A quantitative characterization method of bound water adsorption amount in dynamic hygroscopic process of tobacco particles

Abstract

The application discloses a kind of quantitative characterization methods of bound water adsorption amount in dynamic hygroscopic process of tobacco particles, different moisture states such as bound water, not easy to flow water and free water in tobacco particles are detected using low-field nuclear magnetic resonance technology, and correlation equation y1 between tobacco particle dry basis moisture content and bound water peak area is constructed;By online real-time monitoring the numerical value of bound water peak area and the proportion of moisture state during dynamic hygroscopic process, the bound water adsorption amount in dynamic hygroscopic process of tobacco particles is calculated based on y1, which is model fitted with hygroscopic time t, and the relationship y2 between bound water adsorption amount and hygroscopic time in tobacco particle hygroscopic process is established, thereby establishing the quantitative characterization method of bound water adsorption amount in tobacco particle hygroscopic process.The method of the application is convenient and efficient, effectively solves the problem that moisture state is difficult to be detected online in the existing tobacco particle hygroscopic process, and provides technical support for tobacco particle processing and storage.

Description

Technical Field

[0001] This invention belongs to the field of online moisture detection of tobacco particles, specifically relating to a quantitative characterization method for the amount of bound water adsorbed during the dynamic moisture absorption process of tobacco particles. Background Technology

[0002] Tobacco pellets are the core raw material for new types of heated tobacco products, such as pellet-type cigarettes. Due to their high hydrophilicity in chemical components and the addition of highly hydrophilic additives, they are extremely prone to absorbing moisture and becoming damp under different temperature and humidity conditions, which adversely affects the processing, production, transportation, and storage of cigarette products. Furthermore, the varying moisture content of tobacco pellets, especially changes in their moisture state, has a significant impact on their heat transfer, pyrolysis, component release, and sensory quality.

[0003] Low-field nuclear magnetic resonance (LF-NMR) is a rapid, non-destructive, and environmentally friendly moisture detection technique. It analyzes differences in the transverse relaxation time (T2) of a sample to interpret the internal moisture state and migration patterns of the material from a microscopic perspective. The transverse relaxation time inversion spectrum of tobacco particles typically shows a T2 value within the range of [missing information]. 21 (0.1~1ms), T 22 (1~10ms) and T 23 Three distinct peaks appear within the three intervals (10–100 ms), among which, T 21 (0.1~1ms) represents bound water, T 22 (1-10ms) represents water that is not easily moved, T 23 (10–100 ms) represents free water. Currently, low-field nuclear magnetic resonance (NMR) technology is mostly used in the tobacco industry for determining the moisture content of tobacco. For example, patent CN201610863636.8 discloses a method for testing tobacco moisture content based on the peak area of ​​time-domain NMR inversion; patent CN201410083463.9 discloses a method for measuring tobacco moisture content using low-field NMR. Neither of these methods involves the study of online detection of changes in the moisture state of tobacco particles during the hygroscopic process, especially the amount of bound water adsorbed.

[0004] Therefore, developing a simple and efficient quantitative characterization method for the amount of bound water adsorbed during the moisture absorption process of tobacco particles is of great significance for the production, processing and stable storage of heated cigarette products. Summary of the Invention

[0005] This invention provides a quantitative characterization method for the amount of bound water adsorbed during the dynamic moisture absorption process of tobacco particles. The method is convenient and efficient, effectively solving the problem of difficulty in online detection of moisture status during the moisture absorption process of existing tobacco particles, and providing technical support for the processing and storage of tobacco particles.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A quantitative characterization method for the amount of bound water adsorbed during the dynamic moisture absorption process of tobacco particles is characterized by: employing low-field nuclear magnetic resonance (NMR) technology to detect different moisture states in tobacco particles, including bound water, immobile water, and free water, and constructing a correlation equation y1 between the dry basis moisture content of tobacco particles and the peak area of ​​bound water; by online real-time monitoring of the peak area of ​​bound water and its proportion of the moisture state during the dynamic moisture absorption process, the amount of bound water adsorbed during the dynamic moisture absorption process of tobacco particles is calculated based on y1, and model fitting is performed with the moisture absorption time t to establish a correlation equation y2 between the amount of bound water adsorbed during the moisture absorption process of tobacco particles, thereby establishing a quantitative characterization method for the amount of bound water adsorbed during the moisture absorption process of tobacco particles. The specific steps include the following:

[0008] (1) Preparation of oven-dried tobacco pellets: Following the method in tobacco industry standard YC / T 31-1996, weigh 2-3g of the tobacco pellets to be tested and place them in an aluminum box that has been dried to constant weight. Adjust the electric heating constant temperature forced air drying oven to 100±1℃ to dry the tobacco pellets to constant weight, and obtain oven-dried tobacco pellets, denoted as TG. d The dry basis moisture content WC is obtained by dividing the mass difference of the tobacco particles before and after drying by the mass after drying. d.b. ;

[0009] (2) Low-field nuclear magnetic resonance (LF-NMR) instrument calibration: The standard oil sample was measured using FID pulse sequence to calibrate the center frequency of the time-domain nuclear magnetic resonance instrument and the pulse width of the 90° pulse. The sampling frequency, number of samplings, sampling waiting time, analog gain, digital gain and accumulation count of the instrument were determined to ensure the stability and accuracy of the FID signal.

[0010] (3)TG d Detection of bound water: Dry tobacco particle samples were placed inside the magnet coil of a low-field nuclear magnetic resonance analyzer at a height of 1–3 cm. CPMG sequences were used to acquire signals from the samples. The resulting CPMG sequence attenuation maps were inverted using software to obtain the inversion spectrum, and TG was calculated. d The combined water peak area A TGd ;

[0011] (4) Construction of the correlation equation between the moisture content of tobacco particles and the peak area of ​​adsorbed bound water: The tobacco particle sample to be tested was placed in an LF-NMR sample tube with a height of 1-3 cm. The sample tube containing the sample was placed in a desiccator containing the required saturated salt solution. The sample tube was removed every 24 hours and weighed on an electronic balance. The dry basis moisture content of the tobacco particle sample after dynamic moisture absorption was calculated. The sample was placed in an LF-NMR magnet coil, and the CPMG sequence was used to acquire the signal. The obtained CPMG sequence attenuation spectrum was inverted by software to obtain the inversion spectrum, and then the corresponding transverse relaxation time-signal amplitude distribution curve and the peak area of ​​bound water (A) were obtained. TG ); A dry basis moisture content (WC) model was constructed using model fitting. d.b. ) and the peak area of ​​adsorbed bound water (A TG -A TGd The relevant equation for y1 is y1;

[0012] (5) Online detection of bound water during dynamic moisture absorption process:

[0013] a) Relative humidity correction of the humidity control sample tube: Place the required saturated salt solution in the tray of the humidity control sample tube, and use a real-time humidity detection device (such as USB-logger) to correct the relative humidity in the sample tube. The correction range is 0 to 100%.

[0014] b) Sample preparation: Place the tobacco particles to be tested in a low-field nuclear magnetic resonance humidity control sample tube at a height of 1-3 cm; place different saturated salt solutions in the tray inside the humidity control sample tube to provide the required hygroscopic environment, with an ambient humidity range of 10-98%; and seal the sample tube opening with a rubber stopper.

[0015] c) Online detection of bound water: The tobacco particle sample to be tested is placed in the magnet coil of a low-field nuclear magnetic resonance analyzer. The CPMG sequence is used to automatically acquire signals from the sample at timed intervals of 1 hour, and the online continuous detection is performed for 24 hours. The obtained CPMG sequence attenuation spectrum can be inverted by software to obtain the inversion spectrum, and then the corresponding transverse relaxation time-signal amplitude distribution curve and the peak areas of bound water, immobile water and free water are obtained.

[0016] (6) Quantitative analysis of bound water adsorption during dynamic moisture absorption: The area and proportion of bound water peaks obtained during the dynamic moisture absorption process of tobacco particles are detected online (the absolute adsorption amount is calculated based on the proportion of bound water to (bound water + non-flowing water + free water)). According to the correlation equation y1, the amount of bound water adsorbed during the dynamic moisture absorption process of tobacco particles is calculated. The model is fitted with the moisture absorption time to establish the correlation equation y2 between the amount of bound water adsorbed during the moisture absorption process of tobacco particles, thereby establishing a quantitative characterization method for the amount of bound water adsorbed during the moisture absorption process of tobacco particles.

[0017] Furthermore, the specific parameter settings for the CPMG sequence are as follows: magnetic field center temperature 32.00±0.02℃; main frequency = 21MHz; sampling frequency = 100kHz; analog gain = 20.0dB; digital gain = 3; RF delay = 0.08ms; 180° pulse width = 8.40μs; sampling wait time = 6500ms; echo time = 0.4ms; number of echoes = 16000; number of accumulations = 16; the data inversion is performed with ten million iterations to obtain the inversion spectrum, and then the corresponding transverse relaxation time-signal amplitude distribution curve and the combined water peak area are obtained.

[0018] Compared with existing technologies, the beneficial effects of this invention are reflected in:

[0019] The method of the present invention is convenient and efficient, effectively solving the problem that the moisture state of tobacco particles is difficult to detect online during the existing process of tobacco particle moisture absorption, and providing technical support for tobacco particle processing and storage. Attached Figure Description

[0020] Figure 1 This is a graph showing the correlation between the dry basis moisture content of tobacco particles and the peak area of ​​adsorbed bound water.

[0021] Figure 2 This is the inversion spectrum of the transverse relaxation time (T2) of tobacco particles under hygroscopic conditions in a saturated NaCl solution.

[0022] Figure 3 This is a graph showing the relationship between the moisture absorption time of tobacco particles and the amount of bound water adsorbed under the hygroscopic effect of saturated NaCl solution.

[0023] Figure 4 This is the inversion spectrum of the transverse relaxation time (T2) of tobacco particles under the hygroscopic effect of distilled aqueous solution.

[0024] Figure 5 This is a graph showing the relationship between the moisture absorption time of tobacco particles and the amount of bound water adsorbed under the hygroscopic effect of distilled aqueous solution. Detailed Implementation

[0025] To facilitate understanding by those skilled in the art, the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0026] Example 1: Quantitative characterization of water adsorption capacity during dynamic moisture absorption of tobacco particles at 75% relative humidity

[0027] The experimental method includes the following steps:

[0028] (1) Dried tobacco pellets (TG) dPreparation: Following the method in tobacco industry standard YC / T 31-1996, weigh 2-3g of tobacco granules and place them in an aluminum box that has been dried to constant weight. Adjust the electric heating constant temperature drying oven to 100±1℃ to dry the tobacco granules to constant weight, thus obtaining oven-dried tobacco granules, denoted as TG. d The difference in mass of tobacco particles before and after drying, divided by the mass after drying, yields its dry basis moisture content (WC). d.b The experiment was repeated three times, and the average dry basis moisture content of the tobacco particles was found to be 0.20–0.25 g / g.

[0029] (2) Instrument Calibration: The standard oil sample was measured using an FID pulse sequence to calibrate the center frequency of the time-domain nuclear magnetic resonance spectrometer and the pulse width of the 90° pulse. The sampling frequency was 100kHz, the center frequency of the nuclear magnetic resonance spectrometer was 21MHz, the 90° pulse width was 4-6μs, the number of sampling points was 1024, the sampling waiting time was 1000ms, the radio frequency delay was 0.08ms, the analog gain was 20dB, the digital gain was 3, and the number of accumulations was 8.

[0030] (3)TG d Bound water detection: Dry tobacco particles were placed within the magnet coil of a low-field nuclear magnetic resonance (NMR) analyzer, at a height of approximately 1 cm. A CPMG sequence was used to acquire signals from the sample. The specific parameters for the CPMG sequence were as follows: magnetic field center temperature 32.00 ± 0.02℃; main frequency = 21 MHz; sampling frequency = 100 kHz; RF delay = 0.08 ms; 180° pulse width = 8.40 μs; waiting time = 6500 ms; echo time = 0.4 ms; number of echoes = 16000; accumulation count = 16. Data inversion was performed with ten million iterations to obtain the inversion spectrum, from which TG could be calculated. d The combined water peak area (A) TGd ).

[0031] (4) Construction of the correlation equation between the moisture content of tobacco particles and the peak area of ​​adsorbed bound water: The tobacco particle sample to be tested is placed in a low-field nuclear magnetic resonance sample tube, the specific height of which can be 1 cm. The sample tube containing the sample to be tested is placed in a desiccator containing saturated NaCl solution. The sample tube is taken out every 24 h and weighed on an electronic balance. The change of dry basis moisture content of the tobacco particle sample during dynamic moisture absorption can be obtained by calculation. Then it is placed in the magnet coil of the low-field nuclear magnetic resonance analyzer. The CPMG sequence is used to acquire the signal of the sample. The specific parameters used in the CPMG sequence are the same as in step (3). The data inversion is performed with an iteration number of 10 million to obtain the inversion spectrum, and then the A value of the tobacco particles during dynamic moisture absorption is obtained. TG A dry basis moisture content (WC) model was constructed using model fitting. d.b. ) and the peak area of ​​adsorbed bound water (ATG -A TGd The correlation between the two is investigated. A linear equation was obtained through fitting: y = 24228*x - 3351, where x is the dry basis moisture content (g / g), and y is the peak area of ​​adsorbed bound water. Figure 1 It can be seen that the coefficient of determination R of the linear fitting curve is 2 =0.9853, indicating a good correlation between the peak area of ​​bound water adsorption and the dry basis moisture content. As the dry basis moisture content increases, the peak area of ​​bound water adsorption of tobacco particles shows an increasing trend, and its trend can be predicted by a linear fitting model.

[0032] (5) Online detection of bound water during dynamic moisture absorption process:

[0033] a) Relative humidity correction of the humidity control sample tube: Place the saturated NaCl solution in the tray of the humidity control sample tube, and use a USB-logger to correct the relative humidity in the sample tube. After correction, the equilibrium humidity is 75%.

[0034] b) Sample preparation: Place the tobacco particles to be tested in a low-field NMR humidity-controlled sample tube to a height of 1 cm. Place a saturated NaCl solution in the tray inside the humidity-controlled sample tube to provide an ambient humidity of 75%; seal the sample tube opening with a rubber stopper.

[0035] c) Online detection of bound water: The sample tube to be tested is placed inside the magnet coil of the low-field nuclear magnetic resonance analyzer, and the standard oil sample is calibrated using the Q-FID sequence; the CPMG sequence is used to automatically acquire signals from the sample at timed intervals of 1 hour, and continuous online detection is performed for 24 hours. The specific parameters used in the CPMG sequence are the same as in step (3). The data inversion is performed with ten million iterations to obtain the inversion spectrum, and then the corresponding transverse relaxation time-signal amplitude distribution curve and the peak areas of bound water, immobile water and free water are obtained. Figure 2 It can be seen that tobacco particles under different moisture absorption times all have a transverse relaxation time T 21 T 22 With T 23 Each element exhibits a corresponding peak, with the peak corresponding to bound water being the highest.

[0036] (6) Quantitative analysis of bound water adsorption during dynamic moisture absorption: The peak area and proportion of bound water obtained during the dynamic moisture absorption process of tobacco particles were detected online. Based on the relationship between the change in the peak area of ​​bound water adsorption and the dry basis moisture content during the moisture absorption process of tobacco particles, the amount of bound water adsorbed during the dynamic moisture absorption process of tobacco particles can be calculated. This value is then linearly fitted with the moisture absorption time to obtain the linear fitting equation y = 5.26 * 10 -4 *x+0.196, where x is the moisture absorption time / h, and y is the amount of bound water adsorbed / (g / g). From Figure 3 It can be seen that the coefficient of determination R of the linear fitting curve is 2 =0.9858, indicating that the model can effectively quantify the amount of bound water adsorbed during the moisture absorption process of tobacco particles. Calculations show that the amount of bound water adsorbed by tobacco particles after 24 hours of moisture absorption at 75% relative humidity is 0.1975 g / g.

[0037] Example 2: Quantitative characterization of water adsorption capacity during dynamic moisture absorption of tobacco particles at 95% relative humidity

[0038] The experimental method includes the following steps:

[0039] (1) Dried tobacco pellets (TG) d Preparation: Following the method in tobacco industry standard YC / T 31-1996, weigh 2-3g of tobacco granules and place them in an aluminum box that has been dried to constant weight. Adjust the electric heating constant temperature drying oven to 100±1℃ to dry the tobacco granules to constant weight, thus obtaining oven-dried tobacco granules, denoted as TG. d The difference in mass of tobacco particles before and after drying, divided by the mass after drying, yields its dry basis moisture content (WC). d.b The experiment was repeated three times, and the average dry basis moisture content of the tobacco particles was found to be 0.20–0.25 g / g.

[0040] (2) Instrument Calibration: The standard oil sample was measured using an FID pulse sequence to calibrate the center frequency of the time-domain nuclear magnetic resonance spectrometer and the pulse width of the 90° pulse. The sampling frequency was 100 kHz, the center frequency of the nuclear magnetic resonance spectrometer was 21 MHz, the 90° pulse width was 4–6 μs, the number of sampling points was 1024, the interval between adjacent repeated scans was 1000 ms, the radio frequency delay was 0.08 ms, the analog gain was 20 dB, the digital gain was 3, and the number of accumulations was 8.

[0041] (3)TG d Bound water detection: Dry tobacco particles were placed inside the magnet coil of a low-field nuclear magnetic resonance (NMR) analyzer, at a height of approximately 1 cm. A CPMG sequence was used to acquire the signal from the sample, with the same parameters as in Example 1. The resulting CPMG sequence attenuation spectrum was inverted using software to obtain an inversion spectrum, from which TG could be calculated. d The combined water peak area (A) TGd ).

[0042] (4) Construction of the correlation equation between the moisture content of tobacco particles and the peak area of ​​adsorbed bound water: The tobacco particle sample to be tested is placed in a low-field nuclear magnetic resonance sample tube, the specific height of which can be 1 cm. The sample tube containing the sample to be tested is placed in a desiccator of distilled water. The sample tube is taken out every 24 h and weighed on an electronic balance. The change of dry basis moisture content of the tobacco particle sample during dynamic moisture absorption is obtained by calculation. Then it is placed in the magnet coil of the low-field nuclear magnetic resonance analyzer. The CPMG sequence is used to acquire the signal of the sample. The specific parameters used in the CPMG sequence are the same as in step (3). The data inversion is performed with an iteration number of 10 million to obtain the inversion spectrum, and then the A value of the tobacco particles during dynamic moisture absorption is obtained. TG A dry basis moisture content (WC) model was constructed using model fitting. d.b. ) and the peak area of ​​adsorbed bound water (A TG -A TGd The correlation between the two is investigated. A linear equation was obtained through fitting: y = 24228*x - 3351, where x is the dry basis moisture content (g / g), and y is the peak area of ​​adsorbed bound water. Figure 1 It can be seen that the coefficient of determination R of the linear fitting curve is 2 =0.9853, indicating a good correlation between the peak area of ​​bound water adsorption and the dry basis moisture content. As the dry basis moisture content increases, the peak area of ​​bound water adsorption of tobacco particles shows an increasing trend, and its trend can be predicted by a linear fitting model.

[0043] (5) Online detection of bound water during dynamic moisture absorption process:

[0044] a) Relative humidity correction of the humidity control sample tube: Place distilled water in the tray of the humidity control sample tube and use a USB-logger to correct the relative humidity in the sample tube. After correction, the equilibrium humidity is 95%.

[0045] b) Sample preparation: Place the tobacco particles to be tested in a low-field NMR humidity control sample tube to a height of 1 cm. Place distilled water in the tray inside the humidity control sample tube to provide an ambient humidity of 95%; place a rubber stopper at the mouth of the sample tube to seal it.

[0046] c) Online detection of bound water: The sample tube to be tested is placed inside the magnet coil of the low-field nuclear magnetic resonance analyzer, and the standard oil sample is calibrated using the Q-FID sequence; the CPMG sequence is used to automatically acquire signals from the sample at timed intervals of 1 hour, and continuous online detection is performed for 24 hours. The specific parameters used in the CPMG sequence are the same as in step (3). The data inversion is performed with ten million iterations to obtain the inversion spectrum, and then the corresponding transverse relaxation time-signal amplitude distribution curve and the peak areas of bound water, immobile water and free water are obtained. Figure 4 It can be seen that tobacco particles under different moisture absorption times all have a transverse relaxation time T21 T 22 With T 23 Each element exhibits a corresponding peak, with the peak corresponding to bound water being the highest.

[0047] (6) Quantitative analysis of bound water adsorption during dynamic moisture absorption: The peak area and proportion of bound water obtained during the dynamic moisture absorption process of tobacco particles were detected online. Based on the relationship between the change of the peak area of ​​bound water adsorption and the dry basis moisture content during the moisture absorption process of tobacco particles, the amount of bound water adsorbed during the dynamic moisture absorption process of tobacco particles can be calculated. This value is then linearly fitted with the moisture absorption time to obtain the linear fitting equation y = 8.22 * 10 -4 *x+0.177, where x is the moisture absorption time / h, and y is the amount of bound water adsorbed / (g / g). From Figure 5 It can be seen that the coefficient of determination R of the linear fitting curve is 2 =0.9878, indicating that it can effectively quantify the amount of bound water adsorbed during the moisture absorption process of tobacco particles. Calculations show that the amount of bound water adsorbed by tobacco particles at 95% relative humidity is 0.2091 g / g. Comparative Example 1: Quantitative characterization of bound water adsorption by tobacco particles during moisture absorption at 75% relative humidity (offline detection)

[0048] The experimental method includes the following steps:

[0049] (1) Dried tobacco pellets (TG) d Preparation: Following the method in tobacco industry standard YC / T 31-1996, weigh 2-3g of tobacco granules and place them in an aluminum box that has been dried to constant weight. Adjust the electric heating constant temperature drying oven to 100±1℃ to dry the tobacco granules to constant weight, thus obtaining oven-dried tobacco granules, denoted as TG. d The difference in mass of tobacco particles before and after drying, divided by the mass after drying, yields its dry basis moisture content (WC). d.b The experiment was repeated three times, and the average dry basis moisture content of the tobacco particles was found to be 0.20–0.25 g / g.

[0050] (2) Instrument Calibration: The standard oil sample was measured using an FID pulse sequence to calibrate the center frequency of the time-domain nuclear magnetic resonance spectrometer and the pulse width of the 90° pulse. The sampling frequency was 100 kHz, the center frequency of the nuclear magnetic resonance spectrometer was 21 MHz, the 90° pulse width was 4–6 μs, the number of sampling points was 1024, the interval between adjacent repeated scans was 1000 ms, the radio frequency delay was 0.08 ms, the analog gain was 20 dB, the digital gain was 3, and the number of accumulations was 8.

[0051] (3)TG dBound water detection: Dry tobacco particles were placed inside the magnet coil of a low-field nuclear magnetic resonance (NMR) analyzer, at a height of approximately 1 cm. A CPMG sequence was used to acquire signals from the sample, with the same parameters as in Example 1. Data inversion was performed with ten million iterations to obtain the inversion spectrum, from which TG could be calculated. d The combined water peak area (A) TGd ).

[0052] (4) Construction of the correlation equation between the moisture content of tobacco particles and the peak area of ​​adsorbed bound water: The tobacco particle sample to be tested is placed in a low-field nuclear magnetic resonance sample tube, the specific height of which can be 1 cm. The sample tube containing the sample to be tested is placed in a desiccator containing saturated NaCl solution. The sample tube is taken out every 24 h and weighed on an electronic balance. The change of dry basis moisture content of the tobacco particle sample during dynamic moisture absorption can be obtained by calculation. Then it is placed in the magnet coil of the low-field nuclear magnetic resonance analyzer. The CPMG sequence is used to acquire the signal of the sample. The specific parameters used in the CPMG sequence are the same as in step (3). The data inversion is performed with an iteration number of 10 million to obtain the inversion spectrum, and then the A value of the tobacco particles during dynamic moisture absorption is obtained. TG A dry basis moisture content (WC) model was constructed using model fitting. d.b. ) and the peak area of ​​adsorbed bound water (A TG -A TGd The correlation between the two is investigated. A linear equation was obtained through fitting: y = 24228*x - 3351, where x is the dry basis moisture content (g / g), and y is the peak area of ​​adsorbed bound water. Figure 1 It can be seen that the coefficient of determination R of the linear fitting curve is 2 =0.9853, indicating a good correlation between the peak area of ​​bound water adsorption and the dry basis moisture content. As the dry basis moisture content increases, the peak area of ​​bound water adsorption of tobacco particles shows an increasing trend, and its trend can be predicted by a linear fitting model.

[0053] (5) Dynamic moisture absorption process combined with offline water detection:

[0054] a) Sample preparation: Place the tobacco particle sample to be tested in a low-field nuclear magnetic resonance sample tube, the specific height of which can be 1 cm. Place the sample tube containing the sample to be tested in a desiccator containing saturated NaCl solution, and remove the sample tube after 24 hours.

[0055] b) Bound water detection: The sample tube to be tested is placed inside the magnet coil of the low-field nuclear magnetic resonance analyzer, and the standard oil sample is calibrated using the Q-FID sequence; the CPMG sequence is used to automatically acquire signals from the sample at timed intervals of 1 hour, and continuous online detection is performed for 24 hours. The specific parameters used in the CPMG sequence are the same as in step (3). The data inversion is performed with ten million iterations to obtain the inversion spectrum, and then the corresponding transverse relaxation time-signal amplitude distribution curve and the peak areas of bound water, immobile water and free water are obtained.

[0056] (6) Quantitative analysis of bound water adsorption during the moisture absorption process: According to the equation in step (4), the bound water adsorption of tobacco particles after 24 hours of moisture absorption at 75% relative humidity is 0.1559 g / g. The moisture adsorption amount measured by online detection is 0.1975 g / g, which is 0.0416 g / g higher than that of the offline detection method, indicating that the accuracy of the online quantitative characterization method is higher, which is 26.68% higher than that of the traditional detection method (Table 1).

[0057] Table 1. Bound water adsorption of tobacco particles under dynamic moisture absorption at 75% RH for 24 hours.

[0058]

[0059] The above embodiments are exemplary embodiments of the present invention and are not intended to limit the present invention in any way. Therefore, based on the overall concept of the present invention, any adjustments and modifications made by those skilled in the art to the described process parameters, as long as they do not deviate from the inventive concept or exceed the scope defined in the claims, should fall within the protection scope of the present invention.

Claims

1. A method for quantitatively characterizing the amount of bound water adsorbed during the dynamic hygroscopic process of tobacco particles, characterized in that: Low-field nuclear magnetic resonance (NMR) technology was used to detect different moisture states in tobacco particles, including bound water, immobile water, and free water. A correlation equation between the dry basis moisture content of tobacco particles and the peak area of ​​bound water was constructed. y 1 By monitoring the dynamic moisture absorption process online in real time, combining the water peak area value and the proportion of the water state, based on... y 1 The amount of bound water adsorbed during the dynamic moisture absorption process of tobacco particles was calculated and then correlated with the moisture absorption time. t Model fitting was performed to establish the correlation equation between the amount of bound water adsorbed and the moisture absorption time during the tobacco particle moisture absorption process. y 2 This establishes a quantitative characterization method for the amount of bound water adsorbed during the moisture absorption process of tobacco particles; specifically, it includes the following steps: (1) Preparation of oven-dried tobacco particles: Weigh 2-3 g of the tobacco particles to be tested and place them in an aluminum box that has been dried to constant weight. Adjust the electric heating constant temperature drying oven to 100±1℃ to dry the tobacco particles to constant weight, and obtain oven-dried tobacco particles, denoted as TG. d The dry basis moisture content WC is obtained by dividing the mass difference of the tobacco particles before and after drying by the mass after drying. d.b. ; (2) Low-field nuclear magnetic resonance (LF-NMR) instrument calibration: The standard oil sample was measured using the FID pulse sequence to calibrate the center frequency of the time-domain nuclear magnetic resonance instrument and the pulse width of the 90° pulse. The sampling frequency, number of samplings, sampling waiting time, analog gain, digital gain and accumulation count of the instrument were determined to ensure the stability and accuracy of the FID signal. (3) TG d Detection of bound water: Dry tobacco particle samples were placed inside the magnet coil of a low-field nuclear magnetic resonance analyzer at a height of 1-3 cm. CPMG sequences were used to acquire signals from the samples. The resulting CPMG sequence attenuation maps were inverted using software to obtain the inversion spectrum, and TG was calculated. d The combined water peak area A TGd ; (4) Construction of the correlation equation between the moisture content of tobacco particles and the peak area of ​​adsorbed bound water: The tobacco particle sample to be tested was placed in an LF-NMR sample tube with a height of 1~3cm. The sample tube containing the sample was placed in a desiccator containing the required saturated salt solution. The sample tube was removed every 24 h, weighed on an electronic balance, and the dry basis moisture content of the tobacco particle sample after dynamic moisture absorption was calculated. The sample was placed in an LF-NMR magnet coil, and the CPMG sequence was used to acquire the signal of the sample. The obtained CPMG sequence attenuation spectrum was inverted by software to obtain the inversion spectrum, and then the corresponding transverse relaxation time-signal amplitude distribution curve and the peak area of ​​bound water A were obtained. TG The dry basis moisture content WC was constructed using model fitting. d.b. and the peak area of ​​adsorbed bound water A TG - A TGd Correlation equation y 1 ; (5) Online detection of bound water during dynamic moisture absorption process: a) Relative humidity correction of the humidity control sample tube: Place the required saturated salt solution in the tray of the humidity control sample tube, and use a real-time humidity detection device to correct the relative humidity in the sample tube. The correction range is 0~100%. b) Sample preparation: Place the tobacco particles to be tested in a low-field nuclear magnetic resonance humidity control sample tube at a height of 1-3 cm; place a saturated salt solution in the tray in the humidity control sample tube to provide the required hygroscopic environment, with an ambient humidity range of 10-98%; and place a rubber stopper at the mouth of the sample tube to seal it. c) Online detection of bound water: The tobacco particle sample to be tested is placed in the magnet coil of a low-field nuclear magnetic resonance analyzer. The CPMG sequence is used to automatically acquire signals from the sample at timed intervals of 1 hour, and the online continuous detection is performed for 24 hours. The obtained CPMG sequence attenuation spectrum can be inverted by software to obtain the inversion spectrum, and then the corresponding transverse relaxation time-signal amplitude distribution curve and the peak areas of bound water, immobile water and free water are obtained. (6) Quantitative analysis of bound water adsorption during dynamic hygroscopic process: The area and proportion of bound water peaks obtained during the dynamic hygroscopic process of tobacco particles were detected online, and the relevant relationship equations were used to analyze the bound water adsorption capacity. y 1 The amount of bound water adsorbed during the dynamic moisture absorption process of tobacco particles was calculated, and a model was used to fit this amount with the moisture absorption time to establish a correlation equation between the amount of bound water adsorbed and the moisture absorption time during the moisture absorption process of tobacco particles. y 2 Thus, a quantitative characterization method for the amount of bound water adsorbed during the moisture absorption process of tobacco particles was established. The specific parameter settings used in the CPMG sequence are as follows: magnetic field center temperature 32.00±0.02℃; main frequency = 21 MHz; sampling frequency = 100 kHz; analog gain = 20.0 dB; digital gain = 3; RF delay = 0.08 ms; 180° pulse width = 8.40 μs; sampling wait time = 6500 ms; echo time = 0.4 ms; number of echoes = 16000; number of accumulations = 16; the data inversion was performed with ten million iterations to obtain the inversion spectrum, and then the corresponding transverse relaxation time-signal amplitude distribution curve and the area of ​​the combined water peak were obtained.

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