Determination of Small Amounts of Nicotine on Apples And Adaptation of the Official Method to Apple Foliage W'ILLIA3I RALSTON. Tobacco By-products and Chemical Corporation, Richmond, Va.
A method for determining the small quantities of nicotine found o n sprayed apples is presented. The novelty of the method consists essentially i n washing nicotine from the fruit with a mixture of aqueous sodium hydroxide solution and ethylene dichloride, from which the nico-
tine is recovered. The nicotine is then distilled and precipitated with silicotungstic acid. The results are accurate to 0.1 mg. over the range 0 to 12 m g . of nicotine on a 1-kg. sample. The method applies to both water-soluble and water-insoluble nicotine insecticides.
THE
lvith 25 to 35 nil. of water and the washings ;ire placed in the second separatory funnel. One milliliter of concentrated hydrochloric acid is added and the whole is shaken vigorously. On separation the solvent layer is drained off and the acid layer is added to the first acid treatment in the Kjeldahl. About 50 to 75 ml. are boiled off to expel any solvent present. On cooling, 20 ml. of sodium hydroxide (sp. gr. 1.35) are added and the nicotine is distilled into a 400-ml. beaker containing 10 ml. of hydrochloric acid (1 to 4 ) . The distillation consists of boiling the nicotine down almost to dryness and then passing a current of steam 1hrough it until a volume of about 300 ml. is collected. The volume of liquid in the Kjeldahl should be kept as small as possible. The precipitation of the nicotine in the distillate follows, az given in the official method. The precipitate is filtered and washed four times with hydrochloric acid (1 to 1000). The Gooch crucible and precipitate are ignited at 900" C. for 10 minutes.
distillation procedure in the official inethod of analysis for nicotine ( 1 ) cannot be used in determining the spray deposit vn apples because the sample should be a t least 1 kg.! and removal of the nicotine from this bulk by distillation is impractical. Using only the peelings from the apples does not help because charring inevitably results. T o obviate these difficulties the nicotine is washed from the fruit by dilute sodium hydroxide and ethylene dichloride. The sodium hydroxide frees the nicotine from any salts present, since no salt of nicotine is stable in alkaline solutions and the dichloride dissolves enough of the wax coating of the apples to assure complete residue removal. TABLE 1. S o . of Apples
Weight uf Apples Grama
KECOVERY OF NICOl'ISE
Nicotine Added
.M1.
.trJJ.
Piicotine Recovered
.w/.
Nicutitiexulfate w i t h 1 % curt1 (Kaloi s i r u p , 1 1111. = 0..ili 111 990 0 0 0 , 51; 900 1.0 X 1160 4.li 2.57 12 .~.60 10 1060 10 0 ;i .60 10 1240 10 0 5.60 10 1160 10 0 1192 3.60 10 10 0 11.20 10 1301 20.0 10 10
IIIY.
Percentage Eecovery
Experimental Gooch crucibles were adopted because of speed in filt1.stion and ease of washing. Four washings were found to be sufficient. Trouble was experienced in getting consistent weighings. It was found that cooling the crucibles to room temperature on an Alberene slab gave more accurate weighings than using a desiccator in the usual way. The recovery of nicotine from apples by the proposed method was tested, with the results shown in Table I. The insecticides chosen for this purpose were (1) nicotine sulfate with 1 per cent corn (Karo) sirup and ( 2 ) nicot'ine bentonite. The former represents a class of water-soluble nicotine products, while the latter is largely water-insoluble. From other work it was found that nicotine is lost from these products very slowly, with practically no loss in 10 days from open Petri dishes. The apples were placed in the receptacle used for washing and a measured amount of the solution or suspension rvas pipetted in, in such manner that the stem and calyx cavities n-ould receive some. After standing until dry! usually 24 t o 36 hours, the determinations were made. These results show a recovery high enough to warrant proposal of the method.
ui riicutitir 80 I 100 0 98 3 99 0 99 3 99.3 99 8
Sicotine bentonite, 1 ml. of suspension = 0.62 ins. of nicotine 12.43 100 20.0 12,40 1216 12.3(i 100 90.0 12.40 1305
Dilute hytiiochloric acid is used to extract the nicotine from the solvent. The acid washing is then made alkaline and the nicotine is distilled as outlined in the official method. Gooch crucibles with pads made of long-fiber ignited and acidwashed asbestos are used 1)ecauke of ease and rapidity in filt ra t ion.
Procedure .\ tin can 13
x
x
26 em. with wide mouth and friction top i h uhed for washing the fruit. A nail hole in one of the top corner.3 \ d l allow complete drainage. According to size of fruit and residue expected, 8 to 12 apples are weighed and placed in the can and 175 ml. of ethylene dichloride and 25 ml. of 1 per cent 13
sodium hydroxide solution are added. The top is put on tightly and the n-hole is thoroughly shaken for 1 minute. The liquor is drained from the fruit into a 500-ml. separatory funnel. The fruit is washed again exactly as described and then given a final rinse with about 40 ml. of ethylene dichloride. All n-ashings are collected in the separatory funnel. Five milliliters of roncentrated hydrochloric acid are added and the whole is shaken thoroughly. After separation the bottoni or solvent layer is drawn off into another 500-ml. separatory funnel and the top or acid layer is run into N Kjeldahl flaPk. The first separatory funnel is rimed
Determination of Nicotine o n Apple Foliage The usual method of steam distillation may be employed to determine nicotine on foliage. A sample consisting of 50 leaf disks 3.81 cin. in diameter is taken. About 800 nil. are distilled over and acidified n-ith 15 ml. of hydrochloric acid (1 to 4). By precipitating from this large volume and siphoning off most of the supernatant liquor, the usual tedious 533
INDUSTRIAL AND ENGINEERING CHEMISTRY
334
TABLE 11. RECOVERY OF SICOTINE FROM APPLE FOLIAGE ISample consisted of 50 leaf disks, 3.81 cm. in diameter, t o which was added i h e indicated amount of nicotine. One milliliter of nicotine solution (nicotine eulfate with 1 per cent corn, Karo, sirup) = 0.58 mg. of nicotine.] Nicotine Recovered Nicotine Added
'MI.
.Mn,
n
n
lt.0 20.0 20.0
3.60 11.20 11.20
Mg.
70
0 5.54 11.23 11.16
99 100 100
evaporation to about 100 ml. can he avoided. Table I1 shows some results obtained by this procedure. Whenever it is necessary to keep foliage for some time before analysis, the sample should he placed in a jar with 50 ml. of hydrochloric acid solution (1 to 9). I n this way samples h a r e been kept for 10 weeks with no 105s in nicotine.
YOI,. I O , YO.0
Summary A method for determining the small quantities of nicotine found on sprayed apples is presented. I t s novelty consists essentially in n-ashing nicotine from the fruit with a mixture of aqueous sodium hydroxide solution and ethylene dichloride, from which the nicotine is recovered, then distilled, and precipitated with silicotungstic acid. The results are accurate to 0.1 mg. over the range 0 to 12 mg. of nicotine on a 1-kg. sample. The method applies to hoth water-soluhle and water-insoluble nicotine insecticides.
Literature Cited 11) .Issor. Official Agr, Chem., Offirial a n d Tetitarix-e Slethotls, 4th ed., pp. 60-1 (193.5). REfTAYED
.kpril 22. 1937.
A Simplified and Portable McLeod Gage EARL W. FLOSDORF, LJni+ersity of Penns,l\ania. Philadelphia. Pa.
V
ARIOUS modifications of the McLeod ( 3 ) gage have
been proposed; perhaps the most common uses a low degree of vacuum on the atmospheric side to allow the mercury to be withdrawn from the bulb (1). To cause the mercury either to enter or leave the bulb, the present gage utilizes a metal swivel (2) that bears all the weight of the gage. A reading may be made in 2 to 3 seconds; the gage is compact, uses a minimal quantity of mercury, and is portable. Sudden changes of pressure do not affect the gage, whether it is under vacuum or not. I n Figure 1 the gage is shown diagrammatically in position R for reading, and (in broken lines) when turned to position P for acquiring the pressure of the system to be measured. For pressures above 0.001 mm., in order that the gage may be turned on swivel S , heavy-walled rubber tubing free from sulfur and talc is satisfactory for connection to the vacuum system at point A . For lower pressures a ground joint is
c
used tu permit turning the gage on thp swivel, and glass tubing is brought froni point d to point B , where it is passed out through the back of the metal case. The vacuum connection is attached a t B , in the center of the swivel axis, by a glass-to-metal ground joint, so that all rubber connections are avoided. With either device, the gage may be turned very rapidly in making a reading Tvith no danger of breaking and may also be easily disconnected and rendered portable. Figure 2 is a side view, ,homing details of the swivel. I n position PI which is not exactly horizontal, the mercury will drain completely into bulb C. A constriction at point D prevents the mercury from traveling too rapidly into and out of the capillaries, so that the gage may be swung very rapidly to and from posiF I G U R E 2 . SIMPLItion R. The diameter of bulb C is such FIED GAGE that when a pressure reading is made, Side view showing swivel, case, etc. the mercury in the right-hand capillary always comes to the top line, irrespective of whether or not themercury is high or low in the center capillary. The safety trap, E , permits the portable gage to be carried while full of mercury without loss of mercury even when inverted.
-4cknowledgment The author wishes t o acknowledge the helpful assistance of
J. D. Graham, the University of Pennsylvania glass blower, in the construction of these gages. Gages of several ranges may be obtained through the F. J. Stokes Machine Company, Olney, Philadelphia, Pa.
Literature Cited 11)Kaye, G. W. C., "High Vacua," p. 127, NeF York, Longmans,
'D f- ~3 I NPOSITION R SIMPLIFIED MCLEODGAGE F r o n t view showing t w o positiom
FIGVRE 1.
Green & Co., 1927. (2) Ibid., p. 129.
(3) McLeod, Phil. Mag., 47, 110 (1874). RECEIVED July 11 1938
