Loss of Pyrethrins during Analysis of Mineral Oil-Pyrethrum Extracts by the Seil Method J. J. T. GRAHAM Food and Drug Administration, U. S. Department of Agriculture, Washington, D. C.
M
INERAL oil-pyrethrum sprays for household use are ordinarily perfumed to cover the objectionable mineral oil odor. The perfumes used usually contain esters or other compounds which interfere with the determination of the active principles, pyrethrin I and pyrethrin 11, by methods based on the titration of their mono- and dicarboxylic acids. Seil (2) and Ripert (f) suggest steam distillation of such products to remove the perfume before proceeding with the analysis. Preliminary tests having indicated that there was a loss of pyrethrins in the analysis of these commercial extracts following Seil's procedure, a more complete study of the method was made. Three preparations of the mineral oil-soluble portions of pyrethrum were prepared by extracting 750-gram portions of powdered pyrethrum in a large extractor with petroleum ether (boiling range 35" to 40" C . ) ; the petroleum ether was evaporated by immersing the flask in a water bath, the temperature of which was maintained between 50" and 55" C., and the residue was then treated successively with 200-cc. portions of the oil solvent, filtered, and made to 6 liters with mineral oil. In the preparation of sample A a commercial purified white mineral oil of the type used as a base for commercial household fly sprays was used as a vehicle, and for sam les B and C kerosene highly purified in the Iaboratory was useb: (The purified kerosene used had a distillation range from 165" to 300" c. with 84 per cent distilling between 175" and 250", while the fl spray oil base had a distillation range from 200" to 250" C.) k o perfume or other interfering substances were added. These prepared samples were stored in brown glass bottles in a dark cupboard from which they were removed only during the actual time of sampling.
Sample
Volume of Distillate Water Oil
cc.
b
cc.
... 90
Sample A B
C
Pyrethrins in Distillate Pyreth- PyrethTotal rln I1 rin I Mg./ Mg./ Me./ 100
CC.
100
00.
100 CC.
Pyrethrins in Residue Total, Pyreth- Pyrethrin I1 Total Pyrethrins rin I Mo./ Moa/ MU./ Mo./ 100 CC.
Pyrethrin I
Pyrethrin I1
M g J l O O cc.
Mg./lOO
31.7 36.4 24.6
CC.
Total Mg./100 cc.
46.2 47.5 52.0
76.9 83.9 76.6
Summary
DETERMINXID I N PYRETHRUM EXTRACTS AFTER STEAM DISTILLATION
100 cc.
34.6 7.6 24.0 4.1 3.4 31.3 10.0 24.0 6.4 3.6 33.1 22.4 9.9 6.0 4.9 90 29.4 9.7 19.5 6.4 3.3 95 33.3 26.6 Not detei:mined 105 37.9 6.9 27.6 3.5 2.4 50 35.4 26.7 7.6 4.3 3.2 75 31.5 25.4 6.6 4.8 2.2 80 32.2 6.9 23.7 4.3 2.6 90 34.0 6.3 26.9 3.3 2.0 70 34.0 7.6 12.6 6.6 2.0 50 36.7 10.5 8.0 5.8 2.2 70 33.0 10.4 10.9 7.3 3.1 1000 90 30.8 Q.9 9.5 6.6 2.9 95 1500 Distillation made after addition of 100 cc, of a commercial fi spray oil base. Distillation made after addition of 50 cc. of purified high boifne mineral oil. 250 500 1000 1600 500' 260 500 1000 1500 lOOOb 260 600
a
PYRETHRINS
DETERMINED IN PYRETHRUM EXTRACTB TABLE11. PYRETHRINS WITHOUT STEAM DISTILLATION
I n two cases the method of distillation was modified with the idea of holding a larger proportion of oil in the distillation flask. I n the first case 100 cc. of the fly spray oil base were added to the aliquot to be distilled and in the second case 50 cc. of a highly purified mineral oil having a distillation range of from 300" to 400" C. were added before distillation. In each case there was a slight increase in the pyrethrins recovered but the loss was still considerable. This loss is only partially due to volatilization of the pyrethrins with the steam, A large part is due to decomposition or other chemical change, as is shown by the fact that the sum of the pyrethrins determined in the distillate and in the residue is considerably below the value obtained by direct saponification of the sample.
These preparations were analyzed by the Seil method, subjecting them to steam distillation just as though perfume were present. Since the volume of distillate necessary to remove all the perfume from commercial samples varies within rather wide limits, four 100-cc. aliquots of each sample were distilled and distillates of 250, 600, 1000, and 1500 CC., respectively, were collected, in order to simulate conditions met in the analysis of commercial samples. Pyrethrins were determined in the distillate as well as in the residue remaining in the distillation flask. As a means of comparison pyrethrins were also determined in the original samples without steam distillation. I n making the analyses the procedure outlined by Seil was followed as closely as possible. However, because of the forTABLEI.
mation of emulsions during the steam distillation and also during the boiling off of the alcohol after the saponification, it was necessary to introduce slight modifications. The emulsion formed in the flask during the steam distillation was broken by adding a small quantity of saturated sodium sulfate solution and 25 to 50 cc. of petroleum ether. The emulsion formed during the boiling of the alkaline solution after saponification was more difficult to break, but separation usually was possible after adding a little petroleum ether and a few cubic centimeters of a 20 per cent sodium hydroxide solution. After titrating for pyrethrin I in the portions of the distilled oil, the qualitative color test described by Seil (2) was also applied. In each case the test was positive, showing that the chrysanthemum monocarboxylic acid was definitely present. The analytical results are given in Tables I and 11. The results in Table I show that there is a progressive loss in the pyrethrin content of the sample during the steam distillation.
222
100 cc.
58.6 65.3 56.6 48.9 58.9 65.6 62.1 56.9 65.9 60.9 46.6 40.2 43.9 40.7
100
CC.
66.1 65.3 66.4 68.6
..
71.4 69.6 63.4 62.8 66.2 54.2 64.2 64.3 50.2
A study of the Seil method for the determination of pyrethrins in mineral oil extracts of pyrethrum shows that there is a loss of pyrethrins during the steam distillation for the removal of perfume. The loss is due to volatilization with steam and to decomposition or other chemical change. In the case of the materials here reported the loss approximated 25 per cent of the pyrethrins.
Literature Cited (1) Ripert, Ann. fals.,27,577-95 (1934). (2) Seil, Soap, p. 89 (May, 1934).
RECEIVED March 16, 1936.
