In research studies on the extraction of soybean oil by trichloroethylene it became necessary to determine small amounts of the solvent in the oil. For amounts above 10 percent trichloroethylene the simplest and best method for control purposes is by means of a specific gravity determination. Measamer (3) has shown that the trichloroethylene may be steam-distilled from the oil and weighed or measured. Three percent trichloroethylene in soybean oil may be determined with a maximum error of 10 percent. Greater accuracy should be possible in solutions containing more of the solvent. For amounts above 10 percent the method is more time consuming and no more accurate than the specific gravity method

Arnold, Lionel K.

Hollowell, E. Graham

English

University of Northern Iowa

Proceedings of the Iowa Academy of ScienceVolume 54 | Annual Issue Article 231947The Determination of Small Amounts ofTrichloroethyleneLionel K. ArnoldIowa State CollegeE. Graham HollowellIowa State CollegeCopyright © Copyright 1947 by the Iowa Academy of Science, Inc.Follow this and additional works at: https://scholarworks.uni.edu/piasThis Research is brought to you for free and open access by UNI ScholarWorks. It has been accepted for inclusion in Proceedings of the Iowa Academyof Science by an authorized editor of UNI ScholarWorks. For more information, please contact scholarworks@uni.edu.Recommended CitationArnold, Lionel K. and Hollowell, E. Graham (1947) "The Determination of Small Amounts of Trichloroethylene," Proceedings of theIowa Academy of Science: Vol. 54: No. 1 , Article 23.Available at: https://scholarworks.uni.edu/pias/vol54/iss1/23The Determination of Small Amounts of Trichloroethylene LIONEL K. ARNOLD AND E. GRAHAM HOLLOWELL In research studies on the extraction of soybean oil by trichloro-ethylene it became necessary to determine small amounts of the sol-vent in the oil. For amounts above 10 percent trichloroethylene the simplest and best method for control purposes is by means of a specific gravity determination. Measamer ( 3) has shown that the trichloroethylene may be steam-distilled from the oil and weighed or measured. Three percent trichloroethylene in soybean oil may be determined with a maximum error of 10 percent. Greater accuracy should be possible in solutions containing more of the solvent. For amounts above 10 percent the method is more time consuming and no more accurate than the specific gravity method. Amounts of trichloroethylene between 0.1 and 1.0 percent in soy-bean oil may be determined spectrographically with an error of 7 percent according to Yates ( 4). A copper wire is dipped in the oil and held in the flame, the amount of solvent being indicated by the duration of the copper chloride bands between wave lengths of 4259 and 4518 angstrom units. This method has the disadvantage that, be-cause of differences in color perception, each operator must calibrate his own time-percent trichloroethylene relation. A method for determining very small amounts of chloroform is described by Fujiwara ( 1). He added pyridine to a 10 percent solu-tion of either sodium hydroxide or potassium hydroxide and heated them to boiling. The two liquids remained as separate layers after the heating. When a solution containing chloroform was added to the mixture the pyridine layer turned a blue-red. Fujiwara found that this test is more sensitive than other tests used for this purpose such as insonitrile, resorcin, and napthol tests. He was able to detect one part of chloroform in 1,000,000 parts of water, in 500,000 parts of ether, or in 300,000 parts of alcohol. He re-ports that the test may be. used for other halogen compounds but gives no data on other than chloroform. Gilchrist (2) in this laboratory re-peated Fujiwara procedure with trichloroethylene. The pyridine layer turned a deep cherry red. He found that the intensity of the color varied with the amount of trichloroethylene present thus making it possible to make it a quantitative as well as a qualitative test. Work by Gilchrist and later by the authors developed a method now used for routine determinations of trichloroethylene in soybean oil, soy-bean meal, and water. The method for soybean oil is as follows: 'l'o 11h ml. of 10 percent sodium hydroxide in a test tube add lml of pyridine and heat to boiling. Add.2 drops of the oil. Allow to stand one minute for the color to develop and compare depth of color with color standards. Originally the color standards were made by adding 181 1Arnold and Hollowell: The Determination of Small Amounts of TrichloroethylenePublished by UNI ScholarWorks, 1947182 IOWA ACADEMY OF SCIENCE [VOL. 54 oil containing known amounts of trichloroethylene to pyridine-sodium hydroxide solutions prepared as in the test. The color of these stan-dards faded rapidly so permanent standards were devised. These were made by mixing a water solution of sodium dichromate and cobaltous chloride made acids with hydrochloric acid. A series of these standards from 0.02 to 2.0 percent are used. While this test is the most sensitive test found for the detection of traces of trichloroethylene in soybean oil, it is not as sensitive as is the test for chloroform in water. The smallest amount of trichloro-ethylene in oil that may be detected is less than 0.02 percent, the exact amount being dependent upon the color of the oil, the lighting condition, and the color accuracy of the operators eyes. Tests with both chloroform and trichloroethylene in oil indicate that it requires only one-eighth as much of the former as the latter to give a cer-tain intensity of coloration. In methanol where there is no color to interfere the ratio is one to five. Amounts of trichloroethylene in methanol as low as 5 parts in 1,000,000 have been detected using only 3 drops of the methanol solution. When testing a sample of soybean oil it is helpful to increase the amount of oil added to 3 or 4 drops if there is question as to the presence . of any trichloroethylene. Any additional oil is of doubtful value as the color of the oil tends to in-terfere more when larger amounts are present. For amounts of the solvent above two percent the sample should either be diluted with solvent-free oil or only one drop used in the test. In the latter case for accurate results new standards should be prepared based on one drop of oil added. The determination of traces of trichloroethylene in soybean meal is made by the following modification of the procedure for the sol-vent in oil. Ten grams of the meal are weighed rapidly and added to 125 ml. flask containing 40 ml. of hexane ( "Skellysolve B") and the flask stoppered and allowed to stand for a few minutes. Four drops of the hexane are added to the hot pyridine-sodium hydroxide mixture, and the depth of color compared with standards prepared for this test. The method has also been applied to the determination of trichloro-ethylene in water, using 2 drops of the water and comparing with suitable standards. The three tests have been used successfully in routine control work by the authors in checking operations in a soybean oil extraction plant using trichloroethylene as a solvent. The test for trichloroethylene in the oil is carried out in a routine manner by the plant workmen as a regular check on the oil quality. Several precautions should be observed in using these tests. Pyri-dine is sufficiently toxic that is advisable to carry out the operations in a hood. Only a pure grade of pyridine can be depended upon not to give the red coloration before adding the solution of trichloroethyl-ene. Some bottles of the so-cal¥Jd "practical" pyridine have been found satisfactory; some have not. Care should be taken not to con-2Proceedings of the Iowa Academy of Science, Vol. 54 [1947], No. 1, Art. 23https://scholarworks.uni.edu/pias/vol54/iss1/231947] DETERMINATION OF TRICHLORETHYLENE 183 taminate the pyridine. This may occur if the bottle is left unstoppered in a room containing small amounts of trichloroethylene vapor in the air. ENGINEERING EXPERIMENT STATION, IOWA STATF~ COLLEGE. Literature Cited 1. Fujiwara, K. Uber eine newe sehr emphfindliche Reaktion zum chloroformnachweis Sitz. Abhandl, naturforsch. Ges. Rostock, Newe Folge Band VI. II Abhandlung 33-43. 1914-15. 2. Gilchrist, Wm. G. Colorometric Determination of Trichloroethyl ene in Soybean Oil. Unpublished B. S. Thesis, Iowa State College, 1941. 3. Measamer, G. S. Extraction of Oil from Soybeans using a Mix-ture of Trichloroethylene and Ethyl Alcohol as a Solvent. Ph.D. Thesis. Iowa State College. 1941. 4. Yates, vVm. E. Operation and Control Problems Encountered during the Development of Oil Meal Extraction Plants. Unpub-lished M.S. Thesis, Iowa State College, 1938. 3Arnold and Hollowell: The Determination of Small Amounts of TrichloroethylenePublished by UNI ScholarWorks, 1947

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