July 1948 ET-257
United States Department of Agriculture
Agricultural Research Administration
Bureau of Entomology and Plant Quarantine
A METHOD FOR THE DETERMINATION OF FREON-INSOLUBLE
MATTER IN PYRETHRUM EXTRACTS
By A. C. Hazen and Robert A. Fulton
Division of Insecticide Investigations
Pyrethrum extracts for use in liquefied-gas aerosols vary in their
solubility in Freon-12 (dichlorodifluoromethane). This variation depends
upon the completeness of the removal of impurities by the manufacturer and
the formation of pyrethrin polymerization products. Two methods (l,2)
have been published for the determination of the matter insoluble in Freon-
12, but under some conditions these methods have given erratic results.
Both methods depended upon the formation of deposits on the wall of a con-
tainer of comparatively great weight but small capacity.
In laboratory studies in this Bureau in 1948, a glass container of
greater capacity was used (3), which had been developed to observe lique-
fied gases, especially at the low temperature (-20* F.) encountered in
filling low-pressure aerosol containers. This container was a citrate of
magnesia bottle with a capacity of approximately 450 gin. of Freon-12,
available at any wholesale drug firm.
The amount of Freon-insoluble material in each of several samples was
determined with this container, using concentrations of pyrethrum extract
in Freon-12 of from 0.75 to 5 percent. The concentration of 5-percent
pyrethrum extract (20 percent pyrethrins) most commonly used for this
determination was found to give inconsistent results. More uniform results
were given with 0.75- to 2-percent concentrations of pyrethrum extract in
Freon-12, but with certain types of extracts the insoluble material failed
to adhere to the walls of the container and was subsequently lost when the
Freon-12 was released. This insoluble material, unless allowed to stand
for several hours, will pass through common filters, so a filter was devised
which will retain it when sufficient time is allowed for the suspended mate-
rial to coagulate.
The assembly and arrangement of integral parts is shown in figure 1.
It is essentially the same apparatus as the one described by Fulton and
Berlin (I), with the addition of a filter equipped with a 200-mesh stain-
less steel screen and a lamb's wool plug to retain all of the insoluble
material. A Y valve (D) with a 3/8-inch pipe thread is first machined to
the exact shape of the glass plug furnished with the citrate of magnesia
bottle. The end of the valve is then threaded on a turning lathe to fit
the threads of the screen filter unit (A) furnished on oil burner tips.
A neoprene washer (C) made from 1/8-inch stock is cut to fit in the groove
of the valve. The center of the filter is then filled with lamb's wool (B)
to form a tight fitting plug. This whole unit is thoroughly washed in
acetone and chloroform and dried before use. The bottle is next cleaned
with a freshly prepared solution of ethyl alcohol and sulfuric acid and
rinsed several times with distilled water. Both units are dried in an
oven at 105* C. for 1 hour and cooled in a desiccator.
Six grams of the pyrethrum concentrate to be analyzed is weighed
into the citrate of magnesia bottle. The most satisfactory method of
doing this is to partially fill with the pyrethrum extract a 30-ml. round
dropping bottle, having a ground-in glass dropper equipped with a rubber
bulb. The pyrethrum extract is then put directly into the citrate of
magnesia bottle and the weight determined by difference. The valve is
clamped to the neck of the bottle, and the assembled apparatus is evacu-
ated to a residual pressure of 1 inch (25 mi.) of mercury to remove the
air and to facilitate filling with Freon-12. A filling device such as
described by Fulton et al. (4) is used to add 294 Sn. of refrigeration-
grade Freon-12. As a safety measure the bottle is wrapped with a heavy
cloth before the filling operation. It is then placed in a rack at an
angle which will permit the greatest area of glass surface to contact the
liquid (fig. 1). After the bottles have been put in the rack a safety
glass screen must be placed between them and the operator to give protec-
tion during the period while the bottles are being handled and observed.
The bottles are allowed to stand for 10 minutes and are then rotated
approximately 45 degrees. This operation is repeated every 10 minutes for
2 hours; then the bottles are allowed to stand overnight. At the end of
this time the solution will be clear, in most cases, with all of the insol-
uble matter adhering to the side of the bottle. The insoluble material
from a few commercially prepared extracts has been found to float on the
surface of the Freon-12 for several days, later settling to the bottom of
the container. This material is retained on the filter, when the Freon-
12 is removed from the bottle, by holding the valve down and slowly
releasing the liquefied gas. After all this liquefied gas has been
released, 200 gin. more of Freon is put into the bottle, and the contents
rinsed by shaking the bottle several times. This Freon is then released
in the same manner as described above.
The Y valve is then removed, and the filter is taken out with small
forceps and placed in a 10-ml. beaker. Five to 7 ml. of chloroform is
added and the filter unit allowed to extract while the removal of the
residue from the bottle is completed. This operation is performed by
slowly adding 15 ml. of chloroform while rotating the bottle, which is
then held in a horizontal position and slowly rotated further. The solu-
tion Is transferred to a weighed 125-mi. Erlenmeyer flask to which several
glass beads have been added before weighing. This washing procedure is
repeated with three successive 15-ml. portions of chloroform or until no
visible deposit remains on the wall of the bottle.
The chloroform from the 10-ml. beaker containing the filter assembly
is then transferred to the &rlenmeyer flask. The beaker and filter are
rinsed twice with 5-ml. portions of chloroform, and these portions also
transferred to the flask. The chloroform is then removed from this flask
by letting it slowly evaporate over a steam bath.
After the chloroform has been entirely removed, the flask is placed
in an oven at 105* C. for 1 hour and then transferred to a desiccator and
allowed to cool for 2 hours. The flask is weighed, and the Freon-insoluble
material calculated as follows:
Weight of residue x 100 % Freon-insoluble material
Weight of sample
The results of determinations of the Freon-insoluble material in 2-
percent concentrations in four samples of 20-percent pyrethrum extracts are
shown in the following tabulation:
Sample No. 1 3.18 percent
All of these extracts had insoluble material of different appearance.
(1) Wachs, H., Morriello, C., and Mages, S.
194. Determination of Freon-insoluble solids in twenty per cent
pyrethrum extracts. Indus. and Engin. Chem., Analyt. Ed. 16
(2) Goodhue, L. D.
1947. Determination of Freon-insolubles in pyrethrum extract. Soap
and Sanitary Chemicals 23(1): 133 and 135.
(3) Fulton, R. A. and Berlin, F. D.
1947. A glass container for use in studying aerosol solutions. U. S.
Bur. Ent. and Plant Quar. ET-246. 3 Pp. illus.
(4) Fulton, R. A., Berlin, F, D., and Bochert, R. S.,Jr.
1947. A laboratory method for filling aerosol containers. U. S. Bur.
Ent. and Plant Quar. ET-245. 4 pp. illus.
c. 0.. '
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