Gas chromatographic detection method of n-trimethylsilylimidazole and application thereof

Abstract

The application discloses a gas chromatography detection method for a moisture-sensitive compound and application thereof. The application first identifies that trace moisture in a carrier gas gas circuit is the root cause of systematic low detection results of trimethylsilylimidazole by gas chromatography. In the gas chromatography detection process, the moisture of the whole detection system in which the sample to be detected is located is controlled by active moisture removal of the detection environment and active moisture removal of the carrier gas or auxiliary gas circuit. After the method is used, the detection result of trimethylsilylimidazole is up to 99.07% at the highest. The application solves the long-standing technical problem of low detection results caused by hydrolysis, and has the advantages of simplicity, low cost, good reproducibility and high industrial application value.

Description

Technical Field

[0001] This invention relates to the field of analytical chemistry, specifically to a gas chromatography method for detecting moisture-sensitive compounds, and more particularly to a gas chromatography method for detecting the content of N-trimethylsilimidazole and its application in quality control. Background Technology

[0002] N-Trimethylsilylimidazole (TSIM, CAS No. 18156-74-6) is an important silanization protecting agent widely used in the synthesis of cephalosporin antibiotics, meropenem, and other drugs. It is also a key starting material in the preparation of dexmedetomidine hydrochloride. Current pharmaceutical laws and regulations require the establishment of corresponding quality control standards for starting materials. Without accurate testing of their content, it is impossible to confirm whether their quality meets the standards, and therefore, the quality of the final active pharmaceutical ingredient, dexmedetomidine hydrochloride, cannot be guaranteed.

[0003] N-Trimethylsilimidazole is a colorless or pale yellow liquid. Its Si-N bonds are highly sensitive to moisture; even trace amounts of moisture will cause hydrolysis, producing trimethylsilanol and imidazole. Therefore, strict moisture protection is essential during storage and use. It is typically required to store it in a sealed, light-proof environment at low temperatures under an inert gas atmosphere.

[0004] Gas chromatography (GC) is the mainstream method for the detection of N-trimethylsilimidazole due to its advantages such as high separation efficiency, fast analysis speed, and small sample volume. Existing technology is supported by Chinese patent CN109030688B, entitled "A Method for Detecting N-Trimethylsilimidazole and Related Substances." This patent achieves effective separation of the main component and impurities by optimizing chromatographic parameters such as column oven temperature program (initial column temperature 120-140℃, programmed temperature rise to 140-240℃), injection port temperature (160-280℃), and split ratio.

[0005] However, through long-term practice, the inventors have discovered that:

[0006] 1. When using N-trimethylsilimidazole of analytical grade (nominal content ≥97.00%) for testing, the test result under normal conditions was only 95.33%, which is too low and cannot reach the nominal value;

[0007] 2. Even with the adoption of strict moisture-proof measures recognized in the industry (including the use of drying solvents, fresh sample preparation and use, nitrogen purging, etc.), the test results are still low;

[0008] 3. This phenomenon has long existed in the industry, but the real cause and effective solution have never been found.

[0009] Existing technologies (such as CN109030688B) focus all their improvements on optimizing chromatographic parameters, attempting to "enhance" detection accuracy by improving resolution and peak shape. However, this approach has a fundamental flaw—it fails to recognize that the root cause of low detection results is not the chromatographic conditions themselves, but rather the trace amounts of moisture present in the detection environment (especially the carrier gas path), which continuously induces sample hydrolysis before or during injection.

[0010] Although Chinese patent CN101367828B mentions in its background technology that N-trimethylsilimidazole "easily reacts with water to generate imidazole and hexamethyldisiloxane", this patent belongs to the field of synthesis. Its purpose is to prevent decomposition during the synthesis process by adding stabilizers. It does not involve the detection process at all, and it does not realize the systematic impact of moisture in the detection environment (especially moisture in the carrier gas) on the detection results.

[0011] Therefore, there is an urgent need for a gas chromatography detection method for moisture-sensitive compounds such as N-trimethylsilimidazole. This method can eliminate the interference of trace moisture in the detection system at the source, significantly improve the accuracy of the detection results, and solve the technical problems that have long existed in existing detection methods but have not been effectively solved. Summary of the Invention

[0012] This invention is the first to discover that ambient moisture is the root cause of systematically low detection results when N-trimethylsilimidazole and other moisture-sensitive compounds are detected by gas chromatography, and proposes a simple, low-cost, and efficient technical solution.

[0013] This invention addresses the technical shortcomings of existing gas chromatography methods for detecting moisture-sensitive compounds such as N-trimethylsilimidazole. These shortcomings stem from the presence of trace amounts of moisture (including moisture in the carrier gas and ambient air) in the detection system, which causes continuous hydrolysis of the sample before or during injection. This results in systematically low detection results (analytical pure samples consistently fail to achieve a nominal value ≥97.00%) and fails to accurately reflect sample purity. The invention provides an accurate, stable, and reliable gas chromatography detection method.

[0014] This invention is the first to identify and accurately pinpoint the root cause of the systematically low test results as the presence of trace amounts of moisture in the carrier gas path.

[0015] Through systematic and progressive experiments, the inventors gradually eliminated various possible influencing factors and ultimately identified "carrier gas," a pollution source that had long been overlooked by the industry.

[0016]

[0017] The above progressive experiments prove that:

[0018] 1. Under routine testing conditions (first stage), the test results are too low and the results are unqualified;

[0019] 2. Even with the implementation of environmental humidity control measures (Phase II) that are commonly considered in the industry, the test results were still too low and the results were still unqualified.

[0020] 3. Only under the dual control of "environmental dehumidification + carrier gas path dehumidification" of the present invention (third stage) can the result jump to the qualified level.

[0021] This progressive logic clearly demonstrates that conventional moisture-proof measures (sample storage, solvent drying, and environmental dehumidification) recognized by those skilled in the art cannot solve this technical problem. Only the "carrier gas path moisture control" identified for the first time in this invention is the key to solving the problem.

[0022] Technical solution

[0023] Based on the above findings, the present invention provides the following technical solution:

[0024] A gas chromatography detection method for moisture-sensitive compounds involves reducing the moisture content in the detection system by actively dehumidifying the detection environment and the carrier gas or auxiliary gas path used in the gas chromatograph before gas chromatography detection.

[0025] Furthermore, the method for actively dehumidifying the testing environment involves using an active dehumidification device to control the relative humidity of the testing room, wherein the relative humidity is below 30%.

[0026] The method for actively dehumidifying the carrier gas or auxiliary gas path used by the gas chromatograph is to align the outlet of the active dehumidification device with the inlet of the carrier gas or auxiliary gas generator used by the gas chromatograph, so that the dried gas after dehumidification enters the generator, and the gas dew point at the outlet of the carrier gas or auxiliary gas generator of the gas chromatograph is ≤-40℃.

[0027] Furthermore, the moisture-sensitive compound is N-trimethylsilimidazole.

[0028] On the other hand, the present invention provides a gas chromatographic detection method for N-trimethylsilimidazole, comprising the following steps:

[0029] (1) Prepare the test solution: Dissolve the N-trimethylsilimidazole to be tested in N,N-dimethylformamide and prepare a solution containing 0.5g per 1mL. Prepare the solution immediately before use.

[0030] (2) Environmental dehumidification: Use an environmental dehumidifier to control the relative humidity of the testing room to below 30%;

[0031] (3) Gas path drying: Start the environmental dehumidifier and point the air outlet of the dehumidifier directly at the air inlet of the gas chromatograph carrier gas generator so that the dehumidified dry air enters the carrier gas generator.

[0032] (4) Detection: The test sample is placed in an anhydrous test system and is detected using a gas chromatograph. The chromatographic conditions are as follows:

[0033] Chromatographic column: HP-5 capillary column (30 m × 0.32 mm × 2.5 μm) or equivalent column;

[0034] Detector: Hydrogen flame ionization detector, temperature 300℃;

[0035] Inlet temperature: 280℃;

[0036] Column temperature program: Initially 50℃, hold for 8 minutes, then increase to 260℃ at 20℃ / min and hold for 3 minutes;

[0037] Carrier gas flow rate: 2.0 mL / min;

[0038] Flow split ratio: 20:1;

[0039] Injection volume: 1 μL;

[0040] Blank solvent: Same as diluent;

[0041] Diluent: N,N-dimethylformamide.

[0042] (5) Calculation: Calculate the percentage content of N-trimethylsilimidazole and the peak area percentage of each impurity using the area normalization method.

[0043] Furthermore, in step (3), after aligning the air outlet of the dehumidifier with the air inlet of the gas chromatograph carrier gas generator, the dehumidifier is kept running for at least 30 minutes until the system is stable before proceeding with the detection in step (4).

[0044] Furthermore, the detection system in which the sample to be tested is located in step (4) is anhydrous is determined by the following method: the gas dew point at the outlet of the carrier gas generator of the gas chromatograph is monitored using a dew point meter, and gas chromatograph detection is performed when the dew point is ≤-40℃.

[0045] Furthermore, the carrier gas generator is a nitrogen generator.

[0046] Furthermore, the method can obtain a content detection result of not less than 98.0% in analytical grade N-trimethylsilimidazole samples, and the content of trimethylsilanol impurities is not higher than 1.5%.

[0047] Beneficial effects

[0048] 1. This invention is the first to identify and solve a long-neglected technical problem—carrier gas moisture contamination. The primary contribution of this invention is the first discovery that "trace amounts of moisture in the carrier gas path are the root cause of systematically low N-trimethylsilylimidazole gas chromatography detection results." This technical problem has long existed in the industry but has never been correctly diagnosed. Existing technologies (including CN109030688B) have all focused on optimizing chromatographic parameters, failing to recognize that a dry detection environment is the key to solving the problem. This invention, through systematic progressive experiments and layer-by-layer elimination, ultimately pinpointed the long-neglected contamination source—the carrier gas—and proposed a simple and efficient solution. By presenting "ensuring the entire detection system is water-free" as a complete technical solution, it successfully breaks through a long-standing technical bottleneck in this field—even with strictly moisture-proof sample storage, if trace amounts of moisture exist in the detection environment (including the carrier gas path), the detection results still cannot accurately reflect the sample purity, thus solving a long-standing technical pain point in this field.

[0049] 2. This invention clearly demonstrates the changes in detection results under different moisture control conditions through a progressive detection experiment using the same batch of analytically pure N-trimethylsilimidazole samples:

[0050]

[0051] The above data indicates that:

[0052] Controlling the ambient humidity alone (condition 2) only improved the test result from 95.33% to 96.88%, which is still lower than the analytical purity nominal value of 97.00%.

[0053] Only under the dual control of "environmental dehumidification + carrier gas path dehumidification" of the present invention (condition 3) does the detection result jump to 99.07%.

[0054] This progressive result strongly demonstrates that conventional moisture-proofing measures (sample storage, solvent drying, and environmental dehumidification) recognized by those skilled in the art are ineffective in solving this technical problem. This invention is the first to identify the "carrier gas" as the source of contamination and solves this long-standing technical challenge through carrier gas dehumidification.

[0055] 3. The accuracy of test results has been significantly improved.

[0056] The nominal purity of analytical grade N-trimethylsilimidazole is ≥97.00%, and existing detection methods struggle to detect this nominal value. However, under the anhydrous detection conditions of this invention, the detection result for analytical grade samples reaches 99.07%, significantly higher than its nominal value, eliminating the situation where the detection result cannot reach the nominal value.

[0057] 4. Significantly reduces testing costs, resulting in good economic benefits and industrial application value.

[0058] The method of this invention can obtain accurate and reliable detection results using analytical grade N-trimethylsilimidazole (which is much cheaper than chromatographic grade), significantly reducing detection costs. At the same time, this invention has low equipment requirements—no additional dedicated gas drying equipment is needed; simply adding a simple dehumidification device to the existing gas chromatography detection system and adjusting its position is sufficient to achieve an anhydrous detection system, making it highly operable and valuable for industrial application. Attached Figure Description

[0059] Figure 1 This is a schematic diagram showing the arrangement of the active dehumidification device and the nitrogen generator described in this invention;

[0060] Figure 2 This is a gas chromatogram of the impurity reference solution in the detection method of the present invention;

[0061] Figure 3 The gas chromatogram for the detection and analysis of pure N-trimethylsilimidazole in Comparative Example 1;

[0062] Figure 4 The gas chromatogram for the detection and analysis of pure N-trimethylsilimidazole is shown in Comparative Example 2.

[0063] Figure 5 The gas chromatogram for detecting and analyzing pure N-trimethylsilimidazole in Example 1 is shown. Detailed Implementation

[0064] The present invention will be further described below through specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments.

[0065] In the following examples, all reagents used were commercially available, and the material information is shown in Table 3:

[0066]

[0067] In the following embodiments, the detection conditions are as follows:

[0068] The detection was performed using gas chromatography, with the following chromatographic conditions:

[0069] Chromatographic column: HP-5 capillary column (30 m × 0.32 mm × 2.5 μm) or equivalent column;

[0070] Detector: Hydrogen flame ionization detector, temperature 300℃;

[0071] Inlet temperature: 280℃;

[0072] Column temperature program: Initially 50℃, hold for 8 minutes, then increase to 260℃ at 20℃ / min and hold for 3 minutes;

[0073] Carrier gas flow rate: 2.0 mL / min;

[0074] Flow split ratio: 20:1;

[0075] Injection volume: 1 μL;

[0076] Solution preparation:

[0077] Test solution: Take an appropriate amount of N-trimethylsilimidazole (batch number H24112101, analytical grade, nominal content ≥97.00%) to be tested, accurately weigh it, dissolve it in N,N-dimethylformamide and quantitatively dilute it to prepare a solution containing about 0.5 g per 1 mL, and use it immediately.

[0078] Blank solvent: same as diluent

[0079] Diluent: N,N-dimethylformamide

[0080] Impurity reference solutions are used for the localization and confirmation of chromatographic peaks.

[0081] Preparation of impurity reference solution: Weigh appropriate amounts of trimethylchlorosilane, trimethylsilanol, and imidazole reference standards accurately, dissolve and quantitatively dilute with N,N-dimethylformamide to prepare a mixed solution containing approximately 2.5 mg of trimethylchlorosilane, 7.5 mg of trimethylsilanol, and 1 mg of imidazole per ml, which shall be used as the reference solution.

[0082] Determination Procedure: Inject 1 μL each of the impurity reference solution and the test solution into the gas chromatograph and record the chromatograms. The reference solution is used for the localization and confirmation of chromatographic peaks (trimethylchlorosilane, trimethylsilanol, imidazole). Calculate the content of the main component and the peak area percentage of each impurity using the area normalization method.

[0083] The above-described gas chromatography method for the determination of N-trimethylsilimidazole has undergone systematic methodological validation and meets the requirements for specificity, repeatability, accuracy, and robustness.

[0084] Comparative Example 1 (No environmental dehumidification, no carrier gas path dehumidification)

[0085] Instruments and conditions:

[0086] Testing conditions: The relative humidity of the testing room was approximately 50%-75% (a standard air-conditioned room, without the dehumidifier turned on). The nitrogen generator drew air directly from the environment, and no dehumidification device was installed at the air inlet.

[0087] Sample to be tested: Analytical grade N-trimethylsilimidazole (nominal content ≥97.00%, batch number H24112101), dissolved in N,N-dimethylformamide (DMF) and prepared fresh for immediate use.

[0088] Test results: Calculated by the area normalization method, the area ratio of the main peak of N-trimethylsilimidazole was 95.33%, the content of trimethylsilanol impurity was approximately 4.43%, N-trimethylchlorosilane was 0.04%, and imidazole was not detected. The test result was lower than the nominal value of analytical grade by 97.00%, and therefore unqualified.

[0089] Comparative Example 2 (Ambient dehumidification only, no carrier gas path dehumidification)

[0090] Testing conditions: An industrial dehumidifier was turned on in the testing room to reduce the relative humidity to approximately 30%; however, the nitrogen generator still directly drew air from the environment, and the dehumidifier's outlet was not aligned with the nitrogen generator's inlet. Samples from the same batch (batch number H24112101).

[0091] Test results: Calculated by the area normalization method, the area ratio of the main peak of N-trimethylsilimidazole was 96.88%, the content of trimethylsilanol impurity was about 3.05%, N-trimethylchlorosilane was 0.07%, imidazole was not detected, and the N-test result was still lower than the nominal value of 97.00% for analytical grade, which is unqualified.

[0092] Example 1: The method of the present invention (environmental dehumidification + carrier gas path dehumidification)

[0093] Testing conditions: For the same batch of samples (batch number H24112101), the following moisture control measures were implemented in the laboratory where the gas chromatograph and nitrogen generator were located:

[0094] 1. Turn on the industrial dehumidifier to control the relative humidity of the environment below 30%;

[0095] 2. Direct the dehumidifier's air outlet directly at the nitrogen generator's air inlet, allowing the dehumidified dry air to enter the nitrogen generator. Keep the dehumidifier running continuously for at least 30 minutes. Use a dew point meter to monitor the gas dew point at the carrier gas generator's outlet. Perform the test again when the dew point is ≤-40℃.

[0096] All sample preparation and injection operations were carried out in the aforementioned low-humidity environment (humidity controlled below 30%).

[0097] Test results: The main peak area of ​​N-trimethylsilimidazole accounted for 99.07%, trimethylsilanol impurity was 0.75%, trimethylchlorosilane was 0.02%, imidazole was not detected, other individual impurities were all less than 0.1%, and the total impurities were less than 1.0%. The test results were significantly higher than the N-trimethylsilimidazole content without moisture control, reaching the analytical purity standard of 97.00% or higher.

[0098] Example 2: Reproducibility verification of different batches of samples

[0099] Using the exact same moisture control and chromatographic conditions as in Example 1, another batch (batch number H24071001) of analytical grade N-trimethylsilylimidazole was tested. The results are as follows:

[0100]

[0101] All batches of samples met the quality standard (≥98.0%), with N-trimethylsilyl alcohol content below the 1.5% limit and significantly higher than the analytical grade nominal value of 97.00%. This indicates that the analytical method provided by this invention greatly eliminates the interference of moisture on the determination of the true content of N-trimethylsilylimidazole, thus enabling accurate detection of the true content of N-trimethylsilylimidazole. Furthermore, it exhibits good stability and broad reproducibility, making it suitable for quality control of different batches of samples.

Claims

1. A gas chromatographic detection method for a moisture-sensitive compound, characterized in that, Before gas chromatography detection, the moisture content in the detection system containing the sample is reduced by actively dehumidifying the detection environment and the carrier gas or auxiliary gas path used by the gas chromatograph.

2. The detection method according to claim 1, characterized in that, The method for actively dehumidifying the detection environment involves using an active dehumidification device to control the relative humidity of the detection chamber, where the relative humidity is below 30%. The method for actively dehumidifying the carrier gas or auxiliary gas path used by the gas chromatograph involves aligning the outlet of the active dehumidification device with the inlet of the carrier gas or auxiliary gas generator used by the gas chromatograph, so that the dehumidified gas enters the generator, and the gas dew point at the outlet of the carrier gas or auxiliary gas generator of the gas chromatograph is ≤-40℃.

3. The detection method according to claim 1, characterized in that, The compound that is sensitive to moisture is N-trimethylsilimidazole.

4. A gas chromatographic detection method for N-trimethylsilimidazole, characterized in that, The testing steps are as follows: (1) Prepare the test solution: Dissolve the N-trimethylsilimidazole to be tested in N,N-dimethylformamide and prepare a solution containing 0.5g per 1 mL. Prepare the solution immediately before use. (2) Environmental dehumidification: Use an environmental dehumidifier to control the relative humidity of the testing room to below 30%; (3) Gas path drying: Start the environmental dehumidifier and point the air outlet of the dehumidifier directly at the air inlet of the gas chromatograph carrier gas generator so that the dehumidified dry air enters the carrier gas generator. (4) Detection: Under anhydrous conditions, the test sample is detected by gas chromatography. (5) Calculation: Calculate the percentage content of N-trimethylsilimidazole and the peak area percentage of each impurity using the area normalization method.

5. The gas chromatographic detection method for N-trimethylsilimidazole according to claim 4, characterized in that, The chromatographic conditions are as follows: Chromatographic column: HP-5 capillary column (30 m × 0.32 mm × 2.5 μm) or equivalent column; Detector: Hydrogen flame ionization detector, temperature 300℃; Inlet temperature: 280℃; Column temperature program: Initially 50℃, hold for 8 minutes, then increase to 260℃ at 20℃ / min and hold for 3 minutes; Carrier gas flow rate: 2.0 mL / min; Flow split ratio: 20:1; Injection volume: 1 μL; Blank solvent: Same as diluent; Diluent: N,N-dimethylformamide.

6. The detection method according to claim 4, characterized in that, In step (3), after aligning the air outlet of the dehumidifier with the air inlet of the gas chromatograph carrier gas generator, keep the dehumidifier running continuously for no less than 30 minutes, and then perform the test in step (4) after the system is stable.

7. The detection method according to claim 4, characterized in that, The detection system in which the sample to be tested is in anhydrous condition in step (4) is determined by the following method: use a dew point meter to monitor the gas dew point at the outlet of the carrier gas generator of the gas chromatograph, and perform gas chromatograph detection when the dew point is ≤-40℃.

8. The detection method according to claim 4, characterized in that, The carrier gas generator of the gas chromatograph is a nitrogen generator.

9. The detection method according to claim 4, characterized in that, The method can achieve a content detection result of not less than 98.0% in analytical grade N-trimethylsilimidazole samples, and the content of trimethylsilanol impurities is not higher than 1.5%.

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