R. E. Herbener Hillsdale College Hillsdale, Michigan
Automatic Fraction Collector for Column Chromatography
This article describes the construction of an automatically timed fraction collector for use with chromatographic columns. Materials for the collector cost approximately 835. It holds 48 test tubes, 18 X 50 mm, and could easily be modified in design to increase its capacity. The electrical circuitry is uncomplicated (Fig. I), involving two SPDT micro-type switches operated by simple cams. The cams were made without the use of elaborate machine tools. A "plug-in" feature of interchangeable timers gives a choice of several time intervals. The reliability of the collector permits it to operate unattended for periods up to 12 hours (see Fig. 2). The revolving test tube rack consists of three aluminum discs separated by five pairs of aluminum posts. The base disc (Fig. 3), which also functions as one of the operating cams by means of its serrated edges, rotates on a 4-in.-square ball bearing turntable and is driven by a I/%-rpm motor. This disc, a circle 19 in. in diameter, was cut from 10-gauge sheet aluminum using a sabre saw. Since i t must actuate a switch having a throw of approximately 2 mm, a degree of precision of its circularity had to be attained. The turntable which was later to support the rack during actual use was employed as the center for the "lathe-turning" procedure. This turntable was screwed down on the flat side of a 2 X 4, 30 in. long, near one end. This combination was clamped to the bench top, and the disc aflixed with self-tapping screws. For turning and cutting, the disc was spun by a friction drive arrangement consisting of a used phonograph idler wheel fitted tightly on a 8/ia- X 2-instove bolt and chucked-up in a '/An. electric drill. This power source was held on a ring
stand which was clamped to the bench top. The c u t ting tool used was simply a flat file with its blunt end squared off on a bench grinder. This was clamped flat against a short length of 2 X 4 with the cutting edge of the He extending about a/n in. This assembly was clamped in place with the cutter barely resting against the highest spot on the circumference of the disc. After a little experimentation, optimum rake angle and feed rate were found. With the disc spinning, the cutting tool was gradually fed into the work by gently tapping its pointed end with a hammer. The finished disc, 1818/16in. in diameter, was laid out into 48 segments. A circle of radius 2 mrn less than that of the disc was also scribed on it. Alternating segments were cut out to the 2-mm depth on the grinder, leaving a slight taper a t each end to allow the small wheel on the arm of the switch to run smoothly. A final touch with file and emery cloth finished this cam (see Fig. 4). A base platform was built with a wooden frame of 1 X 3's and a l/r-in. hardboard top. This is in the form of a "T" with the 1 X 3's on edge, to form an open box underneath to house the drive motor and wiring. The motor is located near the crossbar end of the "T", fastened to the underside of the hardboard with only its shaft emerging on top. This shaft is centered in the turntable and base-cam. The motor drives the assembly by a crank and pin arrangement having its hub secured to the motor shaft with a set screw. The two top discs of the rack, both 18 in. in diameter, were cut with shears from &gauge aluminum and then buffed with emery cloth. These are fastened in place to the base-cam and to one another using aluminum spacer posts I/, X 2'/, in. and No. &32 machine screws. Up to this point the holes for test tubes have not been made in the two top discs. The first micro-type switch was fastened to a strip of
Figwe 1. Wiring diagram of turntable circuit. "Motor" 1s turntable motor. A is corn on turntable. B is cam on liming motor. In (01 and (c) the turntabla is moving. In (b) and (dl 0 fraction is being collected.
Figure 2. The ~ o m ~ l e t efraction d collector in "re. The timing devise is housed in the box at the left. The opporent irregularity in the rpocing of the tegttuber i s explained in the text of the orBcle.
Volume 42, Number 8, August 1965
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445
Figvre 3. The boric parts d the rotating t e d tube rock. Background: the bore-cam. Left: Right: '/r-rpm. 4-in. ball beoring turntable. motor which driver the rotation.
Figure 4. Top view rhowing both comr in operation. The expored wiring to the barecom microrwitch ir covered with a piece of polyethylene cut from 0 rmoll rectangular bottle.
'/a-in. aluminum which is pivoted a t the edge of the base-cam. A wing-nut on a bolt through a slot in this strip permits adjustment of the contact of the wheel on the arm of the switch with the edge of the cam. Temporary wiring was installed with a SPDT knife switch in place of the timer. The rack was rotated through its complete cycle several times with each stopping point carefully marked on the circumference of a circle of g3/&in. radius, scribed on the top disc. I n this way the location of the centers of the holes for test tubes was matched to the operation of the cam allowing for any errors in the cutting of the grooves. The rack was disassembled, pilot holes bored, and the 3/4-in.holes for the test tubes cut with a chassis punch. The timing device was built inside a small metal box (2l/4 X 41/2 X 71/2 in.) fastened to the top of the platform a t the end of the "T" away from the drive motor. Holes were bored through it and the hardboard underneath for the wiring. Plug-in timing units (Fig. 5) to give a variety of collection intervals were made by bolting small timing motors to the undersides of platforms made from galvanized ductwork sheeting. The geared shaft of the motor extends through to the top of the platform near one end. The platform fits snugly into the metal box and is held with sheet metal screws. Timing cams were first cut as discs slightly over zs,f4in. in diameter from l/rin. methacrylate plastic using a handsaw, A '/rin.-hole (which snugly fits the gear on the shaft of the timing motor) was bored through the disc. The disc was tightly fastened on a '/r X 2-in. stove bolt and rotated in a drill press against a firmly iixed flat file to obtain a near-perfect circle. Then the appropriate angle was laid out on the surface of the disc along with a circle about 3 mm inside its circumference. The cam was sawed on the bandsaw, and the saw marks erased with file and sandpaper. The
Reminder:
Figure 5 . Plug-in timing unita. Front Left: Top view of timing motor showing geored shaft end. Front Right: Bottom view of complete unit. Back: Top view of 10- and 5-minute timing units. Edges of comr outlined far clarity in picture.
disc was cemented to the geared shaft end using epoxy glue with the following precautions to prevent cementing the gearing inside the case of the timing motor. First, a drop of machine oil was placed on the motor shaft where i t entered the housing with care that no oil got on the gear teeth. A bi-level support was arranged ahead of time so that both the metal platform and cam could be inverted and supported on parallel planes during the setting period of the glue. Then, the viscous cement mixture was spread into the center hole of the cam with the gear inside. As soon as it was full, it was covered with a stripof 3/4-in.cellophane tape and quickly inverted on the prearranged support before any of the glue could run into the motor housing to literally gum up the worlrs. This was allowed to remain undisturbed overnight. The timer microswitch was fitted into place on a second platform inside the box (see Fig. 4). This platform is slightly lower than the motor-cam support in order that the arm of the switch engages the edge of the cam. I n making a number of plug-in units, it is essential that the cam centers be equidistant from the arm of the switch and that the cam radii be uniform. The 15-min timer consists of a 180' cam on a rpm motor. The 5- and 10-mi11 timers are 90' and 180' cams respectively on '/zO rpm motors. Parts L i d
1-20 X 20 in. 10-ga. aluminum, $4; 2-18 X 18 in. 16ga. aluminum, $7; 1-77PP154 CA-Series Humt motar, I/, rpm, $9.25 (Allied Electronics, Chicago); 2-33B970 Standard duty type, micro-type switch, 84.50 (Allied Electronics); 1 0 4 4 H 6 9 5 Aluminum p a t s 2'/. X I/, in. (Allied Elect,ronics); 1 4 6 N 1 7 0 Type 730 round chassis punch, in., $2.29 (Allied Electronics); 1 4 0 , 6 0 1 4 i n . square ball bearing turntable, $1.25 (Edmund Scientific Co., Barrington, N . J.); 2-MO-88 Timing motors, 1l.0 rpm, $1 (OLson Electronics, Akron, Ohio); rpm, $0.69 (Olson Electronics). 1-MO-73 Timing motor,
NSF Fellowships Application Deadlines
Postdoctoral Fellowships: Fall award. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sept. 7, 1965 Senior Postdoctoral Fellowships. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Oct. 11,1965 Science Faculty Fellowships.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Oet. 11, 1965 NATO Postdoctoral Fellowships in Science.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Oct. 11, 1965 Cooperative Graduate Fellowships. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Oct. 29, 1965 Dec. 3, 1965 Graduate Teaching Assietants Fellowships. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10, 1965 Graduate Fellowships. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..Dee. . . 13, 1965 Postdoctoral Fellowships: Spring award.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Dee.
446 / Journal of Chemical Education
