JANUARl 15, 1938 TABLE
Sample
KO.
Iv.
Cell Length
Cm.
5
ANALYTICAL EDITION DETERMISATION OF PHOSPHORUS
SPECTROPHOTOXETRIC
(Bureau of Standards samples) Phosphorus k K Found
so
Phosphorus Present
70
The results using the Bureau of Standards samples are satisfactory and show a relatively small error. The method has been used on routine work and found to be more reliable than the older phosphomolybdate methods when a n inexperienced operator is using them. The only serious interference with the method is brought about by large amounts of silicon, as in 4 per cent silicon steels. I n such cases, this method will not work, for the formation of yellow silicomolybdic acid vitiates any measurement on the color caused by
small amounts of phosphorus. Excepting such cases, the method appears to be very reliable and useful.
Literature Cited ( I ) Dietrich, K., and Schmitt, K., 2. anal. Chem., 109,25 (1937). (2) Getzov, B. B., Zaaodskaya Lab., 4, 349 (1935). (3) Kasline, C. T., and hlellon, M. G., IND. ENQ.CHEM.,Anal. Ed., 8,436 (1936). (4) Landolt-Bomstein, “Physikalische Chemisciie Tabellen,” 5 auflage, Vol. 11, p. 897, Berlin, Julius Springer, 1923. (5) Mehlig, J. P., IND. ESQ. CHEM.,Anal. Ed., 7, 27 (1935). (61 Mellon, M. G., I b i d . , 9, 51 (1937). (7’ Mellor, J. W., “Comprehensive Treatise on Inorganic and Theoretical Chemistry,” Vol. XII, pp. 309-10. New York. Longmans, Green & Co., 1932. (8) Misson, G., Chem.-Zlg., 32,633 (1908). (9) Muller, R. H., ISD.ENG.CHEM.,Anal. Ed., 7, 361 (1935). (IO) Ibid., 7 , 223 (1935). (11) Rollet. A. P., Compt. rend., 183,212 (1936). (12) Schroder. R., Stahl u. Eisen, 38, 316 (1918). (13) Strafford, K., Chem. SOC.Annual Rpts., 33,456 (1937). (14) Willard, H. H., and Greathouse, L. H., J. Am. Chem. Soc., 39, 2366 (1917). (15) Zeiss Mess, 430d/IIIe. See also: Kohlrausch, F., “Praktische Physik,” Leiprig, B. G. Teubner Verlag, 1935; Weigert, P., “Optische Methoden der Chemie,” Leipzig, Akademische Verlagsgosellschaft, 1927. RECEIVED October 28, 1937.
Determination of Pyrethrin I J
In Commercial Insecticides Containing Pyrethrum or Pyrethrum Extract D. A. HOLADAY, Food and Drug Administration, Washington, D. C.
P
YRETHRUM insecticides consist of pyrethrum powder
or mixtures containing it; mineral oil containing pyrethrum extract, a n essential oil or perfume, and frequently other substances such as derris extract or organic thiocyanates; or, in the case of plant sprays, essential oils, a n emulsifier such as soap, a sulfated alcohol or sulfonated oil, pyrethrum extract, derris extract, and a solvent, usually alcohol, acetone, or water. The method proposed by Seil (S) has been largely used for the determination of the pyrethrins in pyrethrum powder. A modification of this method has been used for the determination of pyrethrins in mineral oil-pyrethrum sprays. Graham (I), however, reported a loss of pyrethrin I in the preliminary steam distillation in this method when applied to mineral oil sprays, and Wilcoxon ( d ) , working with purified pyrethrum resins, found that the monocarboxylic acid from the pyrethrin I is not completely recovered after the steam distillation for separating it from the dicarboxylic acid, so that a low value for pyrethrin I is obtained. Wilcoxon determined pyrethrin I in pyrethrum flowers by utilizing the reaction between the monocarboxylic acid and DenigBs’ reagent, by which mercury is reduced, and the determination of the reduced mercury by the iodate method of Jamieson (2). I n the author’s hands this method has given good results on pyrethrum powders, but unsaturated compounds formed by saponification of perfumes, essential oils, or other substances m-hich may be present in many pyrethrum insecticides interfere with the iodate titration by absorption of iodine. By modifying Wilcoxon’s method so as to remove unsaturated organic compounds, a procedure has been developed for the determination of pyrethrin I in many commercial insecticides. This modification has been used on mineral oil sprays containing pyrethrum extract, essential oils, perfumes, derris extract, and organic thiocyanates, and in the analysis of
plant sprays containing essential oils, derris resins, soaps and other spreaders, tobacco extract, alcohol, or acetone. The method depends on the reduction of DenigPs’ reagent by the monocarboxylic acid, precipitation of the reduced mercury as calomel, removal of unsaturated organic compounds with a c e tone and chloroform, and determination of the reduced mercury by titration with iodate solution. The monocarboxylic acid is separated from the dicarboxylic acid by extraction with petroleum ether, in which the free dicarboxylic acid is only slightly soluble. Under the conditions of the determination, the dicarboxylic acid reacts very slowly with DenigBs’ reagent, so no appreciable error is introduced by the small amount present.
Experimental I n the experimental work an alcoholic extract of pyrethrum flowers Yas analyzed by Geil’s method and by the proposed method. After analysis by the Seil method the titrated solution was acidified and the monocarboxylic acid was extracted with petroleum ether and determined by treatment with DenigM reagent. These results are given in Table I. Samples were also made up containing the same amount of extract to which were added 5 per cent of pine oil, 4 per cent of oleic acid, and 2 per cent of derris resins. These samples were TABLEI. PYRETHRW I IN ALCOHOLICP Y R E T HEXTRACTS R~ llercury Reduction Method Alcohclic pyrethrum extract Alcoholic extract pine oil, oleic acid, and derris resins
+
Seil Method
llercury Reduction on Titrsted Solution
75 ..
%
%
0.31 0.32
0.27
0.27
0.21 0.20
0.33 0 32
.. ..
..
..
INDUSTRIAL AND ESGINEERING CHEMISTRY
6
analyzed by the mercury reduction method. Results are also shown in Table I. The official control insecticide prepared by the National Association of Insecticide and Disinfectant Manufacturers was used for experimental work on mineral oil-pyrethrum sprays. One per cent of methyl salicylate, one of the most frequent and serious interfering substances, was added to other portions of this spray, which were analyzed by the Seil method and by the mercury reduction method. The titrated solution from the Seil determination mas acidified, and the monocarboxylic acid was extracted with petroleum ether and determined b y reduction of mercury. Two and one-half per cent of fl-butoxy-fl’-thiocyanodiethyl ether was added to other samples of the spray and these were analyzed by the mercury reduction method. The results are given in Table 11. TABLE11.
PYRETHRCM I IN MINERAL OIL-PYRETHRUM EXTRACTS
Mercury Reduction Method Official control insecticide Insecticide salicylate
+ 1% methyl +
Mercury Reduction on Titiated Solution
%
%
%
0.044 0.044 0.047 0.047
0.042
0 1044 0.045
...
...
Insecticide 2.5% 8-hutoxy,¶‘-thiocyanodiethyl ether
Seil Method
0,041
... ... ...
0 : oio 0,054
0 043
...
...
:
...
... ...
The analyses show that the Seil method and t’he mercury reduction method give comparable results on mineral oil-pyrethrum sprays which contain no interfering substances. An appreciable amount of the acids titrated in the Seil method, however, is not the monocarboxylic acid. This error is in the opposite direction to that caused by incomplete recovery of the monocarboxylic acid in the steam distillation, These results are similar to those found by Wilcoxon. I n mineral oil sprays containing methyl salicylate, it is difficult to remove all traces of the essential oil by steam distillation; so the result by the Seil method is high.
Mercury Reduction -Method Measure a sample containing from 20 to 75 mg. of pyrethrin
I into a 300-cc. Erlenmeyer flask; add 15 cc. of 0.5 A‘ alcoholic
sodium hydroxide solution and reflux on a steam bath or electric hot plate for 1to 1.5 hours. (Moresodium hydroxidemay benecessary in samples containing large amounts of perfumes or essential oils.) Transfer to a 600-cc. beaker and add sufficient water to make the aqueous layer to 200 cc. Add a few glass beads, or preferably use a boiling tube, and boil the aqueous layer down to 150 cc. Transfer the aqueous layer to a 250-cc. volumetric flask and add 1 gram of Filter-Cel and 10 cc. of a 10 per cent barium chloride solution; make to volume and let settle (in some cases more barium chloride may be needed t o obtain a clear solution). Filter off 200 cc., add 5 cc. of sulfuric acid (1 4)! filter into a 500-cc. separatory funnel, and extract with two 50-cc. portions of petroleum ether. Wash the extracts with several 10-cc. portions of water and filter through a plug of cott’on into a clean 250-cc. separatory funnel. Wash the cotton with 5 cc. of petroleum ether. Extract the petroleum ether with 5 cc. of 0.1 N sodium hydroxide, shaking vigorously. Draw off the water layer in@ a 100-cc. beaker, wash the petroleum ether with 5 cc. of water, and add this to the beaker. Add 10 cc. of Denigh’ (U. S. P. XI) reagent to the beaker and let stand 1 hour. Add 20 cc. of acetone to the beaker and precipitate the reduced mercury with 3 cc. of saturated salt solut,ion. Warm to about 60” C., filter through a small filter paper (7 t o 9 cm.), and wash with 10 cc. of hot acetone, transferring all the precipitate to the filter paper. Rash with two 10-ce. portions of hot chloroform, and place the filter paper and contents in a 250-cc. glass-stoppered Erlenmeyer flask. Add 30 cc. of concentrated hydrochloric acid and 20 cc. of water to the flask, cool, and add 6 cc. of chloroform or carbon tetrachloride and 1 cc. of iodine monochloride solution [dissolve 10 grams of potassium iodide and 6.44 grams of potassium iodate in 75 cc. of water; add 75 cc. of hydrochloric acid and 5 cc. of chloroform in a glass-stoppered bottle and adjust to a faint iodine color (chloroform) by adding dilute potassium iodide or potassium iodate solution], and titrate
VOL. 10, NO. 1
with 0.01 M iodate solution (2.14 grams of potassium iodate per liter). Potassium iodate reacts with reduced mercury to form mercuric mercury and iodine. Further addition of iodate in the presence of hydrochloric acid oxidizes the iodine to iodine monochloride.
+
+ +
++
++ + +
+ +
1. 5HgCI 6HC1 KIOB = I 5HgClz KC1 3H20 2. 219 KIOa 6HC1 5ICl KCl 3Hz0 (combining 1 and 2 gives the equation shown by Jamieson) 3. 4HgC1 KIOI 6HC1 = 4HgC12 IC1 KC1 3H20
+
+
+
Addition of iodine monochloride does not change the volume relations between reduced mercury and iodate solution and aids in the titration of small amounts of mercury. The end point is taken when the red color disappears from the chloroform layer. The end point is not permanent; so the titration should be completed rapidly with vigorous shaking after each addition of iodate. One cubic centimeter of the iodate is equivalent to 4,4mg. of pyrethrin I.
Summary The Seilmethod for the determination of pyrethrin I in commercial mineral oil-pyrethrum insecticides containing essential oils or perfumes is not satisfactory, as the monocarboxylic acid is not completely recovered by the usual steam distillation and acidic substances other than the carboxylic acid involved, which may be present in the petroleum ether extract of the distillate, will be titrated as this acid. Wilcoxon’s method for pyrethrin I is satisfactory for pyrethrum powder only. Essential oils and many other substances, however, interfere with the iodate titration for reduced mercury and cause high results for pyrethrin I. Wilcoxon’s method for the determination of pyrethrin I in pyrethrum powder has been modified so that it can be used in the determination of pyrethrin I in insecticides containing pyrethrum powder or pyrethrum extract, mineral oil, essential oils, perfumes, derris resins, and certain other materials.
Literature Cited (1) Graham, J. J. T., IND.ENG.CHEW,Anal. Ed., 8, 222 (1936). (2) Jamieson, G. S., “Volumetric Iodate Methods,” N e w York, Chemical Catalog Co., 1926. (3) Seil, H. A,, Soap, 10, No. 5, 89 (May, 1934). (4) Wilooxon, Frank, Contrih. Boyce Thompson Inst., 8, So. 3, 1758 1 (1936). RECEIVED Octoher 19, 1937.
+
Courtesg, Skinner Le- S h e r m a n , I n c
