Gas Chromatographic Injection Port for Corrosive Liquids and Gases
Donald Fielder and D. L. Williams Materials Engineering Lab Section, Physical Chemistry Branch, Chemical Research Division, Chemical Laboratory, Edgewood Arsenal, Md. 21010
The use of injection ports for the introduction of corrosive compounds into the carrier gas stream of a gas chromatograph is normally limited by the construction material and its compatability with the corrosive compound at the injection temperature. The injection port described here is made exclusively of polytetrafluoroethylene (Teflon, Du Pont) and is thus resistant to practically every chemical and is thermally stable up to 500 O F (260 "C) ( I ) . It was constructed for use with a corrosive gas chromatograph ( 2 ) .
b
0.
Inert injection port: (A) 1-in. 0.d. Teflon body; (B) Swagelok nut; (C) Teflon-faced septum: ( D ) /1&. Swagelok elbow: (E) carrier gas inlet: ( F ) 1/4-in.Teflon connector: ( G ) %-in.connector fitting: (H) column Figure 1.
u
EXPERIMENTAL Figure 1 is a diagram of the injection port that has been successfully used. It is machined from an extruded Teflon rod to a n outer diameter of 1 inch. The septum holding assembly consists of a Teflon Swagelok nut (Crawford Fitting Co.) and a machined male injection nipple with beveled needle guide. A gas channel 0.086 inch in diameter is drilled through the center of the port to the gas exit. The carrier gas is introduced by means of a brass Ys-in. Swagelok male elbow tube fitting which opens into the gas channel. The injection port is connected to the column in either of two ways (Figure l , a and b). The first (Figure l a ) is by use of a y 4 - h diameter Teflon tube which is threaded into the injection port body and opens into the gas channel. A standard Teflon Swagelok union is then used to attach the column. The use of Teflon tape on the threaded joint will help ensure leak-tightness. The second and, perhaps, superior type of connection (Figure l b ) is a short piece of Teflon which is threaded a t the injection port end and so machined a t the column end as to accept a Swagelok nut and ferrules. Use of the latter method reduces not only the number of potential leaks but also the total volume of the connection, since the connector bore can be drilled to any diameter. Again, Teflon tape is used to help prevent leakage a t the threaded joint. The injection port assembly is heated by means of an aluminum block (Figure 2) and two cartridge heaters. The temperature of the block is monitored with a thermocouple. Because of the design, a 2-in. or longer syringe needle must be used to ensure deposition of the sample in the heated zone. The carrier gas may be preheated by merely coiling the delivery tube about the block heater. A totally inert system is provided by use of commercially available Teflon-faced septums.
CONCLUSIONS Teflon injection ports can be easily made and used successfully with corrosive compounds. Although the upper temperature limit may hinder some analyses, the inherent inertness of Teflon permits the examination of corrosive materials heretofore denied because of their reactivity. It is presumed that injection port designs differing drastically from the above can be as easily made and successfully used.
ACKNOWLEDGMENT Figure 2. Block heater assembly: (A) aluminum block; (6)injection port; (C) carrier gas preheating coil: (D) port to column connector; (E) cartridge heaters; (F) thermocouple (1) M . Sneed, J . Maynard, and R. Brasted, "Comprehensive Inorganic Chemistry," Vol. i l l , Van Nostrand, New York. N.Y., 1954, p 45. (2) D. L. Williams and Donald Fielder, unpublished work, 1973.
2304
The authors thank Robert Grula for his many helpful discussions and the Experimental Fabrication Branch (Plastics Lab) of the Manufacturing Technology Directorate for their practical assistance.
Received for review March 15, 1973. Accepted May 2, 1973.
ANALYTICAL CHEMISTRY, VOL. 45, NO. 13, NOVEMBER 1973
