ANALYTICAL CHEMISTRY
1118 INTERFERENCES
If the above procedure is used, the phosphate ion does not give low results when present in amounts less than 29 times the weight of the aluminum. The chromate ion does not interfere. Silicate and fluoride ions should be a t a minimum. Manganous, zinc, and nickel ions do not affect the results. Ferric ions may give positive errors when present in amounts greater than 0.05 mg. Chromic ions give large positive errors. Magnesium ions give small positive errors, and should not be present in an amount greater than 0.05 mg. Copper, reported previously (4) along with titanium (IV) and zirconium as giving similar reactions, doeq not give positive errors unless more than 0.5 mg. is prwrnt. PRECISION
Duplicate results obtained a t different times and with vanoub solutions, with aluminum aliquots running from 0.01 to 0.07
mg., showed average negative deviation from the curve of 1.64% and average positive deviation of 1.48% of the amount of aluminum present. Maximum deviation was -3.07, with 0.01 mg. of aluminum. LITERATURE CITED
Alten, F., Wandrowski, B., and Hille, E., 2. angew. Chem., 48, 273-5 (1935).
Alten, F., Weiland, W., and Knippenberg, E., Z . anal. Chem., 96, 91-8 (1934).
Eegriwe, E., Ibid., 76, 43843 (1929). International Committee on New Analytical Reactions and Heagents of Union Internationale de Chimie, Tables of Keagents for Inorganic Analysis, First Report, p. 117, Leipzig, .ikademische Verlagsgesellschaft,1938. Millner, Theodor, 2. anal. Chem., 113,83(1938). Richter, F.,Ibid., 126, 438-43 (1944). Ibid., 127, 113-39 (1944). RECEIVED .4ugust 1, 1946.
Determination of the Insect Repellent, Dimalone JEROME GOLDENSON AND SAMUEL SASS Chemical Corps, Technical Command, Army Chemical Center, Md. S COSKECTIOS \vith \\\orE; u11 the dimethyl ester of c~s-3,6-
I endomethylene- A'-tetrahydrophthalic acid (6),an efficient insect repellent known also as Dimalone, it became necessary to
devise methods of analysis suitable for various development operations and applicable to clothing impregnated with the compound. A choice of methods is desirable during development stages of work when fixatives and other materials are used which may interfere in one method but not in another. The methods described in this paper, involving determination of methoxyl groups, bromination of the double bond in the compound, saponification, and colorimetric estimation of the methyl alcohol formed by treating the compound with alkali, were found satisfactory for determination of the compound, which has the following structure: CH
Reagents for Saponification Method. Alcoholic potassium hydroxide solution, 0.1 N. Sulfuric acid solution, 0.1 N . Phenolphthalein indicator solution. Reagents for Bromination Method. Carbon tetrachloride, C.P. Hydrochloric acid, C.P. concentrated. Potassium bromatepotassium bromide solution of 3.5 grams of C.P. potassium bromate and 13.0 grams of C.P. potassium bromide, made up to 1 liter with water. Reagents for Colorimetric Method. Potassium permanganate solution prepared by dissolving 3 grams of C.P. potassium permanganate and 15 ml. of C.P. phosphoric acid 85%, in water to make 100 ml. oxalic-sulfuric acid solution prepared by dissolving 5 grams of oxalic acid in 100 ml. of 1 to 1 sulfuric acid solution. Schiff's reagent, prepared as follows: Dissolve 0.2 gram of basic fuchsin in 120ml. of hot water, cool, and add 2 grams of anhydrous sodium sulfite dissolved in 20 ml. of water. Add 2.0 ml. of concentrated hydrochloric acid, dilute to 200 ml., and place in a refrigerator a t least 24 hours before using. Store in an amber bottle.
BUBBLE COUNITER APPARATUS
Methoxyl apparatus, essentially the same as used by Clark (3) with an absorber similar to one described by Niederl ( 6 ) and used in the determination of halogens (Figure 1). This apparatus has also been used by Alexander Sadle at the Army Chemical Center for the determination of dimethyl phthalate (7). Klett-Summerson photoelectric colorimeter with green filter KO.55 (maximum transmittance 520 to 600 millimicrons) and standardized colorimeter tubes.
I2MM.DIA
REAGENTS
Dimalone, obtained from Sowa Chemical Co., 30.5 East 46th St., New York 17, K. Y., and purified by distillation; boiling point a t 9 mm. 130-131.5", n2z 1.4853.; Reagents for Methosyl Method. Hydriodic acid, Merck grade for methoxyl determination (when reagent darkens, shake with small amount of mercury to pale yellow color). Bromine, C.P. or redistilled. Sodium acetate-acetic acid solution made by dissolving 10 grams of c . ~ sodium . acetate trihydrate in 100 ml. of glacial acetic acid. Sodium acetate solution made by dissolving 10 grams of C.P. anhydrous sodium acetate in 90 ml. of distilled water. Potassium iodide, C.P. Formic acid, C.P. Sodium thiosulfate solution, 0.1 X. Starch indicator solution. Carbon dioxide from cylinder. Cadmium sulfate solution made by dissolving 15 grams of c . ~anhydrous . cadmium sulfate in 100 ml. of distilled water. Red phosphorus, powdered. The hydriodic acid may also be prepared or purified as described by Clark ( 2 ) .
ABSORBER SPIRAL 12 TURNS QF4MM.DIA ROD
I BMMDIA.
60MM.DIAM. REACTION FLASK2 Figure 1. Diagram of Apparatus
'1119
V O L U M E 20, N O . 11, N O V E M B E R 1 9 4 8 Table I.
Determination of Dimalone in Impregnated Cloth Dirnalone Ilethoxyl method 1
2
Saponification method
70
7c
4.15 4.50 5.10 0.21
4.19 4.52 5.20 0.23
DEVELQPMWT OF METHODS
Ultraviolet Absorption Method. This method could not be applied to the determination of Dimalone, as it was found that the compound does not have an appreciable absorption in the ultraviolet from 235 to 390 millimicrons. Below 235 millimicrons there is some absorption, but only with relatively high concentrations. Methoxyl Method. Good results were obtained on the estimation of Dimalone by use of a semimicroadaptation of the ViebockSchwappach modification (9) of the original Zeisel method (IO)to determine the methoxyl groups. Recoveries of 98.8 and 98.7Tc were obtained in two determinations by this method on the material as received and, after purification by distillation, recoverieof 99.2 and 99.2% were obtained in two determinations on tht. purified material. In applying the method to cloth impregnated with Dimalone, it mas found that the compound can be satisfactorily extracted from the cloth with petroleum ether, but there is slight loss in evaporating the solvent from the extract; recoveries of 96 to 97y0 are obtained under these conditions. The method can be applied to the impregnated cloth directly without prior solvent extraction, although a small blank correction for the cloth must be made. Thv results given in Table I were obtained by application of tho methoxyl method directly to pilot plant-impregnated cloth Yamples without a fixative. ( ' u t the cloth sample into I-cm. squares and mix to make the sample more homogeneous. Place a weighed cloth sample containing from 10 to 160 mg. of Dimalone in the reaction flask of an apparatus as shown in Figure 1. Fill the bubble counter with a suspension of red phosphorus in cadmium sulfate solution, and place 20 ml. of sodium acetateacetic acid solution and 30 drops of bromine in the absorber. Assemble the apparatus as shown in Figure 1, add 10 ml. of purified hydriodic acid, and attach immediately. Pass in carbon dioxide and adjust the stream to approximately 2 bubbles per second. Heat the reaction flask gradually in an oil bath up to a temperature of 135" to 140" C., and allow the reaction mixture to reflux gently a t this temperature for 45 minutes. The point of reflux should be no higher than one third of the distance up the 35-em. (14-inch) column. Then remove the absorber and drain the contents into a 500-ml. iodine flask containing 10 ml. of a 10% sodium acetate solution. Rinse the absorber with distilled water into the flask to a volume of no more than 125 ml. -4dd formic acid dropwise to the contents of the flask until the bromine color disappears, stopper, and shake to remove bromine vapors in the flask. Add an excess of 3 drops of formic acid. Allow the flask to stand for 3 minutes, add 3 grams of potassium iodide, swirl the contents of the flask until the potassium iodide dissolves, stopper, and allow to stand in the dark for 10 minutes. Titrate with 0.1 S sodium thiosulfate, using htarch as an indicator. Make a blank determination on unimpregnated cloth and correct the titration for this blank. Calculation.
alcoholic potassium hydroxide in the flask of a Soxhlet extraction apparatus and alcohol in the extraction thimble. The potentiometric titration curve relating p H and ml. of 0.1 N sodium hydroxide for cis-3,6-endomethylene- A4-tetrahydrophthalic acid is given in the literature ( 5 ) . Chlorinated paraffin, when used as a fivative, gives high results in the method and Nacconol NR, a wdium alkyl aryl sulfonate, which is 3ometimes used in laundering the cloth, interferes slightly. In Table I, results obtained by the saponification method and methoxyl method on pilot plant-impregnated cloth samples without a fixative are given. C'ut the cloth sample into 1-cm. squares. Place a 3.000- to 5.000-gram sample of coth (enough to contain from 30 to 200 mg. of Dimalone) in the thimble ofasoxhlet extraction apparatus, and add 30.0 ml. of 0.1 N alcoholic potassium hydroxide to the flask. Add alcohol to the thimble in an amount about 10 ml. in excess of that required to fill the thimble portion of the extractor. Extract and saponify for 1.5 hours. Remove the flask from the apparatus, cool, add 50 ml. of distilled water and a few drops of phenolphthalein indicator, and titrate to a colorless end point with 0.1 AV d f u r i c acid. Run a blank determination under the same rondiitons with unimpregnated cloth Calculation.
( (
Dimalone =
iml. of blanh H.SO, titration - nil. of baniule H ~ S Otitration)->( I normalityof HZSOl X 10 511 sample weight
i correction may be made for the interfering effect of chlorinated paraffin by using the Volhard method to determine the liberated chloride in the solution after the titration with standard sulfuric acid and making a correction for the amount of sodium hydroxide consumed by the chlorinated paraffin. Bromination Method. It was found that the double bond in Dimalone can be quantitatively brominated in carbon tetrachloride or acetic acid solution with potassium bromide-bromate solution; recoveries of 99% and better were obtained in trials with known amounts of Dimalone. In trials with known amounts of Diinalone in cloth, it was found that the compound may be extracted from the cloth with carbon tetrachloride in a Soxhlet type extractor or by soaking in several portions of acetic acid and decanting. Slightly higher blanks wcrc obtained when acetic acid was usrd. Cut the cloth sample into 1-em. squares and mix to make the sample more homogeneous. Extract a 3.000- to 5.000-gram 3ample (enough to contain from 25 to 150 mg. of Dimalone) with carbon tetrachloride in a Soxhlet type extractor, transfer the extract to a 500-ml. iodine flask, add a measured amount of potassium bromide-bromate solution (25 to 35 ml., depending on the amount needed to have at least 2- to 5-ml. excess over that required for bromination), and add 4 ml. of concentrated hydrochloric acid. Insert the stopper quickly and shake intermittently for 10 minutes. Add 10 ml. of lOCI, potassium iodide solution, taking care to avoid loss of bromine while the stopper is being lifted. Wash down the stopper and the sides of the flask with STater and titrate the liberated iodine with 0.1 N sodium thiosulfate solution, using starch indicator near the end of the titration. Run a cloth blank under the same conditions. The difference between the titration volume of the blank and that of the sample after bromination is the net titration. Calculation. (net titration of SatS203)X normality of i\rTa&O? X 10.511 Dimalone = sample weight ~~
o/ /@
Dimalone = nil. of Xa&03 X normality of SaaStO? X 1.7518 sample weight
The apparatus should be thoroughly dried before each determination. If high blanks are obtained, extract the Dimalone with petroleum ether in B Soxhlet extraction apparatus, transfer the extract to the reaction flask, and carefully evaporate the solvent. A very slight loss of Dimalone occurs during the evaporation. Saponification Method. It wm found that Dimalone may be extrarted from cloth and saponified in one operation by placing
.la ail alternative procedure, Dimalone may be extracted from the cloth by soaking in six 10-ml. portions of glacial acetic acid, and decanting the extract into the iodine flask. This procedure does not require a Sovhlet extraction apparatus and gives a onephase solution for the titration, but slightly higher blank titrations are obtained. Colorimetric Method. The modified Deniges method ( I , 8,for inethyl alcohol in ethyl alcohol \va\ adapted to estimation of .mallcr amounts of Dimalontl
ANALYTICAL CHEMISTRY
1120.
-1weighed amount of Dimalone was saponified under reflux and the resulting methyl alcohol was distilled from the reaction mixture and determined in the distillate by a method similar to that given in the literature (1, 8). I n place of matching colors in K’essler tubes, the light transmittance a t 520 to 600 millimicrons (Klett green filter No. 5 5 ) \vas read with a Klett-Summerson photoelectric colorimeter. h curve relating Dimalone concentration with colorimeter reading was made by plotting the values obtained using known amounts of Dimalone in the procedure. Small amounts of Dimalone down to 2.5 mg., or 0.025% on a 10-gram cloth-sample basis, could be determined within * 10% by this method, and no interference was experienced with purefinish or sized cloth with or without chlorinated paraffin as R binder. Cut the cloth sample into 1-cm. squares and mix to make the sample more homogeneous. Place a 10-gram cloth sample (or enough to contain a t least 2.5 mg. of Dimalone) in a flask with a standard-taper ground-glass neck, add 50 ml. of 0.2 N aqueous potassium hydroxide solution, fasten t o a reflux condenser, and boil gently for 30 minutes. Cool the flask, wash down the reflux condenser t o the flask, and distill over 100 ml. of liquid, collecting the distillate in a volumetric flask cooled in ice water. Transfer 5.0 ml. of the distillate to a 20-ml. glass-stoppered test tube, add 0 06 ml. of 95% ethanol from a pipet graduated in 0.01 ml., and mix. Add 2 ml. of the potassium permanganate solution and allow to stand 10 minutes with occasional shaking without inverting the tube, and then add 2 ml. of the oxalic-sulfuric acid solution. When the solution is decolorized, add 5 ml. of the modified Schiff’s reagent, mix thoroughly by inverting the tube three times, stopper, and allow to stand 1 hour. Take a reading of the solution in a Klett-Summerson colorimeter, using a green filter S o . 54 (520-600 millimicrons). Prepare a curve relating photoelectric colorimeter readings with Dimalone concentrations, using known amounts of Dimalone treated as described above, and make the quantitative determination of the unknown by applying the reading obtained to the curve. If a reading is obtained which is too high to be read from the curve, prepare several dilutions and make determinations until the right range is obtained. If interfering substances such as aldehydes or phenols are present, modify the distillation t o separate them. The procedure for separating most of the interfering substanceq is described bv Georgia and Morales ( 4 ) .
DISCUSSION
The saponification method has been found to be accurate for amounts down to about 30mg. of Dimalone, and aspecial correction must be made in the presence of fixatives such as chlorinated paraffin. The bromination method is rapid and accurate for amounts down to about 25 mg. and only slight interference has been experienced. The methoxyl method is accurate for amounts down to about 10 mg., and blank corrections and a special apparatus are required. The colorimetric method is applicable for approximations of small amounts down to 2.5 mg., and no interference has been experienced either from pure-finish or sized cloth or from fixatives such as chlorinated paraffin. Although no other repellent was used with Dimalone in the authors’ work, mixtures are frequently used for skin application containing repellents and miticides such as dimethyl phthalate, dibutyl phthalate, benzyl benzoate, Indalone, and others. S o n e of the methods described in this paper is exclusively applicable for Dimalone, but the bromination method, for example, could be used in the presence of dimethyl phthalate, or the methoxyl method would be applicahle in the presence of benzyl benzoate. LITERATURE CITED (1)
(2) (3) (4)
(5) (6)
Bssoc. Officialri gr. Chem., “Official and Tentative Methods of Analysis,” 6th ed., p. 197, 1945. Clark, E. P., IND. ENG.C H E M ANAL. , ED.,10,677 (1938). Clark, E. P., J . Am. Chem. SOC.,51, 1479 (1929). Georgia, F. R., and Morales, R., Ind. Eng. Chem., 18, 304 (1926). Morgan, M. S., Tipson, R. S., Lowy, -4., and Baldwin, W. E., J . Am. Chem. Soc., 66,404 (1944). Niederl, J. B., and Niederl, V., “Organic Quantitative Microanalysis,” 2nd ed., p. 169, New York, John Wiley & Sons, 1942.
(7) Officeof TechnicalServices, U.S. Dept. Commerce,Rept. PB2380. (8) Snell, F. D., and Snell, C. T., “Colorimetric Methods of Bnalysis,” 1st ed., Vol. 2, p. 17, New York, D. Van Nostrand Co., 1939. (9) Viebock, F., and Schwappach, A., Ber., 63, 2818, 3207 (1930): Mikrochemie 10, 188 (1932). (10) Zeisel. S , Monatsh., 6, 989 (1855) RECEIVEDJanuary 29, 1948.
Rapid Wet Combustion Method for Carbon Determination W i t h Particular Reference to Isotopic Carbon ARTHUK LINDENBAUM, JACK SCHUBERT, AND W. D. tRMSTRONG Cnioersity of Minnesota, Minneapolis 14, Minn.
CONVEKIENT wet combustion procedure has been deA veloped for the determination of the total and radioactive carbon content of the same sample of animal tissues, eucreta, and other materials. The sample is oxidized under reduced pressure with the conibustion mixture of Van Slyke and Folch (4),and the evolved carbon dioxide is absorbed directly in a saturated solution of barium hydroxide contained in a centrifuge tube. The BaC1403suspension is centrifuged, and the precipitate is washed and collected in a Buchner-style brass funnel (1). After being dried by washing n4th acetone and ether, and weighed, the BaC‘lOa is ready for determination of its radioactivity (1). A procedure similar in principle was used by Gurin and Delluva ( 3 ) for the oxidation of organic materials, but no details were given. PROCEDURE
The combustion fluid is prepared by mixing, in a glass-stoppered Erlenmeyer flask, 6 gramsof chromic oxide (minimum Cr.08 content 98%), 33 mi. of sirupy orthophosphoric acid (specific gravity 1.710), and 67 ml. of fuming sulfuric acid (20 t o 30% sulfur trioxide). The mixture is heated t o 160” C. and maintained a t a temperature of 140” t o 160’ C. for 15 minutes. The flask rontents are mixed frequently by swirling in order to facilitate
the solution of the chromic oxide and the escape of carbon dioxide from oxidation of contaminating organic material. The neck of the flask is covered with a beaker and, after the contents have cooled t o room temperature, the glass stopper is inserted. The flask neck is protected from dust by a beaker. Larger volumes of the combustion mixture are prepared by a proportionate increase in the amounts of the reagents. Low results are sometimes obtained when old preparations of combustion fluid are employed, presumably because of a reduction in oxidizing power. On this account the combustion fluid should not be used when more than one week old. The samples t o be oxidized should not be grossly wet and should contain not more than 15 mg. of carbon. The apparatus used is s h o m in Figure 1. Tubes A contain Ascarite and Drierite for the removal of carbon dioxide from air entering the apparatus. Ground joints B and D and stopcock C are lubricated with sirupy phosphoric acid. All other glass joints are lubricated with ordinary stopcock grease. The pulverized and weighed sample is placed in the 30-ml. combustion tube, E, together with about 300 mg. of potassium iodate. Liquid samples, such as urine, are prepared for analysis by evaporating a known volume (2 t o 5 ml.) t o dryness in a combustion tube. The filter assembly is connected to the receiver, H (a 100-ml. centrifuge tube), bv uniting joint J with the joint on tube F , and about 25 ml. of saturated barium hydroxide are filtered, by suction, through fritted disk K into the receiver. The vacuum is released by slowly opening A , t o the atmosphere. The filtration of the barium hydroxide into the receiver serves to render the filtrate es-
