Application of Azo Dyes as Matrix in MALDI-TOF Mass Spectrometry Analysis of Silicone Oil

Abstract

The present invention discloses the application of azo dyes as a matrix in the MALDI-TOF mass spectrometry analysis of silicone oil, which includes the following steps: using a weakly polar azo dye as the matrix of MALDI; using a sodium salt or a silver salt as the ionization reagent of MALDI; mixing the matrix solution, the ionization reagent solution, and the silicone polymer solution and then spotting on a target, and performing MALDI-TOF mass spectrometry analysis after air drying. This method first uses a weakly polar azo dye as the matrix for MALDI mass spectrometry analysis, which is beneficial to improving the dispersion of weakly polar polysiloxane in the solid MALDI matrix, and for the first time realizes the effective MALDI ionization and mass spectrometry analysis of various silicone oil samples. Using the azo dye as the matrix for MALDI mass spectrometry analysis, the sample preparation by spotting on a target is simple and convenient, and enables the analyst not to contact the organic base substances with unpleasant odors.

Description

Technical Field

[0001] The present invention belongs to the technical field of silicone oil detection, and specifically relates to the application of azo dyes as matrices in the MALDI-TOF mass spectrometry analysis of silicone oil. Background Art

[0002] Silicone oil is a linear polysiloxane that remains in a liquid state at room temperature. Classified by chemical structure (such as Figure 1 ), silicone oils include methyl silicone oil, ethyl silicone oil, phenyl silicone oil, methyl hydrogen silicone oil, methyl phenyl silicone oil, methyl trifluoropropyl silicone oil, methyl vinyl silicone oil, methyl hydroxy silicone oil, etc. Silicone oil has heat resistance, electrical insulation, weather resistance, hydrophobicity, physiological inertness, and a small surface tension. In addition, it also has advantages such as a low viscosity-temperature coefficient and a high compression resistance. Phenyl silicone oil also has radiation resistance. According to its viscosity (molecular weight) different, silicone oils are used in different industries such as electrical appliances, light industry, cosmetics, and construction, and play an active role.

[0003]

[0004] R is an alkyl group, an aryl group, R' is an alkyl group, an aryl group, hydrogen, a carbon functional group, a polyether chain, etc.; X is an alkyl group, an aryl group, an alkenyl group, hydrogen, a hydroxyl group, an alkoxy group, an acetoxy group, chlorine, a carbon functional group, a polyether chain, etc.; n, m = 0, 1, 2, 3...

[0005] Silicone oil is a type of weakly polar organic polymer, and its molecular weight ranges from several hundred Da to several hundred thousand Da. Gel permeation chromatography (GPC) is currently a common detection method for testing the molecular weight distribution of polymers. However, the reference substance for molecular weight testing by GPC is basically polystyrene. Due to the differences in molecular structure and physical properties, the GPC method calibrated with polystyrene cannot accurately determine the molecular weight analysis of silicone oil. At the same time, GPC is not suitable for the testing of oligomers with a molecular weight of several thousand Da, and the molecular weight distribution of many types of silicone oils is in the range of several thousand Da. Therefore, a more suitable analysis technique is needed for the molecular weight distribution testing of silicone oil.

[0006] Matrix-assisted laser desorption / ionization time-of-flight mass spectrometry (MALDI-TOF MS) is a soft ionization mass spectrometry technology developed in the late 1980s, with advantages such as high sensitivity and a wide mass detection range. The upper limit of mass detection of this instrument is as high as several hundred thousand, and it has become an effective tool for the structural characterization of biological macromolecules and synthetic polymers. During the MALDI-TOF analysis process, the matrix plays a very important role: dissolving and embedding the sample, absorbing laser energy and ionizing itself, and transferring ions to the polymer to ionize the polymer. The selection of a suitable matrix is the key technology for effective ionization of the analyte. Conventional matrices include DHB, CHCA, SA, etc. These compounds are polar compounds and are suitable for the analysis of polar macromolecules such as polypeptides and proteins. However, silicone oil belongs to weakly polar organic polymers and it is difficult to use the above matrices for effective ionization in the MALDI source. Therefore, there are few reports in the literature on the mass spectrometry analysis of silicone oil using MALDI-TOF MS technology.

[0007] The inventors once used an organic base to modify the DHB matrix, effectively improving the uniformity of the dispersion of hydroxyl silicone oil in DHB, thus realizing the MALDI mass spectrometry analysis of hydroxyl silicone oil (Journal of Hangzhou Normal University, 2016, 15, 119-123). However, this method has relatively high requirements for the concentration range of the organic base during the preparation of the matrix solution, and the reproducibility of the analysis results needs to be further improved. More critically, this matrix can only achieve the MALDI analysis of hydroxyl silicone oil, but cannot achieve the MALDI ionization of other silicone oils with weaker polarity (such as methyl silicone oil, vinyl silicone oil, etc.). At the same time, the organic base used in this method has an unpleasant smell, which is not beneficial to the analysts. Summary of the Invention

[0008] The first object of the present invention is to provide the application of azo dyes as matrices in the MALDI-TOF mass spectrometry analysis of silicone oil in view of the deficiencies of the prior art.

[0009] The present invention is realized by the following technical solutions:

[0010] The application of azo dyes as matrices in the MALDI-TOF mass spectrometry analysis of silicone oil is specifically to prepare a matrix solution for MALDI by using a weakly polar organic solvent to dissolve the weakly polar azo dyes.

[0011] Preferably, the azo dye is one of Sudan I, Sudan II, Sudan III, Sudan IV, Sudan R, Sudan G, Sudan 7B, Sudan B, azobenzene, 4-OH azobenzene, methyl red, para red, methyl yellow; more preferably methyl yellow.

[0012] Preferably, the weakly polar organic solvent is one of n-hexane, tetrahydrofuran, toluene;

[0013] The second objective of the present invention is to provide a method for analyzing silicone oil by MALDI-TOF mass spectrometry, comprising the following steps:

[0014] (1) Using a weakly polar azo pigment as the matrix for MALDI and preparing a solution with a weakly polar organic solvent; (2) Using a sodium salt or silver salt as the ionization reagent for MALDI and preparing a dilute solution with an organic solvent;

[0015] (3) Mixing the matrix solution and ionization reagent solution obtained in steps (1) and (2), and the silicone polymer solution to be analyzed, in a certain proportion;

[0016] (4) Spotting the mixture solution obtained in step (3) on a target, and performing MALDI-TOF mass spectrometry after drying.

[0017] Preferably, the azo pigment described in step (1) is one of Sudan I, Sudan II, Sudan III, Sudan IV, Sudan R, Sudan G, Sudan 7B, Sudan B, azobenzene, 4-OH azobenzene, methyl red, para red, methyl yellow; more preferably methyl yellow.

[0018] Preferably, the weakly polar organic solvent described in step (1) is one of n-hexane, tetrahydrofuran, methanol, acetonitrile, toluene, or a mixed solvent thereof;

[0019] Preferably, the concentration range of the azo pigment solution in step (1) is 5-100 mg / mL;

[0020] Preferably, the sodium salt and silver salt in step (2) are silver acetate, sodium formate, sodium acetate, sodium trifluoroacetate, silver trifluoroacetate; more preferably, the ionization reagent is silver trifluoroacetate.

[0021] Preferably, the organic solvent described in step (2) is one of tetrahydrofuran, methanol, acetonitrile, or a mixed solvent thereof;

[0022] Preferably, the concentration range of the ionization reagent solution in step (2) is 1-100 μg / mL;

[0023] Preferably, in step (3), the concentration range of the silicone compound solution is 10-1000 μg / mL;

[0024] Preferably, the mixing volume ratio range of the silicone polymer solution, ionization reagent solution, and matrix solution to be analyzed is 0.1:1:1 - 10:1:1; more preferably 1:1:1.

[0025] Compared with the prior art, the advantages and beneficial effects of the present invention:

[0026] For the first time, a weakly polar azo pigment is used as the matrix for MALDI mass spectrometry analysis, which is beneficial to the dispersion degree of weakly polar silicone oil in the solid MALDI matrix, and improves the sensitivity and reproducibility of the MALDI mass spectrometry analysis of silicone oil.

[0027] For the first time, effective MALDI ionization and mass spectrometry analysis of weakly polar silicone oil samples such as methyl silicone oil, methyl vinyl silicone oil, and methyl phenyl silicone oil have been realized.

[0028] There are many types of azo pigments and they are inexpensive. According to the specific situation of the sample to be measured, a suitable azo pigment can be selected as the MALDI matrix.

[0029] Using sodium salt or silver salt as the ionization reagent for MALDI further improves the ionization efficiency of silicone oil samples.

[0030] When using the azo pigment as the matrix for MALDI mass spectrometry analysis, the laser ionization energy can be appropriately reduced, thereby reducing the probability of fragmentation of the silicone oil quasi-molecular ions during ionization, more truly reflecting the polymer distribution of the silicone oil sample, and at the same time reducing the interference of the matrix background signal.

[0031] Compared with using the organic base-modified DHB matrix as the MALDI matrix, using the azo pigment as the matrix for MALDI mass spectrometry analysis is simple and convenient for spotting sample preparation.

[0032] Compared with using the organic base-modified DHB matrix as the MALDI matrix, when using the azo pigment as the matrix for MALDI mass spectrometry analysis, the analyst does not need to contact the organic base substances with unpleasant odors.

[0033] This detection method can be used for mass spectrometry analysis of various silicone polymers, including products such as hydroxyl silicone oil, methyl silicone oil, methyl vinyl silicone oil, and methyl phenyl silicone oil, and has a very wide range of application fields. Description of the Drawings

[0034] Figure 1 It is the MALDI-TOF mass spectrum of hydroxyl silicone oil in Example 1;

[0035] Figure 2 It is the MALDI-TOF mass spectrum of methyl silicone oil in Example 2;

[0036] Figure 3 It is the MALDI-TOF mass spectrum of methyl vinyl silicone oil in Example 3;

[0037] Figure 4 It is the MALDI-TOF mass spectrum of methyl phenyl silicone oil in Example 4. Detailed Implementation Modes

[0038] The present invention will be further described by the following embodiments. The following description is only for explaining the present invention and does not limit its content.

[0039] Example 1: MALDI-TOF Analysis of Hydroxy Silicone Oil

[0040] Using THF as the solvent, prepare a solution of a certain hydroxy silicone oil (10 μg / mL), a solution of sodium formate (10 μg / mL), and a solution of methyl yellow (50 μg / mL) respectively. Pipette 10 μL of the hydroxy silicone oil solution, 10 μL of the sodium acetate solution, and 10 μL of the methyl yellow solution into a PE tube and mix well. Take the mixed solution to dot the target, dry it, and perform MALDI analysis. The results are as Figure 1 shown. The azo dye used in this example as the matrix for MALDI mass spectrometry analysis can improve the signal-to-noise ratio of the silicone oil sample mass spectrometry analysis, and at the same time, dotting the target for sample preparation is simpler and more convenient. Compared with the organic base-modified DHB matrix as the MALDI matrix, when using the azo dye as the matrix for MALDI mass spectrometry analysis, the analyst does not need to contact the organic base substances with unpleasant odors.

[0041] Example 2: MALDI-TOF Analysis of Methyl Silicone Oil

[0042] Using toluene as the solvent, prepare a solution of methyl silicone oil (50 μg / mL), and using methanol as the solvent, prepare a solution of sodium trifluoroacetate (20 μg / mL) and a solution of azobenzene (80 μg / mL). Pipette 5 μL of the methyl silicone oil solution, 5 μL of the sodium trifluoroacetate, and 10 μL of the azobenzene solution into a PE tube and mix well. Take the mixed solution to dot the target, dry it, and perform MALDI analysis. The results are as Figure 2 shown. This technology uses an azo dye as the matrix for MALDI mass spectrometry analysis, and for the first time realizes the MALDI mass spectrometry analysis of methyl silicone oil, and dotting the target for sample preparation is simple and convenient.

[0043] Example 3: MALDI-TOF Analysis of Methyl Vinyl Silicone Oil

[0044] Using n-hexane as the solvent, prepare a solution of methyl vinyl silicone oil (20 μg / mL), and using methanol as the solvent, prepare a solution of lithium trifluoroacetate (50 μg / mL) and a solution of Sudan G (100 μg / mL). Pipette 10 μL of the methyl vinyl silicone oil solution, 10 μL of the sodium trifluoroacetate, and 5 μL of the Sudan G solution into a PE tube and mix well. Take the mixed solution to dot the target, dry it, and perform MALDI analysis. The results are as Figure 3 shown. This technology uses an azo dye as the matrix for MALDI mass spectrometry analysis, and for the first time realizes the MALDI mass spectrometry analysis of methyl vinyl silicone oil, and dotting the target for sample preparation is simple and convenient.

[0045] Example 4: MALDI-TOF Analysis of Methyl Phenyl Silicone Oil

[0046] Using tetrahydrofuran as the solvent, prepare a phenyl silicone oil solution (100 μg / mL), and use methanol as the solvent to prepare a silver trifluoroacetate solution (20 μg / mL) and a para red solution (50 μg / mL). Respectively pipette 2 μL of the phenyl silicone oil solution, 2 μL of sodium trifluoroacetate and 10 μL of the para red solution into a PE tube, and mix well. Take the mixed solution to spot the target, dry it, and perform MALDI analysis. The results are as Figure 4 shown. This technique uses azo dyes as the matrix for MALDI mass spectrometry analysis, and for the first time realizes the MALDI mass spectrometry analysis of methyl phenyl silicone oil, and the sample preparation by spotting the target is simple and convenient.

[0047] The above embodiments are not limitations on the present invention. The present invention is not limited to the above embodiments. As long as it meets the requirements of the present invention, it belongs to the protection scope of the present invention.

Claims

1. Application of azo dyes as matrix in MALDI-TOF mass spectrometry analysis of silicone oil, characterized in that Prepare a matrix solution for MALDI by using a weakly polar organic solvent to dissolve a weakly polar azo pigment.

2. The application according to claim 1, wherein The azo pigment is one of Sudan I, Sudan II, Sudan III, Sudan IV, Sudan R, Sudan G, Sudan 7B, Sudan B, azobenzene, 4-OH azobenzene, methyl red, para red, and methyl yellow.

3. The application according to claim 2, wherein The azo pigment is methyl yellow.

4. The application according to claim 1 or 2, characterized in that The weakly polar organic solvent is one or a mixture of n-hexane, tetrahydrofuran, and toluene.

5. A method for MALDI-TOF mass spectrometry analysis of silicone oil, characterized in that It includes the following steps: (1) Use a weakly polar azo pigment as the matrix for MALDI and prepare a solution with a weakly polar organic solvent; (2) Use a sodium salt or silver salt as the ionization reagent for MALDI and prepare a dilute solution with an organic solvent; (3) Mix the matrix solution and ionization reagent solution obtained in steps (1) and (2), and the organosilicon polymer solution to be analyzed in a certain ratio; (4) Spot the mixture solution obtained in step (3) on a target, and perform MALDI-TOF mass spectrometry analysis after it dries.

6. The method according to claim 5, wherein The azo pigment described in step (1) is one of Sudan I, Sudan II, Sudan III, Sudan IV, Sudan R, Sudan G, Sudan 7B, Sudan B, azobenzene, 4-OH azobenzene, methyl red, para red, and methyl yellow.

7. The method according to claim 6, wherein The azo pigment described in step (1) is methyl yellow.

8. The method according to claim 5 or 6, characterized in that The weakly polar organic solvent described in step (1) is one or a mixture of n-hexane, tetrahydrofuran, and toluene; the organic solvent described in step (2) is one or a mixture of tetrahydrofuran, methanol, and acetonitrile.

9. The method according to claim 5 or 6, characterized in that The concentration range of the azo pigment solution described in step (1) is 5 - 100 mg / mL; the concentration range of the ionization reagent solution described in step (2) is 1 - 100 μg / mL; in step (3), the concentration range of the organosilicon polymer solution is 10 - 1000 μg / mL.

10. The method according to claim 5 or 6, characterized in that The sodium salts and silver salts described in step (2) are silver acetate, sodium formate, sodium acetate, sodium trifluoroacetate, and silver trifluoroacetate.

11. The method according to claim 5 or 6, characterized in that The mixing volume ratio range of the selected organosilicon polymer solution, ionization reagent solution, and matrix solution to be analyzed is 0.1:1:1 - 10:1:1.

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