POWER SUPPLY DESIGN
The circuit diagram for the power supply, which provides a continuously variable range of 0 to 32 volts d.c. t o the motors, is given in Figure 2. Power from the 110-volt a x . line is applied to a step-down transformer to provide 25 volts a x . to a bridge rectifier consisting of four IN1695 diodes, and partially filtered by a 500-mfd. condenser. A 10-ohm series resistor limits the initial surge current when power is first applied so that the diode ratings are not exceeded. Two identical regulators are employed for the high- and the low-speed motors. By employing transistors as filter elements the need for large bulky chokes is eliminated. The voltage a t the emitter of each transistor is set by the IO-K potentiometer in its base circuit, the emitter voltage being nearly equal to the base voltage. The effective filtering action of the 100-mfd. condensers is magnified by the current gain of the transistors and appears much larger than its actual value. When the operate button is pushed, voltage is Y
applied to the motor through the forward-reverse switch. This switch reverses the polarity of the voltage applied to the motor and permits operation in either direction. The two motors and the relay coil are connected to the power supply through a six-pin, Jones connector. When the relay coil is energized by the titrimeter valve circuit, the relay contacts close, activating the slow-speed motors. The motor remains operational, or is operated intermittently] for the length of time the relay coil is energized. The IN91 diodes are transient suppressors, used to eliminate the large inductive voltages appearing across the motors when switched on or off. If the power supply is used for other applications, current drain should be limited to a maximum of 100 ma. OPERATION OF BURET
Y
The slow motor is automatically started by the titrate control of the titrimeter. The fast motor is simultaneously operated manually as required to move the meter off the extreme
ends of the pH scale, and neutralization is completed with the slow motor. Motor voltage controls are set according to the desired rate of titrant delivery. The buret may be refilled simply by running the fast motor in reverse at an appropriate speed. For somexhat more convenient titrimetry with this motor system, a digital readout buret with manual re-set could be substituted for the buret in present use. Since the power supply is independently lineoperated, provision was made for bypassing the slow motor relay to permit use of the system for manually controlled titrimetry with a standard pH meter or for use of the motors for other than buret drive applications. ACKNOWLEDGMENT
Appreciation is expressed to Anthony Moilliet, R. W. Chappell, and J. W. Parker of the Pacific Kava1 Laboratory, Esquimalt, B. C., for assistance in development of this apparatus. Department of Forestry, Canada, Forest Research Branch Contribution No. 658.
Simultaneous Dual Column Gas Chromatographic Modification Bernard M. Mitzner and Walter V. Jones, International Flavors & Fragrances,
52 1 West 57th St., New York, N. Y. 10019
of multi-column gas T chromatography has become increasingly popular. Most of the comHE APPLICATION
mercial gas chromatographs being manufactured today are dual column instruments. A multi-column gas chromatograph has been described recently which uses a single detector and recorder (4).The advent of dual column chromatography was prompted by the desire to maintain a straight base line when temperature programming. Many workers however, have utilized the dual column chromatograph containing columns with different liquid phases (polar and nonpolar) to have them conveniently available for certain applications without having to bother to change columns. Meritt (3) has described a dual column instrument containing two independent detectors and recorders. This instrument enables the operator to make a single injection and obtain simultaneously gas chromatographs on two different columns. Such a system is very advantageous insofar as saving time is concerned when one wishes to employ the retention volume constant system described by Meritt ( 2 ) or the well known Kovats retention index system (1, 6). By the same token, if one wishes to determine the purity of a sample (in many cases a gas chromato-
O V E N WALL
Figure 1. Construction of tee and its attachment to columns and injector
graphic trapping), one can make a single injection and then observe the separations obtained on the two columns simultaneously. Unfortunately, the gas chromatograph described by Meritt (3) is not available commercially and if it were it would be too expensive for general use, thus prohibiting its widespread application. In our laboratory, we have modified a commercially available dual column instrument in such a manner that a sample is injected into one of the existing injectors, it is then divided by means of a tee (in the oven) so as to go to the two different columns. The tee is shown on Figure 1. The existing single detector is used without any modifications and the recorder supplied with
the unit is also used without change. The pen of the recorder is adjusted so as to ride a t mid scale prior to injecting the sample. A simple schematic is shown in Figure 2. We have found that such a system serves admirably for cataloging materials, according to the Kovats retention index system mentioned previously. I t is also ideal for testing the purity of trapped materials as well as others. The outstanding advantage of the device described in this paper is the saving of 5oQj, in the time required for the applications described previously. EXPERIMENTAL
An F and M Model 810 was modified by placing a tee (shown in Figure 1) after the injector, A . An %foot, 1/4-inch 0.d. by 3/16-in~hi.d. copper column filled with 200/, Carbowax 20M on 60-80 mesh Chromosorb P, was attached to one arm of the tee and the other end of the column was attached to the A portion of the detector. An &foot, 1/4-inch 0.d. by 3/16-inch i.d. copper column filled with 20% SE-35 on 60-80 mesh celite was attached to the other part of the tee and the other end of the column was attached to the B portion of the detector. Column .4 (Carbowax) had a flow rate of 100 ml. per minute a t an inlet pressure of 35 VOL. 37, NO. 3, MARCH 1965
447
W
GO L UYN A"
T EL
b t w E C T o d A.
n LEGTOR ( B Y PASSLO)
Figure 2.
TtYL ( Y I W U T C S ~
Schematic diagram of modified instrument
Figure 3. Programmed gas chromatogram of hydrocarbons plus ethyl caprylate
p.s.i. helium (75' C.). Column B (SE-30) had a flow rate of 70 ml. per minute and an inlet pressure of 35 p s i . of helium. (Columns A and B will always have the same inlet pressure because they are attached to a common tee.) The oven was programmed from 70' C. to 220' C. a t a rate of 2 degrees per minute. The injector was a t 250' C. and the detector was at 300' C. COLUMN
RESULTS
Figure 3 represent's an injection of 2l/* p l . of a mixture of Ce, CeJ Cl0, C14, C16, normal hydrocarbons to which a single material, ethyl caprylate, has been added to show the applicability of this system for cataloging data via the Kovats retention index system. Figure 4 represents an equal mixture of hexyl butyrate and terpinenol-4. (These materials occur in natural, Lavender and could represent a trapping obtained on a nonpolar column.) As can be readily observed, the carbowax column clearly separates the mixture into its components while the SE-30 column shows only a single peak. (21/211. injection). DISCUSSION
We feel that the system described above will be invaluable where equipment is a t a premium and advantage can be taken of the savings of time (especially when cataloging materials for a system such as the Kovats retention index system). One must bear in mind that no permanent change is made to the dual column gas chromatograph since only an inexpensive tee is added, which can be removed in seconds, leaving the instrument in its original State.
448
ANALYTICAL CHEMISTRY
'B "
1
SE-30
HEXYL B U T Y L A T I TERPI:::OL-4
e
IO
PO
40
I D
60
IO
TIME /MINUTESI
Figure 4. Programmed gas chromatogram of mixture of hexyl butyrate and terpinenol-4
It is obvious this system has only one serious drawback-Le., if a peak elutes simultaneously on both columns. However, experience has shown that such an occurrence is easily recognizable by a skewed and distorted peak. This effect can be remedied by changing the flow rate of one of the columns. The flow rates of the two columns can be changed, if desired, by placing a restricting valve a t the exit of the detector to which one of the columns is attached. Also, experience will enable the operator to choose just the correct amount of sample to prevent the recording from going off the chart. The modification described in the paper is intended primarily for instru-, ments equipped with thermal conductivity detectors. However, it is apparent that older instruments designed with only one column can be
easily modified using the method described herein. To accomplish this, one has to connect a second column between one leg of the tee and the reference side of the detector. In many instruments, the reference side of the detector is merely a helium bleed to the atmosphere and is ideally suited for the attachment of the second column. This is actually what is done in dual column instruments equipped with thermal conductivity detectors. LITERATURE CITED
(1) Kovats, E., Helv. Chim. Acta 41, 1915 (1958). (2) Meritt, C., Walsh, J. T., ASAI;. CHEM.34, 903 (1962). (3) Ibid., p. 908. (4) Mitzner, B. M., Gitoneas, P., Ibid., 34, 589 (1962). (5) Van den Dool, H., Kratz, P. D., J . Chromatog. 11, 463 (1963).
