A SIMPLE AND INEXPENSIVE VACUUM FRACTION-COLLECTOR SAUL B. NEEDLEMAN' Illinois Institute of Technology, Chicago, Illinois
WAILE investigating suitable methods for the separation of pure fatty acids from a complex natural mixture, recourse was had to the vacuum distillation of their esters and to the more recent technique of partition chromatography. Anticipating an extensive series of fractions from either technique, it was desired to prepare a fraction-collector which could be readily adapted for use with both vacuum distillation and chromatography. Simplicity of design and minimal expense in the making of the collector were additional factors to be considered. A number of piglets exist for collecting small fractions under vacuum. These are, for the most part, limited to systems providing only one or two receivers and frequently suffer from the inability to effect sharp separations between fractions. The fraction-cutter described herein modifies certain existing designs to gain several important advantages. It is small, easily operated, and can he adaptable to a variety of uses. The shell opens to allow for easy replacement of receiver tubes of a variety of sizes. It can be prepared by any trained glass blower and its nominal cost, about $30, makes it feasible for routine use. The fraction-cutter consists of a glass shell made up of the two halves of a 103/60 standard taper joint. The upper half is sealed off about one inch above the eround elass and a standard taver receivine inlet ( A ) fitted with a small funnel and drip-tip (B) iskroduced to one side. An outlet to the vacuum system (C) is also attached. The length of the lower portion is determined by the maximum size of receiver to be used. The bottom of the shell is closed off and a standard taper joint and plug (D) is fitted through the center of the sealed-off end. The receiver plate ( E ) is a 3.5-inch medium-gage stainless-steel disc which has a series of holes drilled along the outer edge to support the receiver tubes. Plates with holes of various sizes can he stocked to accommodate receivers containing from 0.25- to 3.00-ml. samples. By means of lock nuts (F), the carrier plate is attached to one end of a threaded 3j16-inchsteel shaft (a 5-inch machine screw with the head cut off). The '
Current address: Department of Chemistry, Northwestern University, Chicago, Illinois.
opposite end of the shaft is soldered to a sleeve and pin mechanism (G) which slips over the ground-glass plug projecting through the bottom of the shell. The height location of the carrier plate relative to the driptip is adjusted (raised or lowered) by setting the position of the lock nuts on the shaft. The glass shell is cushioned on cork rings during operation.
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The tip of the chromatographic column or distillation take-off adapter is introduced into the funnel via the standard taper inlet. A stopcock (H) can he provided a t the inlet so that the cutter can be opened or removed entirely without disturbing the remainder of the vacuum system. If a wide-bore stopcock is used, contamination by grease is minimized. The standard taper plug a t the bottom of the shell allows the carrier plate to be rotated from the outside without interrupting the vacuum. Careful greasing of the 103/60 joint facilitates easy opening of the shell for rapid replacement of receivers and does away with the necessity of removing each receiver with forceps.
