Method for measuring total amount of organic acids in tobacco leaves by ultraviolet spectrophotometry

Abstract

The invention discloses a method for measuring the total amount of organic acids in tobacco leaves by ultraviolet spectrophotometry, and relates to the technical field of analytical chemistry, and the method comprises the following steps: taking tobacco leaf powder, adding distilled water, heating in a water bath, cooling to room temperature after the water bath heating is finished, and fixing the volume to obtain a test solution; filtering the test solution to obtain a tobacco leaf extract; the method comprises the following steps: taking multiple parts of tobacco leaf extract liquid, and respectively dropwise adding NaOH solutions with different volumes into the extract liquid to obtain liquid to be detected; detecting the ultraviolet absorption light intensity of the to-be-detected liquid, and judging the titration end point according to the ultraviolet absorption light intensity value of the to-be-detected liquid; and calculating the total amount of the organic acid in the to-be-detected liquid reaching the titration end point. According to the method, the titration end point is judged by measuring the ultraviolet absorption light intensity of the tobacco extract dropwise added with NaOH under the wavelengths of 280 nm and 210 nm through an ultraviolet spectrophotometer, and then the accurate total amount of the organic acids in the tobacco leaves is calculated; the method has the characteristics of simplicity, easiness in use, high efficiency, small error and the like, and has a good application prospect in tobacco leaf total acid detection and analysis.

Description

Technical Field

[0001] The invention relates to the technical field of analytical chemistry, and in particular to a method for determining the total amount of organic acid in tobacco leaves by ultraviolet spectrophotometry. Background Art

[0002] Organic acids are widely present in tobacco, with a content of about 12%-16%. More than 200 kinds of organic acids have been identified in tobacco leaves. Organic acids can increase the acidity, alcohol and smoke of smoke, reduce impurities, and make the smoke sweet and comfortable. Organic acids include volatile low-level fatty acids, semi-volatile high-level fatty acids, and non-volatile dibasic acids and tribasic acids. Non-volatile organic acids are mainly oxalic acid, malic acid and citric acid, which have an important influence on the quality of smoking. They can combine with alkaloids to form salts and adjust the pH of smoke. During the combustion process, the acidic fragments produced by the decomposition of organic acids can adjust the ratio of protonated and free nicotine in the smoke, thereby greatly affecting the strength and taste of tobacco leaves. Therefore, the content of organic acids in flue-cured tobacco leaves has always been highly valued at home and abroad, and has gradually become a research hotspot.

[0003] At present, the methods for determining the total amount of organic acids in tobacco leaves include acid-base neutralization titration and automatic potentiometric titration; the principle of acid-base neutralization titration is to extract all the organic acids in the sample with hot water, and titrate with standard NaOH solution, and calculate the organic acid content in the sample according to the amount of NaOH consumed by the sample; phenolphthalein is used as an indicator, and the solution turns red, which is the titration end point. However, since the test liquid is colored, the error of the indicator in determining the titration end point is large, resulting in inaccurate measurement data. The automatic potentiometric titration method obtains the amount of titration solution used at the titration end point by measuring the electromotive force of the test liquid, and further calculates the organic acid content in the test liquid. Although the automatic potentiometric titration method can accurately determine the titration end point by electromotive force, the determination process is complicated and has high requirements for the test sample. Therefore, it is still necessary to develop a simpler and more universal method for determining the total amount of organic acids in tobacco leaves. Summary of the invention

[0004] The main purpose of the present invention is to provide a method for determining the total amount of organic acids in tobacco leaves by ultraviolet spectrophotometry, aiming to solve the technical problems in the prior art of inaccurate determination data of the total amount of organic acids in tobacco leaves, complex determination process and high requirements for test samples.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] The present invention provides a method for determining the total amount of organic acids in tobacco leaves by ultraviolet spectrophotometry, which is characterized by comprising the following steps:

[0007] (1) taking tobacco leaf powder, adding distilled water and heating in a water bath, cooling to room temperature after the water bath heating is completed and constant volume is obtained to obtain a test solution; filtering the test solution to obtain a tobacco leaf extract;

[0008] (2) taking a tobacco leaf extract, and sequentially adding different volumes of NaOH solution to the tobacco leaf extract to obtain a test solution;

[0009] (3) detecting the ultraviolet absorption intensity of the test solution to which different volumes of NaOH solution are added, and determining the titration end point by the ultraviolet absorption intensity value of the test solution;

[0010] (4) Calculate the total amount of tobacco organic acids in the test solution that reaches the titration endpoint using the formula.

[0011] Specifically, by adopting the above method, the ultraviolet absorption intensity of the tobacco extract with different volumes of NaOH added is measured by ultraviolet spectrophotometer to determine the titration endpoint, thereby quickly and accurately quantifying the total amount of organic acids in tobacco leaves.

[0012] Furthermore, in step (1), the mass volume ratio of the tobacco leaf powder to distilled water is 0.05-0.1:1 g / mL.

[0013] Furthermore, the water bath heating in step (1) is: heating in a water bath at 75°C to 80°C for 0.4 to 0.6h.

[0014] Furthermore, in step (2), the volume ratio of the tobacco leaf extract to the NaOH solution is 1:1.5; and the concentration of the NaOH solution is 0.1 mol / L.

[0015] Furthermore, the ultraviolet absorption intensity in step (3) is determined by adjusting the absorbance of the ultraviolet spectrophotometer to between 0.2 and 0.8, the detection wavelength is 190 to 1000 nm, a background scan is performed using distilled water as a blank sample, and the ultraviolet absorption intensity of the test solution to which different volumes of NaOH are added is detected.

[0016] Furthermore, the titration endpoint is reached when the ultraviolet absorption intensity of the test solution at wavelengths of 280 nm and 210 nm is 54 and 207, respectively.

[0017] Furthermore, the calculation formula for the total amount of organic acid in tobacco leaves is:

[0018]

[0019] P——total organic acid content;

[0020] V——the volume of standard sodium hydroxide solution consumed when titrating the sample solution, mL;

[0021] V 0——The volume of standard sodium hydroxide solution consumed when titrating the blank, mL;

[0022] C——molar concentration of sodium hydroxide solution, mol / L;

[0023] m——mass of the sample, g;

[0024] ω——moisture content of the sample, %;

[0025] K – coefficient converted to appropriate acid: lactic acid 0.090, malic acid 0.067, acetic acid 0.060, citric acid 0.070, tartaric acid 0.075.

[0026] The beneficial effects of the present invention are:

[0027] The invention determines the titration end point by measuring the ultraviolet absorption intensity of the tobacco extract to which NaOH is added at wavelengths of 280nm and 210nm by an ultraviolet spectrophotometer, and then calculates the accurate total amount of tobacco leaf organic acid by a formula; the determination method has the characteristics of being simple and easy to use, high in efficiency, and small in error. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a graph showing the variation of the ultraviolet absorption light intensity with the amount of NaOH added in Example 1 of the present invention;

[0029] Figure 2 This is a graph showing the variation of the ultraviolet absorption light intensity of the test solution at a wavelength of 280 nm with the amount of NaOH added in Example 1 of the present invention;

[0030] Figure 3 This is another graph showing the variation of the ultraviolet absorption light intensity of the test solution at a wavelength of 280 nm with the amount of NaOH added in Example 1 of the present invention. DETAILED DESCRIPTION

[0031] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0032] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0033] The tobacco leaves in the following examples are tobacco leaves from different regions provided by the Dali Redrying Factory and are marked as 1 to 10. The main veins of tobacco leaf samples 1 to 10 are removed, dried in an oven at 40°C for 20 minutes, crushed with a grinder and passed through a 40-mesh sieve, and the sieved samples are collected and placed in an environment with a temperature of 23°C and a relative humidity of 60% for equilibration for 24 hours to obtain tobacco leaf powders 1 to 10.

[0034] Example 1

[0035] (1) Weigh 20 g of tobacco leaf powder 1 and place it in a volumetric flask. Add 150 mL of distilled water and transfer the sample to a 250 mL volumetric flask. Heat in a water bath at 80°C for 0.5 h. After cooling, adjust the volume to 250 mL. Filter with dry filter paper and a funnel to collect the tobacco leaf extract.

[0036] (2) Take 50 mL of tobacco leaf extract and add it into a 250 mL conical flask. Add 8 mL of 0.1 mol / L NaOH solution dropwise each time until the volume of NaOH added reaches 128 mL.

[0037] (3) After the NaOH solution added each time is evenly mixed with the tobacco leaf extract, 0.5 mL of the solution is taken out and transferred to a 100 mL volumetric flask for constant volume (diluted 200 times), and then placed in a cuvette for detection. Each sample is tested twice, and the detection wavelength is 190-1000 nm. A total of 17 samples are tested. The specific experimental process is to turn on the UV-visible spectrophotometer instrument and scan the solvent blank sample as the background to exclude the influence of the solvent itself. Deionized water is used as the blank sample in this experiment.

[0038] The UV detection data of the diluted sample is shown in the figure Figure 1 The specific data are shown in Table 1 (the 17th group of data is discarded in Table 1 because the 17th group of data is inaccurate). Figure 1 It is the light absorption intensity of NaOH solution with different concentrations added after dilution by a certain multiple at 200nm-400nm (since there is no absorption peak after 400nm, the data before 400nm is intercepted); Figure 2 and Figure 3 The absorbance of the undiluted NaOH sample solutions at 210nm and 280nm ( Figure 2 and Figure 3 is through Figure 1 The absorbance at different wavelengths is multiplied by the dilution factor. Figure 1 , Figure 2 and Figure 3It can be seen from Table 1 that when the amount of NaOH added increased from 72 mL to 80 mL, the absorption of the solution at 210 nm and 280 nm decreased significantly and then decreased gradually. Therefore, this point is the detection end point, from which the total amount of organic acids in tobacco leaves can be inferred.

[0039] Table 1

[0040]

[0041] Example 2

[0042] Weigh 20g of tobacco powder 2 from Dali Redrying Plant, transfer the sample into a 250mL volumetric flask with 150mL distilled water, heat in a 75℃ water bath for 0.6h, cool and dilute to 250mL, filter with dry filter paper and funnel, collect tobacco extract; then add 50mL tobacco extract into a 250mL conical flask, add 8mL of 0.1mol / L NaOH solution each time, and measure the ultraviolet absorption light intensity of the tobacco extract titrated by NaOH by ultraviolet spectrophotometer, and stop titration when the ultraviolet absorption light intensity at 280nm and 210nm wavelengths is 54 and 207 respectively. The total amount of organic acid in tobacco leaves from Dali Redrying Plant is 10.28% (reference value 10.28%) calculated by the formula, and the solution pH of the tobacco extract titrated by NaOH is 8.22 measured by the acidometer, and the theoretical pH value of the titration end point is 8.2.

[0043] Embodiment 3:

[0044] Weigh 20g of tobacco powder 3 from Dali Redrying Plant, transfer the sample into a 250mL volumetric flask with 150mL distilled water, heat in a water bath at 80℃ for 0.4h, cool and dilute to 250mL, filter with dry filter paper and funnel, collect tobacco extract; then add 50mL tobacco extract into a 250mL conical flask, add 8mL of 0.1mol / L NaOH solution each time, and measure the ultraviolet absorption light intensity of the tobacco extract titrated by NaOH by ultraviolet spectrophotometer, and stop titration when the ultraviolet absorption light intensity at 280nm and 210nm wavelengths is 54 and 207 respectively. The total amount of organic acid in tobacco leaves from Dali Redrying Plant is 9.87% (reference value 9.87%) calculated by the formula, and the solution pH of the tobacco extract titrated by NaOH is 8.21 measured by the acidometer, and the theoretical pH value of the titration end point is 8.2.

[0045] Embodiment 4:

[0046] Weigh 20g of Dali redrying factory tobacco powder 4, transfer the sample into a 250mL volumetric flask with 150mL distilled water, heat in a water bath at 80℃ for 0.5h, cool and dilute to 250mL, filter with dry filter paper and funnel, collect tobacco extract; then add 50mL tobacco extract into a 250mL conical flask, add 8mL of 0.1mol / L NaOH solution each time, and measure the ultraviolet absorption light intensity of the tobacco extract titrated by NaOH by ultraviolet spectrophotometer, and stop titration when the ultraviolet absorption light intensity at 280nm and 210nm wavelengths is 54 and 207 respectively. The total amount of organic acid in Dali redrying factory tobacco is 11.06% (reference value 11.07%) calculated by the formula, and the solution pH of the tobacco extract titrated by NaOH is 8.19 measured by the acidometer, and the theoretical pH value of the titration end point is 8.2.

[0047] Example 5

[0048] Weigh 20g of Dali redrying factory tobacco powder 5, transfer the sample into a 250mL volumetric flask with 150mL distilled water, heat in a water bath at 75℃~80℃ for 0.5h, cool and dilute to 250mL, filter with dry filter paper and funnel, collect tobacco extract; then add 50mL tobacco extract into a 250mL conical flask, add 8mL of 0.1mol / LNaOH solution dropwise each time, and measure the ultraviolet absorption light intensity of the tobacco extract titrated by NaOH by ultraviolet spectrophotometer, and stop titration when the ultraviolet absorption light intensity at 280nm and 210nm wavelengths is 54 and 207 respectively. The total amount of organic acid in Dali redrying factory tobacco is 10.60% (reference value 10.61%) calculated by formula, and the solution pH of the tobacco extract titrated by NaOH is 8.19 measured by acidometer, and the theoretical pH value of the titration end point is 8.2.

[0049] Embodiment 6:

[0050] First, accurately weigh 20g of Dali redrying factory tobacco powder 6, transfer the sample into a 250mL volumetric flask with 150mL distilled water, heat in a water bath at 75℃~80℃ for 0.5h, cool and dilute to 250mL, filter with dry filter paper and funnel, and collect the tobacco extract; then add 50mL of tobacco extract into a 250mL conical flask, add 8mL of 0.1mol / L NaOH solution each time, and measure the ultraviolet adsorption intensity of the tobacco extract titrated by NaOH by ultraviolet spectrophotometer, and stop titration when the ultraviolet absorption intensity at 280nm and 210nm wavelengths is 54 and 207 respectively. The total amount of organic acid in Dali redrying factory tobacco is 8.48% (reference value 8.48%) calculated by the formula, and the solution pH of the tobacco extract titrated by NaOH is 8.21 measured by the acidometer, and the theoretical pH value of the titration end point is 8.2.

[0051] Embodiment 7:

[0052] First, accurately weigh 20g of Dali redrying factory tobacco powder 7, transfer the sample into a 250mL volumetric flask with 150mL distilled water, heat in a water bath at 75℃~80℃ for 0.5h, cool and dilute to 250mL, filter with dry filter paper and funnel, and collect the tobacco extract; then add 50mL of tobacco extract into a 250mL conical flask, add 8mL of 0.1mol / L NaOH solution each time, and measure the ultraviolet adsorption intensity of the tobacco extract titrated by NaOH by ultraviolet spectrophotometer, and stop titration when the ultraviolet absorption intensity at 280nm and 210nm wavelengths is 54 and 207 respectively. The total amount of organic acid in Dali redrying factory tobacco is 10.72% (reference value 10.71%) calculated by the formula, and the solution pH of the tobacco extract titrated by NaOH is 8.21 measured by the acidometer, and the theoretical pH value of the titration end point is 8.2.

[0053] Embodiment 8:

[0054] First, accurately weigh 20g of Dali redrying factory tobacco powder 8, transfer the sample into a 250mL volumetric flask with 150mL distilled water, heat in a water bath at 75℃~80℃ for 0.5h, cool and dilute to 250mL, filter with dry filter paper and funnel, and collect the tobacco extract; then add 50mL of tobacco extract into a 250mL conical flask, add 8mL of 0.1mol / L NaOH solution each time, and measure the ultraviolet adsorption intensity of the tobacco extract titrated by NaOH by ultraviolet spectrophotometer, and stop titration when the ultraviolet absorption intensity at 280nm and 210nm wavelengths is 54 and 207 respectively. The total amount of organic acid in Dali redrying factory tobacco is 9.08% (reference value 9.08%) calculated by the formula, and the solution pH of the tobacco extract titrated by NaOH is 8.19 measured by the acidometer, and the theoretical pH value of the titration end point is 8.2.

[0055] Embodiment 9:

[0056] First, accurately weigh 20g of Dali redrying factory tobacco powder 9, transfer the sample into a 250mL volumetric flask with 150mL distilled water, heat in a water bath at 75℃~80℃ for 0.5h, cool and dilute to 250mL, filter with dry filter paper and funnel, and collect the tobacco extract; then add 50mL of tobacco extract into a 250mL conical flask, add 8mL of 0.1mol / L NaOH solution each time, and measure the ultraviolet adsorption intensity of the tobacco extract titrated by NaOH by ultraviolet spectrophotometer, and stop titration when the ultraviolet absorption intensity at 280nm and 210nm wavelengths is 54 and 207 respectively. The total amount of organic acid in Dali redrying factory tobacco is 8.94% (reference value 8.94%) calculated by the formula, and the solution pH of the tobacco extract titrated by NaOH is 8.20 measured by the acidometer, and the theoretical pH value of the titration end point is 8.2.

[0057] Embodiment 10:

[0058] First, accurately weigh 20g of Dali redrying factory tobacco powder 10, transfer the sample into a 250mL volumetric flask with 150mL distilled water, heat in a water bath at 75℃~80℃ for 0.5h, cool and dilute to 250mL, filter with dry filter paper and funnel, and collect the tobacco extract; then add 50mL of tobacco extract into a 250mL conical flask, add 8mL of 0.1mol / L NaOH solution each time, and measure the ultraviolet adsorption intensity of the tobacco extract titrated by NaOH by ultraviolet spectrophotometer, and stop titration when the ultraviolet absorption intensity at 280nm and 210nm wavelengths is 54 and 207 respectively. The total amount of organic acid in Dali redrying factory tobacco is 11.72% (reference value 11.73%) calculated by the formula, and the solution pH of the tobacco extract titrated by NaOH is 8.19 measured by the acidometer, and the theoretical pH value of the titration end point is 8.2.

[0059] In summary, the present invention determines the titration endpoint by measuring the ultraviolet absorption intensity of the tobacco extract to which different volumes of NaOH are added at wavelengths of 280nm and 210nm by an ultraviolet spectrophotometer, and then calculates the accurate total amount of organic acids in the tobacco leaf by a formula; the determination method has the characteristics of being simple and easy to use, high efficiency, and small error.

[0060] The specific implementation methods of the invention are described in detail above, but they are only examples, and the invention is not limited to the specific implementation methods described above. For those skilled in the art, any equivalent modification or substitution of the invention is also within the scope of the invention, therefore, the equalization, modification, improvement, etc. made without departing from the spirit and principle of the invention should be included in the scope of the invention.

Claims

1. A method for determining the total amount of organic acids in tobacco leaves by ultraviolet spectrophotometry, characterized in that: The steps include: (1) taking tobacco leaf powder, adding distilled water and heating in a water bath, cooling to room temperature after the water bath heating is completed and constant volume is obtained to obtain a test solution; filtering the test solution to obtain a tobacco leaf extract; (2) taking a tobacco leaf extract, and sequentially adding different volumes of NaOH solution to the tobacco leaf extract to obtain a test solution; (3) detecting the ultraviolet absorption intensity of the test solution to which different volumes of NaOH solution are added, and determining the titration end point by the ultraviolet absorption intensity value of the test solution; (4) Calculate the total amount of tobacco organic acids in the test solution that reaches the titration endpoint using the formula.

2. The method for determining the total amount of organic acids in tobacco leaves by ultraviolet spectrophotometry according to claim 1, characterized in that: The mass volume ratio of the tobacco leaf powder to distilled water in step (1) is 0.05-0.1:1 g / mL.

3. The method for determining the total amount of organic acids in tobacco leaves by ultraviolet spectrophotometry according to claim 1, characterized in that: The water bath heating in step (1) is: heating in a water bath at 75° C. to 80° C. for 0.4 to 0.6 h.

4. The method for determining the total amount of organic acids in tobacco leaves by ultraviolet spectrophotometry according to claim 1, characterized in that: In step (2), the volume ratio of the tobacco leaf extract to the NaOH solution is 1:1.5; the concentration of the NaOH solution is 0.1 mol / L.

5. The method for determining the total amount of organic acids in tobacco leaves by ultraviolet spectrophotometry according to claim 1, characterized in that: The ultraviolet absorption intensity of step (3) is determined as follows: the absorbance of the ultraviolet spectrophotometer is adjusted to between 0.2 and 0.8, the detection wavelength is 190 to 1000 nm, distilled water is used as a blank sample for background scanning, and the ultraviolet absorption intensity of the test solution to which different volumes of NaOH are added is detected.

6. The method for determining the total amount of organic acids in tobacco leaves by ultraviolet spectrophotometry according to claim 5, characterized in that: The titration endpoint is reached when the ultraviolet absorption intensity of the test solution at wavelengths of 280nm and 210nm is 54 and 207 respectively.

7. The method for determining the total amount of organic acids in tobacco leaves by ultraviolet spectrophotometry according to claim 5, characterized in that: The calculation formula for the total amount of organic acid in tobacco leaves is: P——total organic acid content; V——the volume of standard sodium hydroxide solution consumed when titrating the sample solution, mL; V0——the volume of standard sodium hydroxide solution consumed when titrating the blank, mL; C——molar concentration of sodium hydroxide solution, mol / L; m——mass of the sample, g; ω——moisture content of the sample, %; K – coefficient converted to appropriate acid: lactic acid 0.090, malic acid 0.067, acetic acid 0.060, citric acid 0.070, tartaric acid 0.075.

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