E. Hautala and M. 1. Weaver Western Regional
An Inexpensive Linear Temperature
Reseorch Laboratory
U.S. Department o f Agriculture Albany, California 94710
Programmer for Gas Chromatography
G a s chromatography (G. C.) has become an indispensable tool in most analytical laboratories. Since the separation and detection of different classes of compounds by G. C. usually requires a change of columns, and often detectors, as well as adjustment of operating parameters, research output could he accelerated hy having additional sets. However, the cost of additional instruments is often prohibitive. Now with the availability of factory-made detectors and published electrometer circuits, it is often within the budget for an investigator to build the component parts and to construct his own gas chromatograph. One of the most important and expensive components to build is the temperature programmer. At this laboratory, we have utilized commonly available laboratory equipment to fabricate a linear temperature programmer of sufficient accuracy to bc used for G. C. The temperature control mechanism chosen was the capacitanceoperated relay.' These relays have been available for many years and are in common use for isothermal operation of water or oil baths and for forced-air ovens. Construction
The linear programmer is shown in Figure 1. A standard lahoratory timer calibrated in minutes ( A ) was mounted on a plastic stand (B) that had been screwed onto the chromatograph oven lid (C). The shaft (D) of the clock was extended and a narrow plastic drum (E) was attached to the shaft with a knurled nut ( F ) . A nylon monofilament line (G) attached to the drum runs over a pulley on the support ( H ) to a 6 in. long 250°C thermometer (I). The thermometer drops through a glass tube (J)inserted through the oven lid
Sids view 01 clock
(C). The relay input terminal was connected to a clip (K) around the glass tube above the lid, and a ground wire (L) was clipped around the glass tube just under the oven lid. A rubber stopper, ( N ) bored to fit around the thermometer, was used to stop the descent of the thermometer into the oven. Operation
The knurled nut on the timer shaft extension was loosened and the hand on the timer was turned to the desired duration of programed temperature rise. The thermometer was placed into the glass tube, and the relay was turncd on and adjusted for maximum sensitivity. The thermometer was then slowly lowered into the oven until the dcsired starting temperature was reached. This position was marked for future reference and the thermometer was held in this position by the rubber stopper. When the compounds to be separated were injected into the chromatograph, the clock was started, the rubber stopper was raised and the program was begun. The rate of programming was determined by the size of the drum on thc clock shaft. The rubber stopper was set to stop the descent of the thermomcter at a pre-determined point and thus maintain maximum temperature. Results
Thermocouples from a recording thermometer were inserted into the oven and the temperature was recorded at 5 sec intervals. Starting temperature on this run was 42°C and final temperature was 174% Rate of ascent was approximately 4.5'/min. The rclay was adjusted for maximum sensitivity before the program was started. No relay adjustments were made for the rest of the run. When temperature was plotted at 30 sec intervals and a straight line was drawn through the points, the maximum fluctuations were i l . O 0 C (A in Fig. 2). The relay should be readjusted when maximum temperature is reached in order to eliminate fluctuations such as those shown a t the top of curve A, Figure 2. The proximity of the thermometer to the heater coils was critical. Linear temperature change (A in Fig. 2) was obtained with the thermometer positioned 1 in. from the heater coils. When the thermometer was placed approximately 6 in. from the heater coils, its
Reference t o s. eomnanv or oroducl name does not imolv Figure 1. Linear temperature programmer; A, Timer; 0 , Stond; C. Oven lid; D, Shoft; E, Plo.tic drum; F, Knurled nut; G, Monofllment line; H, Support with pulley; I, Thermometer; J, Gloss tube; K, CKp; 1, Gmund wire; M, Heoter coil; N, Rubber ,topper.
122 / Journal o f Chemical Educafion
tories, Andover, New York,
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Figure 2. Programmed temperature change. A, Thermometer placed 1 in. from the heater coil. 8, Thermometer placed 6 in. from the heater coil.
response was sluggish, causing excessive fluctuations in temperature (Fig. 2, B). Long thermometers were not satisfactory. As the oven temperature rose, the greater length of the mercury column caused an increase in relay sensitivity. The heater was turned off before the mercury reached the upper sensing clips ( K ) ,altering the relationship between temperature and thermometer position. Figure 3 shows separation of two different mixtures of methyl esters of five organic acids (C3-C6). Retention times for each acid varied less than 10 see. On the negative side, it can be difficult and time consuming to set the thermometer at the exact starting point used in preceding runs. Also, it may he difficult to duplicate relay sensitivity adjustment. These difficulties are minor, however, and by careful operations, the retention times of the compounds being analyzed are consistent.
MINUTES Figure 3. Separation of a mixture of flve organic acids lCs-Csl using the temperature programmer. Injection 1, solid line; injection 2, broken line.
Acknowledgment
The authors wish to thank Mr. Harold n"IcDona1d and Dr. Milford Brown for t,heir advice and counsel in designing and assembling the programmer.
Volume 46,Number 2, Februory 1969
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