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 to a reflux condenser, and boil gently for 30 minutes. Cool the flask, wash down the reflux condenser to 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 to 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., L o w , -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 to 160” C. and maintained a t a temperature of 140” to 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 to 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 to 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-
1121
V O L U M E 20, NO. 11, N O V E M B E R 1 9 4 8 Table 1. Results Obtained by Wet Combustion Method Compound Cholesterol Cystine Sucrose Tristearin
Carbon Recovered". h
70
100.1 100.2 99.5 99.7
* * * *
0.23 0.2 0.8 0.1
No of Determination. 4 3 8 3
Mean results shown as percentage of theoretical result k average deviation. b Blanks varied from 0.17 t o 0 . 3 rng. of BaCOa, equivalent t o 0.010 to 0.061 mg. of carbon. a
sentially free from carbonate and to this end the precipitate of barium carbonate which collects on pi should not be removed until it interferes with the passage of liquid through the filter. The filter is quickly removed and the apparatus assembled as shown. An ice-water bath is placed around H . A precipitate of barium hydroxide forms but does not interfere with carbon dioxide absorption and the barium hydroxide precipitate dissolves when the contents of H are later warmed to room temperature. The combustion fluid (10ml.) is run into E. The apparatus is then exhausted with a water pump and stopcock L is closed. The mixture in E is warmed with a small flame until boiling begins, then boiled gently for 3 minutes. The flame should be applied directly t o the bottom part of the combustion tube during the early part of this period in order to hasten the solution of the potassium iodate. After the cessation of boiling, 20 minutes are allowed to pass before tube H is removed, in order t o ensure the complete absorption of carbon dioxide. During this time the liquid in H will sometimes be drawn into F. Should this occur, sufficient air is admitted through stopcock C to equalize the pressure differences. Tube H is removed after stopcock C is slowly opened and tube F is rapidly rinsed into H with carbon dioxide-free water. The receiver is stoppered, warmed in a stream of hot tap water, and centrifuged. The precipitate is washed twice with carbon dioxide-free m-ater. The residual barium carbonate n hich clings t o the inlet tube, F , is washed into H , after being dislodged mechanically with a rubber-tipped stirring rod. The barium carbonate is
again washed, centrifuged, transferred to a weighed collection funnel ( I ) , dried, and weighed. Some of the results obtained with pure substances are given in Table I. Five analyses for carbon in dried muscle gave results with an average deviation of 4 parts per thousand from the mean. Duplicate analyses of six urines showed an average deviation of less than 7 parts per thousand from the average result of each pair of duplicate analyses. The radioactivity of the BaC1403 from the combustion, in duplicate, of samples of bone, protein, urine, and liver glycogen of animals treated with radioactive carbon ( 2 ) v a s determined. The average deviation between 14 pairs of such duplicate trials was 1.9%. ACKNOWLEDGMENTS
This work was supported by a grant from the Research Grants Division of the U.S. Public Health Service. The technical assistance of Mary I,. Smersh and Mary L. Gouzr is gratefully acknowledged. LITERATURE CITED
(1) Armstrong, IT. D., and Schubert. J., AXAL.CHEM.,20,270 (1948). (2) Armstrong, IT. D., Schubert. J., and Lindenbaum, A, unpub-
lished work.
(3) Gurin, S., and Delluva, A. M., J . Biol. Chem., 170,545 (1947). (4) Van Slyke, D. D., and Folch, J., Ibid., 136,509 (1940). RECEIVED December 17. 1947.
Determining Total Replaceable in Soils C. J. SCHOLLENBERGER Ohio Agricultural Experiment Station, Wooster, Ohio and Willhite suggested evaporating the ammonium BR.4T acetate leachate of a soil, igniting the residue to carbonates, off carbon dioxide, and (1)
PUMP
dissolving in excess standard acid, boiling back-titrating with standard alkali to the methyl red end point to determine the total exchangeable bases extracted. The procedure has proved useful and the determinations ale usually closely reproducible. However, with certain soils the ignited residue is gray to black and contains much black material insoluble in boiling 1 S hydrochloric acid. This is not alwayb merely carbon, but may consist largely of oxides of manganese, present in the soil as an exchangeable base. This residue may be brought into solution in the acid and its basicity included in the determination by adding 2 or 3 drops of 30% hydrogen peroxide and letting stand for a feiv minutes before boiling. Trials with blanks showed that the added peroxide caused no appreciable error in the titration n-hen the indicator m-as added in alcoholic solution, as is usual with methyl red. The alcohol protected the indicator from bleaching by the peroxide and no determinable amount of acid resulted from the partial oxidation. Methyl red is a satisfactory indicator for this titration. The color change is sharp and vivid, easily seen, even in the presence of suspended carbon. The end point is sufficiently high on the pH scale to ensure that any iron or aluminum present will not be included with the bases, but not so high that there is risk of not including manganese, by precipitation as the dioxide by hydrogen peroxide surviving. In addition, the latter reaction is hindered by the trace of alcohol present. LlTERATURE CITED
(1) Bray, R.H., and Willhite, F. M . , IND. ENQ.CHEM., ANAL.ED.,1, 144 (1929).
Figure 1. Apparatus
RECEIVED April 23, 1948. .Journal Article 1-48
hpproved by the director for publication
as
