279
V O L U M E 2 8 , NO. 2, F E B R U A R Y 1 9 5 6 contact n i t h the inner column wall. This construction provides for violent agitation of the reflux liquid and for intimate contact of descending liquid and ascending vapors. This contact is enhanced by the spiral construction of the band which throws both liquid and va or to the column wall. The pitch and direction of rotation o f the spiral create a downward pumping action 1% hich accelerates the return of the descending liquid to the still pot. The section of band in the still pot ensures smooth boiling and uniform boil-up rates. All of these factors contribute to give a still of high flexibility and efficiency. A guide bearing a t the bottom of the still pot prevents vibration of the shaft. The construction whereby the transverse wires of the spiral band brush the column wall also helps keep the spinning band centered and free of vibration. Take-Off Valve. Reflux ratio of the still is controlled very accurately by means of an adjustable needle valve (Figure 3). The valve is made by threading a stainless steel rod through a plug of Teflon tetrafluoroethylene resin fitted tightly into the top of a glass tube. The lower end of the rod has a Teflon tip which fits into the valve seat located between arms which connect with the still column and the take-off tube. Adjustment of the valve is made by means of a brass turn nut a t the top of the rod.
To give a more precise idea. of thc operatioiial characteristics of a typical still, data are given in Table I. The still used had an interior column diameter of 10 mm., column hand length of 29.75 inches with 12 spirals per foot, and condenser band length of 5.25 inches. The band %*asoperated a t 3300 r.p.m. using a mixture of 25% n-heptane aiid 75% methylcyclohexane by volume. AChNOW LEUGXIENT
The author nishcs to express his acknowledgment axid :tppi vriation to J. TV. Robson for assistance in obtaining distillation data, and to T. *J. Uhrig for help in fabrication of the still. LITERATURE CITED
. (1) Birch, S. F., Gripp, I-.,and Nathan, W. S.,J . SOC. C h c ! ~ Irid. 6 6 , 3 3 - 4 0 (1947). (2) Foster, N. G., and Green. L. E., J r . , AXLL. CHEM.24, 1869 (1952). ( 3 ) hlurray, Ii. E., J . A m . Oil Chemists' SOC.28, 235- 9 (1951 ). CONTRIBUTIOX 340, Chemical Department. Experimental Station, E. I. dri
TEFLON
P o n t de h'emours 8; Co.
1 E 1 R AF 1. UO R O E TH Y L E N E
Simple large Volume Fraction Collector for Column Chromatography Victor Ginsburg, Department of Plant Biochemistry, University of California, Berkeley, Calif.
-
~ V P L inexpensive E
d Figure 3.
fraction collector has bren devised for the automatic fractionation of the eluate from columns. With the increasing use of column chromatography for chemical separations, many automatic fraction collectors have been described. The receivers in these collectors are usually changed by means of electric motors that are activated by impulses from timers or by the closing of circuits after certain volumes of eluate have been collected.
b
Detail of adjustable needle valve
Use of such a valve eliminates the possibility of air leaks or bubbling back such as may occur with a stopcock. OPERATIONAL CHARACTERISTICS
Stills of this design have been made with interior column diameters ranging from 6 to 50 mm. and with column heights of 1 to 6 feet Such stills have been operated readily a t pressures as low as 10-4 mm. Dependent on still size and operating conditions, a height of equivalent theoretical plate as Ion- as 0.74 inch and a pressure drop of 0.04 mm. have been obtained. k column measuring 23 mm. in diameter by 36 inches in height has been used for a large number of distillations a t a through-put late of 4 liters per hour using a 12-liter distillation flask. ii 1-liter distillation flask may be used with this column, provided an adapter of correct length is used for connecting the column and flask. Microstills with columns 6 mm. in diameter and height from 12 to 36 inches are characterized by small holdup, as low as 0.3 ml., and high boil-up rates. Such microcolumns can he operated with a few milliliters of starting material..
Table I.
Operational Characteristics of Spinning Band Still at Different Boil-Up Rates
Boil-up rate, ml./hour Operating hold-up, ml. Pressure drop, inm. H g H.E.T.P., inches
1622 4 3 1.09 3 50
333
0 8 0 23 1.07
20.5 0 7 0 23 0 74
For the separation of nucleotides by column chromatography, it is often necessary to collect up to 100 liters of eluate in 500-ml. fractions or less. In this laboratory, a simple versatile apparatuP
280
ANALYTICAL CHEMISTRY
has been devised that is as satisfactory for this purpose as the more coniplicated machines. APPARATUS
The eluate from the column is introduced into the flared upper end of a glass manifold equipped with outlet tubes a t 4-inch intervals. The manifold is held a t a slope of 1 in 12 inches so that the eluate flows down the manifold into the first outlet which is connected by tygon tubing to a 500-ml. Erlenmeyer flask. When the first flask is filled, eluate rises in its exhaust tube until the pressure head formed equals that of the incoming eluate. The eluate then bypasses the first outlet and flows into the second one until the second flask is filled. In this manner, as many fractions can be collected as there are outlets in the manifold. The volume of the fractions can be varied by using flasks of different capacities. Stationary air bubbles that automatically form in the Tygon tubes after each flask is filled ensure the collection of clean fractions. The filled flasks are removed after the screw clamps have been tightened to avoid contamination of the fractions with the small amounts of eluate trapped above the air bubbles. If contact between the eluate and the rubber stoppers is undesirable, the exhaust tubes may be extended into the flasks.
All die parts are made of stainless steel tooled to fit the press, making slight allowances for evacuation, with the die surfaces properly hardened and polished to optical flatness. The sleeve is beveled on the lower edge for greater ease of removal after pressing. One procedure used is t o put the powder mixture on the sleeved lower die, distributing the powder smoothly with a tamper pin before placing the bored cylinder over the die. Next the upper die and the plunger are inserted. The assembly is then carefully inverted while the dies are held in place (an operation made easier by the fact that the cylinder is magnetized) t o put it in the outer shell. Variations are possible, such as using a loading tube to place the powder on the sleeved lower die after assembly in the cylinder and the outer shell, in which case the upper die and the plunger are then merely slid into place. ACKNOWLEDGMENT
The services of John Stupka and Robert Henry of the machine shop in the construction of the microdie are gratefully acknowledged. Prepublication information from Don H. Anderson and Richard G. Smith facilitated the design descrihed. LITERATURE CITED
(1) Anderson, D. H., and Miller, 0. E., J . O p t . SOC.Amer. 43, 777 (1953).
(2) Anderson, D. H., and Smith, R. G., prepublication communica-
Adaptation of Existing Potassium Bromide Disk Press for Microdisk Pressing in Vacuo
(3)
tion to W. G. Brown. Anderson, D. H., and Woodall, N. B., Ax.4~.CHEST. 25, 1906
(4)
Beckman Instruments, Inc., Beckman Bull. 16, 6 (1955).
(1953).
Roger A. Pickering, Spectroscopy laboratory, Argonne Cancer Research Hospital, Chicago 37, 111.
recent commercial development of silver chloride infrared beam condensing optics ( I ) by the Eastman Kodak Go., Rochester, N. Y., led to an interest in potassium bromide microdisk pressing in this laboratory for possible use in infrared microanalysis. Although some easily constructed microdies have been described ( 2 , s), and a die based on the design of Anderson and Smith ( 2 ) is to be available from the Beckman Co., Fullerton, Calif. (4), no mention has been made apparently of adaptation of existing commercial 0.5-inch disk presses to do microdisk pressing. The simplicity of an adaptation devised in this laboratory for pressing microdisks permits a convenient conversion of a commercially distributed press supplied by the Research and Industrial Instruments Co., 30, Langton Road, Brixton, London, S.W. 9, England. The adaptation utilizes the existing die shell with comparable evacuation through the use of a sleeve holder suggested by Anderson and Smith's description of their microdie ( 2 ) . In this method the disks are pressed directly into a steel sleeve, which then serves as a convenient ring holder for mounting and handling. A disk die 6 mm. in diameter is illustrated in Figure 1. The same principles have been used to construct a die pressing 3 x 10 mm. rectangular pellets.
T
HE
Evaporator Feeder W. 0.Phillips, laboratory Division, Goodyear Atomic Corp., Portsmouth, Ohio
operations of analytical and spectro chemistry, it is Iexamination frequently necessary to evaporate solutions to dryness for of the residue. Large quantities of liquid samples N THE
must often be used to obtain an adequate residue for handling. However, the evaporating dish should be small to reduce contamination and to facilitate removal of the residue.
ROD SUPPORT
0
4hW
a-rs
n
Figure 1. Adaptation for pressing 6-mm. potassium bromide disks in vacuo From left. Cross-sectional view of press. showing position of microdie, lower die, s,leeve, upper die, and tamper pin
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4 3/0"
-
Figure 1. Automatically controlled evaporator feeder
The two aims can be reconciled by an automatically controlled feeder of sufficient reservoir capacity. A device providing these features has been described by Telang [Telang, bl. S., IND. ENG. CHEM.;ANAL.ED. 18, 454 (1946)]. In the laboratories of the Goodyear Atomic Corp., Telang's design has been modified for ease of handling and operation as shown in Figure 1. The re-
