A method for quickly detecting moisture in tobacco leaf processing

Abstract

The invention discloses a method for quickly detecting moisture in tobacco leaf processing. 2+ As the precursor material, dimethyl sulfoxide (DMSO) was used as the solvent. Solvent-dependent rhein-based carbon dots were prepared by microwave method. The interaction between water and aprotic solvent DMSO was used to reduce the fluorescence signal of carbon dots. Combined with smartphone RGB signal acquisition technology, a new method with high sensitivity and selectivity for moisture determination was established by using the good linear relationship between moisture content and R value. The detection limit was 5 mg. This method was applied to the detection and analysis of moisture content in tobacco leaf processing, and the results were consistent with those of the reduced pressure drying method. The method is simple, stable and accurate.

Description

Technical Field

[0001] The invention relates to the technical field of chemical analysis and detection, and in particular to a method for quickly detecting moisture in a tobacco leaf processing process. Background Art

[0002] During tobacco leaf processing, moisture content is particularly important for the initial baking and re-baking of tobacco leaves. Moisture content is one of the technical indicators of tobacco processing, and it plays a vital role in improving the quality of tobacco leaves, subsequent aging of tobacco leaves, and preventing mildew. During tobacco leaf processing, due to different processes, the moisture content of tobacco leaves needs to be adjusted repeatedly. Accurately determining the moisture content of tobacco leaves during tobacco leaf processing is of great significance to tobacco technology. Existing moisture determination technologies mainly include Fischer's method, gravimetric analysis (including atmospheric drying, vacuum drying and thermogravimetric analysis), fluorescent probes, gas chromatography and near-infrared spectroscopy. At present, gravimetric analysis is commonly used for the determination of moisture in tobacco leaf processing. The moisture in tobacco leaves is first determined by vacuum drying, and the processing technology is adjusted using the feedback of the moisture determination results. However, there are large differences in the moisture content of tobacco leaves in different batches, and the existing methods have the disadvantages of long detection time, cumbersome detection process, and difficulty in on-site use, which leads to great difficulties in moisture determination during tobacco leaf processing. The fluorescent probe method has the characteristics of sensitive detection, portability, simplicity and low cost, and has certain advantages in establishing and developing new moisture determination technologies.

[0003] Carbon dots are a type of carbon nanoparticles with a size less than 10nm. Due to their surface defects and other reasons, carbon dots have luminescent properties. Depending on the synthesis materials and methods, different functional groups can be modified on the surface of carbon dots to adjust the fluorescence and other properties. Using carbon dots as fluorescent probes to measure moisture content has the characteristics of simple synthesis, easy access to materials, and simple and fast detection methods. Smartphone-based colorimetry is an emerging rapid detection method in recent years. It has attracted much attention due to its simple equipment and flexible operation. Using a smartphone to record the color related to the concentration of the component to be measured, combined with software, the depth of the color is numerically represented. According to the difference in RGB value, grayscale, etc., colorimetric determination is performed with a standard solution of known concentration to achieve quantitative determination of the target. This method can overcome the disadvantage that visual colorimetry cannot be quantitatively determined, and does not require large instruments, is low in cost, and can achieve real-time detection on site.

[0004] The present invention uses rhein and magnesium nitrate as precursor materials and dimethyl sulfoxide (DMSO) as solvent to prepare solvent-dependent rhein-based carbon dots. The fluorescence quenching effect of water on carbon dots is used. Based on the linear relationship between moisture content and carbon dot fluorescence intensity, a new method for moisture detection with high sensitivity and selectivity is established, with a detection limit of 5 mg. In order to achieve rapid acquisition of fluorescence signals and rapid determination of moisture, the study combines smartphone signal acquisition technology and uses RGB value colorimetry to achieve rapid determination of moisture in tobacco leaf processing. The method has strong temperature tolerance, fast detection speed, and can achieve rapid analysis of moisture content. Summary of the invention

[0005] The purpose of the present invention is to provide a method for quickly detecting moisture in tobacco leaf processing, a method for detecting moisture in tobacco leaf processing by quenching carbon dot fluorescence signals by water molecules, and a new method for detecting moisture in tobacco leaf processing by combining smartphone RGB signal acquisition technology.

[0006] A method for quickly detecting moisture in tobacco leaf processing comprises the following steps:

[0007] (1) Preparation of rhein-based carbon dots: Accurately weigh 0.1 g of magnesium nitrate and add it to 20 mL of 1 mM rhein (DMSO) solution. After dissolution, place it in a microwave digester and microwave heat it at 180°C for 30 min. After taking it out, cool it naturally at room temperature to obtain a light yellow solution. After centrifugation at 10,000 r / min for 15 min, filter it with a 0.22 μm organic filter membrane to obtain rhein-based carbon dots.

[0008] (2) Preparation of water content working curve: 10 μL of rhein-based carbon dots was taken and diluted to 3 mL with anhydrous ethanol. Different amounts of deionized water ranging from 30 to 1000 mg were added and the volume was fixed to 4 mL with anhydrous ethanol. After vortex mixing, the mixture was allowed to stand for 2 min. The emission intensity at 605 nm was measured under an excitation wavelength of 525 nm. The standard curve was drawn with the water content as the horizontal axis and the fluorescence intensity at 605 nm as the vertical axis to obtain the regression equation.

[0009] (3) Tobacco sample processing

[0010] First, cut the tobacco leaves into shreds, accurately weigh 1.0g of shredded tobacco sample, place it in a sealed and dry 20mL conical flask, and heat it at 90℃ for 10min. The generated gas is continuously introduced into the carbon dot solution, and the generated water vapor is completely introduced into the carbon dot solution by injecting dry air with a syringe. After the reaction is completed, the volatilized ethanol is supplemented and the fluorescence intensity of the system is measured.

[0011] (4) Determination of sample moisture content:

[0012] Take 10 μL of rhein carbon dots and dilute it to 3 mL with anhydrous ethanol as the working solution for fluorescence intensity measurement. According to the operation method in step (3), all the water in the sample is introduced into the working solution, and the volume is fixed to 4 mL with anhydrous ethanol. Under the excitation light wavelength of 525 nm, the emission light intensity at 605 nm is measured. The moisture content in the tobacco is calculated by the working curve established in step (2).

[0013] (5) RGB signal acquisition:

[0014] In a light-proof box, a smart phone is used to place the sample treated in step (3) in a light-proof box under 365nm ultraviolet light, and the shooting angle and shooting parameters of the mobile phone are kept consistent. The original camera mode, autofocus, and flash are turned off to collect images of the sample in the colorimetric dish. After the image signal is collected, the image is processed using Adobe Photoshop CC software, and the edges of the colorimetric dish are cut off, only the image of the sample solution is retained, and the RGB values ​​of three points in the image are randomly read using a software tool, and the R value is taken as the average value. The standard curve is drawn with the water content as the horizontal coordinate and the R value as the vertical coordinate. According to the standard curve, the water content in the sample is determined under the same conditions.

[0015] The rhein-based carbon dots are prepared by the following method: magnesium nitrate and rhein are used as precursor materials, dissolved in dimethyl sulfoxide (DMSO), and heated at 180°C for 30 minutes by microwave method. After natural cooling at room temperature, a light yellow solution is obtained, which is centrifuged at 10,000 r / min for 15 minutes and filtered with a 0.22 μm organic filter membrane. The weight ratio of magnesium nitrate, rhein, and DMSO is 0.05-0.2: 0.001-0.01: 15-30.

[0016] The microwave preparation conditions of the carbon dots are reaction time of 10-60 min and temperature of 150-220°C.

[0017] The advantages of the present invention are:

[0018] 1. The present invention utilizes the fluorescence quenching effect of water on rhein-based carbon dots, based on the linear relationship between water content and fluorescence intensity, combined with smartphone RGB signal acquisition technology, to establish a new method for moisture detection with high sensitivity and high temperature tolerance. The method has the characteristics of high sensitivity, fast detection speed, and the ability to realize on-site measurement.

[0019] 2. Using rhein and magnesium nitrate as precursor materials and microwave treatment, carbon dots can have significant solvent dependence, so that the interaction between protic solvents (i.e., water molecules) and non-protic solvents (i.e., rhein-based carbon dot solutions) can be used to achieve fluorescence determination of water. In actual sample determination, the water content can be quickly determined.

[0020] 3. The research combines the RGB signal acquisition technology of smartphones to avoid the use of fluorescence spectrometers and realize the on-site measurement needs of moisture determination in actual use. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the fluorescence quenching spectrum of the water content on the rhein-based carbon dots in Example 1, which is used for water content detection.

[0022] Figure 2 , Figure 3 The linear relationship diagrams of moisture content, fluorescence intensity and R value of carbon dots respectively show that rhein-based carbon dots have a better effect in determining moisture content. DETAILED DESCRIPTION

[0023] The technical solution of the present invention will be further described in detail below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0024] Example 1: Determination of Moisture Content in Cut Tobacco

[0025] 1. Preparation of rhein-based carbon dots: Accurately weigh 0.1 g of magnesium nitrate and add it to 20 mL of 1 mM rhein (DMSO dissolved) solution. After dissolution, place it in a TOP wave microwave digestion instrument and microwave digest it at 180°C for 30 min. After taking it out, cool it naturally at room temperature to obtain a light yellow solution. After centrifugation at 10,000 r / min for 15 min, finally filter it with a 0.22 μm organic filter membrane to obtain rhein-based carbon dots.

[0026] 2. Preparation of water content working curve: Take 10 μL of rhein-based carbon dots, dilute to 3 mL with anhydrous ethanol, add different amounts of deionized water from 30 to 1000 mg, and dilute to 4 mL with anhydrous ethanol. Vortex mix, let stand for 2 minutes, measure the emission light intensity at 605 nm under an excitation wavelength of 525 nm, draw a standard curve with water content as the horizontal axis and fluorescence intensity at 605 nm as the vertical axis, and obtain the regression equation. Figure 1 and Figure 2 , and obtain the fluorescence quenching spectrum, regression equation and correlation coefficient.

[0027] 3. Sample treatment: Accurately weigh 1.0g of tobacco sample, place it in a sealed and dry 20mL conical flask, and heat it at 90℃ for 10min. Introduce the generated gas into the carbon dot solution continuously, and use a syringe to inject dry air to introduce all the generated water vapor into the carbon dot solution. After the reaction is completed, replenish the volatilized ethanol and measure the fluorescence intensity of the system.

[0028] 4. Fluorescence determination of water content in samples: Take 10 μL of rhein carbon dots and dilute it to 3 mL with anhydrous ethanol as the working solution for fluorescence intensity determination. According to the operation method in step 3, all the water in the tobacco sample is introduced into the working solution, and the volume is fixed to 4 mL with anhydrous ethanol. Under the excitation light wavelength of 525 nm, the emission light intensity at 605 nm is measured. Through the working curve established in step 2, the moisture content in the tobacco is calculated to be 143.4 mg / g.

[0029] 5. RGB colorimetric determination of water content in samples: Place the sample treated in step (3) in a light-proof box using a smartphone under 365nm ultraviolet light, keep the shooting angle and shooting parameters of the phone consistent, use the original camera mode, autofocus, and turn off the flash to capture images of the sample in the cuvette. After the image signal is collected, use Adobe Photoshop CC software to process the image, crop the edges of the cuvette, and only retain the image of the sample solution. Use the software tool to randomly read the RGB values ​​of three points in the image, take the average R value, and draw a standard curve with the water content as the horizontal axis and the R value as the vertical axis. See Figure 3 , the regression equation and correlation coefficient between moisture content and R value can be obtained. The moisture content in the tobacco is calculated to be 144.1 mg / g.

[0030] 5. Comparative test experiment: The above-mentioned fluorescence and RGB colorimetric methods were used to determine the moisture content of the same batch of tobacco leaves during processing, and compared with the vacuum drying method. Weigh 3 groups of tobacco samples with the same moisture content and add different amounts of water. Each spike was measured in parallel 3 times, and the spike recovery rate (%) and relative standard deviation (RSD) were calculated. The results are shown in Table 1. It can be seen from the table that the recovery rate of moisture content measured by fluorescence and RGB colorimetry is in the range of 95.43-99.33%, and the RSD is in the range of 3.3% to 4.6%, which is consistent with the results of vacuum drying method, indicating that this method has good accuracy and precision. Compared with the vacuum drying method, the RGB colorimetric method has a shorter operation time, and can realize on-site determination of sample moisture, and does not require large-scale instruments and equipment, and has low cost.

[0031] Table 1 Spiked determination results and RSD (n=3)

[0032]

[0033] Example 2: Determination of moisture content in first-cured tobacco leaves

[0034] 1. Preparation of rhein-based carbon dots: same as in Example 1;

[0035] 2. Preparation of water content working curve: same as in Example 1;

[0036] 3. Treatment of the first-cured tobacco leaves: first cut the tobacco leaves into small pieces, then take 1.0 g of tobacco leaf small pieces sample, and the subsequent steps are the same as those in Example 1;

[0037] 4. Fluorescence determination of water content in the sample: Same as Example 1. The water content in the sample was calculated to be 175.1 mg / g;

[0038] 5. RGB colorimetric determination of water content in the sample: Same as Example 1. The water content in the sample is calculated to be 174.3 mg / g;

[0039] Example 3: Determination of moisture content in redried tobacco leaves

[0040] 1. Preparation of rhein-based carbon dots: same as in Example 1;

[0041] 2. Preparation of water content working curve: same as in Example 1;

[0042] 3. Treatment of redried tobacco leaves: same as in Example 2;

[0043] 4. Fluorescence determination of water content in the sample: Same as Example 1. The water content in the sample was calculated to be 134.1 mg / g;

[0044] 5. RGB colorimetric determination of water content in the sample: Same as Example 1. The water content in the sample is calculated to be 133.9 mg / g;

[0045] In order to evaluate the accuracy of the determination of this method, under the same conditions, 1.0g of tobacco sample was placed in a constant weight weighing dish, the weighing dish was placed in a vacuum drying oven and heated to 80°C, the vacuum pressure was 50KPa-60KPa, and after drying for 12 hours, it was placed in a dryer and cooled for 0.5 hours, and finally weighed to constant weight to determine the moisture content. The results were compared with the results of the method of the present invention in Examples 1-3, and the results are shown in Table 2. It can be seen from the results that the results of the two methods are consistent.

[0046] Table 2 Spiked recovery and relative standard deviation (mg / g)

[0047]

[0048] The method for determining moisture content in tobacco leaf processing established by the present invention has strong temperature tolerance, fast detection speed, low processing cost, simple operation, and no need for large-scale instruments and equipment, and has strong advantages in on-site monitoring. 2+As the precursor material, dimethyl sulfoxide (DMSO) was used as the solvent. Solvent-dependent rhein-based carbon dots were prepared by microwave method. The interaction between water and aprotic solvent DMSO was used to reduce the fluorescence signal of carbon dots. Combined with smartphone RGB signal acquisition technology, a new method with high sensitivity and selectivity for moisture determination was established by using the good linear relationship between moisture content and R value. The detection limit was 5 mg. This method was applied to the detection and analysis of moisture content in tobacco leaf processing, and the results were consistent with those of the reduced pressure drying method. The method is simple, stable and accurate.

Claims

1. A method for rapidly detecting moisture in tobacco leaf processing, comprising the following steps: (1) Preparation of rhein-based carbon dots: Accurately weigh 0.1 g of magnesium nitrate and add it to 20 mL of 1 mM DMSO solution of rhein. After dissolution, place it in a microwave digester and heat it at 180°C for 30 min. After taking it out, cool it naturally at room temperature to obtain a light yellow solution. Centrifuge it at 10,000 r / min for 15 min and filter it with a 0.22 μm organic filter membrane to obtain rhein-based carbon dots. (2) Preparation of water content working curve: Take multiple groups of 10 μL rhein-based carbon dots, dilute to 3 mL with anhydrous ethanol, add different amounts of deionized water (30-1000 mg) respectively, and make up to 4 mL with anhydrous ethanol; after vortex mixing, let it stand for 2 min, and measure the emission intensity at 605 nm under an excitation wavelength of 525 nm. Plot a standard curve with water content as the horizontal axis and fluorescence intensity at 605 nm as the vertical axis to obtain the regression equation; (3) Tobacco sample processing: First, 1.0 g of tobacco sample was accurately weighed and placed in a sealed and dry 20 mL conical flask, and heated at 90°C for 10 min. The generated gas was continuously introduced into the carbon dot solution, and the generated water vapor was completely introduced into the carbon dot solution by injecting dry air with a syringe. After the reaction was completed, the volatilized ethanol was supplemented and the fluorescence intensity of the system was measured. (4) Determination of sample moisture content: Take 10 μL of rhein carbon dots and dilute it to 3 mL with anhydrous ethanol as the working solution for fluorescence intensity measurement. According to the operation method in step (3), all the water in the sample is introduced into the working solution. After the volume is fixed to 4 mL with anhydrous ethanol; under the excitation wavelength of 525 nm, measure the emission light intensity at 605 nm; calculate the moisture content in the tobacco by the working curve established in step (2); (5) RGB signal acquisition: In a light-proof box, use a smart phone to place multiple groups of working solutions in step (2) in a light-proof box under 365 nm ultraviolet light, keep the shooting angle and shooting parameters of the mobile phone consistent, use the original camera mode, auto focus, and turn off the flash to collect images of the samples in the cuvette; after the image signal is collected, use Adobe Photoshop CC software to process the image, crop the edge of the cuvette, and only retain the image of the sample solution, and use the software tool to randomly read the RGB values ​​of three points in the image, take the average value of the R value, and draw a standard curve with the water content as the horizontal axis and the R value as the vertical axis; according to the standard curve, determine the water content in the sample under the same conditions.

2. The method for rapidly detecting moisture in tobacco leaf processing according to claim 1, characterized in that: In step (1), the microwave preparation conditions of carbon dots are reaction time 10-60 min and temperature 150-220°C.

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