CN111007097A - Quantitative nuclear magnetic hydrogen spectrum valuing method for 2, 6-dinitrotoluene standard substance - Google Patents
Quantitative nuclear magnetic hydrogen spectrum valuing method for 2, 6-dinitrotoluene standard substance Download PDFInfo
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- 239000000126 substance Substances 0.000 title claims abstract description 130
- 238000000034 method Methods 0.000 title claims abstract description 60
- XTRDKALNCIHHNI-UHFFFAOYSA-N 2,6-dinitrotoluene Chemical compound CC1=C([N+]([O-])=O)C=CC=C1[N+]([O-])=O XTRDKALNCIHHNI-UHFFFAOYSA-N 0.000 title claims abstract description 58
- 229910052739 hydrogen Inorganic materials 0.000 title claims description 34
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 title claims description 33
- 239000001257 hydrogen Substances 0.000 title claims description 33
- 238000001228 spectrum Methods 0.000 title claims description 31
- DYSXLQBUUOPLBB-UHFFFAOYSA-N 2,3-dinitrotoluene Chemical compound CC1=CC=CC([N+]([O-])=O)=C1[N+]([O-])=O DYSXLQBUUOPLBB-UHFFFAOYSA-N 0.000 claims abstract description 25
- 238000005481 NMR spectroscopy Methods 0.000 claims abstract description 16
- 238000005259 measurement Methods 0.000 claims abstract description 11
- 239000000523 sample Substances 0.000 claims description 60
- VZCYOOQTPOCHFL-OWOJBTEDSA-N Fumaric acid Chemical compound OC(=O)\C=C\C(O)=O VZCYOOQTPOCHFL-OWOJBTEDSA-N 0.000 claims description 44
- 238000005303 weighing Methods 0.000 claims description 26
- VZCYOOQTPOCHFL-UHFFFAOYSA-N trans-butenedioic acid Natural products OC(=O)C=CC(O)=O VZCYOOQTPOCHFL-UHFFFAOYSA-N 0.000 claims description 24
- 238000002474 experimental method Methods 0.000 claims description 22
- 239000001530 fumaric acid Substances 0.000 claims description 22
- UQEAIHBTYFGYIE-UHFFFAOYSA-N hexamethyldisiloxane Chemical compound C[Si](C)(C)O[Si](C)(C)C UQEAIHBTYFGYIE-UHFFFAOYSA-N 0.000 claims description 17
- 239000012086 standard solution Substances 0.000 claims description 17
- 238000004364 calculation method Methods 0.000 claims description 15
- 239000002904 solvent Substances 0.000 claims description 14
- 239000000243 solution Substances 0.000 claims description 13
- OKKJLVBELUTLKV-MZCSYVLQSA-N Deuterated methanol Chemical group [2H]OC([2H])([2H])[2H] OKKJLVBELUTLKV-MZCSYVLQSA-N 0.000 claims description 12
- 238000002360 preparation method Methods 0.000 claims description 11
- 238000012360 testing method Methods 0.000 claims description 11
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- 239000011903 deuterated solvents Substances 0.000 claims description 6
- 238000004090 dissolution Methods 0.000 claims description 6
- 238000011002 quantification Methods 0.000 claims description 6
- 238000004458 analytical method Methods 0.000 claims description 5
- SPSSULHKWOKEEL-UHFFFAOYSA-N 2,4,6-trinitrotoluene Chemical compound CC1=C([N+]([O-])=O)C=C([N+]([O-])=O)C=C1[N+]([O-])=O SPSSULHKWOKEEL-UHFFFAOYSA-N 0.000 claims description 4
- 125000000524 functional group Chemical group 0.000 claims description 4
- 238000013178 mathematical model Methods 0.000 claims description 4
- 125000002496 methyl group Chemical group [H]C([H])([H])* 0.000 claims description 4
- 238000004611 spectroscopical analysis Methods 0.000 claims description 4
- 238000002347 injection Methods 0.000 claims description 3
- 239000007924 injection Substances 0.000 claims description 3
- 238000000425 proton nuclear magnetic resonance spectrum Methods 0.000 claims description 3
- 238000011156 evaluation Methods 0.000 claims description 2
- 230000005311 nuclear magnetism Effects 0.000 claims description 2
- 239000012488 sample solution Substances 0.000 claims description 2
- 238000000926 separation method Methods 0.000 claims description 2
- 238000005160 1H NMR spectroscopy Methods 0.000 abstract description 7
- 238000005516 engineering process Methods 0.000 abstract description 3
- 125000004435 hydrogen atom Chemical group [H]* 0.000 description 8
- 239000012535 impurity Substances 0.000 description 6
- 238000001514 detection method Methods 0.000 description 5
- 239000002360 explosive Substances 0.000 description 4
- 125000001997 phenyl group Chemical group [H]C1=C([H])C([H])=C(*)C([H])=C1[H] 0.000 description 4
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- 238000010168 coupling process Methods 0.000 description 2
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- 230000007123 defense Effects 0.000 description 2
- 238000004811 liquid chromatography Methods 0.000 description 2
- VZCYOOQTPOCHFL-UPHRSURJSA-N maleic acid Chemical compound OC(=O)\C=C/C(O)=O VZCYOOQTPOCHFL-UPHRSURJSA-N 0.000 description 2
- 239000011976 maleic acid Substances 0.000 description 2
- 238000000655 nuclear magnetic resonance spectrum Methods 0.000 description 2
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- DVKJHBMWWAPEIU-UHFFFAOYSA-N toluene 2,4-diisocyanate Chemical compound CC1=CC=C(N=C=O)C=C1N=C=O DVKJHBMWWAPEIU-UHFFFAOYSA-N 0.000 description 2
- 239000000015 trinitrotoluene Substances 0.000 description 2
- 238000013076 uncertainty analysis Methods 0.000 description 2
- CSCPPACGZOOCGX-UHFFFAOYSA-N Acetone Chemical class CC(C)=O CSCPPACGZOOCGX-UHFFFAOYSA-N 0.000 description 1
- 238000012565 NMR experiment Methods 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 238000001675 atomic spectrum Methods 0.000 description 1
- 239000013064 chemical raw material Substances 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- CSCPPACGZOOCGX-WFGJKAKNSA-N deuterated acetone Substances [2H]C([2H])([2H])C(=O)C([2H])([2H])[2H] CSCPPACGZOOCGX-WFGJKAKNSA-N 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
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- 238000002290 gas chromatography-mass spectrometry Methods 0.000 description 1
- 238000004128 high performance liquid chromatography Methods 0.000 description 1
- 230000010354 integration Effects 0.000 description 1
- 238000010813 internal standard method Methods 0.000 description 1
- 238000002075 inversion recovery Methods 0.000 description 1
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- 238000004949 mass spectrometry Methods 0.000 description 1
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- 238000012795 verification Methods 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
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- G01N24/00—Investigating or analyzing materials by the use of nuclear magnetic resonance, electron paramagnetic resonance or other spin effects
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Abstract
The invention discloses a method for valuing a 2, 6-dinitrotoluene standard substance based on a quantitative nuclear magnetic resonance technology (1H NMR), the content of dinitrotoluene, which is a main component in the standard substance, is measured using a standard substance having a measurement traceability as an internal standard substance. The method has the characteristics of simplicity, feasibility, low cost, good stability, high precision, strong specificity and the like, and has wide application prospect in the aspects of standard substance calibration, period checking and the like.
Description
Technical Field
The invention belongs to the field of energetic material measurement and detection, and particularly relates to a quantitative nuclear magnetic hydrogen spectrum value-determining method for a 2, 6-dinitrotoluene purity standard substance, belonging to the field of explosive product analysis and detection.
Background
A standard substance is a substance or material "having one or more sufficiently homogeneous and determined values of a property for calibrating a measuring device, evaluating a measuring method or assigning a value to a material", the underlying property being that it has a magnitude accuracy. Compared with the common pure substance, the characteristic value of the standard substance has traceability, and can be traced to an accurately reproduced metering unit for representing the characteristic value, and an uncertainty of a given confidence level is attached. Purity standards as an important class of standards are used to accurately measure the chemical purity of a substance and assess the corresponding uncertainty. Due to the special characteristics and uses of the standard substance, it is decided that the standard substance must be subjected to frequent stability tests, i.e. quantitative tests of the characteristic quantity of the standard substance at defined time intervals and under ambient conditions.
At present, the most widely used fixed value of the organic purity standard substance is a mass balance impurity deduction method, namely, a plurality of quantitative detection methods are adopted to respectively measure all detectable impurity components, such as measuring the content of organic impurities by liquid chromatography, measuring the content of water by a Karl Fischer method, measuring the content of inorganic impurities by atomic spectrum, and the like. Finally, deducting all measured impurity contents on the basis of 100%, and finally obtaining the purity value of the standard substance. The method has the characteristics that the fixed value result is accurate and reliable, the uncertainty value is small, but in practical application, one fixed value relates to various experimental operations, the operation is complicated, the time period is long, and the fixed value cost is high. The simpler and more feasible method is to directly measure the main component in the standard substance, and the methods of liquid chromatography, mass spectrometry and the like are reported at present to directly measure the main component, but the method needs to use a standard sample of the main component as an internal standard or an external standard and establish a calibration measurement curve, and still has limitations in the aspects of simplicity and rapidity.
Dinitrotoluene, commonly abbreviated as DNT, is an important organic chemical raw material, can be used for producing Toluene Diisocyanate (TDI) and trinitrotoluene (TNT), and can also be directly used for explosives and powders. The production of dinitrotoluene is on the order of millions of tons per year and is increasing at a rate of 4% to 8% per year. The prior art is not suitable for the fixed value of the dinitrotoluene purity standard substance, so that a new method which is quicker, simpler and more convenient and meets the special fixed value requirement of the dinitrotoluene purity standard substance needs to be researched and established.
Disclosure of Invention
Aiming at the requirements of the 2, 6-dinitrotoluene standard substance on accurate fixed value in the production and period check processes of the 2, 6-dinitrotoluene standard substance at the present stage, the invention provides the method for quantitative nuclear magnetic hydrogen spectrum fixed value of the 2, 6-dinitrotoluene purity standard substance, which has accurate and reliable fixed value of characteristic quantity value. The specific technical scheme for realizing the purpose of the invention is as follows:
a method for valuing a dinitrotoluene purity standard substance specifically comprises the following steps:
(1) preparation of internal standard solution: weighing the internal standard substance by a one-tenth-ten-thousandth balance in a proper sealed container by a subtraction method, then adding a deuterated solvent, accurately recording the total mass of the internal standard substance and the dissolved solution, and sealing and ultrasonically mixing for later use;
(2) preparing a quantitative nuclear magnetic hydrogen spectrum sample: precisely weighing a 2, 6-dinitrotoluene standard substance in a nuclear magnetic sample tube with the diameter of 5mm, then transferring a prepared internal standard solution, precisely weighing the mass of the transferred solution, shaking up and sealing the sample to be detected;
(3) and (3) determination of quantitative nuclear magnetic hydrogen spectrum: placing the prepared nuclear magnetic tube in a superconducting nuclear magnetic resonance spectrometer, and measuring the sample solution1HNMR spectrogram, nuclear magnetic testing parameters and conditions are as follows: a pulse sequence zg or zg30, wherein the measurement temperature is 295K-305K, the sampling time is more than 2s, and the scanning times are more than 16;
(4) quantitative results analysis and standard substance quantitation: acquiring a nuclear magnetic resonance hydrogen spectrum under the conditions, performing baseline correction, phase correction and chemical shift correction on the spectrogram, determining the quantitative peaks of the internal standard substance and the 2, 6-dinitrotoluene, respectively performing integral processing on the quantitative peaks, and finally calculating the content of the main component 2, 6-dinitrotoluene in the standard substance according to the integral area, wherein the calculation formula is as follows:
in the formula:
Px-the purity of dinitrotoluene, expressed in% in a sample of standard substance to be tested;
Ps-the value of the purity of the solution of internal standard, expressed in%;
mx-dinitrotoluene standard sample addition mass, in mg;
m-mass of added internal standard solution, unit mg;
Ms-relative molecular mass of internal standard;
Mx-the relative molecular mass of dinitrotoluene;
Hs-1 mole of the number of resonating nuclei on the functional group of the internal standard signature;
Hx-the number of resonant nuclei on a functional group producing a characteristic peak signal for 1 mole of dinitrotoluene;
As-peak area of the internal standard characteristic signal peak;
Ax-peak area of the characteristic signal peak of dinitrotoluene;
(5) uncertainty analysis of standard substance fixed value
The uncertainty analysis of the fixed value is used for evaluating the dispersity of the obtained fixed value result, and the uncertainty of the fixed value result is also an important index of the standard substance. The uncertainties of the 2, 6-dinitrotoluene standard substance mainly include: the uncertainty introduced by the instability of the original standard substance, the uncertainty introduced by the heterogeneity of the original standard substance and the uncertainty introduced during the quantitative nuclear magnetic quantitation. Where heterogeneity and instability-induced uncertainties are obtained from homogeneity and stability tests of 2, 6-dinitrotoluene standards.
The uncertainty in the quantitative nuclear magnetic constant value process can be derived from a nuclear magnetic quantitative theory calculation formula, namely formula (1). However, in the actual quantitative nuclear magnetic measurement process, the dissolution amount of a sample in a solvent is related to temperature and dissolution time, the volatilization of the sample and an internal standard substance also exists in the test process, and the volatilization amount is also related to temperature and experiment time, so the influence of the four additional factors is considered in the measurement uncertainty evaluation, four small black boxes are added in the original mathematical model formula, the corresponding quantitative nuclear magnetic method uncertainty influence factor relation diagram is shown in figure 1, and the measurement model of the method is obtained as formula (2).
In the formula (f)timeThe influence factor of the dissolution amount of the sample in the solvent influenced by the dissolution time;
ftempthe influence factor of the dissolved amount of the sample in the solvent influenced by the temperature;
f′timeinfluence factors of the volatilization quantities of the sample and the internal standard influenced by the experiment time;
f′tempinfluence factors of the volatilization quantities of the sample and the internal standard influenced by temperature;
mu under rootcThe separation represented is the uncertainty introduced by each component in the mathematical model.
Preferably, all the weighing steps in the above steps use a high precision balance with division value lower than 0.1 mg.
Preferably, the internal standard substance is a high-purity certified standard substance with measurement traceability, and all hydrogen in the substance is in the same chemical environment, namely, the nuclear magnetic resonance hydrogen spectrum only has a group of characteristic peaks, such as fumaric acid, maleic acid, hexamethyldisiloxane and the like.
Preferably, the addition amount of the 2, 6-dinitrotoluene standard substance in the nuclear magnetism sample is 15-50 mg.
Preferably, an airtight chromatographic sample injection needle is adopted in the preparation and removal process of the internal standard solution, and the specification of the airtight chromatographic sample injection needle is 50-100 mu L, so that the volatilization of the solvent in the internal standard solution can be effectively prevented.
Preferably, when fumaric acid is used as an internal standard substance, the deuterated solvent is a deuterated methanol solvent, and the deuteration degree is more than 99%; when hexamethyldisiloxane is used as an internal standard substance, the deuterated solvent is a deuterated methanol solvent, and the deuteration degree is more than 99 percent
Preferably, the nuclear magnetic resonance hydrogen spectrum adopts 30-degree pulse, the quantitative experiment pulse sequence is zg30, and the sampling delay time d is the sampling delay time when fumaric acid or maleic acid is selected as an internal standard115s or more is required;
preferably, the quantitative peak of the 2, 6-dinitrotoluene is a characteristic methyl peak with a chemical shift of 2.51ppm of hydrogen spectrum.
Compared with the prior art, the invention has the creativity that: compared with the existing method for directly measuring the standard substance fixed value by the main component, such as high performance liquid chromatography, gas chromatography-mass spectrometry and the like, the method does not need a standard sample of the main component as an internal standard or an external standard, does not need a method for establishing a calibration measurement curve, has greater flexibility in selecting the standard sample, and is simpler and more convenient in later data processing and calculation; compared with the traditional mass balance impurity deduction method, the method adopts a single nuclear magnetic resonance spectrometer to directly finish the main component constant value, and is more convenient and quick to operate. In addition, the definite value uncertainty of the quantitative nuclear magnetic method is evaluated according to the special requirement of the definite value of the standard substance, the volatilization of the sample and the internal standard substance and the relation between the volatilization amount, the temperature and the experimental time are comprehensively considered, the characteristic parameters are introduced into the uncertainty mathematical model, and the accuracy of the definite value result is ensured. The method has the advantages of high sensitivity, good fixed value accuracy, simple and quick operation and suitability for fixed value of the dinitrotoluene standard substance.
Drawings
FIG. 1 is a nuclear magnetic hydrogen spectrum of a 2, 6-dinitrotoluene standard substance;
FIG. 2 is a nuclear magnetic hydrogen spectrum of 2, 6-dinitrotoluene standard substance added with fumaric acid internal standard substance;
FIG. 3 shows different pulse sequences at different d1A relative integral area ratio result line chart of a quantitative peak and an internal standard peak of the dinitrotoluene sample under the condition;
Detailed Description
In order to make the technical solutions of the present invention better for those skilled in the art, the technical solutions of the present invention are further described in detail below with reference to some specific embodiments.
Example 1
And (3) taking the hexamethyldisiloxane standard substance as an internal standard substance, and performing purity value determination on the dinitrotoluene standard substance by adopting a quantitative nuclear magnetic method.
1.1 Instrument and sample preparation
① instrument Bruker Ascend 800 type superconducting nuclear magnetic resonance spectrometer (BRUKER, Germany), Mettler Toledo XP6 type one hundred thousandth of balance (METTLER, Switzerland);
② 5mm standard nuclear magnetic sample tube (NORELL corporation, USA), hexamethyldisiloxane solution standard (Siann's institute of recent chemistry, content 0.102%, U2%), 2, 6-dinitrotoluene standard (national defense science and technology industry explosive first-class metering station)
1.2 preparation and determination of Nuclear magnetic samples to be determined
Accurately weighing about 23mg of 2, 6-dinitrotoluene standard substance to be measured in a 5mm nuclear magnetic tube, directly transferring about 0.6ml of deuterated acetone standard solution of hexamethyldisiloxane, weighing, uniformly mixing, and sealing with a sealing film. Directly carrying out the preparation of the nuclear magnetic sample1H NMR test, after the test is finished, the test parameters and conditions are as follows: the frequency was observed at 800.3MHz, the temperature was measured at 300K, 30 pulses (zg30 pulse sequence), the spectral width was 3 μ s, the data points were sampled 65536, the number of scans was 16, and the delay time was 20 s.
1.3 samples1H NMR Spectrum analysis
According to1H NMR spectrogram literature data, the chemical properties of the 2, 6-dinitrotoluene are integrated, and the Topspin 3.5 pair is adopted for detection1The H NMR spectrum is subjected to calibration, baseline correction and phase adjustment to obtain a nuclear magnetic resonance hydrogen spectrum shown in figure 1. According to the natureThe coupling column conditions and the chemical shift values of the sub-signal peaks are correspondingly assigned, wherein the chemical shift is 8.01ppm of the characteristic peaks of hydrogen atoms at the No. 3 and the No. 5 positions on the benzene ring of the 2, 6-dinitrotoluene, the chemical shift is 7.62ppm of the characteristic peak of hydrogen atoms at the No. 4 position on the benzene ring of the 2, 6-dinitrotoluene, the chemical shift is 4.89ppm of the characteristic peak of active hydrogen atoms, the chemical shift is 2.51ppm of the characteristic peak of methyl hydrogen atoms of the 2, 6-dinitrotoluene, and the chemical shift is 0.06ppm of the characteristic peak of six methyl hydrogen atoms of hexamethyldisiloxane. Based on the principle of quantitative nuclear magnetic characteristic peak selection, the nuclear magnetic spectrogram shows that the internal standard substance characteristic peak is well separated from other signal peaks, is symmetrical and uniform, and meets the basic conditions of quantitative nuclear magnetic. Two characteristic peaks of dinitrotoluene shown on a nuclear magnetic spectrum are both single peaks and can be theoretically used as quantitative peaks, and a methyl peak with a chemical shift of 2.64ppm is determined as a quantitative peak from the angle that the quantitative peak is more accurate when the interference of the peaks around the spectrum is less. This sample was measured in parallel 3 times to obtain the quantitative results of dinitrotoluene standard as shown in Table 1 below.
TABLE 1 internal hexamethyldisiloxane quantitation results
1.4 rating of uncertainty of definite value
Based on the uncertainty calculation equation (3), since both the sample and the internal standard are completely dissolved in the solvent in the experiment, ftimeAnd ftempThe mathematical expected values are all 1; the constant temperature was set to 300K, f 'in a quantitative nuclear magnetic experiment'tempAlso 1, the formula (3) can simplify the formula (4), and the constant value result P is derived from the formula (4)xThe uncertainty of the fixed value is shown in the formula (5).
The following analytical calculations were performed for different sources of uncertainty, respectively:
① uncertainty of integral area ratio calculation (A)x/As) The calculation result of the integral area is subject to various instrument parameters in the nuclear magnetic experiment, such as acquisition time, scanning width, scanning times, data processing method and the like, so the uncertainty of the ratio result can be evaluated by A class, namely expressed by the standard deviation of the quantitative result of the integral area ratio, and the following results are obtained:
② molar mass (M) of sample and internal standardxAnd Ms): the atomic weights and uncertainties of the individual elements in dinitrotoluene and internal hexamethyldisiloxane can be found in the international relative atomic mass table published by IUPAC in table 2 below:
relative atomic masses and uncertainties of Table 2C, H, O, N, Si
The standard uncertainty of the molar masses of 2, 6-dinitrotoluene and of the internal standard hexamethyldisiloxane can be calculated separately:
③ mass (m) of sample and internal standard solutionxAnd m): the weighing adopts a one-tenth-ten-thousandth balance, and the weighing tolerance is 10-5g, the standard uncertainty of single weighing is
Since the actual mass in the weighing process is obtained by the differential subtraction method, the method comprises the following steps
④ internal standard solution purity (P)s): the purity uncertainty of the hexamethyldisiloxane solution standard was provided by the standard certificate with a relative extended uncertainty of 0.011%.
⑤ correction factor (f ') the amount of volatilization of sample and internal standard is influenced by the time of experiment'time): for a nuclear magnetic sample to be tested which is relatively sealed, the volatilization of an internal standard substance is approximately proportional to the time, the change rate of the mass concentration of the dinitrotoluene sample to be tested with the time is determined to be approximately zero, the change rate of the mass concentration of the internal standard substance hexamethyldisiloxane with the time is 0.2%/h, and when the experiment time is controlled within 24 +/-0.5 h, the factor f 'is influenced'timeWithin the range of 1 + -0.5 × 0.002, i.e., 1 + -0.001. Estimated as a rectangular distribution, then f'timeThe expected value is 1 and the relative uncertainty is:
in summary, the final calculation results in the uncertainty of the synthesis standard for determining the purity of the 2,4, 6-dinitrotoluene standard substance by quantitative nuclear magnetic method using hexamethyldisiloxane standard substance as internal standard substance:
example 2
And (3) taking the fumaric acid purity standard substance as an internal standard substance, and performing purity value determination on the 2, 6-dinitrotoluene standard substance by adopting a quantitative nuclear magnetic method.
1.1 Instrument and sample preparation
① instrument Bruker Ascend 800 type superconducting nuclear magnetic resonance spectrometer (BRUKER, Germany), Mettler Toledo XP6 type one hundred thousandth of balance (METTLER, Switzerland);
② deuterated methanol (deuteration degree > 99.8%, CIL corporation, USA), 5mm standard nuclear magnetic sample tube (NORELL corporation, USA), fumaric acid standard (Dr. Ehrensferffer, Germany, purity 99.9%), 2, 6-dinitrotoluene standard (national defense science and technology industry explosive first-class metering station)
1.2 preparation of solution
Accurately weighing about 150mg of internal standard fumaric acid in a 10ml volumetric flask, then adding solvent deuterated methanol to reach the constant volume of 10ml, accurately weighing, and uniformly mixing for later use.
1.3 preparation and determination of Nuclear magnetic samples to be determined
Accurately weighing about 15mg of dinitrotoluene standard substance to be measured in a 5mm nuclear magnetic tube, then accurately transferring about 0.5ml of fumaric acid internal standard solution, weighing, uniformly mixing, and sealing by using a sealing film. Directly carrying out the preparation of the nuclear magnetic sample1HNMR test, after the test, the test parameters and conditions are as follows: the frequency was observed at 800.3MHz, the temperature was measured at 300K, 30 pulses (zg30 pulse sequence), the spectral width was 3 μ s, the data points were sampled 65536, the number of scans was 16, and the delay time was 15 s.
1.3 samples1H NMR Spectrum analysis
According to1H NMR spectrogram literature data, the chemical properties of the 2, 6-dinitrotoluene are integrated, and the Topspin 3.5 pair is adopted for detection1The H NMR spectrum is subjected to calibration, baseline correction and phase adjustment, and the obtained nuclear magnetic resonance hydrogen spectrum is shown in FIG. 2. Corresponding attribution is carried out according to the coupling column conditions and the chemical shift values of proton signal peaks, wherein the chemical shift is 8.10ppm which is the characteristic peak of hydrogen atoms at the No. 3 and the No. 5 positions on the benzene ring of 2, 6-dinitrotoluene, the chemical shift is 7.62ppm which is the characteristic peak of hydrogen atoms at the No. 4 positions on the benzene ring of 2, 6-dinitrotoluene, the chemical shift is 4.89ppm which is the characteristic peak of active hydrogen atoms, the chemical shift is 5.68ppm which is the characteristic peak of two methylene hydrogen atoms of fumaric acid, the chemical shift is 2.51ppm which is the characteristic peak of methyl hydrogen atoms of 2, 6-dinitrotoluene, and the characteristic peak of an internal standard substance can be seen to be well separated from other signal peaks through a nuclear magnetic spectrogram, and is symmetrical and uniform and accords with the basic conditions of quantitative. Three characteristic peaks of the 2, 6-dinitrotoluene shown on a nuclear magnetic spectrum are all single peaks and can be theoretically used as quantitative peaks, and a methyl peak with a chemical shift of 2.51ppm is determined as a quantitative peak from the angle that the quantitative peak is more accurate when the interference of the peaks around the spectrum is less. The sample is measured in parallel for three times, the relative integral area ratio is obtained by taking the average value for three times of integration each time, and finally the calculation is carried outThe results of the calibration to 2, 6-dinitrotoluene standard are shown in Table 3 below.
TABLE 3 results of quantitation of 2, 6-dinitrotoluene standard with fumaric acid as internal standard
1.4 rating of uncertainty of definite value
Based on the uncertainty calculation equation (3), since both the sample and the internal standard are completely dissolved in the solvent in the experiment, ftimeAnd ftempThe mathematical expected values are all 1; the constant temperature was set to 300K, f 'in a quantitative nuclear magnetic experiment'tempIs also 1; fumaric acid standard substance is adopted as solid, so that the volatilization of the sample and the internal standard substance in the system is negligible, f'timeAlso 1. Then equation (3) can simplify equation (6) and derive the constant value result P from equation (6)xThe degree of uncertainty of the fixed value is as shown in the formula (7).
The following analytical calculations were performed for different sources of uncertainty, respectively:
① uncertainty of integral area ratio calculation (A)x/As) The calculation result of the integral area is subject to various instrument parameters in the nuclear magnetic experiment, such as acquisition time, scanning width, scanning times, data processing method and the like, so the uncertainty of the ratio result can be evaluated by A class, namely expressed by the standard deviation of the quantitative result of the integral area ratio, and the following results are obtained:
② molar mass (M) of sample and internal standardxAnd Ms): from the IUPAC published international relative atomic mass tableObtaining atomic weight and uncertainty of each element in dinitrotoluene and internal standard fumaric acid, and respectively calculating standard uncertainty of molar mass of 2, 6-dinitrotoluene and internal standard hexamethyldisiloxane to obtain:
③ mass (m) of sample and internal standard solutionxAnd m): the weighing adopts a one-tenth-ten-thousandth balance, and the weighing tolerance is 10-5g, the standard uncertainty of single weighing is
Since the actual mass in the weighing process is obtained by the differential subtraction method, the method comprises the following steps
④ internal standard solution concentration (P)s): the uncertainty of the fumaric acid solution is mainly derived from the self-purity P of the internal standard substance1Uncertainty u (P)1) And uncertainty u (m) brought by the weighing of the fumaric acid standard substance in the solution preparation processs). The standard uncertainty U of fumaric acid is 0.05% (k is 2), so its standard uncertainty U10.025%; the uncertainty u of the weighing process is determined by using the same balance under the same environmental conditions2The above samples were weighed consistently at 8.1X 10-6g. The standard uncertainty for the concentration of the internal standard solution is then:
in summary, the final calculation results in the standard uncertainty of the synthesis of the 2, 6-dinitrotoluene standard substance with the purity fixed value by using a quantitative nuclear magnetic method and using a fumaric acid standard substance as an internal standard substance:
example 3
Because the relaxations of protons in different chemical environments in the nuclear magnetic sample to be detected are different, the time for the relaxation to completely restore the equilibrium is different after the proton magnetic field environment is excited. The classical nuclear magnetic theory requires that in quantitative nuclear magnetic experiments, 90-degree pulses are adopted to achieve complete relaxation, and the pulse delay time (d)1) More than five times the spin-lattice relaxation time (T)1). The nuclear magnetic samples to be tested of the 2, 6-dinitrotoluene which is internally labeled by the fumaric acid and the hexamethyldisiloxane are subjected to an inversion recovery experiment (pulses of 180 degrees and 90 degrees, d)1The range is as follows: 0.01s to 20s) to T1Measuring the spin-lattice relaxation time T of characteristic hydrogen atoms on several compounds1As shown in table 4 below. Then, as shown in the data in table 4, the pulse delay time (d1) is at least 20s or more to reach the quantification condition in the classical nuclear magnetic theory no matter which internal standard is used, so that under the condition of 16 sampling, the time of a single quantification experiment is about to reach 15min or more.
TABLE 4 internal fumaric acid quantitation results
In order to improve the experimental efficiency, under the condition of the same other experimental parameters, a 30-degree pulse (zg30) and a 90-degree pulse (zg) are respectively adopted for the nuclear magnetic sample to be tested of the 2, 6-dinitrotoluene of the fumaric acid internal standard, and different d is respectively set1And measuring the relative integral area ratio of the quantitative peak and the internal standard peak of the sample to obtain the result shown in figure 3. From FIG. 3, it can be confirmed that at d1After the pulse is larger than a certain value, the fixed value results of the 30-degree pulse and the 90-degree pulse are actually consistent, and the time for completely restoring the hydrogen atom relaxation to the equilibrium is shorter under the condition of excitation of the 30-degree pulse, so that the d required for accurately and stably obtaining the quantitative result1Values shorter than the 90 pulse. Therefore, from the viewpoint of improving the efficiency of the constant value experiment, the method usesSelecting 30-degree pulse (zg30) as a quantitative nuclear magnetic experiment pulse sequence by using enedioic acid as an internal standard system, wherein the pulse delay time d is1Only 10s or more is needed; selecting 30-degree pulse (zg30) as a quantitative nuclear magnetic experiment pulse sequence in a system taking hexamethyldisiloxane as an internal standard, wherein the pulse delay time d is1Only 15s or more is needed;
example 4
Quantitative nuclear magnetic methodology investigation
Stability: taking the same sample of 2, 6-dinitrotoluene standard substance, and respectively carrying out the reaction for 0, 2,4,6, 8, 12 and 24 hours according to the experimental conditions and the method1H NMR experiment, recording the relative integral area ratio of the quantitative peak and the internal standard peak of the sample, and calculating RSD value;
repeatability: taking the same batch of 2, 6-dinitrotoluene standard substance samples, performing quantitative nuclear magnetic hydrogen spectrum experiments according to the experimental conditions and the method, recording the relative integral area ratio of the quantitative peak and the internal standard peak of the samples, and calculating the RSD value;
precision: preparing a certain batch of 2, 6-dinitrotoluene into a nuclear magnetic sample to be detected, continuously measuring for 6 times according to the experimental conditions and the method, recording the relative integral area ratio of a quantitative peak and an internal standard peak of the sample, and calculating an RSD value;
and (3) standard addition recovery rate: taking about 20mg of a certain batch of 2, 6-dinitrotoluene standard substance to prepare a nuclear magnetic sample to be detected, accurately weighing the nuclear magnetic sample and adding 3mg, 5mg and 10mg of dinitrotoluene standard substance after quantitative nuclear magnetic hydrogen spectrum experiments are carried out according to the experimental conditions and the method, recording the relative integral area ratio of a quantitative peak and an internal standard peak of the sample so as to calculate the content of the dinitrotoluene and calculate the recovery rate.
And (3) linear verification: taking a batch of 2, 6-dinitrotoluene standard substance, precisely weighing about 15mg, 20mg, 25mg and 30mg of sample, and respectively carrying out the test according to the experimental conditions and the method1And H NMR experiment, recording the relative integral area ratio of the quantitative peak and the internal standard peak of the sample so as to calculate the absolute mass of the dinitrotoluene of the sample, and counting the linearity of the test result.
The experimental results are shown in table 5 below, and data show that the method has good linear relationship, precision, stability and repeatability, and the benchmarking recovery rate value shows that the method also has good accuracy.
TABLE 5 NMR Hydrogen Spectroscopy for determination of 2, 6-dinitrotoluene Standard substance content methodological examination results
It should be added that the above-mentioned embodiments describe the method for detecting the purity of 2, 6-dinitrotoluene standard substance for illustrative purposes and not for limiting purposes, and the above examples 1-2 are not all examples that can be performed in this patent, and further examples are specifically mentioned according to the scope of the present invention, so that modifications and variations without departing from the general concept of the present invention are within the scope of the present invention.
The invention establishes the quantitative nuclear magnetic hydrogen spectrum method for the 2, 6-dinitrotoluene standard substance with accurate and reliable characteristic quantity value, adopts the nuclear magnetic resonance hydrogen spectrum internal standard method to directly and accurately quantify the content of the main component of the standard substance, has the advantages of simple and convenient operation, less sampling amount, good repeatability and the like, and is suitable for the purity value-determining process in the production and application of the 2, 6-dinitrotoluene standard substance.
Claims (8)
1. A quantitative nuclear magnetic hydrogen spectrum valuing method of a 2, 6-dinitrotoluene purity standard substance is characterized by comprising the following specific steps:
(1) weighing an internal standard substance by a one-hundred-ten-thousand balance in a sealed container by a decrement method, adding a deuterated solvent to prepare an internal standard solution, recording the total mass of the internal standard substance and the dissolved solution, and sealing and ultrasonically mixing for later use;
(2) weighing a 2, 6-dinitrotoluene standard substance in a nuclear magnetic sample tube with the diameter of 5mm, transferring a prepared internal standard solution, weighing the mass of the transferred solution, shaking uniformly, and sealing to be detected;
(3) placing the prepared nuclear magnetic sample tube in a superconducting nuclear magnetic resonance spectrometer, and measuring the sample solution1H NMR spectrum, nuclear magnetic testing parameters and conditions are as follows: pulse sequences zg orzg30, measuring the temperature of 295K-305K, the sampling time is more than 2s, and the scanning times are more than 16;
(4) quantitative results analysis and standard substance quantitation: acquiring a nuclear magnetic resonance hydrogen spectrum under the conditions, performing baseline correction, phase correction and chemical shift correction on the spectrogram, determining the quantitative peaks of the internal standard substance and the dinitrotoluene, respectively performing integral treatment on the quantitative peaks, and finally calculating the content of the main component dinitrotoluene in the standard substance according to the integral area, wherein the calculation formula is as follows:
in the formula:
Px-the purity, expressed in%, of 2, 6-dinitrotoluene in a sample of standard substance to be tested;
Ps-the value of the purity of the solution of internal standard, expressed in%;
mx-2, 6-dinitrotoluene standard substance sample addition mass, in mg;
m-mass of added internal standard solution, unit mg;
Ms-relative molecular mass of internal standard;
Mx-relative molecular mass of 2, 6-dinitrotoluene;
Hs-1 mole of the number of resonating nuclei on the functional group of the internal standard signature;
Hx-the number of resonant nuclei on a functional group producing a characteristic peak signal for 1 mole of dinitrotoluene;
As-peak area of the internal standard characteristic signal peak;
Ax-peak area of characteristic signal peak of 2, 6-dinitrotoluene;
(5) carrying out uncertainty evaluation on the nuclear magnetism quantification of the 2, 6-dinitrotoluene purity standard substance by using a measurement model shown as a formula (2);
in the formula (f)timeThe influence factor of the dissolution amount of the sample in the solvent influenced by the dissolution time;
ftempthe influence factor of the dissolved amount of the sample in the solvent influenced by the temperature;
f′timeinfluence factors of the volatilization quantities of the sample and the internal standard influenced by the experiment time;
f′tempinfluence factors of the volatilization quantities of the sample and the internal standard influenced by temperature;
mu under rootcThe separation represented is the uncertainty introduced by each component in the mathematical model.
2. The method for quantitative nuclear magnetic hydrogen spectrum quantification of the 2, 6-trinitrotoluene purity standard substance as claimed in claim 1, wherein the internal standard substance is a high-purity certified standard substance with measurement traceability, and all hydrogen in the substance is in the same chemical environment, i.e. the nuclear magnetic resonance hydrogen spectrum only has one group of characteristic peaks, such as fumaric acid, hexamethyldisiloxane and the like.
3. The method for quantitative nuclear magnetic hydrogen spectrum quantification of 2, 6-dinitrotoluene purity standard substance according to claim 1 or 2, wherein the nuclear magnetic resonance hydrogen spectrum adopts 30 ° pulse, the quantitative experiment pulse sequence is zg30, and the sampling delay time d is selected when fumaric acid is used as an internal standard1It is required to be 15 seconds or more.
4. The quantitative nuclear magnetic hydrogen spectrum method for the purity standard substance of 2, 6-dinitrotoluene according to claim 1 or 2, wherein when fumaric acid is used as the internal standard substance, the deuterated solvent is a deuterated methanol solvent, and the deuteration degree is more than 99%; when hexamethyldisiloxane is used as an internal standard substance, the deuterated solvent is a deuterated methanol solvent, and the deuteration degree is more than 99%.
5. The quantitative nuclear magnetic hydrogen spectrum quantification method of the 2, 6-trinitrotoluene purity standard substance according to claim 1 or 2, characterized in that the amount of the 2, 6-dinitrotoluene standard substance added to the nuclear magnetic sample is 20-50 mg.
6. The quantitative nuclear magnetic hydrogen spectrometry method for the purity standard substance of 2, 6-dinitrotoluene according to claim 1 or 2, wherein the quantitative peak of 2, 6-dinitrotoluene is a characteristic methyl peak having a chemical shift δ 2.51ppm in the hydrogen spectrum.
7. The quantitative nuclear magnetic hydrogen spectrometry method for the purity standard substance of 2, 6-dinitrotoluene according to claim 1 or 2, wherein all the weighing steps in the above steps are carried out using a high precision balance with an index value of less than 0.1 mg.
8. The quantitative nuclear magnetic hydrogen spectrometry method for the standard substance of 2, 6-dinitrotoluene purity according to claim 1 or 2, characterized in that an airtight chromatographic sample injection needle is used in the preparation and removal process of the internal standard solution, and the standard is 50 μ L-100 μ L, which can effectively prevent the volatilization of the solvent in the internal standard solution.
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