Automatic Weight-Driven Time-Controlled Fraction Collector. W. A. Schroeder and Robert B. Corey, California Institute of Technology, Pasadena 4, Calif. procedures, such as those using I columns ofchromatographic starch or ion exchange resins, it is convenient and N CERTAIN
often necessary to be able to fractionate the effluent from the column automatically into a large number of small fractions and to continue this fractionation without interruption for a week or more. For use with their starch chromatographic methods, Stein and Moore ( 7 ) have described a drop-counting fraction collector which moves an empty test tube under the chromatographic tube after a predetermined number of drops have been collected. Collectors of varied design have been described
( B , Figure 1) so that the parts will fit together properly; they are drilled on a 9-inch radius. B is made of '/Anch Dural and is the same diameter as A . Ei hty holes of 0.166-inch diameter are drilled on a 14.7-inch rajius with tolerances the same as those specified for the holes in A . In the assembled machine, the centers of these holes should be 2' 15' from the centers of the outer row of holes in A . I n addition to the holes on the 9-inch radius, six 0.25-inch holes are drilled for the bolts required to mount part E. The center hole is fitted to the bearing shaft.
(1-5).
s
e
P
a
e3
0
R
Figure 2.
b
n
88 N
Isometric Drawing of Trigger Mechanism
The index pins, C , are 1-inch steel fillister head screws which are fastened to B with two nuts and a lock masher. The grooved wooden wheel, E, is about 12 inches in diameter and accommodates many turns of flexible radio control wire, P , for the driving mechanism. F is passed over pulleys, G , from one of which is suspended the driving weight, H (on the original model about 1pound). The grooved wooden wheel, I , is used to take up wire after H has fallen some distance, thus making it possible to place a large number of turns of wire on E and to run the machine for a long time before it is necessary to rewind the wire on E. For the main bearing, J , any suitable bearing may be used. In the original model it was a grinding arbor bearing No B-41 with reversed bearing obtained from ' 0 Poly Products, 2032 East Walnut St., 0 3 Pasadena. The base, K , is made of 1.5-inch angle iron and 4-inch channel iron. The shorter Stcge 2 pieces of angle iron are 18 inches long and 18 inches apart on outside edges. The longer pieces are 29 inches long and 12 inches apart. The channel iron is 12 inches long and drilled to fit the bearing. I t is placed midway betiveen the shorter pieces of angle iron. All joints are welded. Stage 3 The brass plate, L , supports the trigger mechanism, D , which is fastened by C Figure 3. clamps (not shown) or bolts through slots Operation of (not shown) to permit adjustments relative Trigger Mechto the index pins, C. anism The spacers, M and N , are made of 3/a-inch and ll/d-inch aluminum tubing, Arrow s h o w s direction of respectively. movement i m The trigger mechanism, D , shown in parted by driving detail in Figure 2, is constructed of brass. weight. Solenoid is activated only The trigger bar, 0 , is most easily made during stage 2 from three pieces, two outer pieces of 3//16 X "8 inch brass bar and a middle piece of 5/,6 X 5/n inch brass bar. which are then The-slot mist permit unhindered passage of screxed together. the index pins (C, Figure 1)as shown in F i g a e 3. The containing members, P , should be adjusted for minimum play consistent with the free motion of the trigger bar. The
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Figure 1.
Fraction Collector
The present paper describes a fraction collector in which the samples are taken according to time rather than by volume or weight. The motive power for the turntable which holds the test tubes is supplied by a weight and the movement of the turntable is regulated by a time-controlled, escapementlike trigger. The original model has operated satisfactorily for more than two years. An exploded assembly drawing of the collector is shown in Figure 1. The machine as specified is designed for use with 18 X 150 mm. test tubes. The test tube racks ( A , Figure 1) are made of l/ls-inch Dural and are 30 inches in diameter. The two rows of eighty 0.75inch holes are drilled on concentric circles of 13.4- and 14.4; inch radii. The angle between centers of adjacent holes is 4 30' =t10' and cumulative error of spacing is restricted t o AZO'. The six 0.25-inch holes for the assembly bolts must be drilled simultaneously in the test tube racks and in the index wheel
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ANALYTICAL CHEMISTRY
spring, 0,must have sufficient tension to permit positive return of the trigger 1)ar &8 shown in Figure 3. The rod, R, forward motioin of the trigger bar; its opposite ma determined by the solenoid core. S is a General Electric solenoid (CR9503-207E, Crh l o g No. 4382675-AB20: !, 110 volts, 60 cycles, coil F22D3C%), activated by_f.hetiming Inechanism. T h e fraction collector is most easily assembled in the following manner. The bearing is bolted to the base, and E is bolted through the spacers to B. B is then fastened to the bearing shaft. The index pins, C, are next fastened t o B. Because B may not he entirely flat, each index pin must be adjusted so that when the wheel is rotated the head of each pin passes through a giyen point in order to register properly with the trigger mechanism. The spacers, N , are cut to the proper length and L is bolted onto the frame. The sssembly is completed by attaching the test tube racks, the driving wire, and finally the trigger mechanism. ~~~~~
The period of activation of the solenoid should he as short as possible camistent with the proper functioning of t.he fraction collector, because during stage 2 (Figure 3 ) the test tubes are out of nosition and any droD
Paralysis. Contribution 1464 from the Gate8 and Crellin Laboratories of Chemistry. UTERATURE CITED
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(1) Brimley. R. C., and Snow. A,, J . SA. Inalmments. 26.73 (1949). ,9, . ru " " ~ " n rl a, rT"--:" I*. D T Y., c. rill" "..A e..-"> 73 73 "-. "l.
