CN111007098A - Quantitative nuclear magnetic hydrogen spectrum value determination method for 2,4, 6-trinitrotoluene standard substance - Google Patents
Quantitative nuclear magnetic hydrogen spectrum value determination method for 2,4, 6-trinitrotoluene standard substance Download PDFInfo
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- 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 title claims abstract description 82
- 238000000034 method Methods 0.000 title claims abstract description 61
- 229910052739 hydrogen Inorganic materials 0.000 title claims abstract description 33
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 title claims abstract description 32
- 239000001257 hydrogen Substances 0.000 title claims abstract description 32
- 238000001228 spectrum Methods 0.000 title claims description 32
- 238000005259 measurement Methods 0.000 claims abstract description 12
- 238000004611 spectroscopical analysis Methods 0.000 claims abstract description 4
- 239000000523 sample Substances 0.000 claims description 58
- VZCYOOQTPOCHFL-OWOJBTEDSA-N Fumaric acid Chemical compound OC(=O)\C=C\C(O)=O VZCYOOQTPOCHFL-OWOJBTEDSA-N 0.000 claims description 42
- 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 23
- 238000002474 experimental method Methods 0.000 claims description 21
- 239000001530 fumaric acid Substances 0.000 claims description 21
- UQEAIHBTYFGYIE-UHFFFAOYSA-N hexamethyldisiloxane Chemical compound C[Si](C)(C)O[Si](C)(C)C UQEAIHBTYFGYIE-UHFFFAOYSA-N 0.000 claims description 18
- 239000000015 trinitrotoluene Substances 0.000 claims description 18
- 239000012086 standard solution Substances 0.000 claims description 17
- 238000005481 NMR spectroscopy Methods 0.000 claims description 15
- 238000004364 calculation method Methods 0.000 claims description 15
- 239000000243 solution Substances 0.000 claims description 12
- 239000002904 solvent Substances 0.000 claims description 12
- 238000002360 preparation method Methods 0.000 claims description 11
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- OKKJLVBELUTLKV-MZCSYVLQSA-N Deuterated methanol Chemical group [2H]OC([2H])([2H])[2H] OKKJLVBELUTLKV-MZCSYVLQSA-N 0.000 claims description 8
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- CSCPPACGZOOCGX-UHFFFAOYSA-N Acetone Chemical class CC(C)=O CSCPPACGZOOCGX-UHFFFAOYSA-N 0.000 claims description 5
- 125000002496 methyl group Chemical group [H]C([H])([H])* 0.000 claims description 5
- 238000011002 quantification Methods 0.000 claims description 5
- 238000004458 analytical method Methods 0.000 claims description 4
- 239000011903 deuterated solvents Substances 0.000 claims description 4
- 125000000524 functional group Chemical group 0.000 claims description 4
- 238000013178 mathematical model Methods 0.000 claims description 4
- 238000000425 proton nuclear magnetic resonance spectrum Methods 0.000 claims description 4
- CSCPPACGZOOCGX-WFGJKAKNSA-N deuterated acetone Substances [2H]C([2H])([2H])C(=O)C([2H])([2H])[2H] CSCPPACGZOOCGX-WFGJKAKNSA-N 0.000 claims description 3
- 238000002347 injection Methods 0.000 claims description 3
- 239000007924 injection Substances 0.000 claims description 3
- 238000012545 processing Methods 0.000 claims description 3
- OFOBLEOULBTSOW-UHFFFAOYSA-N Propanedioic acid Natural products OC(=O)CC(O)=O OFOBLEOULBTSOW-UHFFFAOYSA-N 0.000 claims description 2
- 238000011156 evaluation Methods 0.000 claims description 2
- VZCYOOQTPOCHFL-UPHRSURJSA-N maleic acid Chemical compound OC(=O)\C=C/C(O)=O VZCYOOQTPOCHFL-UPHRSURJSA-N 0.000 claims description 2
- 239000011976 maleic acid Substances 0.000 claims description 2
- 239000012488 sample solution Substances 0.000 claims description 2
- 238000000926 separation method Methods 0.000 claims description 2
- 230000005311 nuclear magnetism Effects 0.000 claims 1
- 238000010966 qNMR Methods 0.000 claims 1
- 238000005160 1H NMR spectroscopy Methods 0.000 abstract description 6
- 238000005516 engineering process Methods 0.000 abstract description 3
- 125000004435 hydrogen atom Chemical group [H]* 0.000 description 6
- 239000012535 impurity Substances 0.000 description 6
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- 238000000655 nuclear magnetic resonance spectrum Methods 0.000 description 2
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- 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 determining the value of a 2,4, 6-trinitrotoluene standard substance based on quantitative nuclear magnetic hydrogen spectroscopy technology (1H NMR), and measuring the content of the main component 2,4, 6-trinitrotoluene in the standard substance by using an internal standard substance with measurement traceability. 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 measurement and detection of energetic materials, and particularly relates to a quantitative nuclear magnetic hydrogen spectrum value determination method for a 2,4, 6-trinitrotoluene purity standard substance.
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.
2,4, 6-trinitrotoluene, commonly abbreviated as TNT, is used as a traditional common explosive, is relatively safe to store and use, can be injected, pressed, screwed and the like, and is widely applied to various aeroprojectiles, shells and engineering explosive packages. The prior art is not suitable for the fixed value of the trinitrotoluene purity standard substance, so that a new method which is faster, simpler and more convenient and meets the special fixed value requirement of the trinitrotoluene purity standard substance needs to be researched and established.
Disclosure of Invention
Aiming at the requirements of accurate value determination in the process of production and period check of a trinitrotoluene standard substance at the present stage, the invention provides a quantitative nuclear magnetic hydrogen spectrum value determination method for the trinitrotoluene purity standard substance, which has accurate and reliable characteristic value determination.
The specific technical scheme for realizing the purpose of the invention is as follows:
a method for valuing a 2,4, 6-trinitrotoluene 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 2,4, 6-trinitrotoluene standard substances in a nuclear magnetic sample tube with the diameter of 5mm, then transferring the prepared internal standard solution, precisely weighing the mass of the transferred solution, shaking up and sealing 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 solution1H NMR spectrum, 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 quantitative peaks of the internal standard substance and trinitrotoluene, performing integral processing on the quantitative peaks respectively, and finally calculating the content of the main component trinitrotoluene in the standard substance according to the integral area, wherein the calculation formula is as follows:
in the formula:
Px-the purity of 2,4, 6-trinitrotoluene in the standard sample to be tested, expressed in%;
Ps-the value of the purity of the solution of internal standard, expressed in%;
m-mass of added internal standard solution, unit mg;
Ms-relative molecular mass of internal standard;
Mx-relative molecular mass of 2,4, 6-trinitrotoluene;
Hs-1 mole of the number of resonating nuclei on the functional group of the internal standard signature;
Hx-the number of resonance nuclei on the functional group producing a characteristic peak signal for 1 mole of trinitrotoluene;
As-peak area of the internal standard characteristic signal peak;
Axpeak area of characteristic signal peak of 2,4, 6-trinitrotoluene;
(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 uncertainty of the 2,4, 6-trinitrotoluene standard substance mainly comprises the following components: 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 2,4, 6-trinitrotoluene 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, i.e. the nuclear magnetic resonance hydrogen spectrum only has one group of characteristic peaks, such as fumaric acid, hexamethyldisiloxane, tetrachloroethane and the like.
Preferably, the addition amount of the 2,4, 6-trinitrotoluene standard substance in the nuclear magnetic sample is 20-50 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, the deuterated solvent is deuterated methanol, deuterated acetone or both 1: 5-5: 1 mixing the solvent.
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 standard1The time is more than or equal to 10 s; when hexamethyldisiloxane is selected as an internal standard, the sampling delay time needs to be more than or equal to 15 s;
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 is suitable for fixed value of the 2,4, 6-trinitrotoluene standard substance.
Drawings
FIG. 1 is a nuclear magnetic hydrogen spectrum of 2,4, 6-trinitrotoluene with hexamethyldisiloxane as internal standard;
FIG. 2 is a nuclear magnetic hydrogen spectrum of 2,4, 6-trinitrotoluene with fumaric acid as internal standard;
FIG. 3 shows different pulse sequences at different d1Phase of quantitative peak and internal standard peak of sample under conditionPlotting the integral area ratio result line;
Detailed Description
The technical solution of the present invention will be further described in detail with reference to some specific embodiments.
Example 1
And (3) taking a hexamethyldisiloxane standard substance as an internal standard substance, and performing purity value determination on the 2,4, 6-trinitrotoluene 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 acetone (deuteration degree > 99.8%, CIL corporation, USA), 5mm standard nuclear magnetic sample tube (NORELL corporation, USA), hexamethyldisiloxane solution standard (Siren's near chemical research institute, content 0.102%, U2%), 2,4, 6-trinitrotoluene 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 20mg of 2,4, 6-trinitrotoluene standard substance to be measured in a 5mm nuclear magnetic tube, directly transferring about 0.6ml of 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, combines chemical properties of 2,4, 6-trinitrotoluene, and adopts Topspin 3.5 pair 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. Corresponding attribution is carried out according to the coupling situation of proton signal peaks and chemical shift values, wherein the chemical shift is 8.95ppm and is three hydrogen atoms on a benzene ring of 2,4, 6-trinitrotolueneThe characteristic peaks, the chemical shift of which is 2.64ppm is three hydrogen atom characteristic peaks on the methyl of 2,4, 6-trinitrotoluene, the chemical shift of which is 0.06ppm is six methyl hydrogen atom characteristic peaks of hexamethyldisiloxane, and the nuclear magnetic spectrum shows that the internal standard characteristic peaks are well separated from other signal peaks, are symmetrical and uniform and meet the basic condition of quantitative nuclear magnetic. Two characteristic peaks of 2,4, 6-trinitrotoluene shown on a nuclear magnetic spectrum chart 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. The samples were tested in parallel 6 times to obtain the quantitative results for 2,4, 6-trinitrotoluene 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 that the uncertainty of the ratio result can be evaluated by adopting A-typeExpressed as the standard deviation of the integrated area ratio quantification results, we give:
② molar mass (M) of sample and internal standardxAnd Ms): from the international relative atomic mass table published by IUPAC, the atomic mass and uncertainty of each element in trinitrotoluene and internal standard hexamethyldisiloxane can be found in table 2 below:
relative atomic masses and uncertainties of Table 2C, H, O, N, Si
The standard uncertainty of the molar mass of 2,4, 6-trinitrotoluene and the internal standard substance hexamethyldisiloxane can be calculated respectively as follows:
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 volatilization of sample and internal standard is determined by experiment timeCorrection factor of influence (f'time): for a nuclear magnetic sample to be detected 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 trinitrotoluene sample to be detected 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 synthesis standard uncertainty of the purity fixed value of the 2,4, 6-trinitrotoluene standard substance by using the hexamethyldisiloxane standard substance as the internal standard substance and adopting the quantitative nuclear magnetic method, which is:
example 2
And (3) taking the fumaric acid purity standard substance as an internal standard substance, and performing purity value determination on the 2,4, 6-trinitrotoluene standard substance by adopting a quantitative nuclear magnetic method.
2.1 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%), 2,4, 6-trinitrotoluene standard (national defense science and technology industry primary metering station for explosives and powders)
2.2 preparation of the 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.
2.3 preparation and determination of Nuclear magnetic samples to be determined
Accurately weighing about 20mg of trinitrotoluene standard substance to be measured in a 5mm nuclear magnetic tube, accurately transferring about 0.6ml of fumaric acid internal standard solution, weighing, uniformly mixing, and sealing with 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.
2.4 samples1H NMR Spectrum analysis
According to1H NMR spectrogram literature data, combines chemical properties of 2,4, 6-trinitrotoluene, and adopts Topspin 3.5 pair 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 of 8.95ppm is three hydrogen atom characteristic peaks on a benzene ring of 2,4, 6-trinitrotoluene, the chemical shift of 2.64ppm is three hydrogen atom characteristic peaks on a methyl group of 2,4, 6-trinitrotoluene, the chemical shift of 5.68ppm is two methine hydrogen atom characteristic peaks of fumaric acid, and the nuclear magnetic spectrogram can show that the internal standard substance characteristic peaks are well separated from other signal peaks, are symmetrical and uniform and meet basic conditions of quantitative nuclear magnetic resonance. Two characteristic peaks of 2,4, 6-trinitrotoluene shown on a nuclear magnetic spectrum chart 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. The sample is measured in parallel for three times, the relative integral area ratio is obtained by integrating and averaging for three times each time, and finally the fixed value result of the 2,4, 6-trinitrotoluene standard substance is obtained by calculation and is shown in the following table 3.
TABLE 3 internal fumaric acid for quantification of 2,4, 6-trinitrotoluene standard
2.5 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): the atomic weight and uncertainty of each element in trinitrotoluene and internal standard fumaric acid can be found from an international relative atomic mass table published by IUPAC, and then the standard uncertainty of the molar mass of 2,4, 6-trinitrotoluene and the internal standard hexamethyldisiloxane can be respectively calculated:
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 that the synthetic standard uncertainty of the purity fixed value of the 2,4, 6-trinitrotoluene standard substance by using the fumaric acid standard substance as the internal standard substance and adopting the quantitative nuclear magnetic method is as follows:
example 3
Because the relaxations of protons in different chemical environments in the nuclear magnetic sample to be detected are different, the relaxations are finally induced in the proton magnetic field environmentThe time to fully restore equilibrium is different. 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 2,4, 6-trinitrotoluene which is internally labeled by the fumaric acid and the hexamethyldisiloxane are subjected to inversion recovery experiments (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 (d) is determined regardless of the internal standard used1) The quantitative condition in the classical nuclear magnetic theory can be reached only after reaching at least 20s, so that under the condition of 16 times of sampling, the time of a single quantitative experiment is about to reach more than 15 min.
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 2,4, 6-trinitrotoluene 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 fixed value experiment, a 30 DEG pulse (zg30) is selected as a quantitative nuclear magnetic experiment pulse sequence in a system taking fumaric acid as an internal standard, and the pulse delay time d1Only 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
Precision: preparing a certain batch of 2,4, 6-trinitrotoluene into a nuclear magnetic sample to be tested, 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;
stability: taking the same sample of 2,4, 6-trinitrotoluene standard substance, and respectively carrying out the steps of 0, 2,4,6, 8 and 12h 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 2,4, 6-trinitrotoluene 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;
and (3) standard addition recovery rate: preparing a batch of 2,4, 6-trinitrotoluene standard substance with about 15mg to be used as a nuclear magnetic sample to be tested, accurately weighing the nuclear magnetic sample, adding 5mg, 10mg and 15mg of trinitrotoluene standard substance into the nuclear magnetic sample after carrying out quantitative nuclear magnetic hydrogen spectrum experiments 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 trinitrotoluene, and calculating the recovery rate;
and (3) linear verification: taking a batch of 2,4, 6-trinitrotoluene standard substance, precisely weighing about 15mg, 20mg, 25mg and 30mg of samples, 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 trinitrotoluene 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 2,4, 6-Trinitrotoluene Standard substance content methodology investigation results
It should be added that the above-mentioned embodiments describe the method for detecting the purity of 2,4, 6-trinitrotoluene standard substance for illustrative purposes and not for limiting purposes, and the above examples 1-4 are not all examples that can be performed by this patent, and further examples can be specifically mentioned according to the limited scope, therefore, modifications and variations that do not depart 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 2,4, 6-trinitrotoluene 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, small sampling amount, good repeatability and the like, and is suitable for the purity value-fixing process in the production and application of the 2,4, 6-trinitrotoluene standard substance.
Claims (8)
1. A quantitative nuclear magnetic hydrogen spectrum value determining method of a 2,4, 6-trinitrotoluene purity standard substance is characterized in that: the method comprises the following 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 2,4, 6-trinitrotoluene standard substance in a nuclear magnetic sample tube with the diameter of 5mm, transferring the prepared internal standard solution, weighing 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: 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 quantitative peaks of the internal standard substance and trinitrotoluene, performing integral processing on the quantitative peaks respectively, and finally calculating the content of the main component trinitrotoluene in the standard substance according to the integral area, wherein the calculation formula is as follows:
in the formula:
Px-the purity of 2,4, 6-trinitrotoluene in the standard sample to be tested, expressed in%;
Ps-the value of the purity of the solution of internal standard, expressed in%;
mx2,4, 6-trinitrotoluene standard substance sample adding mass, unit mg;
m-mass of added internal standard solution, unit mg;
Ms-relative molecular mass of internal standard;
Mx-relative molecular mass of 2,4, 6-trinitrotoluene;
Hs-1 mole of the number of resonating nuclei on the functional group of the internal standard signature;
Hx-the number of resonance nuclei on the functional group producing a characteristic peak signal for 1 mole of trinitrotoluene;
As-peak area of the internal standard characteristic signal peak;
Axpeak area of characteristic signal peak of 2,4, 6-trinitrotoluene;
(5) carrying out uncertainty evaluation on the nuclear magnetism quantification of the 2,4, 6-trinitrotoluene 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′timethe volatilization amount of the sample and the internal standard is an influence factor influenced by experiment time;
f′tempthe volatilization amount of the sample and the internal standard is an influence factor 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 2,4, 6-trinitrotoluene purity standard substance according to claim 1 or 2, characterized in that the internal standard substance is a high-purity certified standard substance with measurement traceability, and all the 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 the 2,4, 6-trinitrotoluene purity standard substance according to claim 1 or 2, characterized in that the nuclear magnetic hydrogen spectrum adopts 30-degree pulses, the quantitative experimental pulse sequence is zg30, and the sampling delay time d is selected when fumaric acid or maleic acid is used as an internal standard1The time is more than or equal to 10 s; when hexamethyldisiloxane is selected as the internal standard, the sampling delay time needs to be more than or equal to 15 s.
4. The quantitative nmr spectrum method for quantifying the purity standard substance of 2,4, 6-trinitrotoluene according to claim 1 or 2, wherein the deuterated solvent is deuterated methanol, deuterated acetone or both 1: 5-5: 1 mixing the solvent.
5. The quantitative nuclear magnetic hydrogen spectrum method for the 2,4, 6-trinitrotoluene purity standard substance according to claim 1 or 2, wherein the amount of the 2,4, 6-trinitrotoluene standard substance added to the nuclear magnetic sample is 20-50 mg.
6. The quantitative nuclear magnetic hydrogen spectrum method for determining the quantitative value of the 2,4, 6-trinitrotoluene purity standard substance according to claim 1 or 2, wherein the quantitative peak of the 2,4, 6-trinitrotoluene is a characteristic methyl peak with the chemical shift delta 2.64ppm of the hydrogen spectrum.
7. The quantitative nuclear magnetic hydrogen spectrometry method for the purity standard substance of 2,4, 6-trinitrotoluene according to claim 1 or 2, characterized in that all the weighing steps in the above steps use a high-precision balance with division value lower than 0.1 mg.
8. The quantitative nuclear magnetic hydrogen spectrometry method for the 2,4, 6-trinitrotoluene purity standard substance according to claim 1 or 2, characterized in that an airtight chromatographic sample injection needle is adopted in the preparation and removal process of the internal standard solution, and the specification is 50-100 μ L, which can effectively prevent the volatilization of the solvent in the internal standard solution.
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