pended because of losses from the edges of the chromatograms, a double roller assembly was designed t o hold the chromatograms firmly onto the scanning head. This modification is shown in Figure 2. From a n economic standpoint, the consumption of Q gas was reduced t o a fraction of the amounts expended without the assembly. A plastic window was incorporated in the roller assembly t o prevent dust particles falling into the windowless scanning head when the instrument was
not in use, and a line etched on the window permitted simultaneous and accurate marking of the recording paper coincidental with the appearance of the chromatogram origin line over the center of the scanning head aperture. Flexaframe aluminum rods and Lee lattice connectors were used to position the scanning head. A paper supply reel (11/2 X 4l/*inches) is used to roll a large number of chromatograms joined end to end with cellophane tape for continuous feed.
At the initiation of a scanning run, a lead strip of sufficient length is added to the roll of chromatograms to span the distance between the scanning head and drive shaft assembly. These simple modifications have served well for almost 2 years. Occasionally, the rubber sleeve on the friction roller has been replaced because of excessive cracking resulting from atmospheric pollutants in this area.
Versatile Ionization Detector for Gas Chromatography Roy Teranishi, C. C. Nimmo, and Joseph Corse, Western Regional Research Laboratory, Albany 10, Calif.
sensitive p-ray ionization deV tectors for gas-liquid chromatography have been described b y LoveERY
lock for capillary and large columns [ J . Chromafog.--, 3 5 4 6 (1958); Nature 182, 1663-4 (1958)l. A modification of the Lovelock detectors enables one detector block to be used with either type of column and a t higher temperatures. For p r a y radiation sources, two 10-
me., 1/4-inch-diameter, strontium-90 sources made for thickness and density gages were used (RG-31 source, NUclear-Chicago) . For large diameter column work, the side port, J, is used as the column inlet. il short piece of platinum wire is silversoldered to a spark plug for the center electrode, D'. The detector block itself, E , is the other electrode, and is insulated from the heater box by silicone rubber l/s inch thick. For capillary column TI ork, the side port is used for flushing gas. The spark plug with the platinum electrode, D', is replaced with one that has the center drilled out, D. The hollow spark plug serves as a good insulator a t elevated temperatures and as a holder for the glass capillary tube micro-ionization chamber, A . Room teniperature-vulcanizing silicone rubber (RTU-90, General Electric Co.) is used to seal glass to porcelain. The glass capillary tube is dmn-n with care to fit inside the plug, SO
L
a
Figure 1. Side view of P-ray ionization detector A.
Glass microdetector with platinum electrode, inlet for capillary column 8. Silicone rubber gasket, '/a inch thick C. Stainless steel capillary tubing column D. Spark plug with original electrode removed, 1/9-20 NF threads E. Main block, stainless steel G. @-raysources H. Fitting, '/s-inch pipe threads to flare fitting threads, machined flat to take silicone rubber gasket. Inlet far large column and flushing gas inlet for capillary column work 1. Glass tubing to insulate block from stainless steel J. Stainless steel tubing, '/g-inch. O.D. K. Stainless steel (10-32) socket head cap screw, Inch long
896
ANALYTICAL CHEMISTRY
Figure 2. Front view of detector
F i g u r e 3. Electrode
F. Face plates to hold in sources
D'. Plug
Spark
that the 0.010-inch-diameter platinum wire electrode does not obstruct the flow of gas and yet is not so large as to ruin the resolution of the column. The electrode is inserted through a small hole drilled through the glass and fused so as to avoid pockets in so far as possible. The capillary column is inserted into the microdetector and sealed with a silicone rubber gasket. Because all parts are metal, glass, porcelain, or silicone rubber, the detector can be maintained a t 240" to 250' C. The high detector temperature is desirable for maximum sensitivity and imperative for the analysis of high boiling compounds to minimize condensation. Thiq detector has been used with a number of stainless steel capillary columns 0.010 inch in internal diameter and u p to 240 feet long. iilthough the limit of sensitivity involves the electronic components and recorder used, the microdetector with an amplifier basically similar to that described b y Lovelock gives useful and reproducible peaks in the millimicrogram range. The theoretical plate values vary, but haye been as high as 250,000. The detector has likewise been used successfully with 1/4-inch stainless steel columns of various lengths attached as described. For use ivith ','&ch packed columns, the capillary detector has been allowed to remain in place and the end of the column attached through port J in place of the flushing gas. The capillary electrode suffices for the anode. I n this case, the capillary column is flushed continuously with argon (0.5 ml. per minute) to prevent its contamination. MESTIONof brand names does not imply endorsement by the Department of Agriculture over others of a similar nature not mentioned.
