Determination of nicotine in cigarettes by spectrophotometry - Master's thesis - Dissertation

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Determination of Nicotine Content in Cigarettes by Spectrophotometry

Key words: spectrophotometer; nicotine cigarette; aesthetic instrument ; UV-1100

1 Introduction Nicotine, also known as nicotine, has the molecular formula C10H14N2 and is one of the highly toxic compounds in tobacco alkaloids. It is an unpleasant, bitter, colorless and transparent oily liquid with strong volatility. It is easily oxidized into dark gray in the air. It can be quickly dissolved in water and alcohol. It is easily absorbed by the mouth, nose and bronchial mucosa. Absorption. Nicotine sticking to the surface of the skin can also be absorbed into the body. There are many methods for determining nicotine in tobacco, such as gas chromatography, liquid chromatography, ion chromatography, and electrochemical methods described in a large number of domestic and foreign literatures. There are many literatures on the determination of nicotine content by spectrophotometry. Based on the previous studies, this paper focuses on the study of the determination of nicotine content by simple spectrophotometry. The theoretical basis of this method is that nicotine will be in alkaline solution. Potassium permanganate is oxidized to form a green product, and the amount of nicotine in the cigarette is obtained by measuring the absorption value of the substance. The method is simple and practical, and has quite good accuracy and sensitivity. It is suitable for analyzing nicotine content in cigarette samples quickly and in small batches, and has practical value. 2 Experimental 2.1 Main instruments and reagents analysis V-1100 spectrophotometer; pHS-5 type acidity meter; digital thermostat water bath HH-2 nicotine standard solution: 1000μg/ml nicotine, imported from Germany high-purity nicotine configuration Potassium permanganate solution, 0.125mol/L: zinc acetate solution, 1.0mol/L; K4Fe(CN)6 solution, 10.6%(w/v), dissolve 6.10g K4Fe(CN)6 ?3H2O in 50ml distilled water . 2.2 Experimental method Prepare to remove the required amount of nicotine, add 2m16.25mol / L NaOH to a 25ml volumetric flask, gently rotate and mix, then add 1.4ml 0.0125mol / L KMnO4, and then add 20ml of distilled water to the volumetric flask, The mixture was heated in a water bath at 100 ° C for 7.5 min, cooled to room temperature and made up to volume with distilled water, shaken and mixed, and the absorbance was measured at 610 nm using a 1 cm absorption cell. 2.3 Calibration curve Under the optimized conditions (CKMnO4 = 7 × 10-4mol / L; CNaOH = 0.5mol / L; heating temperature 100 ° C; heating time 7.5min), the system adheres to the concentration range of 0.1 ~ 7.5μg / ml Beer's law, and as shown in Figure 1, has a correlation coefficient of 0.9996 (n = 6). The detection limit of this method is 0.08 μg / ml. The 4 μg/ml sample was repeatedly measured 10 times, and the reproducibility was good, and the relative deviation was 2.17%. 2.4 Extraction Process of Nicotine The nicotine extraction method adopted in this paper is based on the experimental method of Rai et al. A milled sample of a certain mass of nicotine was placed in a 100 ml beaker, 10 ml of methanol was added, and the mixture was stirred with a glass rod and allowed to stand for 30 min. Add 1ml 2mol / L NaOH and 25ml distilled water, the whole process needs to be stirred. The mixture was heated in a water bath and boiled for 1 min, cooled, filtered through a No. 41 advanced filter paper (0.45 μm) into a 50 ml 2 volumetric flask, the beaker was rinsed and the wash was gently poured out of the flow filter paper to meet the filtrate. 1 ml of zinc acetate solution was added to the filtrate, mixed, and then 1 ml of K4Fe(CN)6 solution was added, shaken and diluted to the mark with distilled water. Centrifuged for 5 min, the supernatant was poured into a 50 ml beaker, and the residue was discarded. Add 1 mg of bleaching earth to the supernatant liquid just obtained, mix and centrifuge for 5 min, discard the supernatant (pour the supernatant), rinse the residue with distilled water and centrifuge again for 5 min. Pour off the supernatant, leave the residue, add 5ml of 0.01mol / L NaOH and heat it. Filter the above solution with No.41 advanced filter paper, the filtrate into a 50ml volumetric flask, dilute to the mark with distilled water, as recommended The procedure analyzes the nicotine content. 3 Results and Discussion Under alkaline conditions, nicotine reacts with KMnO4 to form a green product, which is converted from MnO-4 to MnO2-4. This green product has maximum absorbance at 610 nm (Figure 2). This absorption value is directly related to the content of nicotine and can be used for trace analysis. The order of addition of the absorption spectrum reagents of the reaction solution is very important. During the experiment, KMnO4 was first mixed with NaOH and then added with nicotine. The sensitivity of the experimental results was found to be very low. Then, KMnO4 was mixed with nicotine and heated to form a brown substance. When NaOH was added and heated, the brown substance was added. Will disappear. Later, NaOH was first added to the nicotine, and it was found that a dark blue substance was formed immediately. This phenomenon is similar to the results of previous studies. Therefore, only nicotine, NaOH and KMnO4 are mixed together and heated to form a green substance. The order of addition is nicotine, NaOH, KMnO4. The reaction must depend on various parameter values, such as the amount of KMnO4, NaOH, and the reaction. Conditions such as temperature affect the final reaction results, so consider one by one for better sensitivity. 3.1 Effect of KMnO4 KMnO4 oxidizes nicotine in NaOH solution to form a green product. As a result, it can be seen from the conversion of MnO-4 to MnO2-4, from 1×10-4 mol/L to 1×10-3 mol/L of different concentrations of KMnO4. It was investigated that the highest absorption value can be obtained with a 7×10-4 mol/L KMnO4 solution. Fig. 3 Effect of KMnO4 on color reaction: CNicotine=4.g/mL; CNaOH=0.5mol/L3.2 Effect of NaOH The oxidizability of MnO-4 in alkaline solution can be used to determine organic compounds, which is one of its The most important application. The reaction of nicotine with KMnO4 occurs in a solution containing HaOH as an alkali solution, and KOH can be used instead of NaOH, but its sensitivity is lowered. Therefore, NaOH is selected as the lye, and nicotine is measured at a concentration of 0.025 to 1.5 mol/L NaOH in the experiment. Absorption value, 0.5mol / L NaOH has the best sensitivity, the more the amount of NaOH added, the worse the linearity. 3.3 Effect of temperature As mentioned above, when the solution is heated, green products are produced, so the temperature-dependent conditions are still to be tested. Continuous heating at different water bath temperatures for 7.5 min, the results of the reaction were found to increase the absorption temperature, the maximum absorption value can be reached at 100 ° C water bath temperature, indicating that nicotine has been completely oxidized to form a green product. Effect of temperature on color reaction: CNicotinc=4.g/mL; CKMnO4=7×10-4mol/L; CNaOH=0.5mol/L 3.4 Effect of heating time The length of heating time is also important to ensure the completeness of the reaction. Therefore, the experimental results at different heating times at 100 ° C were also studied. It was found that sufficient reaction occurred in 7.5 min, and the effect of heating time on the color reaction was CNicotine=4.g/mL; CNaOH=0.5 mol/L; CKMnO4 = 7 × 10 -4mol / L 3.5 Nicotine recovery rate determination experiment A certain amount of nicotine standard sample was added to each brand of tobacco sample, extracted and determined according to the experimental method, the tobacco sample was spiked and the recovery rate was determined. Nicotine content / mg added nicotine amount / mg measured value / mg recovery rate /% 1.285.006.1697.61.46 5.00 6.20 94.8 1.205.006.23100.61.40 5.00 6.15 95.0 The average value of each of the three determinations is shown in Table 1, Using this method to determine the nicotine recovery rate is greater than 94%, the recovery is basically complete, which proves that the method is suitable for the determination of nicotine in tobacco. 3.6 Detection of nicotine in cigarettes The nicotine content in tobacco was determined by spectrophotometer. The nicotine content of several brands of cigarettes commonly found in the Chinese market was determined. The wrapper of the cigarette was removed, and the shredded tobacco was dried in an oven at 40 ° C for 30 min and then weighed. Ten cigarettes were weighed separately, shredded, ground into powder, and the same amount of cut tobacco as the standard was weighed and placed in a 100 ml beaker for the extraction step. The amount of nicotine was measured by spectrophotometry under standard conditions, and the results are shown in Table 2. 2 Nicotine content in cigarettes The price of nicotine (mg) measured by the price of cigarettes (mg) —21.201.12—31.101.03—81.201.25—121.201.15—20 1.20 1.23 Note: Each result is determined three times. Average 4 Conclusion The method mentioned above is based on the reaction of nicotine with KMnO4 in NaOH solution, which will form a green product and the product will have an absorption value at 610 nm. This is a simple, relatively fast and certain The method of sensitivity, the chemical reagents involved are rarely a major advantage of this method, and this method can be used to determine the small amount of nicotine in various cigarette samples. Key words: spectrophotometer; nicotine cigarette; aesthetic instrument ; UV-1100

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