Ind. Eng. Chem. Res. 1994,33,3238-3240
3238
Distribution Coefficients of Nicotine between Hexane and Water D. Leslie C. Millen' and W. Raymond Murphy Department of Chemical Engineering, The Queen's University of Belfast, Belfast, Northern Ireland
The influence of initial nicotine concentration, temperature, and pH on the distribution coefficients of nicotine between hexane and water has been studied. The coefficient was found to be independent of initial concentration, over the range studied, but was temperature and pH dependent. al. (1950) as
Introduction Solvent extraction is an operation which has traditionally been used for the recovery of nicotine from tobacco extracts. The solvent which has most frequently been used is kerosene and a number of workers have reported studies on this system. Norton (1940) studied the distribution coefficient of nicotine between water and kerosene at 25 "C and concentrations of 0.01 t o more than 500 g of nicotinek of solution. Claffey et al. (1950) studied the water-nicotine-kerosene system a t temperatures ranging from 5 to 98 "C and concentrations ranging from 1 to 794 g of nicotinek of water. Recently Millen (1988) identified hexane as a better solvent for the solvent extraction operation and studied it in some detail. One aspect of this work was the determination of the distribution coefficients of nicotine between hexane and water a t the temperature and pH values of interest in the solvent extraction stage of the process.
Experimental Section The investigations were carried out in 250 mL conical flasks. This scale permitted the use of 50 mL of each phase, i.e., the solvenffliquid ratio was 1:l in all of the work. The flasks were then placed in a water bath fitted with a mechanical shaker and permitted to attain equilibrium. Materials. The hexane used in this work was obtained from BDH Ltd. and was sold as a 60-80 "C fraction from petroleum; it had an experimental e = 0.675 g/cm3 (20 "C). The nicotine solutions were made up using domestic drinking water and purified distilled nicotine, described as high grade (98-99%), obtained from Nicobrand Ltd. The pH was adjusted by the addition of sodium hydroxide to the solutions. Analysis. The concentration of nicotine in the aqueous solutions was estimated using ultraviolet spectrophotometry as proposed by Willits et al. (1950). Their method was modified with reference to Harvey et al. (1967) and Bangarayya et al. (1971). The modification permitted the deletion of a time-consuming steam distillation and its replacement with an activated carbon, Darco G60, cleanup stage to remove impurities which interfered with the analysis. The absorbance was measured using a Perkin-Elmer W-vis Model 550S, at three wavelengths: at Am= which was 259 nm and a t 23 nm on either side of the maximum, i.e., 236 and 282 nm. The relationship between the absorption values was given by Willits et
* To whom correspondence should be addressed. Present address: DuPont (UK)Ltd., Maydown Works, P.O. Box 15, Londonderry,BT47 lTU, Northern Ireland.
where A1259 is the corrected absorbance contributed by the nicotine in the solution. A calibration line of absorbance versus nicotine concentration was produced and used to read off the concentration of nicotine in the samples. The concentration of nicotine in the hexane was estimated using a nonaqueous titration detailed by Aktiebolaget Leo (1987). A n aliquot of the solvent (containing nicotine) was dissolved in acetic acid and titrated with a standard solution of perchloric acid in acetic acid, using crystal violet as an indicator.
Results and Discussion The influence of three variables on the distribution coefficient was investigated. The variables were concentration of the aqueous phase, the pH of the aqueous solution, and the temperature of the system. The investigations were carried out over the concentration range 1-8.5 g/L, the temperature range 5-20 "C,and at two pH values, 11 and 13. The measured pH of 13 actually represented a 0.5 M solution of sodium hydroxide. Before commencing the work, the time taken to reach equilibrium was estimated by sampling the aqueous phase every 10 min until two consecutive samples produced essentially the same result on analysis. Thirty minutes was sufficient time to reach equilibrium. After the contents of the flasks had reached equilibrium, the shaker was stopped and the layers were permitted to settle before samples were taken from each layer for analysis. All investigations were carried out in duplicate and the results reported are average values. The distribution coefficient is reported as C'IC where C' is the concentration of nicotine in the solvent and C is the concentration of nicotine in the water phase. Figures 1 and 2 show the variation in the nicotine concentration in the hexane layer with the concentration of nicotine in the aqueous layer, a t the two pH values. These graphs are linear, indicating that for a particular temperature, over the range investigated, the distribution coefficient is independent of initial concentration. These data agree with those published by both Norton (1940) and Claffey et al. (1950) for kerosene who found that the distribution is constant up to 10 g/L. The results are shown clearly in Figures 3 and 4, where the distribution coefficient is plotted against the initial nicotine concentration before distribution. Figure 5 shows the variation of the distribution coefficient with temperature and also shows the considerable increase in coefficient obtainable by operating at a high pH value
0888-588519412633-3238$04.5010 0 1994 American Chemical Society
Ind. Eng. Chem. Res., Vol. 33, No. 12, 1994 3239 5
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A
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Concentration of nicotine in water phase (C) (g/L)
Figure 1. Distribution of nicotine between hexane and water. 5-
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Concentration of nicotine in water phase (C) (glL)
Figure 2. Distribution of nicotine between hexane and water.
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The hexane-water-nicotinesystem atpH 11
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Initial nicotine concentration (g/L)
Figure 3. Distribution coefficient versus initial concentration.
and a t moderate temperatures. Once again these data agree with those of previous workers. Norton (1940)
reported that concentrations of alkali higher than 0.1 M pushed the nicotine into the kerosene phase.
3240 Ind. Eng. Chem. Res., Vol. 33, No. 12, 1994 L."
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Figure 4. Distribution coefficient versus initial concentration. .." 1.4
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The hexane-water-nicotine system
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Temperature (oC)
Figure 5. Distribution coefficient versus temperature.
Conclusions The influence of initial nicotine concentration, pH, and temperature on the distribution coefficient of nicotine between hexane and water has been investigated. Over the range studied, 1-8.5 g/L, the initial concentration was found to have no effect on the distribution coefficient. Temperature and pH were both found to have a significant influence on the distribution coefficient. In particular at 20 "C the distribution coefficient at pH 13 is approximately twice the value obtained at pH 11.
Bangarayya, M.; Narasimhamurty, Y. C. H.; Pal, N. L. Total Alkaloids in Tobacco-A Simple and Rapid Method of Determination. Tob. Sci. 1971, 15, 114.
Acknowledgment The authors thank Mr. J. A. Humphrey, owner and managing director of Nicobrand Ltd., for his assistance and the generous supply of nicotine used in the investigations.
Norton, L. B. Distribution of Nicotine Between Water and Petroleum Oils. Ind. Eng. Chem. 1940, 32 (21, 241.
Claffey, J. B.; Badgett, C. 0.; Skalamera, J. J.; MacphersonPhilips, G. W. Nicotine Extraction from Water with Kerosene. Ind. Eng. Chem. 1950,42 (11,166. Harvey, W. R.; Badgett, C. E.; Resnik, F. E. Alkaloids in Tobacco Leaf, Cigarette Filler and Particulate Matter of Smoke by AcidMethanol Extraction. Tob. Sei. 1967, 11, 84. Millen, D. L. C. The Recovery of Nicotine from Tobacco. Ph.D. Thesis, The Queen's University of Belfast, 1988.
Willits, C. 0.; Swain, M. L.; Connelly, J. A.; Brice, B. A. Spectrophotometric Determination of Nicotine. Anal. Chem. 1950,ZZ (3),430.
Nomenclature C' = concentration of nicotine in the solvent, g L C = concentration of nicotine in the water phase, gL
Received for review January 14, 1994 Revised manuscript received August 4, 1994 Accepted August 15, 1994"
Literature Cited The Aktiebolaget Leo Pharmaceutical Co., Sweden, private communication to Nicobrand Co., Northern Ireland, 1987.
Abstract published in Advance ACS Abstracts, October 1, 1994. @
