Determination of Volatile Materials in Polymers J. N. Roper, Jr. Research Laboratories, Tennessee Eastman Company, Division of Eastman Kodak Company, Kingsport, Tenn. 37662
THISLABORATORY has been involved for a number of years in the determination ofvolatiles contained in polymeric materials. Several different methods have been employed which usually involved the use of heat and the sweeping action of an inert gas stream to separate the volatile components from the polymer. The volatiles are then analyzed by gas chromatography. When there is a low concentration of volatile material, it is advantageous to concentrate it in order to improve the shapes of the chromatographic peaks. Our most recently evolved method employs a trap-tube, shown in Figure 1. The capillary portion of the tube is packed with a gas chromatographic column packing consisting of 20 to 30 of a suitable liquid phase on a granular diatomaceous type support. The tube is fitted with a suitable hypodermic needle so that it can be connected to the gas chromatograph through the injection port. The apparatus is arranged as in Figure 2. The gas chromatograph is equipped with a temperature programmer and any suitable column which will separate the various volatile components. The polymer sample to be analyzed is weighed into the trap-tube, the sample size being chosen to give suitably sized peaks for measurement. The tube is connected to an inert-gas stream by means of butyl rubber tubing and heated to the proper temperature while the gas stream sweeps the volatile material into the packed section of the tube, which is usually cooled with dry ice. The temperature, sweeping rate, and sweeping time should be determined experimentally and will vary with the type of polymer being investigated. Melting the polymer is often necessary to rid it of volatiles. A suitable heater for the trap-tube is a micro combustion furnace, such as A. H. Thomas No. 5676-A, which is light enough and small enough to be held by hand if necessary. After the volatiles have been adsorbed in its packed section, the trap-tube is disconnected from the butyl rubber tube and moved to the chromatograph. With valve A open and valve B closed, the tube is connected to the butyl rubber tube with the heater positioned away from the capillary end. Then, with valve A closed, too, the hypodermic needle is inserted in the injection port and valve B is opened. The heater, already
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ANALYTICAL CHEMISTRY, VOL. 42, NO. 6, M A Y 1970
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Figure 2. Arrangement of apparatus
at the proper temperature, is then moved to the capillary portion of the tube where the heat and carrier gas flow sweeps the volatiles from the packing through the hypodermic needle and into the gas chromatograph. In some cases it is necessary to program the oven temperature of the chromatograph to get a suitable chromatogram. It is advantageous to use an electronic integrator to determine the response in counts per microgram for the various components to be measured. With this information, the percentage of each volatile component of the sample can be calculated from the number of integrator counts in each peak. RECEIVED for review January 29, 1970. Accepted February 25, 1970.
