316
*
INDUSTRIAL AND ENGINEERING CHEMISTRY
of the concentration of methyl chloride present in a given sample of air may be expected by the method. Therefore this correction factor is included in the calculation to compensate for the systematic error. It is believed that the systematic error is attributable to the retention in the reactor of combusion products that are not completely removed by rinsing 7%-ithchloride-free air.
Vol. 18, No. 5
done. With complete combustion no interference resulted from the presence of organic sulfur compounds. ACKNOWLEDGMENT
OTHER APPLICATIONG
The authors wish to thank the Humble Oil & Refining Company, under whose auspices this work was accomplished, for permission to publish the present article.
It is contemplated that the‘ method described in this article will prove useful in the detection and determination of traces of
LITERATURE CITED
various organic halogen compounds such as refrigerants in air. The method may, with proper modifications, be applied to the determination of traces of methyl chloride in hydrocarbon gases. Although a few determinations of methyl chloride in hydrocarbons containing organic sulfur compounds have been made by this mcthod, no controlled work to evaluate its accuracy has been
(1) Luce, E. N., Denice, E. C., and Akerlund, F. E., IND. ENG. CHEX.,ANAL.ED.,15,365 (1943). (2) Martinek, AM. J., and Marti, W. C., Ibid., 3, 408 (1931). (3) Patty, F. A . , Schrenk, H. H., and Yant, W. P., Ibid., 4, 259 (1932). (4) Williams, D., Haines, G. S., and Heindel, F. D., Ibicl., 17, 289 (1945).
Field Test for Surface .HENRY A. STIFF, JR.*,
AND
DDT
JULIO C. CASTILLO, Antilles Department, Medical Laboratory, United States A r m y
A simple field test for surface DDT is presented by which a dotermination can be completed in 4 to 3 minutes. Conditions which may be encountered in using the test are indicated.
HE application by spray of DDT in solution or in an emul- . sion, so as to leave a surface residue, presents numerous op-
T
portunities for using a fast simple field test to detect the presence of this substance on the surface. By means of such a test the many factors which may affect the concentration of D D T left on a surface after spraying may be studied and perhaps controlled, thus bringing about the development of more efficient and economical methods of application. The present communication presents a test based upon a development of the xanthydrol-potassium hydroxide-pyridine reaction for D D T (2). It is simple, sensitive, rapid, and may be used in the field. PRINCIPLE
PROCEDURE
An area of about 12 square inches (3 X 4 inches) of the surface supposed to contain DDT is thoroughly scrubbed with the oilimpregnated swab. A test tube is then inserted into the hydroxide bottle, and two pellets are picked up on the lip and allowed to slide to the bottom of the tube. The bottle is immediately recapped to prevent absorption of moisture. Two milliliters of 0.4% xanthydrol in pyridine are then added t o the tube by means of the pipet. Using the holder, the tube is kept a t a gentle boil over the alcohol lamp by moving it in and out of the flame. When the coments turn green, the swab is inserted, and the tube boiled for a few seconds longer. If D D T is present, the color changes to red. If no DDT is present, the green fades quickly to yellow. The *entire procedure takes from 2 to 3 minutes. EXPERIMENTAL
D D T is removed from a surface by scrubbing with a cotton swab impregnated with mineral oil. The swab is then subjected to a modified xanthydrol-potassium hydroxide-pyridine reaction. In the presence of D D T a red color is secured. REAGENTS AND APPARATUS
Only two reagents are required: a o.4y0 solution of xanthydrol in pure anhydrous pyridine, and potassium hydroxide pellets, U.S.P. (either Merck or Baker). Some lots of C.P. pyridine are sufficiently anhydrous for use without purification, but most samples contain water. This may be easily removed by allowing the compound to stand in contact with stick sodium hydroxide for several days and then distilling. The xanthydrol-pyridine solution must be kept in a glass-stoppered bottle, and may be used for several days without deterioration. The hydroxide should be kept in a tightly capped container when not in use, in order that the pellets may absorb as little water as possiblc. The apparatus consists of a supply of clean dry 17 X 150 mm. test tubes, a small alcohol lamp, a test tube holder, a 2-ml. pipet, and a number of oil-impregnated swabs. The swabs are prepared by wrapping a bit of cotton tightly around the end of an applicator stick, dipping it in clear liquid petrolatum, and then squeezing out the excess against the side of the container. The reagents and apparatus may be packed into a suitable box or case for ease in carrying. The set used by the authors consists of a 72-tube wire test-tube rack such as is used for Wassermann tests. Wires ivere cut out to provide space for the reagent 1 Captain, Sanitary Corps, A r m y of t h e United States. 4904 West Stanford St., Dallas 9, Texas.
bottles and the lamp, as well as for a large tube containing swabs. This arrangement provides a rack for a dozen or more test tubes. The pipet may be carried in one of the tubes or may be secured to the rear, together with the test-tube holder, by means of clips.
Preaent address,
A large number of different surfaces known not to contain DDT, such as brick, cement, stone, tile, glass, paper, plaster, screen, wood, paint, metal, plastics, canvas, fruit, foliage, grass, etc., were swabbed and tested. No false positives were secured. D D T in ether solution in concentrations varying by increments of 5 micrograms was measured directly onto a series of swabs. The ether was allowed to evaporate a t room temperature and the swabs were subjected to the test. Twenty-five micrograms of DDT were detectable by comparison with a blank, while 75 micrograms gave a very distinct pink color. DDT in 59” kerosene solution and 5y0 aqueous triton-xylene emulsion was applied to 3 X 4 inch (12 square inches) surfaces of commonly encountered materials in concentration varying by increments as follows: 1 mg. per square foot from 1 to 10 mg. per square foot, 5 mg. per square foot from 10 to 100 mg. per square foot, 25 mg. per square foot from 100 to 1000 mg. per square foot, 50 mg. per square foot from 1000 to 2000 mg. per square foot. Except in concentrations up to 10 mg. per square foot where 1 to 10 dilutions with kerosene and water were made, the solution or emulsion was applied without dilution. Application was made directly to the surface by means of micropipets, spotting the entire surface so as to obtain a uniform distribution of small drops in the lower concentrations, and a film of liquid in t,he higher concentrations. This was done to approximate the action of a spray, i n d a t the same time accurately control the amount applied, as accurate control of the amount applied with a spray would have been impossible. After exposure for 48 hours a t room conditions, the entire surface was scrubbed with a swab and tested for DDT. A positive test was considered as one which matched the color secured with a swab containing 75 micrcgrams of DDT. The minimum concentrations a t which t,hr test was positive are glven in Table I.
ANALYTICAL EDITION
May, 1946 Table
I. Minimum Concentration of DDT in Positive Test '
( M g , per square foot, as applied, a t which positive tests were secured on various surfaces after a plication of DDT as a 570 kerosene solution and a triton-xylene-water emulsion.) Kerosene Triton Material Solution Emulsion Tent canvas, untreated Celotex building board, unpainted Rubber matting, ribbed Soft pine hoard, unpainted Celotex building hoard, oil paint surface Plaster, oil paint surface Soft pine hoard, oil paint surface Plaster, fresh, smooth surface, unpainted Sheet metal, galvanized surface Glass, plate
58
DISCUSSION
The xanthydrol-potassium hydroxide-pyridine reaction is not specific for 2,2-bis-(p-chlorophenyl)-l,l,l-trichoroethane but is given by a number of related compounds containing aliphatic halogen (1, 2 ) . With due caution in using the test, hon-ever, this factor should not seriously affect its value, as the presence of such compounds is usually known. There are obviously many factors which may influence the concentration of D D T upon a surface after its application in solution or emulsion. It is the purpose of this communication to present a simple method which may aid in the study of these factors, rather than to give detailed consideration to the factors themselves. Such things as the porosity of the surface t o the
317
solvent used, the presence or absence of moisture on the surface or in the material, the size of the droplets deposited by the spray, and even the temperature and relative humidity a t the time the spray was applied may be important in determining the amount of D D T left on a surface. For this reason a statistical evaluation of the application of the test is impossible a t the present time, and the data are presented only to convey an idea as t o what may be expected in using the method. On the same basis, it is impossible t o control all the conditions of experimental work, so that the figures are more a representation of order or magnitude than exact data. One rather definite conclusion can be drawn from the experiments, however. If conditions are such that more than 0.075 mg. of D D T can be picked up on the swab by scrubbing the surface, a positive test will be secured. The experimental data presented deal with the surfaces of building materials. These materials were used because of their availability and because they suited the conditions of the experiment. Application of the test to fruit, grass, vegetation, and foliage leads the authors to believe that the conditions encountered in testing building materials apply t o these surfaces also. In general, fruit and green foliage, being relatively nonporous, will retain a high concentration of D D T on the surface, while dry vegetation, absorbing more of the solution or emulsion, will have less of a surface residue. LITERATURE CITED
(1) Irreverre, F., and Sharpless,N. E., Science, 102,304 (1945). (2) Stiff, H.A., and Castillo, J. C.,Ibid., 101,440 (1945).
Colorimetric Determination of Fatty Acids and Esters UNO T. HILL, Inland Steel Company, East Chicago, Ind. A rapid colorimetric method for determination of fatty acids and esters is based on the formation of hydroxamic acid from fatty esters b y the use of hydroxylamine hydrochloride in alkaline media. O n the addition of an acidified solution of alcoholic ferric pcrchlorate, a stable red colored complex of ferric hydroxamate is formed, proportionate in intensity to the esters present. Fatty acids are first quantitatively methylated in an anhydrous ether solution with diazomethane or thionyl chloride. The method has been applied to the quantitative determination of oil on tin plate The results are in good agreement with a gravimetric determination,
EXISTING
methods for the estimation of fatty acids and their esters are time-consuming and tedious and often are inaccurate when interfering substances are present. This investigation was undertaken to develop a rapid and accurate method for the determination of small amounts of palm oil, cottonseed oil, dibutyl sebacate, and lanolin applied to tin plate and other sheet metal surfaces for rust prevention, lubrication, or other purposes in subsequent manufacturing operations. EQUIPMENT USED
Coleman Model 11 spectrophotometer and Cenco-SheardSanford filter photelometer. EXPERIMENTAL
The spot tests for carboxylic acids and esters are the basis for the proposed method (1). When an ester is warmed in an alkaline media with hydroxylamine, hydroxamic acid is formed. Feigl (I)reports the following reaction: R.CO.OR
+ XHZOH == R.CO(KHOH) + ROH
Ferric iron forms a bright red or a lavender complex with hydroxamic acids in acid media according to the reaction (I):
H R.CO(NHOH)
+ F e + + + = R-C(
N-0
0...Fk,3
The red colored complex is readily soluble in aqueous ethanol, isopropanol, or methasol, being least stable in the isopropanol. The stability decreases with increased water content, about 5% of water being optimum for the three alcohols. The ferric hydroxamate complex gains about 0.1yo transmittancy per minute for the first 20 minutes but becomes rather stable beyond this, the rate being less than 0.05% per minute. A rise in temperature produces a gain of 0.2% transmittancy per degree a t room temperature. The addition of a small amount of sodium carbonate increases the color stability beyond the figures shown above. Hydrochloric acid and ferric chloride are used in a spot test by Feigl (1) to form ferric hydroxamate. The complex follows Beer's law when perchloric acid and ferric perchlorate are substituted for hydrochloric acid and ferric chloride. Fatty acids do not form hydroxamic acid directly but are first quantitatively methylated in a n anhydrous ether solution according to one of the following procedures and the esters determined in the usual way. With thionyl chloride:
+ SOClp R.CO.CI + C&OH
R.CO.OH
=i
+ SO2 + HCI R.CO.OCHs + HCl
R.COC1
Or with diazomethane: R.CO.OH
+ CHSNI
R.CO.OCHs
+ N,
