Vol. 17, No. 7
INDUSTRIAL AND ENGINEERING CHEMISTRY
438
CONCLUSIONS Table 11.
Digestion-Time Study of Nicotinic A c i d and Pyridine Analyses
Compound Nicotinic acid
Catalyat
(theory 11.38R N:
Sitrogen Found after Digesting for: 1 2 2 5 3 0 4 0 hour hours hours hours hours
% .. .. .. ..
CUSO, SCOCIZ Hg
Hg f SeOClz
4.33 5.59 8.91 8.41
..
P!-iidine CUSO, (theory 17,72% S ) SeOClz Hg Hg
+ SeOCIz
%
S
5.73 5.36 3.90 4.08 10.78 1O.li 10.18 10.91 5.49
. . . . . . . . 4.56 . . . . . . . . 14.40 .. 13.49 . . 16.72 . . 17.38
o 5.62
5.05 5.19 4.48 10.83 10.21 10.77 10.97
...
. . ... . . ... ... ...
...
%
%
6.36 6.68 6.34 6.34 11.14 10.00 11.31 11.37 7.49 5.55 7.58 5.13 17.50 17.46 17 46 17.44
,, ,
., ,. .., ,
,
11.33 11.35
Mercury alone or mercury plus selenium oxychloride has been found a satisfactory catalyst for the Kjeldahl determination of the nitrogen content of compounds containing a refractory ringtype nitrogen, as in pyridine, nicotine, nicotinic acid, or quinoline. A digeation-time study showed that 3 to 4 hour3 are required for complete digestion of these compounds by the mercury catalysts. Copper sulfate and selenium oxychloride yielded extremely low resulti, even on prolonged dige-tion
...
...
ACKNOWLEDGMENT
..
The authors wish to thank Beatrice Weaver for perforniing many of the analyses reported in this article.
.. ..
...
17.66 17.69 17.48 17.52
In the case of the mercury plus selenium oxychloride catalytic mixture, the solution became clear in a short time, yet additional digeation for 2 to 3 hours was required. Because the time of digestion ordinarily is not watched too closely, it is believed that the erratic results obtained in the past on pyridine ring-type compounds (even when mercury was used as the catalyst) were probably caused by insufficient digestion time. n'hen running unknown samples, it is advisable to run a known sample, whose structure approximates that of the sample being analyzed, in order to establish the digestion time required.
LITERATURE CITED
Acree, Fred, J . Assoc. Oficial Agr. C h e w , 24, 648-51 (1941). k 3 S O C . Official Agr. Chem., Official and Tentative Methods of Analysis, 5th ed., p. 25, 1940. Belcher, R., and Godbert, A. L., J . SOC.Chem. I n d . , 60, 196-3 (1941).
Bradstreet, R. B., Chem. Reviews, 27, 331-50 (1940). Clark, E. P., J . Assoc. Oficial Agr. Chem., 24, 641-7 (1941). Ma, T. S., and Zuazaga, G., ISD. Eso. CHEM.,- 4 s ~ED., ~ .14, 280-2 (1942).
Osborn, R. A., and Krasnita, -i.,J. Issoc. Oficia2 Bgr. Chem., 17, 339-42 (1934).
Phelm. I. K.. and Daudt. H. W.. Ibid.. 3. 218-20 (1919). Prince. A. L.. Ibid.. 17. 246-50 (19341'. Sreenivasan, 'A., and Sadasivan, V., IND.ENG.CHEJf., . h 4 L . ED.,11, 314-15 (1939). Taylor, L. V., Ibid., 5, 263 (1933). .
Colorimetric M e t h o d for Determination of
I
DDT
EUGENE L. BAILES AND MERLE G. PAYNE, Colorado Agricultural Experiment Station, Fort Collins, Colo.
A
RAPID culvrimetric method for the determination of l-trichloro-2,2-bi~(p-clilorophenyl)ethane has been developed, using the Friedel-Crafts reaction. This compound, principal ingredient of technical DDT, can be determined in concentrations ranging from 0.001 t o 0.01%. The use of DDT as an insccticide has created an interest in methods for its detection and quantitative determination in such fields as spray residues and pharmacology. The high chloriiie content of D D T has been utilized as a basis for its indirect chemical analysis. Winter (7) has described a method for determining halogens in organic compounds, by burning the compound in a stream of gas and recovering the halogen in a form suitable for determination by standard methods. Hall et al. (3)have employed a modification of the Winter method for the determination of DDT in emulsions and various other materials. Fahey (1) also uses a modification of the Winter method. Gunther ( 2 ) and Neal (4)report a method for determining DDT based upon dehydrohalogenation with alcoholic alkali; a chloride ion is liberated from each molecule of DDT and the quantity of free chloride ion is determined. Schechter (6) reports that a sensitive color test based on nitration to polynitro derivatives will be described in a later paper. The method herein described is a colorimetric procedure using the Friedel-Crafts reaction. The reaction produces a compound with a stable color, orange by transmitted light and greenishorange by reflected light. This colored compound is being investigated and will be described in a later paper. APPARATUS
The Lumetron photoelectric colorimeter, model 400, made by the Photovolt Corporation was used in this study. This colorim-
eter has an optical density and per cent trailmission scale and when Beer's law applies the scale readings are proportional to the concentration. Measurements were made in an absorption tube of 1 6 . k n m . inside diameter, with a color filter transmitting about 420 millimicrons. Nissen and Peterson ( 5 ) have given a general discussion of the method; and problems of colorimetric studieq. REAGENTS
Purified DDT, prepared in this laboratory and purified by recrystallization with an alcohol-ether mixture (25% ether) until it melted a t a constant temperature of 107" C. Technical DDT, Geigy Company product, softening a t 80" C. and completely melting at 96.5" C. Benzene. The benzene used in the procedure was Merck's reagent, thiophene-free. Freezing point minimum, 5.2' C. Anhydrous aluminum chloride, Eimer and -4mend's technical and resublimed product. Ethylene chloride, Eastman 132. PROCEDURE
Purified DDT (0.1 gram) was dissolved and made up to 50 ml. with benzene, and 10 ml. of this solution were heated in a constant-temperature water bath at 66' C. for 5 minutes. Then the solution was treated with 0.5 gram of anhydrous aluminum chloride, and the mixture was heated for 1 hour at 66' C. The complex was decomposed with 3 ml. of water and 30 ml. of benzene were added. This product was treated with 1.5 grams of anhydrous calcium chloride. The mixture was allowed to stand until the turbidity disappeared. The benzene layer was decanted into a 100-ml. volumetric flask. The residue was washed with small portions of benzene to remove the last traces of color, added to the volumetric flask, and diluted to volume with benzene. The per cent transmission was read in the photoelectric colorimeter. If the benzene layer was turbid, it was necessary to allow it to stand before reading. Thi. turbidity often occurred in fruit strippings.
.
ANALYTICAL EDITION
July, 1945 Table
1.
Per Cent Transmission
1Ip
1 111.
2 MI.
3 111.
4 111.
5 111.
370
85.0 a5 5 85 0
77.0 77.0 78.0
i? 5 22 5
20.5 ,a 0
69.0
76.0 77.0 78.0 96.0 96.5 97.0 97.0 96.0 96.5 99.0 99 0 99 0 100 0 100 0 100 0
59.0 61.0 60.0
47.0 47.0 48.0
39.0 40.0 39.5
31.0 32 0 31.5
93.0 92.5 92.5
87 0 8i 0 87 5
78.0 80.0 79.0
91.0 92.0 91.5
86.0 86 5 87.0
83.0 84 0 83.5 92.0 83 0 8.' 5 96 0 96 0 96 0 100 0 100 0 100 0
420 4GKl
33 0
7\11
ti ir)
97 97 97 100 100 100
0 0 0 0 0 0
43 0
97 96 96 100 100 100
0 5 0 0 0 0
71 0
70 0
69 5
77.0 77.5 77.0 95 95 95 100 100 100
0 0 0
0 0 0
.\ ternpeiitture above 66" C. decreases the intensity of color; the reaction is completed in one hour. The color developed as soon :LS the, complex was decomposed with water and the product dissolved iii benzene. Samples of fruit may be stripped nith small quantities uf henzene diluted to a definite volume and an aliquot part treated according to the above procedure. The aliquot part for fruit strippings would vary with the per cent of D D T used in the spray. For maximum accuracy, dilutions should be chosen so that readings on the galvanometer of the photoelectric colorimeter would fall in the central portion of the scale.
Pears sprayed several times during the season with 0.06 to 0.08% D D T were sampled, 10 to 12 pears in each sample. The samples were stripped with benzene and concentrated or diluted to a volume of 250 ml., and a 10-ml. aliquot of these solutions was used in the D D T determination. The benzene left in the samples was recovered by distillation.
439
above and dilutiiig the benzene layer to 100 ml. Then 1, 2, 3, 4, and 5 ml., respectively, of each sample were measured in duplicate from a buret into a 10-ml. volumetric flask and diluted to volume \vith benzene. The per cent transmission values obtaincd :Lt 120 mp appear in T:ihle TI. RANGE OF CONCENTRATION AND ACCURACY
The best \\.orking range for the method is bet\\eeu 0.001 and 0.01% of DDT. Tlic higher concentrations were diluted and when lower concentratioiis n-ere rncountered in fruit strippings larger aliquot p:irts were taken. 4 number of &terminations xere run on knokvn amounts of purified DDT and a maximum error of 3% was found by the method h
