Pretreatment method for determining residual solvents such as triethylamine in adapalene raw material based on imine alkali assistance

Abstract

A novel HS-GC pretreatment method is developed, a specific and proper amount of imine alkali is introduced to replace ionic alkali (such as NaOH) used in a traditional method, the imine alkali is competitively combined with electron withdrawing groups in triethylamine and chemical raw material medicine structures, the matrix effect is avoided, the accuracy of determination of triethylamine in raw materials is remarkably improved, and the method is suitable for industrial production. Meanwhile, synergistic accurate determination of triethylamine and other residual solvents can be realized, and experimental steps are simplified. The pretreatment method is suitable for detection of residual solvents such as triethylamine in adapalene raw materials, detection objects can be expanded to other chemical raw materials and other alkaline residual solvents, and the pretreatment method has reference significance for detection of the alkaline residual solvents in other chemical raw material medicines.

Description

Technical Field

[0001] The invention belongs to the technical field of drug analysis, and particularly relates to a pretreatment method for determining residual solvents such as triethylamine in an adapalene raw material drug by using a headspace-gas chromatography (HS-GC) method. Background Art

[0002] Adapalene is a third-generation retinoid widely used to treat acne. Triethylamine is often used as an acid-binding agent in its synthesis process, which may result in residual triethylamine in the finished product.

[0003] The determination of triethylamine by GC direct injection or traditional headspace injection has great limitations. When using the GC direct injection method, the raw material will be enriched in the injection port and cause contamination, affecting the gasification efficiency and liner inertness of subsequent injections, and the results are prone to deviations. When using the traditional GC headspace injection method, the test solution is not treated with alkali, and the actual measured value of triethylamine is often low. This is generally believed to be due to the matrix effect, that is, the electron-withdrawing groups in the raw material combine with triethylamine to form salts, making it impossible for triethylamine to dissociate into the test solution. Although commonly used headspace solvents (such as DMF) are weakly alkaline, they cannot dissociate the more alkaline triethylamine from the raw material, resulting in a low recovery rate of only 82.2%. The result no longer meets the recovery rate requirements of triethylamine under the pharmacopoeia limit.

[0004] To address the matrix effect of adapalene, the current pharmacopoeia (such as USP) pretreatment method uses alkaline sodium hydroxide aqueous solution to dissociate triethylamine to determine its residual amount, but it has the following defects:

[0005] 1. Triethylamine determination accuracy has not improved. The hydrophobic nature of the adapalene raw material means that it precipitates upon contact with water, causing the solution to become turbid and unable to redissolve even with equilibrium heating. The large amount of sodium hydroxide present in the aqueous phase prevents it from reacting with the suspended raw material particles to dissociate triethylamine. Compared to pretreatment methods without the addition of sodium hydroxide aqueous solution, triethylamine recovery is lower, at only 79.0%.

[0006] 2. Simultaneous determination of multiple residual solvents is difficult. Sample turbidity complicates the solution composition, making it difficult to achieve ideal gas-liquid equilibrium in the sample solution. The relative standard deviations (RSDs) of the results for multiple residual solvents are generally large. For example, the RSDs for the residual amounts of tetrahydrofuran and toluene measured in six samples were >10%. Furthermore, aqueous alkaline solutions hydrolyze certain analytes, such as ethyl acetate, causing the disappearance of relevant peaks in the chromatogram.

[0007] Based on the above technical difficulties, it is urgent to find some special substances that can fully dissociate triethylamine from the raw materials and realize the combined determination of triethylamine and other residual solvents to make the method accurate and simple.

[0008]

[0009] Organic aprotic strong bases have been gaining increasing attention since the 1980s due to their super-strong basicity. They may provide a shortcut for the analysis of alkaline residues such as triethylamine in chemical raw materials. These substances have the advantage of being natural solvents for analyzing alkaline residuals and have the following common characteristics:

[0010] 1. Very strong alkalinity, with various types. The alkalinity of organic aprotic strong bases is higher than pK a Triethylamine and other lower aliphatic amines with a pK of 18.8 (in MeCN) are stronger. Their types include: a (in MeCN) imine bases with a pK of 23 to 26 (such as DBN, DBU, TBD, MTBD, TMG), a Proton sponges with a pK of 18 to 25 (in MeCN) a Proazaphosphatranes with a pK of 32 to 35 (in MeCN) a Phosphazene bases with a moiety (in MeCN) of 26 to 46 (such as P2-Et) and nitrogen heterocyclic carbenes (such as 1,3-di-tert-butylimidazol-2-ylidene).

[0011] 2. Widely used and easily available. Organic aprotic strong bases have been widely used in organic synthesis. They can effectively remove active hydrogen from compounds, involving catalysis, condensation, rearrangement and ring opening. They are cheap and readily available.

[0012] 3. Strong compatibility with organic matter. Compared with traditional ionic bases such as sodium hydroxide and sodium methoxide, it has higher affinity with organic solvents and organic raw materials. Summary of the Invention

[0013] The present invention develops a novel HS-GC pretreatment method, which replaces the ionic base (such as NaOH, sodium methoxide) used in the traditional method by introducing a specific and appropriate amount of imine base, competitively combining with the electron-withdrawing group in the raw material structure of triethylamine, avoiding the matrix effect, significantly improving the accuracy of triethylamine determination, and simultaneously achieving the coordinated and accurate determination of triethylamine and other residual solvents, simplifying the experimental steps. The pretreatment method of the present invention is applicable to the detection of residual solvents such as triethylamine in adapalene raw materials, and the detection objects can be extended to other chemical raw materials and other alkaline residual solvents. It has reference significance for the detection of alkaline residual solvents in other chemical raw materials, but the imine base dosage needs to be re-explored. The technical advantages of the present invention include:

[0014] 1. The accuracy of triethylamine determination is high. a The strong alkalinity of the imine base with a (in MeCN) of 23 to 26 can efficiently dissociate the bound triethylamine in the raw material, achieving accurate determination (recovery rate of 85 to 110%). After optimizing the ratio, precise determination (recovery rate of 92 to 105%) is achieved.

[0015] 2. Imine bases have good compatibility with headspace solvents. Imine bases have excellent affinity with headspace solvents (such as DMF and NMP). After mixing, the headspace solvent's solubility for the raw materials is almost not consumed. Liquid imine bases such as DBU, DBN, and MTBD can be mixed with the headspace solvent in almost any ratio.

[0016] 3. The detection process is simple. At the set ratio of imine base and raw materials, triethylamine and other residual solvents can be detected together, meeting the requirements for the accurate determination of other residual solvents with polarity between 2 and 5 (recovery rate 92-105%).

[0017] The steps of the present invention include:

[0018] 1. Select the appropriate imine base and headspace solvent. The pK of the selected imine base a (in MeCN) should be between 23 and 26, preferably amidines or guanidines, more preferably DBU, DBN, TBD, MTBD or TMG. The specific classification of imine bases can be found in Figure 1 The headspace solvent may be DMF, DMA, DMI, DMSO, NMP, etc., preferably NMP, which has good solubility for the raw material, so that sufficient raw material can be dissolved to achieve better detection sensitivity.

[0019] 2. Pretreatment of the test solution. The test solution is prepared by mixing appropriate amounts of imine base, headspace solvent and raw materials in proportion. There is no requirement for the order of adding the three. It is preferred to mix appropriate amounts of imine base and headspace solvent to prepare a diluent, then mix and dissolve it with appropriate amounts of raw materials in the headspace bottle, seal it, and obtain the test solution. a The mass ratio (mg / mg) of imine base with (in MeCN) < 25 to raw material is 1:10 or more, which can make the recovery rate of triethylamine and other residual solvents in the narrow polarity range of 4 to 5 reach 85-110% and 92-105% respectively. The ratio of 1:5 to 1:2.5 is preferably used to make the recovery rate of triethylamine and other residual solvents in the broad polarity range of 2 to 5 reach 92-105%. aDue to its stronger basicity, an imine base with a mass ratio (mg / mg) of ≥25 (in MeCN) to the raw material of 1:20 or higher can achieve recoveries of 85-110% for triethylamine and 92-105% for other residual solvents with a narrow polarity range of 4-5. A ratio of 1:10 to 1:2.5 is preferred, achieving a combined recovery of 92-105% for triethylamine and other residual solvents with a broad polarity range of 2-5. The raw material to diluent ratio in the headspace vial can be 1:100 to 1:20, with a preferred ratio of 1:20 (e.g., 250 mg of raw material to 5 ml of diluent) when NMP is used as the headspace solvent. This means that sufficient raw material is dissolved in the diluent to achieve optimal detection sensitivity. The ratio of imine base to headspace solvent in the diluent can be calculated using the formula below.

[0020] The ratio of imine base to headspace solvent in the diluent = a × b

[0021] Where:

[0022] a is the mass ratio of imine base to raw material in the headspace bottle (mg / mg);

[0023] b is the material-liquid ratio of raw material to diluent in the headspace bottle (mg / ml).

[0024] 3. Pretreatment of reference solution. Referring to the limit values of each residual solvent in the raw material, mix appropriate amounts of imine base, headspace solvent, triethylamine and other residual solvents in proportion to prepare a reference solution. The amount of imine base contained in the reference solution should be equivalent to that of the test solution to match the solution environment. Therefore, it is preferred to use a diluent to dilute the appropriate amount of triethylamine and other residual solvents to the limit concentration, measure an appropriate amount, place an empty bottle on the head, and seal to obtain the reference solution. The calculation formula for the concentration of triethylamine and other residual solvents in the reference solution is as follows:

[0025]

[0026] Where:

[0027] m is the sample amount of raw material in the headspace bottle (mg);

[0028] n is the limit value of each residual solvent (%);

[0029] V is the volume of the diluent in the headspace bottle (ml).

[0030] 4. GC detection. The test solution and the reference solution are injected into the headspace according to the predetermined chromatographic conditions. The substances to be tested are separated and respond in the gas chromatograph, and the chromatogram is recorded. There are no special requirements for the chromatographic conditions, as long as the separation and sensitivity of each substance to be tested meet the requirements. The heating program and headspace parameters in the triethylamine determination method of the raw material of adapalene in the United States Pharmacopoeia can be preferred, and the chromatographic column stationary phase is replaced from the weak polarity of 5% phenyl-95% methylpolysiloxane to the medium polarity of 6% cyanopropylphenyl-94% polydimethylsiloxane to adapt to the detection of multiple residual solvents.

[0031] 5. Calculate the residual amount of the substance to be tested by the external standard method. The calculation formula for the residual amount is as follows:

[0032]

[0033] Where:

[0034] A 供 is the peak area of the analyte in the test solution;

[0035] A 对 is the peak area of the analyte in the reference solution;

[0036] m 供 is the sample weight of the test product (mg);

[0037] C 对 is the concentration of the analyte in the reference solution (mg / ml);

[0038] V 供 is the volume of the test solution (ml).

[0039] 6. Typical chromatograms. Using NMP as the headspace solvent, and using the pretreatment method of "TBD to raw material mass ratio = 1:5" and "raw material to diluent material ratio = 1:20" and the chromatographic conditions in the table below, the triethylamine, dichloromethane, ethyl acetate, tetrahydrofuran, toluene, and diethylene glycol dimethyl ether that may be contained in a certain adapalene raw material were determined. The typical chromatograms of the obtained reference solution and test solution are shown in Figures 2-3 .

[0040]

[0041]

[0042] English abbreviations and their meanings

[0043] HS-GC: headspace gas chromatography;

[0044] pKa: acidity coefficient of a chemical substance;

[0045] MeCN: acetonitrile;

[0046] DBU: 1,8-diazabicyclo[5.4.0]undec-7-ene;

[0047] DBN: 1,5-diazabicyclo[4.3.0]non-5-ene;

[0048] TBD: 1,5,7-triazabicyclo[4.4.0]dec-5-ene;

[0049] MTBD: 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene;

[0050] TMG: 1,1,3,3-tetramethylguanidine;

[0051] DMAN: 1,8-bis(dimethylaminonaphthalene);

[0052] NMP: N-methylpyrrolidone;

[0053] DMF: N,N-dimethylformamide;

[0054] DMSO: dimethyl sulfoxide;

[0055] DMA: N,N-dimethylacetamide;

[0056] DMI: 1,3-dimethyl-2-imidazolidinone. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 Imine base classification chart

[0058] Figure 2 Gas chromatogram of reference solution (TBD to raw material ratio = 1:5)

[0059] Figure 3 Gas chromatogram of test solution (TBD to raw material ratio = 1:5) DETAILED DESCRIPTION

[0060] The present invention is further described in detail below through specific examples and comparative examples, which are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. According to the USP triethylamine assay in adapalene and the Chinese Pharmacopoeia analytical method guidelines, the reasonable recovery range of triethylamine with a lower limit (limit: 80ppm) is set to 85-110%, and meeting this range is considered to be an accurate determination; according to the ICH Q3C residual solvent guidelines and the Chinese Pharmacopoeia analytical method guidelines, the recovery range of other residual solvents with higher limits is set to 92-105%, and meeting this range is considered to be an accurate determination. If the recovery rate of triethylamine does not meet the higher requirement of 92-105%, or the application range of other residual solvents is a narrow polarity value of 4-5, it is considered a non-preferred condition. If the recovery rates of triethylamine and other residual solvents are both between 92-105%, and the application range of other residual solvents can be expanded from polarity values of 4-5 to 2-5, it is considered to be a preferred condition. The polarity values of other residual solvents used are shown in the table below.

[0061]

[0062]

[0063] Example 1 uses 23≤pK a (in MeCN)<25 Non-preferred conditions for imine base pretreatment (relatively low imine base dosage).

[0064] ①Select an imine base. Select 23≤pK a DBU (or TMG) with a (in MeCN) value < 25 was used as the imine base in this example to eliminate the matrix effect of the raw material, and NMP was used as the headspace solvent.

[0065] ② Prepare the diluent. Using a DBU:raw material ratio of 1:10 (or TMG:raw material ratio of 1:10) and a raw material:diluent ratio of 1:20, and using the formula in step 2 of the present invention, the diluent used is calculated to be 0.5% DBU (or 0.5% TMG). Therefore, pre-prepare 100 ml of a 0.5% DBU (or 0.5% TMG) solution in NMP as the diluent.

[0066] ③ Prepare the test solution. Take about 250 mg of the raw material and accurately measure 5 ml of the diluent, place an empty bottle on top, and seal.

[0067] ④ Prepare a reference solution. According to the raw material synthesis process, the residual solvents it may contain are triethylamine, dichloromethane, ethyl acetate, tetrahydrofuran, toluene and diethylene glycol dimethyl ether. According to the limit values required in the pharmacopoeia, about 250 mg of raw materials and 5 ml of diluent are added to the headspace bottle, and the formula under step 3 of the invention is used to calculate that the limit concentrations of the residual solvents of triethylamine, dichloromethane, ethyl acetate, tetrahydrofuran, toluene and diethylene glycol dimethyl ether are 4 μg / ml, 30 μg / ml, 250 μg / ml, 36 μg / ml, 44.5 μg / ml and 25 μg / ml, respectively. Take an appropriate amount of each residual solvent and dilute it with a diluent to the above concentration as a reference solution. Accurately measure 5 ml, place the headspace bottle, and seal it.

[0068] ⑤ Prepare the recovery solution. Take about 250 mg of the raw material and accurately measure 5 ml of the reference solution, place an empty bottle on top, and seal.

[0069] ⑥ Detection and calculation. Apply the preferred chromatographic conditions under step 4 of the invention to sample the test solution, reference solution, and recovery solution, and use the formula under step 5 of the invention to calculate the content of residual solvents such as triethylamine in the raw materials and calculate the recovery rate.

[0070] Results show that using a DBU:raw material ratio of 1:10 (or TMG:raw material ratio of 1:10) during pretreatment yields triethylamine recovery rates meeting the requirement of 85-110%, while recoveries of other residual solvents range from 92-105%. This ratio essentially guarantees the accuracy of triethylamine in the raw material. The results are shown in the table below.

[0071]

[0072] Example 2 uses 25≤pK a (in MeCN)<26 Non-preferred conditions for imine base pretreatment (relatively low imine base dosage).

[0073] ①Select imine base. Select 25≤pK a TBD with (in MeCN) < 26 was used as the imine base in this example to eliminate the matrix effect of the raw material, and NMP was used as the headspace solvent.

[0074] ② Prepare the diluent. Using a TBD:raw material ratio of 1:20 and a raw material:diluent ratio of 1:20, and using the formula in step 2 of the invention, the diluent used is calculated to be 0.25% TBD. Therefore, prepare 100 ml of a 0.25% TBD-containing NMP solution as the diluent.

[0075] ③ Prepare the test solution. Take about 250 mg of the raw material and accurately measure 5 ml of the diluent, place an empty bottle on top, and seal.

[0076] ④ Prepare a reference solution. According to the raw material synthesis process, the residual solvents it may contain are triethylamine, dichloromethane, ethyl acetate, tetrahydrofuran, toluene and diethylene glycol dimethyl ether. According to the limit values required in the pharmacopoeia, about 250 mg of raw materials and 5 ml of diluent are added to the headspace bottle, and the formula under step 3 of the invention is used to calculate that the limit concentrations of the residual solvents of triethylamine, dichloromethane, ethyl acetate, tetrahydrofuran, toluene and diethylene glycol dimethyl ether are 4 μg / ml, 30 μg / ml, 250 μg / ml, 36 μg / ml, 44.5 μg / ml and 25 μg / ml, respectively. Take an appropriate amount of each residual solvent and dilute it with a diluent to the above concentration as a reference solution. Accurately measure 5 ml, place the headspace bottle, and seal it.

[0077] ⑤ Prepare the recovery solution. Take about 250 mg of the raw material and accurately measure 5 ml of the reference solution, place an empty bottle on top, and seal.

[0078] ⑥ Detection and calculation. Apply the preferred chromatographic conditions under step 4 of the invention to sample the test solution, reference solution, and recovery solution, and use the formula under step 5 of the invention to calculate the content of residual solvents such as triethylamine in the raw materials and calculate the recovery rate.

[0079] The results show that using a TBD:raw material ratio of 1:20 during pretreatment yields triethylamine recovery rates of 85-110%, while recoveries of other residual solvents range from 92-105%. This ratio essentially guarantees the accuracy of triethylamine in the raw material. The results are shown in the table below.

[0080]

[0081] Example 3 uses 23≤pK a (in MeCN)<25Preferred conditions for imine base pretreatment (moderate imine base dosage)

[0082] ①Select an imine base. Select 23≤pK a DBU (or DBN) with a (in MeCN) value < 25 was used as the imine base in this example to eliminate the matrix effect of the raw material, and NMP was used as the headspace solvent.

[0083] ② Prepare the diluent. Using a DBU:raw material ratio of 1:2.5 (or DBN:raw material ratio of 1:5) and a raw material:diluent ratio of 1:20, and using the formula in step 2 of the invention, the diluent used is calculated to be 2% DBU (or 1% DBN). Therefore, prepare 100 ml of a 2% DBU (or 1% DBN) solution in NMP as the diluent.

[0084] ③ Prepare the test solution. Take about 250 mg of the raw material and accurately measure 5 ml of the diluent, place an empty bottle on top, and seal.

[0085] ④ Prepare a reference solution. According to the raw material synthesis process, the residual solvents it may contain are triethylamine, dichloromethane, ethyl acetate, tetrahydrofuran, toluene and diethylene glycol dimethyl ether. According to the limit values required in the pharmacopoeia, about 250 mg of raw materials and 5 ml of diluent are added to the headspace bottle, and the formula under step 3 of the invention is used to calculate that the limit concentrations of the residual solvents of triethylamine, dichloromethane, ethyl acetate, tetrahydrofuran, toluene and diethylene glycol dimethyl ether are 4 μg / ml, 30 μg / ml, 250 μg / ml, 36 μg / ml, 44.5 μg / ml and 25 μg / ml, respectively. Take an appropriate amount of each residual solvent and dilute it with a diluent to the above concentration as a reference solution. Accurately measure 5 ml, place the headspace bottle, and seal it.

[0086] ⑤ Prepare the recovery solution. Take about 250 mg of the raw material and accurately measure 5 ml of the reference solution, place an empty bottle on top, and seal.

[0087] ⑥ Detection and calculation. Apply the preferred chromatographic conditions under step 4 of the invention to sample the test solution, reference solution, and recovery solution, and use the formula under step 5 of the invention to calculate the content of residual solvents such as triethylamine in the raw materials and calculate the recovery rate.

[0088] Results show that using a DBU: starting material ratio of 1:2.5 (or DBN: starting material ratio of 1:5) during pretreatment yields triethylamine and other residual solvent recoveries between 92% and 105%. This ratio is the preferred choice, providing more accurate triethylamine determination and maintaining accuracy for residual solvents in the polarity range of 2 to 5. The results are shown in the table below.

[0089]

[0090] Example 4 uses 25≤pK a (in MeCN)<26Preferred conditions for imine base pretreatment (appropriate amount of imine base).

[0091] ①Select imine base. Select 25≤pK a TBD (or MTBD) with (in MeCN) < 26 was used as the imine base in this example to eliminate the matrix effect of the raw material, and NMP was used as the headspace solvent.

[0092] ② Prepare the diluent. Using a TBD:raw material ratio of 1:2.5 (or MTBD:raw material ratio of 1:10) and a raw material:diluent ratio of 1:20, and using the formula in step 2 of the invention, the diluent used is calculated to be 2% TBD (or 0.5% MTBD). Therefore, prepare 100 ml of a 2% TBD (or 0.5% MTBD) solution in NMP as the diluent.

[0093] ③ Prepare the test solution. Take about 250 mg of the raw material and accurately measure 5 ml of the diluent, place an empty bottle on top, and seal.

[0094] ④ Prepare a reference solution. According to the raw material synthesis process, the residual solvents it may contain are triethylamine, dichloromethane, ethyl acetate, tetrahydrofuran, toluene and diethylene glycol dimethyl ether. According to the limit values required in the pharmacopoeia, about 250 mg of raw materials and 5 ml of diluent are added to the headspace bottle, and the formula under step 3 of the invention is used to calculate that the limit concentrations of the residual solvents of triethylamine, dichloromethane, ethyl acetate, tetrahydrofuran, toluene and diethylene glycol dimethyl ether are 4 μg / ml, 30 μg / ml, 250 μg / ml, 36 μg / ml, 44.5 μg / ml and 25 μg / ml, respectively. Take an appropriate amount of each residual solvent and dilute it with a diluent to the above concentration as a reference solution. Accurately measure 5 ml, place the headspace bottle, and seal it.

[0095] ⑤ Prepare the recovery solution. Take about 250 mg of the raw material and accurately measure 5 ml of the reference solution, place an empty bottle on top, and seal.

[0096] ⑥ Detection and calculation. Apply the preferred chromatographic conditions under step 4 of the invention to sample the test solution, reference solution, and recovery solution, and use the formula under step 5 of the invention to calculate the content of residual solvents such as triethylamine in the raw materials and calculate the recovery rate.

[0097] Results show that using a TBD: starting material ratio of 1:2.5 (or MTBD: starting material ratio of 1:10) during pretreatment yields triethylamine and other residual solvent recoveries between 92% and 105%. This ratio is the preferred choice, providing more accurate triethylamine determination and maintaining accuracy for other residual solvents in the polarity range of 2 to 5. The results are shown in the table below.

[0098]

[0099] Example 5 Using 23≤pK a (in MeCN)<25 Non-preferred conditions for imine base pretreatment (relatively high imine base dosage).

[0100] ①Select an imine base. Select 23≤pK a TMG with (in MeCN) < 25 was used as the imine base in this example to eliminate the matrix effect of the raw materials, and NMP was used as the headspace solvent.

[0101] ② Prepare the diluent. Using a TMG:raw material ratio of 2:1 and a raw material:diluent ratio of 1:20, and using the formula in step 2 of the invention, the diluent used is calculated to be 10% TMG. Therefore, prepare 100 ml of a 10% TMG-containing NMP solution as the diluent.

[0102] ③ Prepare the test solution. Take about 250 mg of the raw material and accurately measure 5 ml of the diluent, place an empty bottle on top, and seal.

[0103] ④ Prepare a reference solution. According to the raw material synthesis process, the residual solvents it may contain are triethylamine, dichloromethane, ethyl acetate, tetrahydrofuran, toluene and diethylene glycol dimethyl ether. According to the limit values required in the pharmacopoeia, about 250 mg of raw materials and 5 ml of diluent are added to the headspace bottle, and the formula under step 3 of the invention is used to calculate that the limit concentrations of the residual solvents of triethylamine, dichloromethane, ethyl acetate, tetrahydrofuran, toluene and diethylene glycol dimethyl ether are 4 μg / ml, 30 μg / ml, 250 μg / ml, 36 μg / ml, 44.5 μg / ml and 25 μg / ml, respectively. Take an appropriate amount of each residual solvent and dilute it with a diluent to the above concentration as a reference solution. Accurately measure 5 ml, place the headspace bottle, and seal it.

[0104] ⑤ Prepare the recovery solution. Take about 250 mg of the raw material and accurately measure 5 ml of the reference solution, place an empty bottle on top, and seal.

[0105] ⑥ Detection and calculation. Apply the preferred chromatographic conditions under step 4 of the invention to sample the test solution, reference solution, and recovery solution, and use the formula under step 5 of the invention to calculate the content of residual solvents such as triethylamine in the raw materials and calculate the recovery rate.

[0106] The results show that using a 2:1 ratio of TMG to raw material during pretreatment yielded recoveries of triethylamine, ethyl acetate, tetrahydrofuran, and diglyme that met the 92-105% requirement. However, recoveries of dichloromethane and toluene did not meet the 92-105% requirement. While a relatively high dosage of imine base ensured accuracy for triethylamine determination, it did not guarantee accuracy for residual solvents with polarity ranging from 2 to 4. The results are shown in the table below.

[0107]

[0108] In Comparative Example 1, no sodium hydroxide solution or imine base was added, and the headspace solvent was directly used as a diluent to dissolve the raw materials, which failed to accurately determine triethylamine (the weak alkalinity of the headspace solvent was insufficient to dissociate triethylamine).

[0109] ① Prepare the reference solution: According to this raw material synthesis process, the residual solvents it may contain are triethylamine, dichloromethane, ethyl acetate, tetrahydrofuran, toluene, and diethylene glycol dimethyl ether. Based on the limit values required in the pharmacopoeia, add approximately 250 mg of raw material and 5 ml of diluent to the headspace bottle, and apply the formula under step 3 of the invention to calculate the limit concentrations of the residual solvents of triethylamine, dichloromethane, ethyl acetate, tetrahydrofuran, toluene, and diethylene glycol dimethyl ether to be 4 μg / ml, 30 μg / ml, 250 μg / ml, 36 μg / ml, 44.5 μg / ml, and 25 μg / ml, respectively. Take an appropriate amount of each residual solvent and dilute it with diluent to the above concentrations as the reference solution. Accurately measure 5 ml, place the headspace bottle, and seal.

[0110] ②Prepare the test solution: take about 250 mg of the raw material and accurately measure 5 ml of the diluent, place an empty bottle on top, and seal it.

[0111] ③ Prepare the recovery solution: take about 250 mg of the raw material and accurately measure 5 ml of the reference solution, place an empty bottle on top, and seal it.

[0112] ④ Detection and calculation. Apply the preferred chromatographic conditions under step 4 of the invention to sample the test solution, reference solution, and recovery solution for detection, and use the formula under step 5 of the invention to calculate the content of residual solvents such as triethylamine in the raw materials and calculate the recovery rate.

[0113] The results showed that without the addition of sodium hydroxide solution or imine base, the triethylamine recovery rate was only 82.2%, which did not meet the 85-110% requirement. The recovery rates of other residual solvents ranged from 92-105%. This method cannot guarantee the accuracy of triethylamine determination in the raw material. The results are shown in the table below.

[0114]

[0115] Comparative Example 2 was conducted according to the pretreatment method in the USP adapalene raw material triethylamine determination method, but triethylamine could not be accurately determined (NaOH could not fully contact the raw material to dissociate triethylamine).

[0116] ① Preparation of reference solution: According to the raw material synthesis process, the residual solvents that may be contained are triethylamine, dichloromethane, ethyl acetate, tetrahydrofuran, toluene, and diethylene glycol dimethyl ether. According to the limit values required in the pharmacopoeia, about 200 mg of raw materials and 4 ml of diluent (DMSO) are added to the headspace bottle, and the formula under step 3 of the invention is used to calculate that the limit concentrations of triethylamine, dichloromethane, ethyl acetate, tetrahydrofuran, toluene, and diethylene glycol dimethyl ether residual solvents are 4 μg / ml, 30 μg / ml, 250 μg / ml, 36 μg / ml, 44.5 μg / ml, and 25 μg / ml, respectively. Take an appropriate amount of each residual solvent and dilute it with diluent (DMSO) to the above concentrations as the reference solution. Accurately measure 4 ml of the reference solution and 1 ml of 1N NaOH solution, place the headspace bottle, and seal it.

[0117] ②Prepare the test solution: take about 200 mg of the raw material, and accurately measure 4 ml of the diluent (DMSO) and 1 ml of 1N NaOH solution, place an empty bottle on top, and seal it.

[0118] ③Prepare the recovery solution: take about 200 mg of the raw material, and accurately measure 4 ml of the reference solution and 1 ml of 1N NaOH solution, place an empty bottle on top, and seal it.

[0119] ④ Detection and calculation. Apply the preferred chromatographic conditions under step 4 of the invention to sample the test solution, reference solution, and recovery solution for detection, and use the formula under step 5 of the invention to calculate the content of residual solvents such as triethylamine in the raw materials and calculate the recovery rate.

[0120] The results showed that the triethylamine recovery rate using this method was only 79.0%, which did not meet the 85-110% requirement. Regarding other residual solvents, ethyl acetate hydrolyzed in NaOH solution, resulting in the disappearance of the relevant peaks. The recoveries of dichloromethane, tetrahydrofuran, and toluene did not meet the 92-105% requirement. This method cannot guarantee the accuracy of the determination of triethylamine, dichloromethane, tetrahydrofuran, and toluene in the raw materials, and it is unable to determine ethyl acetate.

[0121]

[0122] Comparative Example 3 using pK a The pretreatment of 1,8-bis(dimethylaminonaphthalene) (DMAN, a proton sponge compound) with a pKa of 18.2 (less than 23-26) failed to accurately determine triethylamine (adding sufficient DMAN with a pKa of less than 23 could not dissociate triethylamine in the raw material).

[0123] ① Prepare the diluent. Using a DMAN:raw material ratio of 2:1 and a raw material:diluent ratio of 1:20, and using the formula in step 2 of the invention, the diluent used is calculated to be 10% DMAN. Therefore, prepare 100 ml of a 10% DMAN solution in NMP as the diluent.

[0124] ② Prepare the test solution. Take about 250 mg of the raw material and accurately measure 5 ml of the diluent, place an empty bottle on top, and seal.

[0125] ④ Prepare a reference solution. According to the raw material synthesis process, the residual solvents it may contain are triethylamine, dichloromethane, ethyl acetate, tetrahydrofuran, toluene and diethylene glycol dimethyl ether. According to the limit values required in the pharmacopoeia, about 250 mg of raw materials and 5 ml of diluent are added to the headspace bottle, and the formula under step 3 of the invention is used to calculate that the limit concentrations of the residual solvents of triethylamine, dichloromethane, ethyl acetate, tetrahydrofuran, toluene and diethylene glycol dimethyl ether are 4 μg / ml, 30 μg / ml, 250 μg / ml, 36 μg / ml, 44.5 μg / ml and 25 μg / ml, respectively. Take an appropriate amount of each residual solvent and dilute it with a diluent to the above concentration as a reference solution. Accurately measure 5 ml, place the headspace bottle, and seal it.

[0126] ⑤ Prepare the recovery solution. Take about 250 mg of the raw material and accurately measure 5 ml of the reference solution, place an empty bottle on top, and seal.

[0127] ⑥ Detection and calculation. Apply the preferred chromatographic conditions under step 4 of the invention to sample the test solution, reference solution, and recovery solution, and use the formula under step 5 of the invention to calculate the content of residual solvents such as triethylamine in the raw materials and calculate the recovery rate.

[0128] The results showed that the recovery rate of triethylamine was 84.4% when the ratio of DMAN to raw material was 2:1 during the pretreatment process, which did not meet the requirement of 85-110%. The recovery rates of dichloromethane, ethyl acetate, tetrahydrofuran, toluene, and diethylene glycol dimethyl ether met the requirement of 92-105%. a The values are basically the same as those of triethylamine, and even when used in large quantities, triethylamine cannot be dissociated. The results are shown in the table below.

[0129]

[0130] Comparative Example 4 uses 23≤pK a The pretreatment of DBU with (in MeCN) < 25 failed to accurately determine triethylamine (very low imine base dosage).

[0131] ①Select an imine base. Select 23≤pK aDBU with (in MeCN) < 25 was used as the imine base in this example to eliminate the matrix effect of the raw material, and NMP was used as the headspace solvent.

[0132] ② Prepare the diluent. Using a DBU:raw material ratio of 1:50 and a raw material:diluent ratio of 1:20, and using the formula in step 2 of the invention, the diluent used is calculated to be 0.1% DBU. Therefore, prepare 100 ml of a 0.1% DBU-containing NMP solution as the diluent.

[0133] ③ Prepare the test solution. Take about 250 mg of the raw material and accurately measure 5 ml of the diluent, place an empty bottle on top, and seal.

[0134] ④ Prepare a reference solution. According to the raw material synthesis process, the residual solvents it may contain are triethylamine, dichloromethane, ethyl acetate, tetrahydrofuran, toluene and diethylene glycol dimethyl ether. According to the limit values required in the pharmacopoeia, about 250 mg of raw materials and 5 ml of diluent are added to the headspace bottle, and the formula under step 3 of the invention is used to calculate that the limit concentrations of the residual solvents of triethylamine, dichloromethane, ethyl acetate, tetrahydrofuran, toluene and diethylene glycol dimethyl ether are 4 μg / ml, 30 μg / ml, 250 μg / ml, 36 μg / ml, 44.5 μg / ml and 25 μg / ml, respectively. Take an appropriate amount of each residual solvent and dilute it with a diluent to the above concentration as a reference solution. Accurately measure 5 ml, place the headspace bottle, and seal it.

[0135] ⑤ Prepare the recovery solution. Take about 250 mg of the raw material and accurately measure 5 ml of the reference solution, place an empty bottle on top, and seal.

[0136] ⑥ Detection and calculation. Apply the preferred chromatographic conditions under step 4 of the invention to sample the test solution, reference solution, and recovery solution, and use the formula under step 5 of the invention to calculate the content of residual solvents such as triethylamine in the raw materials and calculate the recovery rate.

[0137] The results showed that using a DBU:raw material ratio of 1:50 during pretreatment resulted in a triethylamine recovery of 84.7%, which did not meet the 85-110% requirement. The recoveries of dichloromethane, ethyl acetate, tetrahydrofuran, toluene, and diglyme met the 92-105% requirement. Using too little DBU did not guarantee accurate triethylamine determination in the raw material. The results are shown in the table below.

[0138]

Claims

1. A pre-treatment method based on the assisted determination of residual solvents such as triethylamine in adapalene raw materials, characterized in that: 23≤pK measured using acetonitrile as solvent a <26 imine base (Ⅰ) to eliminate the matrix effect caused by the raw materials in the test solution to ensure the accuracy of triethylamine determination alone or triethylamine and other residual solvents combined determination; wherein R1, R2, R3 in the structural formula (Ⅰ) are selected from H or organic groups 2. The pretreatment method according to claim 1, wherein the pretreatment method comprises the following steps: The imine base has an amidine (II) or guanidine (III) structure; wherein in the structural formulas (II) and (III), R1, R2, R3, R5, and R6 are selected from H or an organic group, and R4 is selected from H or an organic group other than an amino group.

3. A pre-treatment method based on imine base-assisted determination of residual solvents such as triethylamine in adapalene raw materials according to claim 2, characterized in that: The imine base is DBU (IV), DBN (V), TBD (VI), MTBD (VII) or TMG (VIII) 4. The pretreatment method according to claim 1, wherein the method comprises the following steps: In the test solution, acetonitrile was used as the solvent for the determination of 23≤pK a The mass ratio of the imine base of <25 to the raw material is not less than 1:10, so that the accuracy of triethylamine determination reaches 85-115%, and the accuracy of other residual solvents with polarity values between 4 and 5 reaches 92-105%.

5. The pretreatment method according to claim 1, wherein the method comprises the following steps: In the test solution, acetonitrile was used as the solvent to measure 25≤pK a The mass ratio of the imine base of <26 to the raw material is not less than 1:20, so that the accuracy of triethylamine determination reaches 85-115%, and the accuracy of other residual solvents with polarity values between 4 and 5 reaches 92-105%.

6. A pretreatment method based on imine base-assisted determination of residual solvents such as triethylamine in adapalene raw materials according to claim 4, characterized in that: In the test solution, acetonitrile was used as the solvent for the determination of 23≤pK a The mass ratio of the imine base of less than 25 to the raw material is between 1:5 and 1:2.5, so that the determination accuracy of triethylamine and other residual solvents with polarity values between 2 and 5 can reach 92 to 105%.

7. The pretreatment method according to claim 5, wherein the method comprises the following steps: In the test solution, acetonitrile was used as the solvent to measure 25≤pK a The mass ratio of the imine base of <26 to the raw material is between 1:10 and 1:2.5, so that the determination accuracy of triethylamine and other residual solvents with polarity values between 2 and 5 can reach 92 to 105%.

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