ANALYTICAL CHEMISTRY
458
’
(4) Brownsett, T., and Clibbens, D. A,, J . Textile Inst., 32, T32 (22) Mease, R. T., and Gleysteen, L. F., Ibid., 27, 543 (1941). (1941). (23) Neale, S. M., and Waite, R., T r a n s . Faraday Soc., 37, 261 (1941). (5) Clibbens, D., Tech. Assoc. Papers, 25, 734 (1942). (24) Ost, H., 2. angew. Chem., 24, 1892 (1911). (6) Clibbens, D,A., and Geake, A,, J . TextileInst., 19, T77 (1928). (25) Rich, E. D., Paper Trade J., 112, 35 (Feb. 6, 1941). (7) Committee on Viscosity of Cellulose, AM. CHEx SOC., IND. (26) Russell, W. W., and Woodberry, N. T., IXD. EXG. CHEM., EXG.CHEM., AN.4L. ED.. 1, 49 (1929). ANAL. ED., 12, 151 (1940). (8) Corey, A. B., and Gray, H. L., I n d . Eng. Chem., 16, 853, 1130 (27) Sakurada, I., B e r . , 63, 2027 (1930). (1924). -(28) Scheller, E., Melliand Textilber., 16, 787 (1935); in Tech. Assoc (9) Dawson, H. M., J . Chem. Soc., 95, 370 (1909). Papers, 25, 551 (1942). (10) Dept. of Scientific and Industrial Research, Fabrics Research (29) Schtltz, F., Klandita, W., and Winterfeld. P., Papier-Fabrikant, Committee, London, 1932. 35, 117 (1937). (11) Doering, H., Papier-Fabrikant, 38, 80 (1940). (30) Schweieer, Eduard, J . prakt. Chem., 72, 109, 334 (1857). (12) Farrow, F. D., and Neale, S. M.,J . Textile Inst., 15, T157 (31) Small, J. O., I n d . Eng. Chem., 17, 515 (1925). (1924). (32) Snedecor, G. W.,“Statistical Methods,” p. 60, Ames, Iowa, (13) German Association of Pulp and Paper Chemists and En,’Vineers, Iowa State College Press, 1946. Papier-Fabrikant, 34, 113 (1936). (14) Gibson, W. H., Spencer, L., and McCall, R., J . Chem. Soc., (33) Starnm, A J., J . Phgs. Chem., 35, 659 (1931). 117, 493 (1920). (34) Stiauss, F L., and Levy, R. M., Paper Trade J., 114, 31 (Jan. (15) Hatch, R. S.,Hammond, R. N.,and McNair, J. J., Tech. 15, 1942); 118, 29 (Feb. 10, 1944). Assoc. Papers, 25,426 (1942). (35) Tankard, J., and Graham, J., J . TestiZeInst., 21, T260 (1930). (16) Hisey, W. O., andBrandon, C. E., Ibid., 27, 697 (1944). (36) Technical Assoc. of Pulp and Paper Industry, Standard T206m(17) Howlett, F., and Belward, D., J. TextileInst., 40, T399 (1949). 44. (18) Jolley, L. J., Ibid., 30, T4, T22 (1939). (37) Traube, Wilhelrn, Bw., 54, 3220 (1921). (19) Joyner, R. A., J. Chem. Soc., 121, 1511 (1922). (38) Van Bemmelen, J. >I., 2. anorg. Chem., 5, 466 (1894). (20) Kumiohel. W.. Pavier-Fabrikant. 36. 173, 497 (1938). (39) Woolwich Research Dept., Rept. 22 (1923). ( 2 1 ) Mease, R. T., J. Research N a t l . Birr. Standards, 22, 271 (1939); 27, 551 (1941). RECEIVED September 13, 1949.
Determination of Safrole in Soap NORMAN H. ISHLER, EMANUEL BORKER, AND CATHERINE R. GERBER Central Research Laboratories, General Foods Corporation, Hoboken, N . J . An analytical method based on the ultraviolet absorption characteristics of safrole in9.5%aqueousalcohol has been developed for the determination of safrole in soap. The safrole is steam-distilled from the sample after treatment with silver nitrate to precipitate the soap. The distillate is examined in a Beckman DU spectrophotometer and the concentration of safrole is determined from the observed absorbence. Statistical evaluation indicates a reproducibility of results within the range *6970 of the safrole value when dealing with samples containing approximately O.lV0 safrole.
A
S ANALYTICAL method for the determination of sniall amounts of safrole (4-allyl-1,2-methylenedioxybenzene)in soap was needed for production control and t o permit storage studies of its retention in soap. Previously developed gravimetric ( I , 3 , 4 ) and cryoscopic methods ( 7 ) were readily applicable only t o large quantities of safrole. A method based on the ultraviolet absorption characteristics of safrole appeared t o offer a possible solution. These absorption characteristics have been reported in the literature by several investigators (b, 5, 6). A sample of Brazilian safrole of specific gravity (20/4) 1.096 and refractive index (~O/D) 1.538 was used in this investigation. Because safrole is insoluble in water, some suitable solvent was necessary t o enable study of its ultraviolet absorption characteristics. Absorbence-wave-length curves were determined with chloroform, 9.5% aqueous alcohol, and hexane as solvents. Reagent grade chloroform and hexane solutions of safrole gave satisfactory curves. When these organic solvents were saturated with water, the observed absorbence was greater than before saturation and consistent results could not be obtained. A 9.5% aqueous alcohol solution gave a satisfactory absorption curve in the Beckman spectrophotometer with absorption maxima a t 286 and 232 mp with slit widths of 0.80 and 1.6 mm., respectively. Because the 9.5% aqueous alcohol solution of safrole gave such satisfactory results, it was used as a standard solvent in the investigation. To estimate safrole quantitatively, an accurate determination of its absorbence (loglo 100/per cent transmittance) was necessary to calculate a factor. Fifty observations were made t o evaluate the
safrole factor. Solutions of varying concentration from 1.096 to 4.384 mg. of safrole per 100 ml. in 9.5% alcohol-water were prepared and the absorbence a t 285 mp was determined in a Beckman Model DU spectrophotometer. Averages of the data are presented in Table I. The average that best suits the data is an absorbence of 0.207per mg. of safrole per 100 ml. of 9.5% alcohol solution. The data show a satisfactory conformance to the BeerLambert law. Each independent observer should determine the absorbence for the safrole and the instrument used. Separation of safrole from soap by distillation was attempted but only 26% of the oil was recovered. Recovery from 9.5% alcohol by steam distillation was then tried. Various amounts of safrole (2.0t o 9.0 mg.) were steam-distilled with water and 20 ml. of alcohol t o make a 9.5% aqueous alcohol distillate. TWO hundred milliliters of distillate were collected, followed by addition of 20 ml. of alcohol t o the distilling flask and collection of
Table I.
Determination of Safrole Factor in 9.5970 Alcohol Solution
Safrole, RIg./100 M I . 1.096 1.534 2.192 3.288 4.384
No. of Observations 10 10 IO 10 10
Av. Absorbence at 285 mp, Loglo loo/% Trans. 0.226
0.318 0.453 0.678 0,897
4 VI Safrole Factor.
Absorbenae/
Sk./lOO M1. 0.207 0.208 0.207 0.206 0.205
V O L U M E 22, NO. 3, M A R C H 1 9 5 0 Table 11.
459
Loss of Safrole in 9.5% Aqueous Alcohol after Refluxing with Various Reagents
(Calculated from absorbence of flask contents) Loss of Safrole Reagents i n Reflux 16-minute 45-minute Flask reflux reflux Distilled water 0 . 5 N acetic acid 0 . 5 A' sulfuric acid 0 . 5 N sodium hydroxide
%
%
8.3 5.6 6.6 7.3
42.5 27.4 40: 3
200 ml. more of distillate. .4n average recovery of 83.8% of the safrole initially present was obtained in the first portion. No appreciable absorbence a t 285 mp was found either in the second portion of distillate or in the residue in the distilling flask. The effect of the presence of acid and alkali in the distilling flask on the recovery of safrole was studied by refluxing 9.5% aqueous alcohol solutions of safrole with several reagents for periods of 15 and 45 minutes. The values obtained by measurement of the absorbence of the flask contents, as shown in Tablr 11, show loss of safrole to be least in the presence of a weak acid. In confirmation of this, steam distillation of a 9.5% aqueous alcohol solution of safrole containing 0.5 N acetic acid yielded an average safrole loss of 5.5% for five determinations. Inasmuch as the best recovery of safrole after refluxing was obtained in the presence of acetic acid, safrole was steam-distilled from a soap solution which had been acidified with acetic acid. This proved ineffective because the distillates were very turbid, interfering with the observation of their ultraviolet absorption characteristics. Safrole is retained by filter paper; thus filtration could not be used to clarify these turbid distillates. Various prrcipitants for soap were tried with the acid, but the distillates were still turbid. A steam trap inserted between the distilling flask and the condenser failed t o eliminate the difficulty. Apparently, fatty acid constituents of the soap were distilling over. The use of acid was discontinued to prevent the formation of a fatty acid layer in the distilling flask.
Table 111. Weight of Soap, Grains 1
3 5
Soap Turbidity Correction Terms for 9.59" Aqueous Alcohol No. of Determinations 8 8 8
a
10
Standard deviation
=
Term, I(.ihaorbence) 0.024 0.056 0.075 0.118
Standard Deviation 0 . no6 0.007
o.nio
0.015
z m k = T -
where ?. = arerage 2: = individual obserrations n = number of observations
A study of many metallic salts as soap precipitants was made. Silver nitrate was found to be the best reagent because the silver salt formed was the only insoluble soap that did not coalesce to a semifluid mass on prolonged heating. The maintenance of a granular structure by the silver soap was considered desirable because it lessened the observed tendency toward occlusion of safrole. The excess silver nitrate apparently provides the necessary conditions to prevent the loss of absorbenre indicatrd in Table 11. The steam distillates from mixtures of safrole, soap, and silver nitrate solutions showed a very slight turbidity which could not be dispelled by increasing the alcohol concentration to as high as 50%. Correction terms for the observed absorbence to eliminate the error due to this turbidity were determined. Varving amounts of soap, water, silver nitrate solution, and alcohol to make 9.57,
alcohol in 200 ml. were steam-distilled. -4known amount of safrole was added to the distillates and the absorbence was observed. The soap correction term was calculated by subtracting the absorbence due to the known safrole from the observed absorbence. The correction term was not determined from the direct reading of the turbid distillates from a reagent blank because of the error inherent in the extremes of the absorbence scale of the spectrophotometer. The correction terms obtained, shown wit'h their standard deviations in Table 111, are for the soap used in this investigation and may be espected t,o vary with different soap types. A series of recovery tests from steam distillation was made using 1gram of soap, 5 ml. of 207, silver nitrate solution, varying quantities of safrole ranging from 1.0 to 4.5 mg. per 100 ml., and alcohol to make a 9.5% solution in 200 ml., the volume of distillate collected. An average recovery of 95.5% of the safrole was obtained in twenty determinations. These results are correct,ed using a soap turbidity term as described above. Average recoveries with different quantities of safrole originally present, are shown in Table IT'. Standard deviations are also given as a measure of the dispersion of thc data.
Table I\'. Recovery of Safrole by Steam Distillation from Solution of Safrole, Silver Nitrate, and 1 Gram of Soap Original Concn. of Safrole, Mg.,'lOO MI.
?io. of Detns. 4
' Safrole Recovered, .\Ig./lOO JI1. 1,039
Recovery,
%
Standard Deviation
96.6
4 n
1 473
:. I60 .iverage recovery (20 observations) = 95.5% Standard deviation (20 observations) = 2 . 9 .
~
.
94.9
...
~~
.4NA LYTlCAL I11 ETHOD
Apparatus. Standard all-glass steam-distillation equipment with 2-liter steam generator and 1-liter distillation flask. A steam trap is used between the distilling flask and the condenser, and an adapter feeds the condensate to the receiver. Reagents. Silver nitrate solution, 20% in water. Ethyl alcohol, 95%. Procedure. Weigh a quantity of sam le estimated to cont,ain about 4 mg. of safrole and transfer into t i e distilling flask. Then introduce 20 ml. of ethyl alcohol and enough water to dissolve the soap. .Add silver nitrate solution (5 ml. per gram of soap are usually sufficient) with constant swirling to precipitate the soap. Connect t,he steam trap and condenser and attach an adapt,er leading into a wide-necked 200-ml. volumetric flask. Add water to the boiling flask, heat, and connect to the distilling flask. Control the rate of boiling t o complete distillation in about 20 minutes. Collect exactly 200 nil. of distillate in the volumet,ric flask, mix well, and mrasurr its ahsorbanre in the Model DU Beckman spectrophotometer at 283 mp. Calculations. Observed absorbenre -(soap turbidity term for wt. of soap used) 216 mg. of safrole/100 ml. of distillate Mg. of safrole per 100 ml. of distillate X 0.1 Grams of sample a t . equivalent to 100 ml. of distillate 7, safrole in original sample The figure 216 was calculated from the experimentally determined factor on the basis of the observed recovery of safrole by steam distillation from soap. Time required per analysis, 45 minutes. APPLICABILITY OF METHOD
The method described has been used in this laboratory for about 6 months and has been found entirely reliable. Using this procedure, i t has been possible to determine as little as 0.0047, safrole in soap. During the investigation, it became necessary to determine safrole in soap containing other known perfume con-
ANALYTICAL CHEMISTRY
460 stituents. I n this specific case, it waa found possible to perform the analysis by changing the solvent to 50% aqueous alcohol and by redetermining the necessary factor and terms. In addition to soap analysis, the method has been applied to the determination of safrole where present in known detergent and/or water-softening formulations. In these cases, 1 gram of soap and 5 ml. of 20%silver nitrate solution were added to permit using the recovery data already developed for soap. This would have been unnecessary if recoveries had been developed for the specific formulations being analyzed. The method is not general for the determination of safrole beCause of possible interference from other constituents in unknom n safrole-containing perfumes. However, the method can be used directly when safrole is the only perfume constituent in soap. The method can be applied to the analysis of safrole in soaps with known perfume formulations where the interference from other constituents can be determined and the necessarv correction made.
ACKNOWLEDGMENT
The use of ultraviolet absorption to measure safrole concentration was suggested by H . A I . Barnes and H. M. Cole of this laboratory. LITERATURE CITED (1) Fujita, Y . , and Yamashita, T., J . Chem. SOC.J a p a n , 63, 410 (1942). (2) Herzog, R. O., and Hillmer, A., Ber., 64B,1288 (1931). (3) Huzita, Y., and Nakahara, K., J . Chem. Soc. J a p a n , 62, 5 (1941). (4) Ikeda, T., and Takeda, S., Ibid., 57, 565 (1936). ( 5 ) Patterson, R. F., and Hibbert, J., J . Am. Chem. Soc., 65, 1862 (1943). (6) Ramart-Lucas, Mme., and Amagat, P., Bull. SOC.Chim., 51, 108 (1932). (7) Shukis, A. J., and Wachs, H., ANAL.CHEM.,20, 248 (1948). RECEIVED July 13, 1949. Presented before the Division of Analytical and Micro Chemistry at the 116th Sleeting of the AMERICAN CHEMICAL SOCIETY, Atlantic City, N. J.
Determination of 2,4=Dichlorophenoxyacetic Acid in Soil BENJAMIN WARSHOWSKY AND EDWARD J. SCHANTZ Camp Detrick, Frederick, M d .
A method for determining 2,4-dichlorophenoxyacetic acid in soil consists of leaching the soil with water, acidifying and extracting the leachate with ethyl ether, evaporating the extract to dryness, and partitioning the residue between tributyl phosphate and phosphate buffer of pH 7. For the distribution between the two solvents, a 24-plate countercurrent
I
N SPITE of the extensive use of 2,Pdichlorophenoxyacetic acid as 8 herbicide and a growth-regulating substance, no satisfactory chemical mcithod for its determination in complex mixtures has been described. Such ~tmethod would be particularly valuable in studies involving the retention and movement of 2 , 4 D in various types of soils, and also, if sufficiently sensitive, for investigating the uptake of 2 , 4 D by plants. Studies of this type have been reported by Hanks (S), who used a modification of the bioassay method of Swanson (6). This method involves the inhibitory effect of 2,4D on the elongation of the primary root of corn seedlings. I t was shown that a relationship exists between the concentration of 2 , 4 D and the root length after 48 hours' growth. Although the bioassay method is extremely sensitive-morking best in the range of 0.01to 2.0 p.p.m. -it is not sufficiently specific for 2,4-D; any substance that inhibits the growth of the root will be included in the estimate for 2,4-D and, therefore, the method may yield erroneously high results. Bandurski ( I ) determined 2,4-D in soil leachates spectrophotometrically by measuring the extinction a t a wave length of maximum absorption-Le., 284 mp. The relationship between concentration and absorption was found to obey Beer's law within 5%. Good results were reported on soil leachates, providing no other interfering substances were present. It was recommended that, for low concentrations of 2,4-D, the acidified leachate first be extracted with several portions of ethyl ether and the extiriction compared with a blank which had been treated in the same manner. Because soil leachates usually contain substances that absorb light of a wave length of 284 mp, the procedure is not specific for 2,4-D. A very sensitive colorimetric method for detecting 2,4-D has been described by Freed ( 3 ) . Xhen 2,4-D is heated a t 150" C. for 2 minutes with a solution of chromotropic acid in concentrated
distribution procedure, using the Craig instrument, was performed. The concentration of 2,4-D in the tributyl phosphate layer of each tube was determined by measuring the extinction at a wave Iength of 284 m p . From the amount found in a selected series of tubes the concentration of 2,4-D in the original sample can be calculated.
sulfuric acid, a red color is produced. As little as 0.05 microgram per ml. of 2,4D can be detected. The method, however, has not been satisfactory for quantitative estimations. In addition, a number of other organic compounds have been found to produce a color that interferes with the determination. Rooney ( 4 ) described a procedure for the determination of 2 , 4 D and its compounds in commercial herbicides. Essentially, the method consists of the determination of 24-D by first extracting it from any inert material with ethyl ether and then titrating the acid group. A check is made also by determining the total chloride content. It is apparent that acids and halogens will affect the reliability. The method described in this paper for the determination of 2,4D in soils combines the principle of countercurrent distribution with the spectrophotometric procedure of Bandurski. The technique of applying countercurrent distribution methods to the analysis of complex mixtures of chemically similar substances has been reported by several groups of workers (5, ?'-,9). In this study the practice outlined in a previous publication by the present authors on t,he determination of phenol and m-cresol in mixtures (8) was followed. Specifically, the steps entailed in the determinations are: The soil is leached with a relatively large quantity of water; the leachate is acidified with strong sulfuric acid and extracted twice with ethyl ether; the ether extract is evaporated t,o dryness and the residue dissolved in a definite volume of phosphate buffer of p H 7; an aliquot of this solution which contains the dissolved 2,4-D is subjected to a 2Pplate countercurrent distribution between phosphate buffer of p H 7 and tributyl phosphate; a sample of the tributyl phosphate layer from each tube is examined spectrophotometrically a t a wave length of 284 nip; and from t,he extinction nieasured, calculations can be made to determine the concentration of 2,4-D in the leachate and consequently in the soil itself.
