diameter spring. I n addition] for more efficient emptying, the diagonal stopcock bore was enlarged from 2-mm. diameter as supplied to 1 2 0 i inch. l~ Depending on the solvent, nonglass reservoir junctions may be used or completely glass systems may be used. I n either case, lubricants or components other than glass and Teflon are not necessary for operation of the system. Initially, a volumeter (Instrumentation Specialties Co., Lincoln, Yeb.) was used to operate the dispensing device. However, limitations of the device prompted the design and assembly of the power sulqily shown in Figure 2. This latter system allows the actuating 45' rotary solenoid (No. A-35243-030, Ledex, Inc.. Dayton, Ohio) to be used a t a distance from the power supply. This physical removal from the power supply
plus the low voltage to the solenoid minimizes possible spark hazard The variable duty cycle of this system will depend on both the solenoid and the time delay relay used. Although rigid speed us. accuracy tests have not been attempted, the system as described in Figures 1 and 2 has allowed unattended collection of 15-ml. additions by a fraction collector a t a rate of 10 per minute. The system as described is also adaptable to stopcocks of other dimensions with a minimum of machining effort. The system has also been utilized with a three-way syringe stopcock (Tomac No. 17136) by using a rotary solenoid of 90" rotation (Licon No. F-1350, Illinois Tool Works, Chicago, Ill.). -4 switch selector has also been devised so that any one of 5 different thermistorsolenoid pairs in place with a given dis-
penser can be driven by a single power supply. As an addendum not shown in Figure 2, it should be noted that the insertion of a 0.05-pf. capacitor from the wiper arm of the 1K potentiometer to the blue transformer lead will minimize the effects of line transients. ACKNOWLEDGMENT
The authors thank Harold Shipton, Division of Medical Electronics, State University of Iowa College of Medicine, for consultation on the design of the stopcock actuating power supply. Work supported by U.S. Public Health Service Research Grants GM-09784 and SB-04925. Author J. L. S.is a Research Career Development Awardee of C . S. Public Health Service ( GAM-K3-5271)and hiarkle Scholar in Academic Medicine.
Use of Trifluorotrichloroethane-Methylene Chloride in Adsorption Elution Chromatography John A. Attaway, Florida Citrus Commission, Lake Alfred, Fla.
of organic subon columns of alumina or silica gel, it is standard practice to use solvents of increasing polarity for elution] thus basing separation on the relative polarities of the components of the mixture. The solvent most frequently employed for the elution of aldehydes, ketones, and esters is benzene. This solvent functions quite satisfactorily for use with solids and high boiling liquids, u
THE SEPARATION
1-stances
However, when relatively volatile compounds are under study, this solvent is undesirable; conditions necessary for its removal may cause losses and result in poor yields. In addition, changes may occur in heat sensitive compounds. To eliminate this difficulty, experiments using thin layer chromatoplates were conducted to evaluate other possible solvents. h combination of trifluorotrichloroethane (TF) and methylene
ville, Ill.) attached to aspiratovr vacuum. A hot water bath and a mechanical vacuum pump were available for completing difficult separations. Trifluorotrichloroethane was obtained from both the E. 1. du Pont de Semours & Co. under the trade name Freon TF. and the General Chemical Division, Allied Chemical Co. under the trade name Genesolv D. RESULTS
Table 1.
Comparative R, Values Using Benzene and TF-MC Solvents on Thin Layer Chromatoplates
Compound Carvyl acetate Carvone Citronellal Terpinvl butyrate GeranZ-1 acetate
Benzene R f 0 56 0 30 0 62 0 70
0.55
TF-lIC Rj's 60-40 mixture 50-50 mixture 40-60 mixture 0 59 0 61 0 80 0.29 0.33 0.51 0.63 0.66 0.81 0.70 0.72 0.90 0.53 0.59 0.75
Table II. Comparative Recovery of Volatile Compounds from Benzene a n d TF-MC
Compound Ethyl acetate Ethyl propionate Propyl acetate
Isobutyl acetate Ethyl butyrate Hexana Octanal
2224 *
F.P. C,
77
Recovery, sc 60-40 Ben- TFzene
99.1
0
116,5
30
121.0 131.1 163.4
56 88 92
lol,
ANALYTICAL CHEMISTRY
as Developing
chloride (MC) was found to have the same elution properties as benzene but a much lower stripping temperature. EXPERIMENTAL
Solvent evaluations were carried out R l ~ on 8- X 8-inch thin layer chromatoplat8es containing Silica Gel G layers lo of 6O-nlicron thickness prepared using a 54 62 Research Specialties Co. spreader. 88 Ascending development !!-as used in all 96 cases. 96 The solvent stripping operations were 98 performed using a Rinco Rotary Evaporator (Rinco Instruments Co., Green-
The evaporation of the TF-1IC mixtures proceeded readily a t room temperature with the formation of frost on the outside of the vessel, whereas the stripping of benzene was slow and required either heating with warm water or the use of the mechanical vacuum pump for satisfactory results. Table I shows the R, values of some representative volatile carbonyl compounds and esters using both benzene and three separate mixtures of TF-lI C as d~veloping solvents. The 60-40, TF-3IC mixture gives R , values practically identical to those from benzene. The boiling point of the 60-40 TF-3IC mixture is constant at 36" C.!whereas the boiling point of benzene is 80" C. Table I1 shows comparative recovery data for some relatively volatile conipounds. In each case exactly 5.0 grams of solute were dissolved in 500 ml. of benzene. and the same quantity in 500 ml. of 60-40 TF-11'2. The solvent:: were removed by stril)ljing and the residual solute weighed.
