Method for detecting nitrogen content and uniformity of nitrocotton by high performance liquid chromatography

Abstract

The invention discloses a method for detecting the nitrogen content and uniformity of nitrocotton through high performance liquid chromatography, and belongs to the technical field of chemical analysis. The invention provides a method for detecting nitrogen content and uniformity of nitrocotton by high performance liquid chromatography by utilizing a linear relationship between HPLC retention time and nitrogen content of nitrocotton, which comprises the following steps: preparing a series of nitrocotton standard solutions with nitrogen content, performing HPLC analysis, and establishing a linear equation by taking the nitrogen content as an abscissa and the retention time as an ordinate; and substituting the retention time of the nitrocotton sample to be detected into the linear equation to obtain the nitrogen content of the nitrocotton sample to be detected. The sample application range is wide, the sample pretreatment operation is simple, the result is accurate, mixed nitrocotton sample detection can be achieved, and nitrocotton uniformity analysis can be guided.

Description

Technical Field

[0001] This invention belongs to the field of chemical analysis technology, specifically relating to a method for determining the nitrogen content and uniformity of nitrocellulose (also known as nitrocellulose) based on high performance liquid chromatography (HPLC). It can be widely used in the quality inspection and production process monitoring of nitrocellulose products in the fields of explosives, propellants, and biotechnology consumables (such as nitrocellulose membranes). Background Technology

[0002] Nitrocellulose (NC), also known as cellulose nitrate ester or nitrocellulose cotton, is a product of the esterification reaction of cellulose with nitrate. Nitrocellulose has two main applications: military and civilian. The civilian application is primarily used in coatings, inks, films, leather, plastics, nail polish, celluloid, and many other fields. The military application is mainly used in the weapons and explosives industry, serving as a crucial raw material for propellants and explosives. In industrial production, nitrogen content is expressed as the weight percentage of nitrogen atoms in nitrocellulose, reflecting its degree of esterification, and is represented by N%. It is a very important technical indicator for nitrocellulose. In single-base propellants, nitrocellulose is the main component, and the nitrogen content directly affects the propellant's energy and mechanical properties. In the production of double-base propellants, nitrocellulose with lower nitrogen content and better solubility is required for better plasticization and molding. Therefore, depending on the intended use of different weapons, the nitrogen content of nitrocellulose needs to be controlled within different ranges. For civilian nitrocellulose, nitrogen content affects its solubility, viscosity, and stability. Therefore, the nitrogen content must be controlled within an appropriate range according to the performance requirements of different products. Thus, accurate and rapid determination of the nitrogen content of nitrocellulose is crucial for the production efficiency, quality stability, performance testing, and development of new processes and methods for both military and civilian products. It is an extremely important aspect of nitrocellulose quality control.

[0003] Numerous studies, both domestically and internationally, have explored methods for testing the nitrogen content of nitrocellulose (NC). These methods primarily include the five-tube nitrogen meter method, ferrous sulfate reduction method, Diwald alloy reduction method, Schulze-Tiemann method, salicylic acid-titanium method, elemental analyzer method, interferometer method, combustion calorimetry method, and polarized light microscopy method. The five-tube nitrogen meter method is extremely harmful to human health and is largely obsolete. The Diwald alloy reduction method, Schulze-Tiemann method, and salicylic acid-titanium method are cumbersome, time-consuming, and difficult to master, and are generally no longer used. The ferrous sulfate reduction method offers relatively good precision and accuracy, making it suitable as a standard method at present, but its long analysis cycle, complex operation, and difficulty in mastering hinder its development. The interferometer method is simple and fast, but the discontinuation of interferometers limits its development. The combustion calorimetry method has not demonstrated advantages in operation, cost, or accuracy, limiting its widespread application. The elemental analyzer method suffers from issues such as instrument stability and poor method precision. The polarized light microscopy method for studying NC nitrogen uniformity also suffers from long analysis cycles and complex operation.

[0004] CN101101258A discloses a method for determining the uniformity of ammonia and nitrogen content in nitrocellulose. This method employs a quarter-wave plate method using polarized light microscopy to measure the compensation angle of each NC fiber or a relatively straight segment in a batch (approximately 100 fibers). The nitrogen content of the NC fiber is then calculated from the compensation angle (the numerical relationship between the compensation angle and ammonia content is obtained by measuring the compensation angles of several batches of NC fibers with known nitrogen content). The average ammonia content of all NC fibers in the batch is taken as the ammonia content of that batch, and the standard deviation of the nitrogen content in that batch is used as an indicator of the ammonia distribution. However, the polarized light microscopy method for studying the uniformity of NC nitrogen content also suffers from problems such as long analysis cycles and complex operation.

[0005] CN105784701A discloses an automated nitrogen content measurement system and method for nitrocellulose based on the principle of alloy reduction reaction. This system achieves automated nitrogen content testing of nitrocellulose based on the Dewald alloy reduction principle. However, this method has a long analysis cycle, is complex to operate, and is difficult to master. Furthermore, its accuracy in determining nitrogen content based on statistical data of the compensation angle needs improvement.

[0006] CN117647495A discloses a method for determining the nitrogen content of nitrocellulose, comprising the following steps: (1) adding the nitrocellulose sample to be tested into a sodium hydroxide solution, hydrolyzing it completely at 60~80℃, filtering the hydrolysate with a 0.22μm nylon filter membrane, diluting it with pure water, and then adding aminosulfonic acid solution to the diluted hydrolysate to obtain a mixed solution; (2) using pure water as a reference, measuring the absorbance of the mixed solution at wavelengths of 219nm and 275nm to obtain the NO content. 3- The absorbance, and then based on NO 3-The linear regression equation of the standard curve is used to calculate NO. 3- Concentration; (3) Using the absorbance of the mixed solution at a wavelength of 219 nm as a reference, add an equal volume of pure water to the diluted hydrolysate as the aminosulfonic acid solution in step (1), and measure its absorbance at a wavelength of 219 nm to obtain NO. 2- The absorbance value, according to NO 2- The linear regression equation of the standard curve is used to calculate NO. 2- Concentration; (4) Based on the nitrogen content and NO of the nitrocellulose standard. 2- with NO 3- The nitrogen content of the nitrocellulose sample was calculated using a linear regression equation derived from the molar ratio standard curve. However, this method is time-consuming, complex, and difficult to master, and its accuracy, derived from spectrophotometry, needs improvement.

[0007] Therefore, it is essential to develop a rapid, accurate, and widely applicable method for detecting the nitrogen content of nitrocellulose. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a highly efficient, accurate method for determining the nitrogen content of nitrocellulose that can simultaneously analyze nitration uniformity. HPLC technology enables rapid detection of different types of nitrocellulose samples (including unstable, unrefined, and wet acid / water-containing samples), while simultaneously acquiring information on nitrogen distribution and nitration uniformity, providing data support for production process optimization.

[0009] This invention provides a method for detecting nitrogen content in nitrocellulose using high-performance liquid chromatography, comprising the following steps: A. Preparation of a series of nitrocellulose standard solutions with nitrogen content: Dissolve a series of nitrocellulose standards with nitrogen content in a solvent to obtain a series of nitrocellulose standard solutions with nitrogen content; B. Inject a series of nitrocellulose standard solutions with nitrogen content into HPLC for HPLC analysis. Obtain the retention time of the series of nitrocellulose standards with nitrogen content. Plot nitrogen content / % on the x-axis and retention time / min on the y-axis to establish a linear equation. C. Preparation of the nitrocellulose sample to be tested: Dissolve the nitrocellulose sample to be tested in a solvent to obtain the nitrocellulose sample solution to be tested; D. Inject the nitrocellulose sample solution to be tested into HPLC. Under the same conditions as in step B, perform HPLC analysis to obtain the retention time of the nitrocellulose sample to be tested. Substitute the result into the linear equation to calculate the nitrogen content of the nitrocellulose sample to be tested. In steps A and C, the solvent is selected from at least one of 1,2-ethylene glycol dimethyl ether, acetone, ethyl acetate, tetrahydrofuran, butyl acetate, acetone / water, 2-butanone, or acetonitrile; In step A, the nitrogen content of the series of nitrocellulose standards is 11%~14% (mass percentage of N in nitrocellulose). In step C, the nitrogen content of the nitrocellulose sample to be tested is 11%~14% (mass percentage of N in nitrocellulose). In steps B and D, the HPLC analysis conditions are as follows: HPLC: Reversed-phase HPLC; Chromatographic column: silica-based stationary phase column or silica-surface-modified C6-C30 alkyl column; Injection volume: 5~20 μl; Elution solvent and gradient elution procedure: a. Acetonitrile / water gradient elution: The initial ratio is V acetonitrile: V water = 90~70: 10~30. The linear gradient changes to 100% acetonitrile within 4~6 minutes, and the flow rate is controlled at 1~2 ml / min. Alternatively, b, elution with a gradient of 1,2-ethylene glycol dimethyl ether / water; initial ratio V 1,2-ethylene glycol dimethyl ether : V water = 90~70 : 10~30, linear gradient change to 100% 1,2-ethylene glycol dimethyl ether within 5~15 minutes, flow rate 1~2 ml / min; Alternatively, c. Acetone / water gradient elution: the initial ratio is V acetone: V water = 90~70: 10~30, and the linear gradient changes to 100% acetone within 5~10 minutes, with the flow rate controlled at 1~2 ml / min; Detector: Ultraviolet detector, detection wavelength 200~220nm; or, evaporative light scattering detector, drift tube temperature 30~40℃.

[0010] In the above-mentioned method for detecting nitrogen content in nitrocellulose by high performance liquid chromatography, in step C, the nitrocellulose sample to be tested is refined nitrocellulose, unstable nitrocellulose, or unrefined nitrocellulose.

[0011] In the above-mentioned method for detecting nitrogen content in nitrocellulose using high performance liquid chromatography, step C involves the nitrocellulose sample being tested being either dry or wet.

[0012] In the above-mentioned method for detecting nitrogen content in nitrocellulose using high performance liquid chromatography, the concentration of nitrocellulose in the solution in steps A and C is 3~15 g / L.

[0013] In the above-mentioned method for detecting nitrogen content in nitrocellulose by high performance liquid chromatography, step A involves using the interferometer reference method GJB 337 to determine the nitrogen content of the standard.

[0014] Preferably, in the above-mentioned method for detecting nitrogen content in nitrocellulose by high performance liquid chromatography, the solvent in steps A and C is selected from 1,2-ethylene glycol dimethyl ether or acetone.

[0015] Preferably, in the above-mentioned high-performance liquid chromatography method for detecting nitrogen content in nitrocellulose, the chromatographic column is: a single octadecyl silica column, a spherical octadecyl silica column, or a spherical octyl silica column.

[0016] More preferably, in the above-mentioned high-performance liquid chromatography method for detecting nitrogen content in nitrocellulose, the chromatographic column is: PhenomonexOnyx™ C18 column, Varian 65 Microsorb MV C18 column, Rainin 65 Microsorb MV C18 column, VarianMicrosorb MV C8 column, or Rainin Microsorb MV C8 column.

[0017] Preferably, in the above-mentioned high-performance liquid chromatography method for detecting nitrogen content in nitrocellulose, the injection volume is 10~20 μl.

[0018] In the above-mentioned method for detecting nitrogen content in nitrocellulose by high performance liquid chromatography, in step A, the nitrogen content of the series of nitrocellulose standards is 11.34%, 12.01%, 12.25%, 12.77%, 13.12%, 13.18%, 13.32% and 13.45%, respectively.

[0019] In the above-mentioned high-performance liquid chromatography method for detecting nitrogen content in nitrocellulose, when 1,2-ethylene glycol dimethyl ether is used as the dissolving solvent, in step B, the linear equation is y1=1.0991x1-10.453, R 2 =0.9929, x1 is the nitrogen content in % and y1 is the retention time in min.

[0020] In the above-mentioned method for detecting nitrogen content in nitrocellulose using high-performance liquid chromatography, when acetone is used as the dissolving solvent, the linear equation in step B is y² = 1.0615x² - 9.9117, R0 2 =0.9974, x2 is the nitrogen content in % and y2 is the retention time in min.

[0021] This invention also discloses a method for detecting the uniformity of nitrocellulose using high-performance liquid chromatography (HPLC). Based on the aforementioned method for detecting nitrogen content in nitrocellulose using HPLC, this method determines the non-uniformity of the average nitrogen content in the nitrocellulose sample by observing the deviation of the chromatographic peak apex from a uniform distribution; and estimates the nitrogen distribution of the nitrocellulose sample by observing the peak width. This method is a qualitative assessment method.

[0022] The beneficial effects of this invention are: 1. Wide range of applicable samples: The types of nitrocellulose samples that this invention can cover include unstable nitrocellulose, unrefined nitrocellulose, and refined nitrocellulose; the sample state is not limited, and both dry nitrocellulose and wet nitrocellulose can be used directly (the presence of acid or water in wet nitrocellulose does not affect subsequent analysis, and no additional pretreatment for acid removal or dehydration is required).

[0023] 2. Strong support from key principles: The core basis of this invention is that "the HPLC retention time of nitrocellulose is linearly related to its nitrogen content". By pre-constructing the linear relationship between "retention time and nitrogen content" for samples with different nitrogen contents, the nitrogen content of the sample can be quickly deduced directly from the retention time of the sample to be tested, without the need for complicated calculations or titration operations.

[0024] 3. Low sample pretreatment requirements: Before HPLC analysis, the nitrocellulose sample only needs to be dissolved in a suitable solvent (such as acetone, acetonitrile, 1,2-ethylene glycol dimethyl ether, etc.) as specified in this invention to prepare a homogeneous solution for injection. The pretreatment steps are simple and easy to operate.

[0025] 4. This invention uses HPLC to determine the nitrogen content of each nitrocellulose in a mixed nitrocellulose sample, solving the problem that the interferometer method can only measure the nitrogen content of a single nitrocellulose. Attached Figure Description

[0026] Figure 1 This is a linear relationship graph showing the nitrogen content of nitrocellulose in 1,2-ethylene glycol dimethyl ether as a function of retention time in Example 1.

[0027] Figure 2 This is a graph showing the linear relationship between the nitrogen content of nitrocellulose in acetone and the retention time in Example 2.

[0028] Figure 3 The HPLC chromatogram of the TS955 P1 PO20 nitrocellulose sample in Example 3 is shown.

[0029] Figure 4 The image shows the HPLC chromatogram of the BG34019 nitrocellulose sample from Example 3.

[0030] Figure 5 The image shows the HPLC overlap chromatogram of the nitrocellulose two-component sample in Example 3.

[0031] Figure 6 The image shows the HPLC overlap chromatograms of three nitrocellulose samples with different nitrogen contents in Example 3. Detailed Implementation

[0032] The core of this invention is to utilize the linear relationship between the HPLC retention time and nitrogen content of nitrocellulose, combined with a reversed-phase HPLC system, to determine the nitrogen content. The specific steps are as follows: 1. Sample preparation Sample range: Covers all nitrocellulose raw materials, including but not limited to unstable nitrocellulose, unrefined nitrocellulose, and refined nitrocellulose; the sample state can be dry or wet (wet samples may contain acid or water, and do not need to be pre-dried or deacidified), especially suitable for propellant nitrocellulose and unrefined intermediate samples in the production process.

[0033] Dissolution: Dissolve the nitrocellulose sample in a suitable solvent to prepare a homogeneous HPLC injection solution. The solvent is selected from 1,2-ethylene glycol dimethyl ether, acetone, ethyl acetate, tetrahydrofuran, butyl acetate, acetone / water, 2-butanone, acetonitrile, or a combination of the above solvents. If the sample is wet, it can be directly diluted with the above solvents without additional pretreatment.

[0034] 2. HPLC analysis system parameters Chromatography type: Reversed-phase HPLC is used to separate nitrocellulose components based on macromolecular properties. It is suitable for nitrocellulose with a nitrogen content of 11% (w / w) or higher, and can accurately determine samples with a nitrogen content range of 11%-14% (corresponding to nitrocellulose with 2 < n ≦ 3 in the molecular formula).

[0035] Chromatographic column: A silica-based stationary phase column is selected, with the silica surface modified with C6-C30 alkyl and other hydrocarbon groups; specifically, a single octadecyl silica column (such as Phenomonex Onyx™ C18 column), a spherical octadecyl silica column (such as Varian / Rainin 65 Microsorb MV C18 column), or a spherical octyl silica column (such as Varian / Rainin Microsorb MV C8 column) can be selected.

[0036] Solvent system: A polar solvent system is used, and gradient elution can be performed according to the HPLC run time. Specifically, the following three systems can be selected: Acetonitrile / water gradient elution: The initial ratio is Vacetonitrile:Vwater = 90~70:10~30, with a linear gradient change to 100% acetonitrile within 4~6 minutes, and the flow rate is controlled at 1~2 ml / min; 1,2-ethylene glycol dimethyl ether / water gradient elution: The initial ratio is V1,2-ethylene glycol dimethyl ether:Vwater = 90~70:10~30, with a linear gradient change to 100% 1,2-ethylene glycol dimethyl ether within 5~15 minutes, and the flow rate is controlled at 1~2 ml / min; Acetone / water gradient elution: The initial ratio is Vacetone:Vwater = 90~70:10~30, with a linear gradient change to 100% acetone within 5~10 minutes, and the flow rate is controlled at 1~2 ml / min.

[0037] Detector: Select a detector that can detect nitrocellulose, preferably a 200~220nm ultraviolet detector (nitro groups in nitrocellulose have characteristic absorption at 210nm, and acetonitrile has low absorption at this wavelength, resulting in less interference); an evaporative light scattering detector can also be used, with a drift tube temperature of 30~40℃.

[0038] 3. Nitrogen content determination and data processing Correlation curve establishment: Using nitrocellulose with known nitrogen content determined by traditional standard methods (such as interferometry) as standard samples, a correlation curve of "nitrocellulose HPLC retention time-nitrogen content" was established; within the main nitrogen content range of nitrocellulose, the correlation showed a linear relationship (correlation coefficient R). 2 It can reach above 0.99, such as Figure 1 and Figure 2 (As shown).

[0039] Generally, when plotting a standard curve, standards need to be prepared into standard solutions separately and then injected individually. However, through experimentation, it has been found that in this invention, since the retention times of nitrocellulose with different nitrogen contents are different in the chromatogram, nitrocellulose with different nitrogen contents can be mixed to prepare a solution or injected together. The corresponding relationship between the nitrogen content and retention time of each standard can be obtained directly from a single mixed chromatogram. Therefore, in step A of this invention, a series of nitrocellulose standards with different nitrogen contents can be prepared into standard solutions individually, or a series of nitrocellulose standards with different nitrogen contents can be mixed to prepare a mixed standard solution; in step B, a mixed solution of nitrocellulose standards with different nitrogen contents can be injected directly, or a standard solution of nitrocellulose standards with different nitrogen contents can be injected individually.

[0040] Nitrogen content calculation: The nitrogen content of the sample can be determined by comparing the retention time corresponding to the peak apex of the target peak in the HPLC chromatogram of the sample with the above correlation curve. The accuracy of this method can reach ±0.1%, and the results are highly consistent with those of the traditional interferometer method (as shown in Table 3, the difference between the two does not exceed 0.10%).

[0041] 4. Analysis of nitrification uniformity and nitrogen distribution (additional function) The non-uniformity of the average nitrogen content of nitrocellulose can be determined by analyzing the peak shape (degree of deviation from the normal distribution) of the HPLC chromatogram: the greater the peak asymmetry, the greater the difference in the molecular composition of the sample, and the lower the nitration uniformity. The nitrogen distribution of nitrocellulose can be estimated by analyzing the peak width: the wider the peak width, the wider the range of nitrogen content in the nitrocellulose of different molecular compositions in the sample, which can provide guidance for optimizing the nitro group distribution in production. This method can quickly determine the uniformity differences between different nitrocellulose samples.

[0042] The present invention will be further described in detail below through embodiments, but the scope of protection of the present invention is not limited to the embodiments described herein.

[0043] Example 1 1. Preparation of standard products: (1) Take 8 nitrocellulose standards and test the nitrogen content using the interferometer method. The results are shown in Table 1.

[0044] (2) Take 0.10g of each of the eight nitrocellulose standards, add 10ml of 1,2-ethylene glycol dimethyl ether, and sonicate for 5 minutes to prepare a homogeneous solution of the standard.

[0045] 2. Plotting the standard curve: (1) HPLC parameter settings: Chromatographic column: Varian Microsorb MV C8 column (150mm × 4.6mm); Solvent gradient elution system: 1,2-ethylene glycol dimethyl ether / water gradient, initial 90:10 (v / v), linear transition to 100% 1,2-ethylene glycol dimethyl ether in 8 min, flow rate 1.2 ml / min; Detector: Evaporative light scattering detector, drift tube temperature 40℃.

[0046] (2) Injection and data acquisition: Inject 10 μl of the homogenized solution of the above standard, run HPLC until elution is complete, record the chromatogram, and read the retention time of the target peak.

[0047] (3) Data Analysis: A standard curve was established with the nitrogen content (%) by interferometer method as the abscissa and the retention time (min) as the ordinate. The results are shown in Table 1 and Table 2. Figure 1 As shown, nitrogen content and retention time exhibit a linear relationship, with the linear equation y = 1.0991x - 10.453, R0 2 = 0.9929.

[0048] Table 1. Nitrogen content of nitrocellulose and retention time in 1,2-ethylene glycol dimethyl ether Example 2 1. Preparation of standard products: (1) Take 8 nitrocellulose standards and test the nitrogen content using the interferometer method. The results are shown in Table 2.

[0049] (2) Take 0.10g of each of the eight nitrocellulose standards, add 10ml of acetone to each, stir thoroughly until completely dissolved, and prepare a homogeneous solution of the standard.

[0050] 2. Plotting the standard curve: (1) HPLC parameter settings: Chromatographic column: Phenomonex Onyx™ C18 column (250 mm × 4.6 mm); Solvent gradient elution system: acetonitrile / water gradient, initial 85:15 (v / v), linear transition to 100% acetonitrile in 5 min, flow rate 1.5 ml / min; Detector: 210nm ultraviolet detector, sensitivity 0.01AUFS.

[0051] (2) Injection and data acquisition: Inject 10 μl of the homogenized solution of the above standard, run HPLC until elution is complete, record the chromatogram, and read the retention time of the target peak.

[0052] (3) Data Analysis: A standard curve was established with the nitrogen content (%) by interferometer method as the abscissa and the retention time (min) as the ordinate. The results are shown in Table 2 and... Figure 2 As shown, nitrogen content and retention time exhibit a linear relationship, with the linear equation y = 1.0615x - 9.9117, R0. 2 = 0.9974.

[0053] Table 2. Nitrogen content of nitrocellulose and retention time in acetone As can be seen from Examples 1 and 2, the present invention first uses the interferometer reference method to establish a linear relationship between the nitrogen content of nitrocellulose and the retention time. Based on the HPLC retention time of the sample to be tested, the HPLC retention time of the sample to be tested is obtained at the interpeak, and then the nitrogen content of the sample to be tested can be detected.

[0054] Example 3 Table 3 compares the results of four samples obtained using the interferometer reference method (GJB 337) and HPLC determination (method of Example 1). Figure 3 This is the HPLC chromatogram of the TS955 P1 PO20 sample, showing a single target peak. The retention time corresponding to the peak apex is used for nitrogen content calculation. (From Table 3 and...) Figure 3 It can be seen that the results obtained by the HPLC method of the present invention are basically consistent with the results obtained by the interferometer method.

[0055] Table 3 Results of four samples determined by interferometer reference method and HPLC Following the method in Example 1, the BG34019 nitrocellulose sample was analyzed using interferometric reference method and HPLC. The results are shown in [Figure 1]. Figure 4 . Figure 4The HPLC chromatogram of sample BG34019 nitrocellulose shows a retention time of 3.30 min. The nitrogen content of this sample, as determined by HPLC, is 12.51%, which is basically consistent with the nitrogen content of 12.49% obtained by the interferometer reference method.

[0056] Following the method in Example 1, 0.05 g of each of two nitrocellulose samples were taken, mixed to prepare a homogeneous solution, and analyzed by HPLC. The results are shown in [Figure 1]. Figure 5 . Figure 5 The image shows an overlay HPLC chromatogram of a two-component nitrocellulose sample. The first peak corresponds to the first component of the nitrocellulose sample, with a nitrogen content of 12.7%, and the second peak corresponds to the second component, with a nitrogen content of 13.3%.

[0057] Following the method in Example 1, 0.033 g of each of the three nitrocellulose samples were mixed to prepare a homogeneous solution, and then analyzed by HPLC. The results are shown in [Figure 1]. Figure 6 . Figure 6 The images show overlay HPLC chromatograms of three nitrocellulose samples with different nitrogen contents. The HPLC retention times differed depending on the nitrogen content. The nitrogen contents of the three samples were 12.00%, 12.64%, and 13.64%, respectively, and the retention times increased with increasing nitrogen content.

[0058] As can be seen, the present invention uses HPLC to determine the nitrogen content of each nitrocellulose in a mixed sample, which solves the problem that the interferometer method can only measure the nitrogen content of a single nitrocellulose.

[0059] Example 4: Determination of nitrogen content in unrefined wet nitrocellulose (containing moisture) 1. Sample preparation: Take 0.1g of unrefined wet nitrocellulose sample (containing water, no drying required), add 10ml of acetone, stir thoroughly until completely dissolved, and prepare HPLC injection solution.

[0060] 2. HPLC parameter settings: Chromatographic column: Phenomonex Onyx™ C18 column (250 mm × 4.6 mm); Solvent system: acetonitrile / water gradient, initial 85:15 (v / v), linear transition to 100% acetonitrile in 5 min, flow rate 1.5 ml / min; Detector: 210nm ultraviolet detector, sensitivity 0.01AUFS.

[0061] 3. Injection and data acquisition: Inject 10 μl of the above sample solution, run HPLC until elution is complete, record the chromatogram, and read the retention time of the target peak as 4.202 min.

[0062] 4. Nitrogen content calculation: Retrieve the pre-established linear curve of "retention time-nitrogen content" (y = 1.0615x - 9.9117, R0). 2 = 0.9974), substituting the retention time of 4.202 min, the nitrogen content of the sample was calculated to be 13.30%, which is 0.04% different from the result of the interferometer method (13.34%), meeting the accuracy requirements. Example 5: Analysis of Nitrification Uniformity of Refined Dry Nitrocellulose for Propellants 1. Sample preparation: Take 0.08g of refined dry nitrocellulose sample for propellant, add 8ml of 1,2-ethylene glycol dimethyl ether, and sonicate for 5 minutes to prepare a homogeneous solution.

[0063] 2. HPLC parameter settings: Chromatographic column: Varian Microsorb MV C8 column (150mm × 4.6mm); Solvent system: 1,2-ethylene glycol dimethyl ether / water gradient, initial 90:10 (v / v), linear transition to 100% 1,2-ethylene glycol dimethyl ether in 8 min, flow rate 1.2 ml / min; Detector: Evaporative light scattering detector, drift tube temperature 40℃.

[0064] 3. Data Analysis: The HPLC chromatogram showed a single symmetrical peak with a peak width of 0.35 min, and the peak shape did not deviate significantly from the normal distribution; the retention time was 3.43 min. A pre-established linear curve of "retention time-nitrogen content" was retrieved (y = 1.0991x -10.453, R0). 2 = 0.9929), the nitrogen content was calculated to be 12.63% based on the retention time, and the nitrogen content distribution range was estimated to be 12.58%-12.70% based on the peak width, indicating that the sample has good nitration uniformity and meets the quality requirements of nitrocellulose for propellants.

[0065] Example 6: Determination of Nitrogen Content in Unstable Nitrocellulose 1. Sample preparation: Take 0.10g of unstable nitrocellulose sample, add 10ml of 1,2-ethylene glycol dimethyl ether, and sonicate for 5 minutes to prepare a homogeneous solution.

[0066] 2. HPLC parameter settings: Chromatographic column: Varian Microsorb MV C8 column (150mm × 4.6mm); Solvent system: 1,2-ethylene glycol dimethyl ether / water gradient, initial 90:10 (v / v), linear transition to 100% 1,2-ethylene glycol dimethyl ether in 8 min, flow rate 1.2 ml / min; Detector: Evaporative light scattering detector, drift tube temperature 40℃.

[0067] 3. Data Analysis: Retention time 4.07 min. The pre-established linear curve of "retention time-nitrogen content" was retrieved (y = 1.0991x - 10.453, R²). 2 = 0.9929), the nitrogen content calculated by retention time is 13.21%, which deviates from the result of the interferometer method (13.30%) by 0.09%, and meets the accuracy requirements.

Claims

1. A method for determining the nitrogen content of nitrocellulose using high performance liquid chromatography, characterized in that: Includes the following steps: A. Preparation of a series of nitrocellulose standard solutions with nitrogen content: Dissolve a series of nitrocellulose standards with nitrogen content in a solvent to obtain a series of nitrocellulose standard solutions with nitrogen content; B. Inject a series of nitrocellulose standard solutions with nitrogen content into HPLC for HPLC analysis. Obtain the retention time of the series of nitrocellulose standards with nitrogen content. Plot nitrogen content / % on the x-axis and retention time / min on the y-axis to establish a linear equation. C. Preparation of the nitrocellulose sample to be tested: Dissolve the nitrocellulose sample to be tested in a solvent to obtain the nitrocellulose sample solution to be tested; D. Inject the nitrocellulose sample solution to be tested into HPLC. Under the same conditions as in step B, perform HPLC analysis to obtain the retention time of the nitrocellulose sample to be tested. Substitute the result into the linear equation to calculate the nitrogen content of the nitrocellulose sample to be tested. In steps A and C, the solvent is selected from at least one of 1,2-ethylene glycol dimethyl ether, acetone, ethyl acetate, tetrahydrofuran, butyl acetate, acetone / water, 2-butanone, or acetonitrile; In step A, the nitrogen content of the series of nitrocellulose standards is 11%~14%; In step C, the nitrogen content of the nitrocellulose sample to be tested is 11%~14%; In steps B and D, the HPLC analysis conditions are as follows: HPLC: Reversed-phase HPLC; Chromatographic column: silica-based stationary phase column or silica-surface-modified C6-C30 alkyl column; Injection volume: 5~20 μl; Elution solvent and gradient elution procedure: a. Acetonitrile / water gradient elution: The initial ratio is V acetonitrile: V water = 90~70: 10~30. The linear gradient changes to 100% acetonitrile within 4~6 minutes, and the flow rate is controlled at 1~2 ml / min. Alternatively, b, elution with a gradient of 1,2-ethylene glycol dimethyl ether / water; initial ratio V 1,2-ethylene glycol dimethyl ether : V water = 90~70 : 10~30, linear gradient change to 100% 1,2-ethylene glycol dimethyl ether within 5~15 minutes, flow rate 1~2 ml / min; Alternatively, c. Acetone / water gradient elution: the initial ratio is V acetone: V water = 90~70: 10~30, and the linear gradient changes to 100% acetone within 5~10 minutes, with the flow rate controlled at 1~2 ml / min; Detector: Ultraviolet detector, detection wavelength 200~220nm; or, evaporative light scattering detector, drift tube temperature 30~40℃.

2. The method for detecting nitrogen content in nitrocellulose by high performance liquid chromatography according to claim 1, characterized in that: In step C, the nitrocellulose sample to be tested is refined nitrocellulose, unstable nitrocellulose, or unrefined nitrocellulose.

3. The method for detecting nitrogen content in nitrocellulose by high performance liquid chromatography according to claim 1, characterized in that: In step C, the nitrocellulose sample to be tested is either dry or wet.

4. The method for detecting nitrogen content in nitrocellulose by high performance liquid chromatography according to claim 1, characterized in that: In steps A and C, the concentration of nitrocellulose in the solution is 3~15 g / L.

5. The method for detecting nitrogen content in nitrocellulose by high performance liquid chromatography according to claim 1, characterized in that: In step A, the nitrogen content of the standard was determined using the interferometer reference method GJB 337.

6. The method for detecting nitrogen content in nitrocellulose by high performance liquid chromatography according to claim 1, characterized in that: At least one of the following must be met: In steps A and C, the solvent is selected from 1,2-ethylene glycol dimethyl ether or acetone; Chromatographic column: monolithic octadecyl silica column, spherical octadecyl silica column or spherical octyl silica column; preferably, chromatographic column: Phenomonex Onyx™ C18 column, Varian 65 Microsorb MV C18 column, Rainin 65 Microsorb MVC18 column, Varian Microsorb MV C8 column or Rainin Microsorb MV C8 column; Injection volume: 10~20μl.

7. The method for detecting nitrogen content in nitrocellulose by high performance liquid chromatography according to claim 1, characterized in that: In step A, the nitrogen contents of the series of nitrocellulose standards were 11.34%, 12.01%, 12.25%, 12.77%, 13.12%, 13.18%, 13.32% and 13.45%, respectively.

8. The method for detecting nitrogen content in nitrocellulose by high performance liquid chromatography according to claim 7, characterized in that: When 1,2-ethylene glycol dimethyl ether is used as the solvent, in step B, the linear equation is y1 = 1.0991x1 - 10.453, R 2 =0.9929, x1 is the nitrogen content in % and y1 is the retention time in min.

9. The method for detecting nitrogen content in nitrocellulose by high performance liquid chromatography according to claim 7, characterized in that: When acetone is used as the solvent, in step B, the linear equation is y² = 1.0615x² - 9.9117, R0 2 =0.9974, x2 is the nitrogen content in % and y2 is the retention time in min.

10. A method for detecting the uniformity of nitrocellulose using high performance liquid chromatography, characterized in that: Based on any one of claims 1 to 9, the non-uniformity of the average nitrogen content of the nitrocellulose sample to be tested is determined by the deviation of the chromatographic peak apex from the uniform distribution; the nitrogen distribution of the nitrocellulose sample is estimated by the peak width of the chromatographic peak.

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