three methods: smearing a sample within a volume of 0.1 µL and wiping it with a new cotton swab, smearing a sample with a volume of about 0.1 µL without wiping it with a new cotton swab, and smearing a sample with a volume of about 0.5 µL without wiping it with a new cotton swab. The spotting condition is preferably to directly smear a sample within a volume of 0.1 µL and wipe it with a new cotton swab.

[0027] In an embodiment of the present invention, the mass spectrometer used is the Shimadzu benchtop MALDI-TOF mass spectrometer MALDI-8030. The implementation of the present invention is applicable to the same type of MALDI-TOF mass spectrometer. The instrument type is time-of-flight mass spectrometry, and the actually adopted ionization method is Ag salt-assisted laser desorption ionization (Ag-LDI), which is non-traditional MALDI.

[0028] In an embodiment of the present invention, in S3, after preprocessing the mass spectrometry data, PCA analysis is performed to obtain a PCA analysis graph. The software used is the Shimadzu data statistics software eMSTAT Solution. Principal component analysis (PCA) is a statistical method for extracting the core features of data through mathematical dimensionality reduction. In the present invention, the complex mass spectrometry data (thousands of m / z ion signals) of white petrolatum is compressed into a two-dimensional map, visually distinguishing the molecular composition differences of different manufacturers, and realizing rapid and objective quality traceability.

[0029] Beneficial effects:

[0030] This method innovatively uses silver salt (AgTFA) to replace the traditional organic matrix, completely eliminating the matrix background interference in the low molecular weight range (<m / z 500), and improving the signal-to-noise ratio of the mass spectrometry; combined with the original direct smear sampling method, only a white petrolatum sample with a size within 0.1 μL volume needs to be smeared on the target plate and wiped with a cotton swab to complete sample preparation, eliminating the solvent extraction step, avoiding the composition change caused by dichloromethane dissolution, simplifying the experimental operation, greatly shortening the sample pretreatment time, and saving reagent costs. The Ag-LDI-TOF MS detection is carried out on a time-of-flight mass spectrometer, and the single sample analysis time is only 6 seconds, realizing high-throughput detection of 100 samples within 10 minutes. Through the principal component analysis (PCA) algorithm, thousands of m / z mass spectrometry signals are compressed into a two-dimensional score map, accurately distinguishing the molecular composition differences of white petrolatum produced by different manufacturers (such as the ion characteristics of series 2 of manufacturer A and the long-chain hydrocarbon distribution of manufacturer D). The detection cost of this method is very low (only a微量 of Ag salt reagent is required for the sample, and the consumables are only tips, cotton swabs, etc.), the operation is simple, and the in-situ molecular composition analysis of semi-solid white petrolatum is realized for the first time, providing an efficient solution for the quality traceability of pharmaceutical excipients. Description of the drawings

[0031] Figure 1 It is an example of the mass spectrometry graph of white petrolatum detected under different metal salt conditions without adding a matrix in Example 2;

[0032] Figure 2 It is an example of the mass spectrometry graph of white petrolatum detected under different matrix conditions with AgTFA as the metal salt in Example 2;

[0033] Figure 3This is a crystallization diagram of white vaseline samples under AgTFA conditions with different solvents and salt concentrations in Example 3;

[0034] Figure 4 This is an example of the mass spectrum of white vaseline samples under AgTFA conditions with different solvents and salt concentrations in Example 3;

[0035] Figure 5 The crystallization diagram of white vaseline sample under different spotting conditions in Example 4;

[0036] Figure 6 The mass spectra of white vaseline samples under different spotting conditions in Example 4 are shown;

[0037] Figure 7 Examples of mass spectra of white vaseline from five manufacturers in Example 5 (m / z 1-2000);

[0038] Figure 8 This is a partial magnified view of the mass spectra of white vaseline from five different manufacturers in Example 5 (m / z 350-1000);

[0039] Figure 9 This is the PCA analysis score graph of white vaseline from five manufacturers in Example 5. DETAILED DESCRIPTION

[0040] It is worth noting that the raw materials used in the present invention are all common commercially available products, and their sources are not specifically limited.

[0041] Example 1 Preliminary sample preparation

[0042] White vaseline is commercially available. At room temperature, use a pipette tip to apply a small amount (about the size of a needle tip) of white vaseline to the target spot on the stainless steel target plate. Use a cotton swab to evenly spread the sample and wipe off any excess. This will yield a white vaseline sample suitable for mass spectrometry analysis. The target spot should be free of visible solid matter but should have a distinct sample mark distinguishable from the sample-free area. Any visible semi-solid sample should be removed with a clean cotton swab.

[0043] Example 2 Screening and Optimization of Metal Salt Ions and Matrix Conditions

[0044] Preparation of metal salt solution

[0045] The salt ion conditions used for screening included: no salt, sodium salt (Na TFA), potassium salt (KI), and silver salt (Ag TFA). Weigh NaTFA, KI, and Ag TFA powders separately and dissolve them in water to prepare a 2 mg / mL aqueous solution. Prepare the sample according to Example 1. Apply 1 µL of each NaTFA, KI, and Ag TFA aqueous solution dropwise to the sample target surface and allow to air dry.

[0046] 2) Preparation of matrix solution

[0047] Five matrix conditions were optimized: no matrix, 2,5-dihydroxybenzoic acid (DHB), α-cyano-4-hydroxycinnamic acid (CHCA), anthracenetriol, and trans-2-[3-(4-tert-butylphenyl)-2-methyl-2-propenylidene]malononitrile (DCTB). The matrix preparation methods were as follows: 2,5-dihydroxybenzoic acid (DHB) and α-cyano-4-hydroxycinnamic acid (CHCA) solids were dissolved in ACN / H2O / TFA (volume ratio 1:1:0.01) to form a 10 mg / mL matrix solution; anthracenetriol was dissolved in tetrahydrofuran to form a 10 mg / mL matrix solution; and trans-2-[3-(4-tert-butylphenyl)-2-methyl-2-propenylidene]malononitrile (DCTB) was dissolved in dichloromethane to form a 10 mg / mL matrix solution.

[0048] 3) Sample preparation

[0049] Apply the sample to the target site according to the method described in Example 1. Apply 1 µL of salt solution and 1 µL of matrix solution (DHB, CHCA) to the target site in sequence and allow to air dry. When using DCTB and anthracenetriol as matrices, allow the salt solution to dry before adding the matrix solution. Each matrix type (no matrix, DHB, CHCA, anthracenetriol, DCTB) corresponds to four metal salt ion conditions (no salt, NaTFA, KI, AgTFA), for a total of 20 experimental conditions. Two targets were prepared in parallel for each experimental condition.

[0050] 4) Mass spectrometry acquisition

[0051] The target plate was placed in a Shimadzu MALDI-8030 time-of-flight mass spectrometer to acquire a mass spectrum of a white vaseline sample. Initial exploration of mass spectrometry parameters for a single sample revealed that the sample's mass spectrometric signal distribution was concentrated within m / z 2000, with optimal ionization in positive ion mode. Based on the molecular weight of the target compound and to increase sample detection speed, the following mass spectrometry analysis conditions were confirmed: positive ion linear mode, a 355 nm solid-state laser, a scan range of m / z 1-2000, pulse delay extraction of 1500 Da, laser energy of 40%-50%, and a laser scan frequency of 100 Hz. Each sample was analyzed with 150 profiles, each consisting of four shots. Peak processing parameters were baseline subtraction at 3 and smoothing at 2. The analysis time for a single sample was 6 seconds.

[0052] 5) Analyze the results

[0053] Some mass spectrometry signals were detected under all 20 analysis conditions. Taking no matrix as an example, when AgTFA was used as the added metal salt, the mass spectrometry signals detected in the sample were more abundant. Similar situations were observed for the other matrices ( Figure 1 ), so Ag salt is the best metal salt to use for sample analysis.

[0054] The analysis results of different matrices were compared. When AgTFA was used as the metal salt and no matrix was added, the sample was effectively ionized without background interference and the signal-to-noise ratio was good ( Figure 2 ), and the subsequent parameter optimization was carried out under this condition. When Ag was used as the metal salt and anthracenetriol was used as the matrix, the sample mass spectrum was rich in ions, but there was matrix peak interference on the mass spectrum ( Figure 2 Therefore, no matrix was added as the subsequent test condition.

[0055] Example 3 Optimization of solvent and salt concentration for dissolving AgTFA

[0056] Preparation of metal salt solution

[0057] Weigh AgTFA powder and dissolve it in water and tetrahydrofuran to prepare a 20 mg / mL AgTFA solution, which is then diluted to 10 mg / mL, 5 mg / mL, and 2 mg / mL in sequence to prepare 8 AgTFA solutions in total.

[0058] Sample preparation

[0059] Apply the sample to the target plate as described in Example 1. Use a pipette to apply 0.5 µL of the AgTFA solution to each target surface coated with white vaseline. Allow to dry naturally. Prepare two target surfaces for each sample. Observe the crystallization state of the sample.

[0060] Ag-LDI-TOF MS determination

[0061] The target plate was placed in the mass spectrometer to acquire a mass spectrum of the white vaseline sample. The mass spectrometry analysis conditions were as follows: positive ion linear mode, a 355 nm solid-state laser, a scan range of m / z 1-2000, pulse delay extraction at 1500 Da, laser energy at 40%-50%, a laser scan frequency of 100 Hz, 150 profiles per sample, each acquired with four shots, and peak processing parameters: baseline subtraction at 3 and smoothing at 2. The analysis time for a single sample was 6 seconds.

[0062] Analysis results

[0063] Comparison of crystallization state: The crystallization state of 8 samples is shown in Figure 3When AgTFA was dissolved in water and spotted, the salt crystals were unevenly distributed, with some localized aggregation. As the salt concentration increased, the salt crystals grew larger. When AgTFA was dissolved in tetrahydrofuran, the sample drying time was shorter, and the salt crystals were relatively evenly distributed. As the salt concentration increased, the salt crystals increased, with localized enrichment in several locations. The 2 mg / mL salt solution dissolved in tetrahydrofuran had the most uniform distribution.

[0064] Comparison of mass spectra: At the same concentration, the mass spectrometric signal intensity of white vaseline ionized with AgTFA assisted by tetrahydrofuran is significantly higher than that with water as solvent ( Figure 4 Using different concentrations of AgTFA dissolved in tetrahydrofuran as the auxiliary salt, the mass spectra and signal intensities of each sample were generally similar. In summary, water was eliminated due to its uneven crystallization and weak signal. The final metal salt ion condition was 2 mg / mL AgTFA dissolved in tetrahydrofuran.

[0065] Example 4 Exploration of sample spotting method

[0066] 1) Sample preparation

[0067] Two sample spotting methods were investigated: dissolving the sample before spotting and applying the sample directly to the target plate. Dichloromethane effectively dissolves white petrolatum and is a commonly used solvent in laboratory MALDI experiments. A small amount of white petrolatum was weighed and dissolved in dichloromethane (DCM) to prepare a 10 mg / mL sample solution. This solution was then diluted with dichloromethane to 5 mg / mL, 1 mg / mL, 0.5 mg / mL, and 0.1 mg / mL, and mass spectra were obtained for each of the five sample solution concentrations. 0.5 µL of the sample solution and 0.5 µL of a 2 mg / mL AgTFA solution in THF were then applied to the target plate and allowed to air dry. Two target spots were prepared in parallel for each analytical condition.

[0068] Three direct smearing conditions were tested: a. Using a 10 µL pipette tip, apply a small but visible volume of white vaseline (less than 0.1 µL) to a stainless steel target. Apply the sample evenly with a cotton swab and wipe with a fresh cotton swab to remove any visible solid matter and ensure that the dark mark from the sample smear is evenly distributed and covers the entire target. b. Using a 10 µL pipette tip, apply a small but visible volume of white vaseline (less than 0.1 µL) to a stainless steel target. Apply the sample evenly with a cotton swab without using a fresh cotton swab. c. Apply a larger amount of white vaseline (e.g., approximately 0.5 µL) to a target. Apply the sample evenly with a cotton swab without using a fresh cotton swab. Two target spots were smeared in parallel for each condition. 0.5 µL of a 2 mg / mL AgTFA solution in tetrahydrofuran was applied to the target and allowed to dry naturally.

[0069] 2) Ag-LDI-TOF MS determination

[0070] The target plate was placed in a MALDI-TOF mass spectrometer to acquire a mass spectrum of a white vaseline sample. Mass spectrometry analysis conditions were as follows: positive ion linear mode, a 355 nm solid-state laser, a scan range of m / z 1-2000, pulse delay extraction at 1500 Da, laser energy at 40%-50%, a laser scan frequency of 100 Hz, 150 profiles per sample, each acquired with four shots, and peak processing parameters set to baseline subtraction at 3 and smoothing at 2. The analysis time for a single sample was 6 seconds.

[0071] 3) Analysis results

[0072] See the pictures of target crystallization status under 8 different spotting conditions. Figure 5 , mass spectrum see Figure 6As shown in the figure, when the sample load is small (0.1 mg / mL dissolved in DCM; 0.5 mg / mL dissolved in DCM; less than 0.1 µL applied and wiped with a new cotton swab), the sample on the target spot shows fewer and more dispersed crystals, resulting in higher mass spectrum signal intensity and a greater abundance of ions above m / z 400. The mass spectrum of the 0.1 mg / mL (DCM) sample is superior to that of the 0.5 mg / mL (DCM) sample. As the sample concentration increases or the amount of sample applied to the target plate increases, more greasy solids are visible on the target spot, the mass spectrum signal intensity decreases, and the ionization effect above m / z 400 deteriorates. This may be due to the greasy sample affecting the crystallization state, which in turn affects sample ionization. Therefore, effective sample detection can be achieved by dissolving white vaseline in dichloromethane for spotting (requiring a low sample concentration, such as 0.1 mg / mL) or by directly applying a small amount of white vaseline to the target and wiping it with a new cotton swab. This ensures that the sample volume on the target meets the test sample requirements without affecting crystal formation. Because the direct smear method does not require sample dissolution and sample solution preparation, it is more convenient to operate. Therefore, the direct smear method (sample volume within 0.1 µL and wiping with a new cotton swab) was selected for subsequent experiments.

[0073] Example 5: Identification of white vaseline produced by different manufacturers using the optimized analytical conditions

[0074] 1) Sample preparation

[0075] White vaseline from five different manufacturers was purchased commercially. A small amount (less than 0.1 µL) of white vaseline sample, visible to the naked eye, was smeared onto a stainless steel target using a pipette tip. The sample was evenly spread with a cotton swab and then wiped with a fresh cotton swab to ensure that no visible solids remained on the target and that the dark mark left by the sample smearing was evenly distributed and covered the entire target. 0.5 µL of a 2 mg / mL AgTFA solution in tetrahydrofuran was then applied to the target and allowed to air dry. Twelve targets were prepared for each sample.

[0076] Ag-LDI-TOF MS determination

[0077] The target plate was placed in a MALDI-TOF mass spectrometer to acquire a mass spectrum of a white vaseline sample. Mass spectrometry analysis conditions were as follows: positive ion linear mode, a 355 nm solid-state laser, a scan range of m / z 1-2000, pulse delay extraction at 1500 Da, laser energy at 40%-50%, a laser scan frequency of 100 Hz, 150 profiles per sample, each acquired with four shots, and peak processing parameters set to baseline subtraction at 3 and smoothing at 2. The analysis time for a single sample was 6 seconds.

[0078] 3) Data processing and principal component analysis (PCA)

[0079] The collected mass spectra were analyzed and the mass spectrometry data were exported as ASCII format files. PCA analysis was performed using the data statistics software eMSTAT Solution to obtain the PCA analysis score graph.

[0080] 4) Experimental Results

[0081] Mass spectrum analysis: Sample mass spectrum is shown in Figure 7-Figure 8 As can be seen from the figure, the sample's ion peaks are primarily distributed within the m / z 1-2000 range, with good signal-to-noise ratios. The 12 mass spectra from the same manufacturer show good reproducibility. The mass spectra of white vaseline from different manufacturers have similar distributions of major high-abundance ions, but also exhibit significant differences. Ion peaks at m / z 107, m / z 216, m / z 235, m / z 333, m / z 451, m / z 539, m / z 667, m / z 755, m / z 769, and m / z 971 were detected in all samples, but their relative abundances varied, with m / z 107, m / z 216, and m / z 333 being more abundant. Among the detected ion peaks, there are two regularly distributed series, such as series 1: m / z 107, m / z 333, m / z 539, m / z 755, m / z 971…, which differ by about 216 Da, and series 2: m / z 235, m / z 451, m / z 667…, which differ by 216 Da.

[0082] There were significant differences in the distribution of alkanes in the white vaseline samples from the five manufacturers. For example, the mass spectrometry signals of series 1 ions from manufacturer D were more significant than those from other manufacturers, with m / z 755 and m / z 971 being more prominent. In addition, significant distributions of ion peaks at m / z 1186, m / z 1402, m / z 1618, and m / z 1834 were detected at intervals of 216 Da. Compared with other manufacturers, manufacturer C had ion mass spectrometry signal distributions with molecular weight intervals of 14 Da between m / z 550 and 740, which may correspond to alkanes with a difference of one -CH2-. In addition, the signal intensity of m / z 769 in the mass spectrum of manufacturer C was higher. The content of S1 and S2 ions with high mass numbers (>m / z 600) from manufacturer E was relatively low, but the distribution of m / z 389 and m / z 519 was more prominent than that from other manufacturers. Manufacturer B detected higher intensities of m / z 575, the content of this ion is low in samples from other manufacturers; the distribution of series 2 ions (m / z 235, m / z 451, m / z 667) in the mass spectrum of manufacturer A is more obvious than that of other manufacturers, and a small amount of m / z 883 distribution can be detected.

[0083] Principal component analysis (PCA): The mass spectrometry data were exported as ASCII format files and PCA analysis was performed using the data statistics software eMSTATSolution. The score graph is shown in Figure 9 . In the PCA score graph, the horizontal axis (PC1) represents the first principal component, which is the direction with the largest variance in the data; the vertical axis (PC2) represents the second principal component, which is orthogonal to the first principal component and has the second largest variance. PC1 and PC2 together reflect the main sources of variation in the data. Different samples are clustered into one category and are completely separated, indicating that there are significant differences in the mass spectra of the samples. The mass spectra from different manufacturers are relatively different. This shows that principal component analysis can effectively identify white vaseline from different manufacturers and different batches.

[0084] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for rapidly identifying white vaseline from different manufacturers based on silver-assisted laser desorption ionization-time of flight mass spectrometry, characterized in that: The method includes preparation of a sample to be tested, Ag-LDI-TOF MS determination, data processing and PCA analysis; S1, preparation of the sample to be tested: take a white vaseline sample and evenly apply it on the target plate; take an Ag salt solution and dot it on the target plate and let it dry naturally; S2, Ag-LDI-TOF MS determination: The target plate obtained by S1 was placed in a MALDI-TOF mass spectrometer, and the following mass spectrometry conditions were applied for mass spectrometry acquisition: the tuning mode was positive ion linear mode, the laser type was a 355 nm solid-state laser, the scan range was set to m / z 1-2000, the pulse delay extraction was set to 1500 Da, the laser energy was set to 40%-50%, and the laser scanning frequency was 100 Hz; S3, data processing and PCA analysis: perform data analysis on the collected mass spectra and export the mass spectrometry data into ASCII format files; PCA analysis was performed using the data statistics software eMSTAT Solution.

2. The method according to claim 1, characterized in that In S1, the white vaseline sample is directly applied to the target plate for spotting, the sample volume is within 0.5 µL, and a new cotton swab is used to wipe.

3. The method according to claim 2, characterized in that In the above-mentioned S1, the sample sampling volume is within 0.1 μL.

4. The method according to claim 1, wherein In S1, the white vaseline sample is dissolved in dichloromethane and then spotted, and the sample concentration is 0.1-10 mg / mL.

5. The method according to claim 3, characterized in that In S1, the white vaseline sample was dissolved in dichloromethane and then spotted, and the sample concentration was 0.1-0.5 mg / mL.

6. The method according to claim 1, characterized in that In the above-mentioned S1, the Ag salt solution is an AgTFA solution, which is dissolved in tetrahydrofuran or water.

7. The method according to claim 1, characterized in that In the S1, the concentration of the Ag salt solution is 2-20 mg / mL.

8. The method according to claim 7, characterized in that In the S1, the concentration of the Ag salt solution is 2 mg / mL.

9. The method according to claim 1, characterized in that In the above-mentioned S1, the spotting volume of the Ag salt solution is 0.5-1 μL.

10. The method according to claim 9, characterized in that In the above-mentioned S1, the spotting volume of the Ag salt solution is 0.5 μL.

11. The method according to claim 1, wherein In the above-mentioned S3, the mass spectrum is subjected to baseline subtraction and peak smoothing processing.

Images