An Improved Soxhlet Extractor M. H. NEUSTADT Agricultural hIarketing Administration, United States Department of Agriculture, Washington, D. C.
I
S THE course of work on the analysis of commercial soy
sample, although if the extraction is allowed to proceed long enough, a complete extraction is obtained in 16 hours.
flours at the laboratory of the Agricultural Marketing Administration, Beltsville, Md., it was necessary to report the oil content values the same day that the samples of soy flour were received. The accepted method for determining the oil content of ground soybeans is to make the extractions in a Soxhlet or Butt extractor with petroleum ether. This method requires from 16 to 20 hours or a 4-hour extraction with regrind after 2 hours. It was much too slow for the needs of the laboratory workers, since results for reports were needed in from 4 to 5 hours. Among the rapid methods for determining the oil content of oil-bearing seeds are the refractometric method (5), the method based on the change in density of a solvent (1, 2 ) , and various shaking procedures (4) that employ different types of solvents. All these are not accepted as standard or official for soy flour, but the extraction method is the one adopted by the Soybean Analysis Committee of the Oil Chemists’ Society (5). In the author’s laboratory, where 3 battery of 36 Soxhlet extractors is in use, the color of the extract frequently indicates that some extractions proceed faster than others. These differences are probably due to variations in the porosity of the paper thimbles as well as to the manner in which the samples pack themselves within the thimbles. I n some cases the retardation of the flow of the solvent is so great that the solvent will flow over the top of the cotton wad in the thimble, rather than through the sides and base of the thimble. Hence, in such cases, very little solrent really percolates through the FIGURE 1
It occurred t o the writer that having the base of the thimble next to the base of the extractor might retard the flow of solvent through the thimble. Therefore the thimble was elevated by inserting a piece of glass rod at an angle into the extractor and resting the thimble upon the rod (Figure 1). This rod was long enough to raise the thimble 3.75 cm. (1:5 inches) off the base, but the sample (10 grams) within this thimble was still below the overflow siphon of the extractor, so that at intervals the sample was completely immersed in the solvent and channeling was avoided. Another means of achieving the elevation was t o make three depressions in the extractor, about 3.25 cm. (1.5 inches) from the base and 120 degrees apart, upon which to rest the paper thimble. The sample was then extracted with Skellysolve F at a rate equivalent to one siphoning about every 3 minutes, whereas with the common method about one minute was required.
The value of the improvement in the Soxhlet extractor can be seen by comparison of the results of extractions by the two methods (Table I). Extraction flasks mere changed a t the end of 1, 2, and 3 hours, so that each value represents the extraction for each successive hour except in the overnight extraction. All of the soy flours do not extract a t the same rate of speed by any method. Extractions varied at the end of the first hour anywhere from 20 to 92 per cent of the total fat content. By use of the elevated thimble method, however, more than 98 per cent of the total fat was extracted during the first hour from all but one of the six samples. The differences between samples are probably due to the nature of each sample as regards its fineness and the distribution of the oil film through the sample. Differences that might be due to variations in porosity of the thimble were eliminated by interchanging the thimbles used in the common extraction in one sample to a position of elevation in the next sample and the elevated one to the common position.
Summary
A more rapid method of determining the oil content of soy flour was sought, SO that oil content values could be reported the same dav samdes of SOY flour were received by ihe la6oratory bf the Agricultural Marketing Administration a t TABLEI. EXTR.4CTIONS OF OIL FROM SOY FLOUR Beltsville, Md. To this end an im(By common method of setting the thimble as corn ared with improved method of using an elevated provement was made in the Soxhlet thimgle) extractor, the use of which, with petroElevated Common Elevated Common Per Per Per Per Per Per Per Per leum ether, is an accepted method of cent cent cent cent cent cent cent cent Fraction fat of total fat of total fat of total fat of total extraction. Sample 2 Sample 1 This improvement would no doubt 1st hour 8.36 41.32 20.23 22.40 99.29 20.63 91.95 99.30 help to shorten the time required to 2nd hour 4.38 21.66 0.04 0.18 0.07 0.35 1.65 7.33 3rd hour 3.38 16.70 0.01 0.03 0.11 0.32 0.03 0.07 extract other types of materials, such Overnight 4.11 20.32 0.07 0.09 0.42 0.32 0.09 0.40 as oil-bearing seeds and plant materials. 7
7 -
Total
20.23 7 -
1st hour 2nd hour 3rd hour Overnight
21.28 0.79 0.07 0.09
Total
22.23
100.00 20.38 Sample 3 95.71 22.02 3.57 0.05 0.31 0.00 0.41 0.10
100.00
99.34 0.20 0.00 0.46
10.81 8.89 2.52 0.00
100.00
22.22
98.45 0.86 0.05 0.64
3.81 2.95 2.11 9.68
20.54 15.91 11.35 52.20
14.58 3.88 0.03 0.18
78.06 20.79 0.18 0.97
100.00
18.55
100.00
18.67
100.00
1st hour 2nd hour 3rd hour Overnight
13.41 7.67 0.77 0.23
100.00 22.17 Sample 5 60.75 21.78 34.74 0.19 3.49 0.01 1.02 0.14
Total
22.08
100.00
7
22.12
--.
7
22.44
?
7
7
100.00 22.56 Sample 4 22.53 48.66 40.01 0.00 0.02 11.33 0.05 0.00
100.00
100.00 22.60 Sample 6
100.00
43 1
99.67 0.00 0.09 0.24
7
Literature Cited (1) McKinney, R. S., and Rose, W. G., Oil & Soap, 18, 25-7 (1941). (2) Sohwarz, R., Oil & Fat Industries, 7,
336-6, 347 (1940). (3) Soybean Analysis Committee, Oil Chemists’ Society, Oil & Soap, 17, 126 (1940). (4) Werr, F.,Chem.-Ztg., 62,367-8 (1938). (5) Zeleny, L., and Neustadt, M. H., U. S. Dept. Agr., Tech. BuEl. 748 (1940).
