The circuit diagram for operation of the reversible synchronous motors is shown in Figure 2. To operate the control knobs, the operator depresses either foot switch 3 or 3'. The synchronous motor then drives the knob either clockwise or counterclockwise until the desired position of equilibrium is obtained. If the operator accidentally moves the knobs too far in either direction, the pins on the knobs contact snap-action switch 2 or 2' and immediately stop the motors. In manipulating the vernier knob, the operator should reverse the motor momentarily to obtain precise control, as these motors tend t o overrun slightly. The I-r.p.m. motor drives the vernier control, while the 4-r.p.m. motor drives the pan-release knob. To weigh a sample on the balance, the operator first enters the dry box through the glove ports and removes the plug from the hole in the top of the dry box. It is convenient to tap the hole and use a machine screw as a plug. Argon is then caused to flow out the hole a t a rate sufficient to prevent air from entering. The auxiliary balance pan in the dry box is then coupled to the balance pan by means of the stirrup provided by Mettler plus a 12-inch section of bare No. 12 copper wire. The sample is then placed on the balance pan, and is weighed by techniques customarily used on single-pan balances. If the sample weighs more than 1200 mg., one or more of the weight control knobs must be operated by another person. At the moment a reading is taken, the flow of argon must be stopped, as it disturbs the equilibrium of the balance. For this reason, a toggle valve should be provided on the
llo v.
Figure 2. Circuit diagram for remote operation of balance controls 1. Hurst reversible synchronous motor, Type R.S.M.-1 (1 r.p.m.) or R.S.M.-4 ( 4 r.p.m.) 2,2'. Unimax snap-action switcher, Type USMW, normally closed 3,3'. Linemaster foot switches, Model T-5 1 -S, normally open
argon inlet line inside the dry box so that the operator can control the flow of argon. The Mettler H5 single-pan balance is especially well suited for remote operation, because it can be equipped for weighing beneath the balance a t moderate cost. The 1200-mg. optical scale provides a wide range for weighing with manipulation of only one knob. The construction of the balance also permits easy adjustment for any tare. The wires connecting the two pans must not touch either the balance platform or the dry box. Experience has shown that once the proper adjustments have been made, few additional changes are necessary. With the arrangement
shown, the balance can also be used for weighing operations outside the dry box. Because argon must not flow out of the hole in the dry box during the actual weighing, trace amounts of air may enter the box. Thus, efficient removal of oxygen and water from the atmosphere inside the dry box is a necessity. In the dry box used in conjunction with the Mettler balance, sodium-potassium eutectic (available from MSA Research Corp., Callery, Pa.) is used to remove water and oxygen. It is stored inside the box in a stainless steel pan, and the surface is kept free of oxides by a stainless steel skimmer driven by a 4-r.p.ni. synchronous motor. A midget blower that delivers 15 cu. feet per minute moves the dry box atmosphere; it must be turned off when weighings are being made. Argon (Spencer Chemical Co., available from Southern Oxygen Co.) used for the dry box atmosphere contains so little water and oxygen that no purification train is necessar,y. This balance has been used successfully for weighing Tic13 and Tic14 with no detectable oxidation or hydrolysis of the sample. Weighings routinely require 2 to 4 minutes, once the sample is in the dry box and the operator has entered the box through the glove ports. LiTERATURE CITED
(1) Gibb, T. R. P., Jr., ANAL.CIIEM.29, 584 (1957). (2) Sherfey, J. M., Ind. Eng. Chen. 40, 435 (1954). (3) Williams, A. F., Park, T. O., Analyst 85,126 (1960).
A KBr Powder Trap for Gas Chromatographs for Obtaining Infrared Spectra Herman W. Leggon, Parma Research Center, Union Carbide Corp., Parma 30, Ohio of gas chromatoIliquid graphic techniques to the study of and solid organic compounds at N THE APPLICATION
temperatures up to 400" C., the finding of unknown components is extremely common until the system has been explored thoroughly. Errors in sample reporting are minimized by establishing or verifying the identity of these unknowns by obtaining their infrared spectra. A number of traps (1-6) have been reported for capturing desired components issuing from the chromatograph either by a freeze-out technique or by simple condensation. Samples are then transferred to an infrared spectrometer and scanned, A trapping technique was needed in this laboratory which would permit the component to be run in a KBr
pellet in the infrared spectrometer. Such a technique was developed. Any piece of straight glass tubing capable of quick attachment and/or detachment to the outlet of the chromatograph is appropriate. A straight piece of open glass tubing with a 7 / 1 6 ground glass female outer joint is satisfactory for the Kromo-Tog Model K-2 used in this laboratory.
KBr POWDER7
"TEFLON" PLUNGER
7 / 1 5 GROUND GLASS JOINT'
Figure 1 .
A KBr trap
7
The trap is prepared by inserting a Teflon plunger to the desired depth into the joint end of the glass tube. Next a weighed quantity of infrared quality KBr is added carefully through a small funnel or with the aid of glazed paper into the other end of the tube. The tube is lightly tapped, while in a vertical position, to pack the KBr powder against the plunger and make a plug in the tube (Figure 1). The Teflon plunger is removed and the prepared trap is stored in a desiccator to protect it from moisture. When the desired component begins to emerge from the detector cell, the trap is quickly attached to the heated outlet of the gas chromatograph. As the carrier gas passes through the loosely packed KBr, the eluted fraction is deposited on the powder. After the component has been trapped, the Kl3r VOL 33, NO. 9, AUGUST 1 9 6 1
1295
-=OAR
1-28 6 1
O I ( U 1 W . L -
nulw
NO-
.
1
1 1 1 -
figure
2. Spectra of 1,2,4-trichlorobenrene obtained using trapping technique
is poured into a mortar. The sides of the tube are scraped with a microspatula to remove any powder remaining On the walls* The scrapings are added t o the iiiOrtX and the KBr is ground thoroughly. A KBr disk is made in the usual manner and scanned on the infrared spectrophotometer. This technique has all the advantages of the KBr pelleting technique necessary in infrared work. With the use of this KBr plug, it is possible to trap out the desired component a t room temperature, thus eliminating the necessity of the
1296
ANALYTICAL CHEMISTRY
cold trap. This technique also reduces the number of times the purified component is handled in transferring it from the trap and ultimately into the infrared instrument. oncethe disk is formed, the sample can be stored for future reference or comparison. The above technique has been used in this laboratory in trapping aromatics, polynuclear aromatics, and similar types of compounds that are easily condensed at room temperature. Examples of spectra obtained in this manner are shown in Figure 2.
LITERATURE CITED
(1) Anderson, D, M. IT.,rinalyst 84, 50-55 (1959). ( 2 ) Anderson, D. M. IT.,Duncan, J. L., Chem. & Ind. (London) 1958, 1662.
(3) Gohlke, R.
s., &fcLaffertY,F. w.,
129th Meeting, ACS, Dallas, Tex.,
lgS6.
( Applied 4 ~Spectroscopy, 2 ~~ ~~ May 'i5 ~ $ c~ , f e~ ~ ~~ ; ~ 1960.
20, ( 5 ) xapier, 1. M., ~ ~ d H.d J,,~ chern. , & I&. ( L ~ & o 1958, ~ ) 1319. (6) Weinstein, A,, ANAL.CHEM.29, 1899-
1900 (1957).
