6. A. Parkin and G. W. Hedrick U. S. Department of Agriculture Olustee, Florida'
I1 I
I
"lromatographic Fraction Collector
The frequent need for chromatographic analyses of reaction products prompted the construction of a fraction collector which would take up to sixty samples. A collector, Figure 1, entirely automatic and merhanical in operation, based on a tipping sipholl was constructed. Although most of the individual const,ruction features have been employed in fract,ion collect,ors previously described,? the combination used by the authors has resulted in an apparatus low in cost and simple to build and operate. In operation, the chromatographic column is placed over the center of the instrument where the eluent drops into the siphon drip cup ( A ) , and runs to the siphon through the connecting tube. As the siphon begins t,o load, it tips down, disengaging the lower pin of the swing stop (Q) from the square screw hook (8). The siphon swings t o the next position where the upper pin of the swing stop engages the screw hook stopping the siphon discharge tube over the sample receiver (T) held in the circular rack. In this position the siphon loads completely and discharges. After discharge the siphon tips up, the upper swing stop pin clears the screw hook, and the lower one eugages it. The cycle then repeats with the siphon swinging t o the next position when it t,ips domi aft,er being partially loaded wit,h the next sample. The siphon design shomm provides for a small surface area a t the discharge level thus reducing errors caused by differences of liquid head at discharge resulting from droplets hanging in the discharge tuhe. The siphon is also made adjustable by insertion of a I Naval Stores Research Station, one of the laboratories of the Southern Utilization Research and Development Division, Agricultural Research Service, U S . Department of Agriculture. JAMES.A. T.. MARTIN.A. J. P.. AND RANDALL. , S. S.. , Bioehem. J., 49, 293 (1951); DUPU;, P., A& MORCAU, C., Bull. soe. chim.
Fronee, 1957, 521.
Figure I.
Froctian collector orsembly.
glass tube through an airtight rubber sleeve on the tube a t the top of the siphon bulb. Raising or lowering the tuhe varies the volume of air trapped in the bulb and thus the final volume of eluent a t discharge. A change in fraction size may necessitate adjustment of the counterbalance weight (E). The siphon is fastened firmly in the body of its holder by means of a paper bushing around the drip cup. The siphon tips with its holder on 60" knife edges (C) set in the 90' V bearings ( F ) and the entire carrier and siphon rotate on the point of the swing pivot post (P) bearing in a smooth depression in the bottom of the tip pivot support (K). The heavy plate a t the bottom of the siphon carrier lowers the center of gravity and eliminates binding on the swing pivot post when the siphon loads. The swing pivot post is made of 'f4-inch steel rod machined or carefully hand-shaped t o a smooth 30' point and
Volume 36, Number 5, Moy 1959
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Figure 2.
Receiver rack with syphon and carrier in pbce.
welded or threaded and fastened with nuts top and bottom into a steel plate which is screwed to the instrument base. Rotational force is supplied by a weight (R) attached to a string wound around the inch pipe ( M ) one or two turns and leading over a smooth steel rod ( V ) situated high enough that the weight does not come t o rest on the receiver rack before it completes its travel. The swing stop is fashioned from L/8-inchbronze welding rod and fastened to the
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Journal of Chemical Education
siphon with a rubber padded hose clamp. The receiver rack is made of half-inch plywood. The upper hoard haa a 15-inch diameter hole cut from the center. The '/rinch holes which hold the 18 X 150-mm rimless test tube receivers, are spaced a t 6' intervals on a circle of 9L/2-inch radius and are drilled about '/,-inch deep in the lower board. The rack is assembled with suitable pipe separators (U) and six-inch stove bolts. The square screw hooks used are commercial1.y available with short threaded sections on the long ends. These are screwed into the rack on a line through the center of the tuhe hole and the center of the rack where it inches. crosses a circle having a radius of The apparatus is assembled as shown and adjustments are made in the counterbalance, turn or swing weight, tipping adjustment screws (J),and swing stop until smooth operation is obtained. Final individual adjustment of the siphon position over each tuhe may he made by turning the screw hooks in the rack. The authors wish to thank their co-workers for their many helpful suggestions and especially R. A. Tyre and H. R. Lanier who constructed the apparatus.
