8
A N AUTOMATIC CONSTANT-VOLUME FRACTION COLLECTOR' JOSEPH E. VARNER and WILLIAM A. BULEN The Ohio State University, Columbus, Ohio
Tm
widespread use of chromatographic and ion exchange columns has established the need for automatic fraction collecting devices. To supply this need in our laboratory an inexpensive constant volume fraction collector has been designed. Various types of automatic fraction collectors have already been described (1-8). Those employing electronic units cannot be considered if initial expense and maintenance are primary factors in determining the choice of a fraction collector. If an inexpensive unit is to be satisfactory it must have a positive and reliable action, deliver fractions of constant volume and invalve no features of assembly or adjustment that cannot be handled by ordmary laboratory personnel. The apparatus in use in our laboratory employs an intermittent siphon as a fraction cutter, and a simple electrical mechanism controlling the position of the receiver rack which is mounted on a spring-driven phonograph turntable. The apparatus is sketched in the accompanying diigram. The manner in which the liquid is delivered from intermittent siphon A activates the control mechanism. The bulk of the liquid falls vertically from the delivery tube directly into the receiver. The last few drops emerge with increased velocity and strike paddle B before fallmg into the receiver. C is a copper bar 3 X 3 X 110 mm. supported by a steel needle through a hole a t the approximate balance point and resting on pin D. The sensitivity of the movement of C about the fulcrum is controlled by adjusting the nuts a t the threaded end. The force against B elevates the threaded end of C mak'mg a brushing contact with E (the copper conducting strip of the cam-activated part of a set of automobile distributor points). The position of E is adjusted by rotation about the mounting screw. The contact of C with E closes the coil circuit of F, a single-pole single-throw, normally open 115-volt a.-c. relay (MR3A Potter and Bmmfield). This relay controls the 115-volt a.-c. circuit energizing electromagnet H which consists of a Potter and Brumfield MSZA relay rewound with No. 28 enameled copper wire. An electric light bulb, J, (50-150 watts) is placed in series with this circuit to limit the current, dram by the electromagnet. When the electromagnet is enerthe gieed, assembly I is withdrawn from pin J, turntable to turn. Since the "blurpl' from the siphon position for only a fratdisplaces bar C from its
tion of a second, the electromagnet is energized for an equally short period and allows the moving assembly to spring back to engage the next pin on the receiver rack. 'The receiver rack is made from pressed fiber board with the pins set in the periphery of the bottom section spaced to correspond to the receivers. When small receivers are used a funnel is placed between B and the receiver. When the liquid to be fractionated is conducting and noninflammable, two platinum wires, arranged so that the "blurp" completes the circuit of the relay, may be used to replace the mechanical switch shown.
An Automatic Constent-Volums Fraction Collecto~
. Although this particular apparatus has been described m some detail, we wish to emphasize that most of these
details are not critical. The bend in the delivery arm of the intermittent siphon is of course necessary. It is also important that the electromagnet be energized for a period sufficientlylong to allow I to be withdrawn. The brushing contact of bar C with E makes possible the fulfillment of this requirement. The details of the 1 Work supported in part by a contract between the Charles F. receiver rack, the turntable, and the electrical circuit ~ ~ t~ t ~ ~ ~and ~ ~h~ ~ university ~ i ohio d~ state t i ~~~~~~~~h ~ are all subject to the individuals' needs and ingenuity. Foundation.
626
LITERATURE CITED
