Method for determining content of various residual solvents in clozapine bulk drug by capillary gas chromatography

Abstract

The invention discloses a method for determining the content of various residual solvents in a clozapine bulk drug by using capillary gas chromatography, and belongs to the technical field of drug analysis. According to the method, a gas chromatographic method is adopted, a capillary chromatographic column with 6% of cyanopropyl phenyl-94% of dimethyl polysiloxane as a stationary liquid is adopted, an FID detector is adopted for detection, and the content of the residual solvent is calculated by peak area according to an external standard method; wherein the multiple residual solvents are methanol, ethanol, isopropanol, n-amyl alcohol, n-butyl alcohol and toluene. The method disclosed by the invention is good in specificity, good in linearity, reliable in accuracy and high in sensitivity; the gas chromatographic method can be used for rapidly, effectively, accurately and reliably separating and detecting the content of various residual solvents in the clozapine raw material medicine, the product quality of the clozapine raw material medicine is improved, and the medication safety of a patient is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of drug analysis, and more specifically, relates to a method for measuring the contents of multiple residual solvents in clozapine raw materials by using capillary gas chromatography. Background Art

[0002] As a new antipsychotic drug, clozapine has high efficacy, rapid results, and mild extrapyramidal symptoms. It can also be used as a broad-spectrum neuroleptic drug with rapid onset of action. Clozapine is not only effective for positive symptoms of psychosis, but also has a certain effect on negative symptoms.

[0003] Organic solvents used in the synthesis of clozapine raw materials include methanol, ethanol, n-butanol, isopropanol, n-pentanol, and toluene; in the General Chapter 0861 "Determination of Residual Solvents" of the 2020 edition of the Chinese Pharmacopoeia, toluene is specified as a Class II solvent, and methanol, ethanol, n-butanol, isopropanol, and n-pentanol are Class III solvents; Class II solvents are non-genotoxic animal carcinogens, or may cause other irreversible toxicities such as neurotoxicity or teratogenicity, and may have other serious but reversible toxic solvents, and their use should be restricted; Class III solvents (solvents with low potential toxicity to humans, negative genotoxicity, no need to establish health-based exposure limits, and low potential toxic solvents) and solvents for which there are insufficient toxicological data.

[0004] At present, there is no relevant literature reporting the residual solvent content in clozapine APIs. Methanol, ethanol, isopropanol, n-pentanol, n-butanol and toluene in clozapine have low boiling points. In theory, the limit method "loss on drying method" (drying temperature 105°C) can be used to determine whether the residual amount is qualified. However, if the sample and the solvent form a crystallization solvent, the general heating and drying conditions cannot effectively dry out the residual solvent, and the results will be distorted. Therefore, a method that can better detect the residual solvents in clozapine APIs, namely the residual amount of methanol, ethanol, n-butanol, isopropanol, n-pentanol and toluene, is needed to ensure the safety of medication. Summary of the invention

[0005] In view of the above problems existing in the prior art, the technical problem to be solved by the present invention is to provide a method for determining the contents of various residual solvents in clozapine raw materials by using capillary gas chromatography. The capillary gas chromatography can quickly, effectively, accurately and reliably detect the contents of various residual solvents in clozapine raw materials, which is beneficial to improving the product quality of the raw material clozapine.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0007] The invention discloses a method for determining the contents of various residual solvents in a clozapine raw material drug by using a capillary gas chromatography method. The method adopts a gas chromatography method, a capillary chromatographic column with 6% cyanopropylphenyl-94% dimethylpolysiloxane as a stationary liquid, an FID detector for detection, and calculates the contents of the residual solvents by peak area according to an external standard method; wherein the various residual solvents are methanol, ethanol, isopropanol, n-pentanol, n-butanol and toluene.

[0008] Preferably, the detection conditions are as follows: the carrier gas is nitrogen; the carrier gas flow rate is 1.0 mL / min; the initial column temperature is 35°C, maintained for 1 min, increased to 220°C at a rate of 15°C / min, and maintained for 2 min; the FID detector temperature is 300°C; and the injection port temperature is 200°C.

[0009] Preferably, the split ratio is 50:1, the injection method is headspace injection, and the injection volume is 5 mL.

[0010] Preferably, the equilibrium temperature of the headspace bottle is 85° C. and the equilibrium time is 30 minutes.

[0011] Preferably, the test solution and the reference solution are prepared using the solvent N,N-dimethylformamide.

[0012] Preferably, the preparation process of the test solution is: accurately weigh 0.5 g of clozapine, place it in an empty bottle, accurately add 5 mL of N,N-dimethylformamide solution, seal it, and dissolve it by ultrasonication to obtain the test solution.

[0013] Preferably, the preparation process of the reference solution is: take appropriate amounts of methanol, ethanol, n-butanol, isopropanol, n-pentanol, and toluene, dissolve and dilute them with N,N-dimethylformamide to form a solution containing 300 μg of methanol, 500 μg of ethanol, 500 μg of isopropanol, 500 μg of n-pentanol, 500 μg of n-butanol, and 89 μg of toluene per 1 mL, as the reference solution.

[0014] Preferably, the test solution has a peak in the chromatogram with the retention time consistent with that of the reference solution, and calculated by the peak area using the external standard method, methanol does not exceed 0.3%, ethanol does not exceed 0.5%, isopropanol does not exceed 0.5%, n-pentanol does not exceed 0.5%, n-butanol does not exceed 0.5%, and toluene does not exceed 0.089%.

[0015] Preferably, according to the chromatogram, a linear regression equation is made with the peak area A as the ordinate and the linear solution concentration C as the abscissa. The linear equation of methanol is A=3.2841C+6.7434, and the linear concentration range is 0.96μg / mL to 145.38μg / mL; the linear equation of ethanol is A=3.1498C+11.421, and the linear concentration range is 0.97μg / mL to 253.20μg / mL; the linear equation of n-butanol is A=9.3467C+7.609, and the linear concentration range is 0.73μg / mL~85.44μg / mL; the linear equation of isopropanol is A=3.1131C+8.948, and the linear concentration range is 0.60μg / mL~257.62μg / mL; the linear equation of n-pentanol is A=18.855C-0.3517, and the linear concentration range is 0.84μg / mL~41.90μg / mL; the linear equation of toluene is A=1.5314C+1.293, and the linear concentration range is 0.35μg / mL~91.77μg / mL.

[0016] Preferably, the limit of quantification of methanol is 2.98 μg / mL, and the limit of detection is 1.19 μg / mL; the limit of quantification of ethanol is 2.99 μg / mL, and the limit of detection is 1.20 μg / mL; the limit of quantification of n-butanol is 4.98 μg / mL, and the limit of detection is 1.99 μg / mL; the limit of quantification of isopropanol is 1.50 μg / mL, and the limit of detection is 0.60 μg / mL; the limit of quantification of n-pentanol is 9.84 μg / mL, and the limit of detection is 3.94 μg / mL; the limit of quantification of toluene is 0.35 μg / mL, and the limit of detection is 0.14 μg / mL.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1) The method of the present invention has good specificity, good linearity, reliable accuracy, high sensitivity, and can be applied to most pharmaceutical companies;

[0019] 2) The capillary gas chromatography method of the present invention can quickly, effectively, accurately and reliably separate and detect the contents of various residual solvents in the clozapine raw material, which is beneficial to improving the product quality of the clozapine raw material and improving the safety of patients' medication. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The chromatogram is a capillary gas chromatography method for determining the residual solvent content in clozapine raw materials, wherein: Figure 1 a is the reference solution spectrum of the method of the present invention; Figure 1 b is the spectrum of the mixed reference solution of the method of the present invention; Figure 1 c is a mixed solution spectrum of the method of the present invention;

[0021] Figure 2 is a linear curve diagram of the method of the present invention; wherein, Figure 2 a is the linear curve of methanol; Figure 2 b is the linear curve of ethanol, Figure 2 c is the linear curve of n-butanol, Figure 2 d is the linear curve of isopropanol, Figure 2 e is the linear curve of n-pentanol, Figure 2 f is the linear curve of toluene;

[0022] Figure 3 It is the quantitative limit diagram of each residual solvent in the method of the present invention;

[0023] Figure 4 Graph showing the detection limits of various residual solvents in the method of the present invention. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described below in conjunction with specific embodiments. In the following embodiments, unless otherwise specified, the technical means used are conventional means well known to those skilled in the art.

[0025] In the following examples, the gas chromatograph used was Agilent 7890B / 7697A; all reagents used were analytical grade; the test sample clozapine used was from Jiangsu Cixing Pharmaceutical Co., Ltd., batch number 201907001.

[0026] Example 1

[0027] A method for determining the contents of various residual solvents in clozapine bulk drug by capillary gas chromatography comprises the following steps:

[0028] 1) Prepare the test solution and control solution:

[0029] The preparation method of the test solution is as follows: accurately weigh 0.5 g of clozapine, place it in an empty bottle, accurately add 5 mL of N,N-dimethylformamide, seal it, and dissolve it by ultrasonication as the test solution;

[0030] The preparation method of the reference solution is as follows: take appropriate amounts of methanol, ethanol, n-butanol, isopropanol, n-pentanol, and toluene, dissolve and dilute with N,N-dimethylformamide to make a solution containing 300 μg of methanol, 500 μg of ethanol, 500 μg of isopropanol, 500 μg of n-pentanol, 500 μg of n-butanol, and 89 μg of toluene per 1 mL, as the reference solution;

[0031] 2) Setting gas chromatography detection conditions: a capillary column with 6% cyanopropylphenyl-94% dimethylpolysiloxane as the stationary phase; nitrogen as the carrier gas; a carrier gas flow rate of 1.0 mL / min; an initial column temperature of 35°C, maintained for 1 min, raised to 220°C at a rate of 15°C / min, maintained for 2 min; an FID detector temperature of 300°C; an injection port temperature of 200°C; a split ratio of 50:1, an injection method of headspace injection, and an injection volume of 5 mL; an equilibrium temperature of the headspace bottle of 85°C, and an equilibrium time of 30 min;

[0032] 3) Accurately pipette 5 mL of the test solution and the control solution respectively, inject them into the gas chromatograph, detect and record the chromatogram, and calculate the content of the residual solvent by the peak area according to the external standard method; wherein the multiple residual solvents are methanol, ethanol, isopropanol, n-pentanol, n-butanol and toluene;

[0033] 4) According to the chromatogram, a linear regression equation was made with the peak area A as the ordinate and the linear solution concentration C as the abscissa. The linear equation of methanol was A=3.2841C+6.7434, the linear concentration range of methanol was 0.96μg / mL~145.38μg / mL, the limit of quantification was 2.98μg / mL, and the detection limit was 1.19μg / mL; the linear equation of ethanol was A=3.1498C+11.421, the linear concentration range of ethanol was 0.97μg / mL~253.20μg / mL, the limit of quantification was 2.99μg / mL, and the detection limit was 1.20μg / mL; the linear equation of n-butanol was A=9.3467C+7.609, the linear concentration range of n-butanol was 0.73μg / mL~85.44μg / mL, and the limit of quantification was 4.98μg / mL. g / mL, the detection limit is 1.99μg / mL; the linear equation of isopropanol is A=3.1131C+8.948, the linear concentration range of isopropanol is 0.60μg / mL~257.62μg / mL, the limit of quantification is 1.50μg / mL, and the detection limit is 0.60μg / mL; the linear equation of n-pentanol is A=18.855C-0.3517, the linear concentration range of n-pentanol is 0.84μg / mL~41.90μg / mL, the limit of quantification is 9.84μg / mL, and the detection limit is 3.94μg / mL; the linear equation of toluene is A=1.5314C+1.293, the linear concentration range of toluene is 0.35μg / mL~91.77μg / mL, the limit of quantification is 0.35μg / mL, and the detection limit is 0.14μg / mL.

[0034] Example 2

[0035] The residual solvents and their sources that may be contained in the clozapine raw material during the synthesis process are shown in the table below, among which the residual control of benzene and xylene is not within the scope of the present invention.

[0036]

[0037]

[0038] The diluent used in the following experiments was NN-dimethylformamide.

[0039] 1. Exclusivity

[0040] Take 1.5 g methanol, 2.5 g ethanol, 2.5 g n-butanol, 2.5 g isopropanol, 2.5 g n-pentanol, about 1.085 g xylene, 0.445 g toluene, and 0.5 g N-methylpiperidin, place in different 50 mL volumetric flasks, add diluent and dilute to the scale, as the positioning solution of each solvent;

[0041] Take 0.1g of benzene, put it in a 100mL volumetric flask, add diluent to dilute to the mark, as the benzene positioning solution;

[0042] Accurately measure 1 mL of each of the above solvent-based solutions, place in a 100 mL volumetric flask, and dilute to the mark with diluent as the mixed reference solution;

[0043] Accurately measure 1 mL each of methanol, ethanol, isopropanol, n-pentanol, n-butanol, and toluene solution, place in a 100 mL volumetric flask, and dilute to the mark with diluent as the reference solution;

[0044] Take 0.5 g of clozapine, weigh it accurately, put it in an empty bottle, add 5 mL of the reference solution accurately, seal it, and use it as a mixed solution;

[0045] Take 0.5 g of clozapine, weigh it accurately, place it in an empty bottle, and accurately add 5 mL of diluent as the test solution.

[0046] Accurately measure 5 mL of each solvent, each positioning solution, mixed reference solution, and reference solution, place them in a headspace bottle, seal them, and perform headspace sampling. Ultrasonic dissolve the test solution and mixed solution, perform headspace sampling, record the chromatogram, and examine the peak time and separation of each component. The results are shown in Table 1 and Figure 1 .

[0047] Table 1 Specificity results

[0048]

[0049]

[0050] From Table 1 and Figure 1 It can be seen that the method of the present invention has good specificity, the diluent does not interfere with the determination of each target solvent, the separation between the solvent peaks in the reference solution is not less than 1.5, and the unknown impurity peaks in the test sample do not interfere with the determination of the solvent content.

[0051] 2. Limit of quantification and detection limit

[0052] Take appropriate amount of methanol, ethanol, n-butanol, isopropanol, n-pentanol and toluene reference substances, dissolve them with diluent, and dilute them step by step until the signal-to-noise ratio of each solvent to be tested is 8-30, which is the quantitative limit solution. On the basis of the quantitative limit solution, the solution diluted 2-3 times is used as the detection limit solution. The results are shown in Table 2.

[0053] Table 2 Results of limit of quantitation test

[0054]

[0055]

[0056] As shown in Table 2, the solution concentration of each solvent when the signal-to-noise ratio is 8-30 is much less than half of the standard limit, the peak area RSD (n=6) is less than 20%, and the retention time RSD value is less than 2.0%, which meets the quantitative detection requirements. The quantitative limit concentration does not exceed half of the limit, and the sensitivity of the method of the present invention is good.

[0057] Table 3 Detection limit test results

[0058]

[0059]

[0060] It can be seen from Table 3 that the solution concentration of each solvent when the signal-to-noise ratio is between 3 and 7 is less than half of the standard limit and can meet the detection requirements.

[0061] 3. Linearity and range

[0062] Take appropriate amount of methanol, ethanol, isopropanol, n-butanol, n-pentanol and toluene reference substances, dilute with diluent to prepare a series of linear solutions (8 concentration points are taken within the range of 160% of the limit of each solvent), accurately measure 5mL of each linear solution into a headspace bottle, inject into a gas chromatograph, record the chromatogram, measure the peak area, use the concentration of the linear solution as the abscissa and the peak area as the ordinate, perform linear regression with the least square method, and calculate the linear regression equation and correlation coefficient of each solvent. The results are shown in Table 4.

[0063] Table 4 Linearity determination results

[0064]

[0065]

[0066] As shown in Table 4, each solvent to be tested has good linearity within the range of the quantitative limit to 160% of the limit, the correlation coefficient r is greater than 0.99, and the absolute value of the Y-axis intercept at 100% response value is no more than 10%, indicating good linearity.

[0067] 4. Accuracy

[0068] Take appropriate amount of each solvent reference substance, add it to the clozapine raw material at a ratio of 80% to 120% of each impurity limit (methanol 0.3%, ethanol 0.5%, n-pentanol 0.5%, n-butanol 0.5%, isopropanol 0.5%, toluene 0.089%), and prepare 3 portions for each concentration. The preparation process is as follows:

[0069] Take 0.6g of methanol, 1g of ethanol, 1g of n-butanol, 1g of n-pentanol, and 0.18g of toluene, place them in the same 20mL measuring bottle, dissolve and dilute to the scale with a diluent, and take 1g of isopropanol, place it in a 20mL measuring bottle, dissolve and dilute to the scale with a diluent, as each solvent reference substance stock solution I; accurately measure 1mL of each of the above solvent reference substance stock solutions I, place it in a 100mL measuring bottle, add a diluent and dilute to the scale, as the reference substance solution;

[0070] Accurately measure 5 mL of each solvent reference substance stock solution I, place it in a 50 mL volumetric flask, add diluent to dilute to the scale, and use it as the reference substance stock solution II;

[0071] 80% recovery solution: accurately measure 2 mL of reference substance stock solution II, place it in a 25 mL volumetric flask, add diluent to dilute to the mark, and use it as the impurity limit 80% solution; take 0.5 g of clozapine, place it in an empty bottle, accurately add 5 mL of the impurity limit 80% solution, seal it, and dissolve it by ultrasonication;

[0072] 100% recovery solution: Take 0.5 g of clozapine, place it in an empty bottle, accurately add 5 mL of the reference solution, seal it, and dissolve it by ultrasonication;

[0073] 120% recovery solution: accurately measure 3 mL of reference substance stock solution II into a 25 mL volumetric flask, add diluent to dilute to the mark, and use it as the impurity limit 120% solution; take 0.5 g of clozapine, place it in an empty bottle, accurately add 5 mL of the impurity limit 120% solution, seal, and dissolve by ultrasonication;

[0074] Take 0.5 g of clozapine, place it in an empty bottle, accurately add 5 mL of diluent, seal it, and dissolve it by ultrasonication as the unspiked sample solution;

[0075] Accurately measure 5 mL of solvent, reference solution, test solution, and recovery sample solution into different headspace bottles, record the peak area of ​​each known impurity, calculate the measured amount by peak area according to the external standard method, deduct the background amount of the test sample, and calculate the recovery rate and RSD. The results are shown in Table 5.

[0076] Table 5 Accuracy test results

[0077]

[0078]

[0079]

[0080] As can be seen from Table 5, the recoveries of the residual solvents at the three concentration levels of high (limit 120%), medium (limit 100%), and low (limit 80%) were all between 80% and 120%, and the recovery RSD (n=9) was less than 10%. The recovery was good and the accuracy of the method was high.

[0081] 5. Repeatability

[0082] The sample contains isopropanol solvent, and other solvents are almost undetectable. The content of each solvent is calculated by adding samples. The repeatability of the method is investigated. Appropriate amounts of other solvents (methanol 0.3%, ethanol, n-pentanol, n-butanol 0.5% and toluene 0.89%) are added to the clozapine raw material according to the limit of 100%, and 6 portions are prepared in parallel. The preparation process is as follows:

[0083] Take 0.6g of methanol, 1g of ethanol, 1g of n-butanol, 1g of n-pentanol, and 0.18g of toluene, place them in the same 20mL measuring bottle, dissolve and dilute to the scale with a diluent, and take 1g of isopropanol, place it in a 20mL measuring bottle, dissolve and dilute to the scale with a diluent, as each solvent reference substance stock solution I; accurately measure 1mL of each of the above solvent reference substance stock solutions I, place it in a 100mL measuring bottle, add a diluent and dilute to the scale, as the reference substance solution;

[0084] Accurately measure 1 mL of reference substance stock solution I containing methanol, ethanol, n-pentanol, n-butanol and toluene, place in a 100 mL volumetric flask, add diluent to dilute to the mark, and use as reference substance stock solution II;

[0085] Take 0.5g of clozapine, place it in an empty bottle, accurately add 5mL of reference substance reserve solution II, seal, dissolve by ultrasonic, and prepare 6 portions in parallel; take the above solution, test the chromatographic conditions according to the application, inject and test, and calculate the content of each solvent by peak area according to the external standard method. The results are shown in Table 6.

[0086] Table 6 Results of the residual solvent content in the repeatability test

[0087]

[0088]

[0089] It can be seen from Table 6 that the RSD of each solvent content to be tested is no more than 10.0%, and the method of the present invention has good repeatability.

[0090] 6. Solution stability

[0091] Take an appropriate amount of each solvent to be tested, prepare a reference solution according to the method under "Specificity", divide it into headspace bottles, inject it into the gas chromatograph at different times, and examine the stability of the reference solution at different times by the change in peak area.

[0092] Table 7 Results of the stability peak area study of the reference solution

[0093]

[0094] As shown in Table 7, when the reference solution was placed at room temperature for 24.5 hours, the relative standard deviation of the peak area of ​​each solvent was no more than 5%, indicating that the reference solution was relatively stable when placed at room temperature for 24.5 hours.

[0095] 9. Durability

[0096] The mixed reference solution, reference solution and test solution were prepared according to the residual solvent method. The chromatographic conditions (initial column temperature, column flow rate) were adjusted to investigate the effect of slight changes in the determination conditions on the determination results. The test results are shown in Tables 8, 9 and 10.

[0097] Table 8 Effect of flow rate change on system suitability

[0098]

[0099]

[0100] Table 9 Effect of column temperature change on system suitability

[0101]

[0102] Table 10 Effect of different chromatographic conditions on the determination of solvent content in the test solution

[0103]

[0104] It can be seen from Tables 8-10 that the chromatographic conditions changed slightly, the flow rate (±0.1mL / min), column temperature (±5℃), and the RSD (n=6) of the peak area of ​​the reference solution were all no more than 10%. In the mixed reference solution, the separation degree of each solvent was greater than 1.5, achieving baseline separation. Under different chromatographic conditions, there was no significant difference in the detection results of each solvent in the test solution (the absolute difference compared with normal conditions was no more than 0.05%), and the system durability was good.

[0105] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the embodiments. The embodiments in this application and the features in the embodiments can be combined with each other in any way without conflict. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principle of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention. In addition, the technical details not described in detail in this specification belong to the common technology of those skilled in the art, so this specification will not be repeated.

Claims

1. A method for determining the content of various residual solvents in clozapine bulk drug using capillary gas chromatography, characterized in that: Gas chromatography was used with a capillary column using 6% cyanopropylphenyl-94% dimethylpolysiloxane as the stationary liquid and an FID detector for detection. The content of residual solvents was calculated by peak area using the external standard method. Among them, the various residual solvents were methanol, ethanol, isopropanol, n-pentanol, n-butanol and toluene.

2. The method for determining the content of various residual solvents in clozapine bulk drug by capillary gas chromatography according to claim 1, characterized in that: The test conditions are: The carrier gas is nitrogen; The carrier gas flow rate was 1.0 mL / min; The initial column temperature was 35 °C, maintained for 1 min, then raised to 220 °C at a rate of 15 °C / min and maintained for 2 min; The FID detector temperature is 300°C; The injection port temperature was 200 °C.

3. The method for determining the content of various residual solvents in clozapine bulk drug by capillary gas chromatography according to claim 1, characterized in that: The split ratio was 50:1, the injection method was headspace injection, and the injection volume was 5 mL.

4. The method for determining the content of various residual solvents in clozapine bulk drug by capillary gas chromatography according to claim 1, characterized in that: The equilibration temperature of the headspace vial was 85°C and the equilibration time was 30 minutes.

5. The method for determining the content of various residual solvents in clozapine bulk drug by capillary gas chromatography according to claim 1, characterized in that: The test solution and the reference solution were prepared using the solvent N,N-dimethylformamide.

6. The method for determining the content of various residual solvents in clozapine bulk drug by capillary gas chromatography according to claim 5, characterized in that: The preparation process of the test solution is as follows: accurately weigh 0.5 g of clozapine, place it in an empty bottle, accurately add 5 mL of N,N-dimethylformamide solution, seal it, and dissolve it by ultrasonication to obtain the test solution.

7. The method for determining the contents of various residual solvents in clozapine bulk drug by capillary gas chromatography according to claim 5, characterized in that: The preparation process of the reference solution is: Take appropriate amounts of methanol, ethanol, n-butanol, isopropanol, n-pentanol, and toluene, and dissolve and dilute them with N,N-dimethylformamide to make a solution containing 300 μg of methanol, 500 μg of ethanol, 500 μg of isopropanol, 500 μg of n-pentanol, 500 μg of n-butanol, and 89 μg of toluene per 1 mL as the reference solution.

8. The method for determining the contents of various residual solvents in clozapine bulk drug by capillary gas chromatography according to claim 1, characterized in that: There is a peak in the chromatogram of the test solution with the same retention time as the reference solution. Calculated by peak area using the external standard method, methanol does not exceed 0.3%, ethanol does not exceed 0.5%, isopropanol does not exceed 0.5%, n-pentanol does not exceed 0.5%, n-butanol does not exceed 0.5%, and toluene does not exceed 0.089%.

9. The method for determining the contents of various residual solvents in clozapine bulk drug by capillary gas chromatography according to claim 1, characterized in that: According to the chromatogram, a linear regression equation was drawn with the peak area A as the ordinate and the linear solution concentration C as the abscissa. The linear equation of methanol was A=3.2841C+6.7434, and the linear concentration range was 0.96μg / mL to 145.38μg / mL; the linear equation of ethanol was A=3.1498C+11.421, and the linear concentration range was 0.97μg / mL to 253.20μg / mL; the linear equation of n-butanol was A=9.3467C+7.609, and the linear concentration range was 0.7 3μg / mL~85.44μg / mL; the linear equation of isopropanol is A=3.1131C+8.948, and the linear concentration range is 0.60μg / mL~257.62μg / mL; the linear equation of n-pentanol is A=18.855C-0.3517, and the linear concentration range is 0.84μg / mL~41.90μg / mL; the linear equation of toluene is A=1.5314C+1.293, and the linear concentration range is 0.35μg / mL~91.77μg / mL.

10. The method for determining the contents of various residual solvents in clozapine bulk drug by capillary gas chromatography according to claim 1, characterized in that: The quantification limit of methanol is 2.98μg / mL, and the detection limit is 1.19μg / mL; the quantification limit of ethanol is 2.99μg / mL, and the detection limit is 1.20μg / mL; the quantification limit of n-butanol is 4.98μg / mL, and the detection limit is 1.99μg / mL; the quantification limit of isopropanol is 1.50μg / mL, and the detection limit is 0.60μg / mL; the quantification limit of n-pentanol is 9.84μg / mL, and the detection limit is 3.94μg / mL; the quantification limit of toluene is 0.35μg / mL, and the detection limit is 0.14μg / mL.

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