March, 1945
ANALYTICAL EDITION
+0.01 mg. of fluoride; and lo00 p.p.m. of chloride are equivalent to about -0.01 mg. of fluoride. Since the errors introduced by sulfate and chloride are plus and minus, respectiv&ly, the effect of the one tends to counteract the effect of the other. However, the effects of interfering ions are not completely additive. On the basis of 100-ml. samples an alkalinity of 200 p.p.m. (bicarbonate 244 p.p.m.) is equivalent to about -0.01 mg. of fluoride. For accurate results it is necessary to neutralize the alkalinity with nitric acid when it exceeds about 100 p.p.m. (bicarbonate 122 p.p.m.). The effect of nitrate in the nitric acid and of nitrate present in natural waters is negligible. Table I shows the interference of sulfate, chloride, and unneutralized bicarbonate. Bicarbonate may be converted to alkalinity as calcium carbonate by multiplying the bicarbonate by the factor 0.82. The interference of sulfate causes the fluoride measurement to be high and the interference of chloride and unneutralized alkalinity cause the fluoride measurement to be
149
low by the amounts shown in Table I. Neutralization of the alkalinity as prescribed eliminates the error caused by the alkalinity of the samples. Fluoride corrections may be applied instead of neutralizing the alkalinity of the samples. However, neutralization of the alkalinity is recommended. LITERATURE CITED
(1) Am.Public Health Assoc. and Am. Water Works Assoc., “Standard Methods for the Examination of Water and Sewage”, 8th ed.. pp. 36-8.1936. (2) Am. Water Works Assoc., Committee Report, J. Am. Water Work8 ASSOC., 33, 1966-2017 (1941). (3) Elvove, Elias, Pub. HeaZth Repts., 48,1219-22 (1933). (4) Lamar, W. L.,and Seegmiller, C. G . , IND.ENG.CHEM.,ANAL. ED., 13,901-2 (1941). ( 5 ) Sanchis, J. M., Ibid., 6,134-5 (1934). (6) Ssott, R.D., J. Am. Water Works Assoc., 33,2018-20 (1941).
PUBLISHED by permission of the Director, Geological Survey, United Stated Department of the Interior.
Quantitative Estimation of DDT and of Dust Deposits
DDT Spray
or
FRANCIS A. GUNTHER University of California Citrus Experiment Station, Riverside, Calif.
A method for the quantitative estimation of the amount of DDT in a wmple containins DDT is bared upon the quantitative dehydrohalogenation of DDT under certain conditions. A specific application to the determination of spray or dust deposits is discussed in detail. Data are presented to show both the accuracy and the reproducibility of the method, and possible sources of error are discussed.
M
molecule of hydrochloric acid per molecule of parent compound upon boiling with alcoholic potassium hydroxide. Recently Brand and Busse-Sundermann (1) synthesized and studied D D T and many new analogs. That phase of their work concerned with dehydrohalogenation indicated that 50 ml. of 0.5 N alcoholic potassium hydroxide completely dehydrohalogenated 5 grams of D D T within 2 to 3 minutes under reflux. These studies form the basis for the analytical method herein described. When the sample containing the D D T (I) is treated with excess alcoholic potassium hydroxide, the following transformation is effected:
ANY workers have shown D D T [2,2-bis-(p-chlorophenyl)l,l,l-trichloroethane] to be such a promising insecticidal material that the lack of a method of analysis suitable for its quantitative estimation has become a serious hindrance to its further insecticidal evaluac1 tion. (The alphabetical symbol derives from II the loosely descriptive name, dichlorodi)C = C-C1 KC1 Hz0 -C-C1 KOH 3phenyltrichloroethane.) A total halogen determination on a materid containing D D T c l ~ / c1 appears impractical because of the probable contamination with extraneous chlorides, (1) such as those found in hard waters, for example. I n addition, all organic halogen-conSince one, and only one, chloride ion is liberated from each taining contaminants, such as those found in technical DDT, molecule of DDT, the ,remainder of the method involves deterwould also respond to such a drastic method of analysis. mining the quantity of free chloride ion in the products of hyIt has been brought to the attention of the author, and subsedrolysis; this is accomplished by precipitating the chloride ion quently verified by him, that technical D D T may contain some with excess silver ion, and then determining the excess of the of the o,p‘ isomer. Theoretically, both isomers should yield one latter by means of a Volhard titration with ferric nitrate as inmole of hydrogen chloride under the experimental conditions dicator. described herein. Actually, however, slightly more than one mole may be obtained from the purified o,p’ isomer. This behavior is not without justification, and i t will be discussed in dePROCEDURE tail in a later report. These considerations led to the development of a more specific e i ~ ~ ~ i P b ~ h ~ ~ ~ ~ ~ ~ ~ method based upon dehydrohalogenation. In 1874, Zeidler (4) washing them individualIy with a stream of benzene from a wash bottle. The quantity of stripping solvent used is immaterial, reported that long boiling of the compound now popularly known as ’ D D T (I) with alcoholic potassium hydroxide resulted in for the entire Sample Will be used in One analysis. Filter the benzene strip solution through a plug of cotton or of solid foreign matter, and catch the filtrate dehydrohalogenation, yielding 2,2-bis-(p-chlorophenyl)-l,l-di- glass wool to cuoroethylene (11). Fischer (2) extended this study to several in a standard-taper 500-ml. Erlenmeyer flask. If preliminary analogs of DDT and reported that most of them readily lost & experiments have shown benzene-soluble inorganic chlorides to be
I
+
+
+
~ ~ ~ ~ e ~ j ~ b ~ e~
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
150
present in the sample, extract the ,above filtrate with several portions of water before proceeding to the next step. Evaporate this solution nearly to dryness on an electric hot plate set for 80' C., and a t the same time draw a slow current of air through the flrsk to hasten evaporation and t o prevent the objectionable liberation of benzene vapors into the room. DO not allow the temperature of the residue to exceed 95" C., 88 D D T may decompose seriously above this temperature. To the flask add 50 ml. of 1 N alcoholic potassium hydroxide, being careful not to wet the ground joint with this alkaline solution. Fit a standard-taper reflux condenser to the flask and gently reflux the solution on the same hot plate for exactly 30 minutes. Remove the hot plate, and through t,he top of the condenser add 50 ml. of distilled water, 50 ml. of 2 N nitric acid, and an additional 50 ml. of water, in the order mentioned, to the reaction mixture. Remove the condenser, and add to the flask approximately 5 ml. of nitrobencene, followed by exactly 20 ml. of standard 0.1 N silver nitrate by means of a calibrated pipet. Stopper the flask with a standard-taper plug and shake i t vigorously for a few seconds. This operation coagulates the silver chloride formed, and then coats these particles with a layer of nitrobenzene, so as to prevent their later double decomposition during the titration. Rinse down the stopper and sides of the flask with water, add 3 ml. of 1N ferric nitrate as indicator, and titrate the excess silver ion with standard 0.1 N potassium thiocyanate.
Table I. Purified D D T Introduced MU*
DDT Recovery Data D D T Found
Mu.
Recovery
It.-%
Vol. 17, No. 3
Table II. Reproducibility of Method in Tests on Citrus Treatment 3 7 technical D D T , talc diluent, pound per tree
!
6 gals. of kerosene containing 2 pounds of technical D D T per 100 gals. of spray; 1 gal. per tree Geaarol AK20" 10 pounds per 100 gals. of spray: 1 gal. per tree Geaarol SHN2Ob 1.2 gals. per 100 gab. of apray; 'I gal. per tree 3 gals. of kerosene containing 1 pound of technical D D T per 100 gals. of spray' 1.75 gals. of !ight-medium, tank-mix oil containmg 0.5 pound of technical D D T per 100 ea!@. of ipray
Mg of DDT per t3q. Cm. of Surface 4.1 4.3 4.0 100 lemon leavea 8.5 each 7.4 8.1 100 lemon leaves 10.4 each 10.6 10.1 100 lemon leaves 8.2 each 8.5 8.2 12,6 6 mature grape12.0 fruit each 12.0 25 Valencia oranges 6,O each 6.7
Sample 100 lemon leaves each
a A proprietary product of the Geigy Co., Inc., containing 20% technical D D T rnicronieed with pyrophyllite a8 the diluent. b A proprietary product of the Geigy Co., Inc., containing 20% technical D D T in solution in petroleum oil. e Applied in the laboratory with precision spray equipment.
excellent solvent for the hydrocarbon-type oils employed 88 carriers in most spray mixtures, the oil carried over into the final sample is of no consequence. This fact was demonstrated by adding 4 cc. of kerosene and 4 cc. of alight-medium oil, respectively, to 2 strip samples containing 200 mg. of DDT each; the '(recovery" of D D T in both experiments was above 98.5%. SOURCES OF ERROR
A C C U R A C Y AND REPRODUCIBILITY
As outlined above, the method was applied to the quantitative estimations of D D T in various amounts of a strip solution of benzene containing 2 mg. of purified D D T per ml. The results, presented in Table I, show that the variation was confined to 1.5% within the range 2 to 625 mg. of D D T per sample. Because the method was developed primarily for studies of spray residues, it has been applied assiduously only to this adaptation. In this connection, certain data pertinent to the reproducibility of the method as applied to studies in the field are collated in Table II. All the dusts and spray treatments mentioned were applied to mature citrus in a conventional manner. As may be seen from these data, the degree of reproducibility within any one experiment is very satisfactory. DISCUSSION
The various quantities of reagents specified in the procedure are those found t o be most convenient for the determination of quantities of D D T within the range 2 to 625 mg. per sample. This range may be increased readily by changing the quantity of standard silver nitrate used; a decrease in the range desired will make this a micro process, however, and will thus necessitate the use of a microburet and a weaker standard solution in the titration. Theoretically, the specified amount of alcoholic potassium hydroxide will successfully dehydrohalogenate about 17 grams of DDT per sample. Benzene was selected as the stripping solvent because at room temperature it will dissolve about 45 weight-% of D D T ( S ) , and it will not dissolve appreciably any of the inorganic halides expected to occur in ordinary sprays or dusts containing DDT. For example, inorganic halides in the spray water (hard water) will not be carried over into the strip solution, and thus will have no effect upon the analytical results. Although benzene is an
As mentioned previously, the possibility of errors introduced by inorganic chlorides in the spray materials in general need not be considered. Furthermore, contaminants of organic chlorides in general will not introduce errors unless they are capable of being dehydrohalogenated under the recommended conditions; such compounds will probably not be found in the usual spray or dust mixtures. Technical DDT contains polymers and condensation products of chloral and possibly tracea of chlorobenzene; the first two contaminants would not be expected to dehydrohalogenate readily, whereas contamination due to chlorobenzene is of no consequence, for it will not hydrolyze under the specified conditions. Since the reagents may contain traces of chlorides, however, it may be necessary to apply a small correction factor, determined with a blank run, to the results. The Volhard method is recommended for the determination of the excess silver ion because of its sensitivity. Although the end point may be hard to recognize at h t , a little practice enables one to duplicate results very satisfactorily. Overstepping of the end point need cause no concern, for the Volhard end point is reversible. Only two exact measurements are necessary-that is, one pipetting operation and one titration. All other volumetric measurements are gross, for all are greatly in excess of those theoretically required. Consequently, errors due to faulty readings of volumetric apparatus are reduced to a minimum. ACKNOWLEDGMENTS
The writer wishes to express his appreciation to Walter Ebeling, David Lindgren, and Charles Persing for applying the field treatments mentioned in Table 11, and to Leland Brown and Athalie Thomas for valuable assistance in the laboratory. LITERATURE CITED
(1) Bfand, K.,and BusseSundermann, A., Be+., 75B,1819 (1942). (2) Flrcher, O.,Zbid., 7,1191 (1874). (3) Gunther, F.A., J. Am. Chem. Soc:, 67,189(1945). (4) Zcidler, O.,Be+.,7,1180 (1874).
