ANALYTICAL CHEMISTRY
1424
Fraction Collector for Chromatography. Eric Schram and Edward John Bigwood, Faculty of Medicine, University of Brussels, Brussels, Belgium. types of fraction collectors have been described and M several are available commercially, among them the excellent apparatus designed by Stein and Moore (8). The present ANY
model offers several advantages: I t is particularly simple and inexpensive, although completely automatic and its accuracy is a t least equal to that of other systems. A siphon, especially suitable for delivering small fractions (1 ml.) with good reproducibility (better than 1 %), is used as a fractionating device. ‘ Siphon devices recently described by Desreux ( I ) , Gilson ( 2 ) > Grant and Stitch (S),and Harris ( 4 ) are well adapted to preparative scale chromatography. The present model, however, operates according to a different principle, allouhg accurate delivery of smaller fractions, and hence quantitative analytical work. DESCRIPTION OF COLLECTOR
Siphon (Figure 1). The siphon is a very different type from thst used by Randall and Martin (5, 7).
A joint, 3, allows for adjustment of its capacity by varying the height of the upper elbow, 8. One of the platinum electrodes, 5, is welded through the glass wall; the other, 6, is fixed through a stopper of insulating material, 7 . The inner diameter of the elbow, 9, gradually decreases from that of the large branch, 1 (about 5 mm.), to that of the narrower one (about 2 mm.), in order to ensure proper draining. Turntable and Actuating Mechanism (Figure 2). The turntable supporting the receivers is made of three aluminum disks mounted on a central shaft and assembled with bolts. The solenoid, 5 , when activated, acts through 3 shaft 4, lever 3, and spring pawl 1 upon the lower cogged disk and causes the turntable to move. A spring blade, 7 , keeps the spring paw1 firmly in the notch in n-hich it is engaged, so that the table does not turn beyond its new popition by inertia. When activation of the solenoid stops, the spring pawl is pulled back into the nest notch by a spring, 6. A fork-shaped spring, 8, prevents Figure 1. Siphon a backward shift of the turntable.
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Figure 3.
Electronic Circuit
Electronic Circuit (Figure 31. Electrolytic contact betReexi the electrodes occurs as the liquid level rises a t the proper height in the siphon. It modifies the grid potential of a “cutoff” triode. The amplified signal causes the relay (SO00 megohms) controlling the solenoid circuit to close in. I n order to prevent any appreciable current from passing through the solution, the triode is subvolted (heating as well as plate potential) so that the grid current is practically eliminated, while a very high resistance (20 megohms) reduces the current from the polarization cell to practically nil (1 pa.). Even a solution of very low conductivity (acetone or alcohol) will allow the device to work even n-ith several times 10 megohms in the siphon circuit. In the model described direct cuirent is supplied by the laboratory storage battery unit. Any model of solenoid may be chosen in accordance with the available power supply. Operation. The tip of the chromatographic column is fitted into the side arm, 4 (Figure I), of the siphon and kept in close contact with its wall to ensure a continuous flow. The siphon delivers a fraction of desired volume each time the liquid level reaches the upper elbow, 8 After emptying, some liquid remains in the tip of branch 2 (as in a pipet); it is driven out by the inner air pressure as a new fraction is being collected. A cut tip of plastic material prevents the formation of bubbles a t stage 10. The shift of the next receiver occurs a little before the nest fraction is to be delivered-when the previous fraction has been given enough time to drain completely. The siphon is connected v i t h a plug to the collector, so that several siphons of different capacity can be used on the same apparatus. The entire collector is inserted in a bos. A hole in its cover allows the lower part of the siphon to be fitted in its normal position. It is consequently easy to protect the receiver against dust or other contaminating agents. The cover is made in two parts. Even in delicate chromatographic separations the same results have been obtained with a drop-counter collector and with the siphon collector used for many months in this laboratory for the chromatography of amino acids by the Moore and Stein method (6). ACKNOWLEDGMENT
Robert Lombaert’s most helpful collaboration in elaborating the electrical circuit and Edward Jaggli’s advice in mounting the mechanical parts are acknowledged. The expenses of this investigation were covered by a grant from the Centre National de Recherches sur la Nutrition of the Belgian Institute of Food and Sutrition. LITERATURE CITED
Figure 2.
Turntable and Actuating Mechanism
(1) Desreux, V., Rec. traa. chim., 68, 789 (1949). (2) Gilson, A. R., Chemistry & Industry, 1951, 185. (3) Grant, R. A , and Stitch, S. R., Ibid., 1951, 230. (4) Harris, J. O., Ibid., 1951, 255. ( 5 ) James, A. T., Martin, A. J. P., and Randall, S. S., Biochem. J . , 49, 293 (1951). ( 6 ) Moore, S., and Stein, W. H., J . Biol. Chem., 192, 663 (1951). (7) Randall, S. S.,and Martin, A. J. P., Biochem. J., 44,ii (1949). (8) Stein, W.H., and Moore, S., J . B i d . Chem., 176,337 (1948).
