sented on strips 2 and 5. Strip 12 shows a purified sample of pheophytin b. (The small white specks visible in the black and white photograph are due to imperfectionsi n the layer of sugar.) The fluorescent areas clearly visible under ultraviolet can he marked, scraped from the plate, and eluted from the sugar to recover the desired material for further identification.
LITERATURE CITED
(1) Anwar, M. E.,J . Chem. Educ. 40, 29 (1963). (2) Gamp, A., Studer,, P., Linde, H., Meyer, K., Ezpermtla 18, 292 (1962). (3) Hendshury, E., Obt, D. G., Perrings, J. J., J . Chem. Educ. 40, 31 (1963).
Kirchner, J. G., Miller, J. M., Keller, G. J., ANAL.CHEM.23,420 (1951). ( 5 ) Mangald, H. K., J . Am. Oil Chemials’ SOC.38, 708 (1961). (4)
(6)
Randerath, K., “Thin-Layer Chro-
mapgrnphy,” Verlag Chemie! GmhH., Wemheim/Bergstr., Academic Press, New York and London, 1963. (7) Stahl, E., Parfcmerie Kosmetik 39, 564 (1958). (8) Wilson, John R., Nutting, MarvelDare, ANAL. CHEM.33, 144 (1963).
REFERENCE to a company or product name does not imply approval or recommeudation of the product by the U. S. Department of Agriculture to the exclusion of others that may he suitable.
Variable-Speed, Motorized Buret for Rapid, Semiautomatic Neutralization of Small Volumes Lome F. Ebell, Department of Forestry of Canada, Victoria, British Columbia’
INsoxhletlaboratory large numbers of residues of woody tissues are THIS
ground in 15-ml., tapered, glass tissue grinders with 6 ml. of 1N HCI. After hydrolysis, the ground material requires precise neutralization prior to enzymatic determination of starch ‘as glucose. The standard electromagnetic, pinchcock-type, titrimeter valve proved unsatisfactory for the purpose. This valve provided extremely slow delivery of titrant during the initial phases of neutralilisation, when set finely enough for a good end point, required excessively large volumes of relatively weak titrant, and constant attention to avoid disastrous overshoot. Commercially available, motor-driven burets were too limited in speed flexibility for the logarithmically decreasing titrant volumes required for a fast approach to neutrality. The inexpensive, motordriven buret described in this note has permitted use of concentrated sodium hydroxide for neutralization of hydrolyeates, with a time requirement of approximately 1 minute per sample under good mixing conditions.
Table 1.
Output Shaft Speed and Titrant Delivery Characteristics with 2-ml. Micrometer Buret Delivering 0.1 ml. per Revolution
Output shaft r.p.m.
Motor Fast motor Slow motor
over operational voltage 30 volts 3 volts 4 0.1 0.1 ,005
GENERAL DESCRIPTION
A stepless, buret drive-speed control of 800:l was obtained by varying the voltage to two 30-volt d.c. motom driving a common output shaft through a differential gear system (Cramer type 800 d.c. motors on type 152 dual motor gearing system, Cramer Division, Gianinni Controls Corp., Centerbrook, Conn.). A 2-ml. capacity, . . micrometer SYringe was mounted to the motor gear hcbusing and connected to the dualm otor, output shaft with a slotted drive SYstem, as illustrated in Figure 1. The ouitput, shaft speed and titrant delivery
Range of speed reduction
Range of titrant delivery rate #I. per minute
402 20:1
400 to 10 10 to 0.5
rate ranaes obtainable over the operationaj voltage range of the motors are given in Table I. Motor speeds are linearly proportional to applied voltage. Further reduction in the rate of titrant delivery, providing a smooth, automatically controlled approach to the end point, w&s obtained by intermittent operation of the slow-speed motor through a relay compatible with the valve circuit output of an automatic titrimeter. Under intermittent opersr tion delivery rate is governed by motor voltage setting, titrimeter proportional band setting, and proximity to the end point.
valve circuit
Figure 1 . buret
Mounting of variable-speed, motcbrized
Buret 11 aligned and held l o the duo1 motor geor houring by two rods and (I finger-tight screw clamp. A machined nylon, dotted drive exlension, press-fllled to the micromeler barrel, permits odwncemenl of the mi~rometer(IS it is turned by the ~ u l pshaft ~ t of the motors
446
ANALYTICAL CHEMISTRY
2N671
Fiaure 2.
Circuit dioaram of Dower
SUDD~V
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
