GAS CHROMATOGRAPH-,
G.C. SEPTUM
WITH CONAX T E F L O N SEAL-\
MANOMETER HAND-DRIVEN KNOB-
HOT JAW COLD JAW
-
’\ L
Figure 3. Sample injection into gc septum
produced ghost peaks in the programmed temperature analysis. Between analyses, the hole in the plug is sealed by a metal rod. Before the injector attachment, the U-tube between the cross and the injector attachment end is heated under helium flush to remove impurities, and then kept immersed in liquid nitrogen to block off any impurities that cannot be removed from the bellows-manometer system. The bellows system is maintained in the back-flush mode between analyses. For analysis, the injector needle is transferred to the chromatograph and clamped between the copper blocks, cooled by
sidebars immersed in liquid nitrogen. One end is inserted in the septum, the other connects to the bellows system. The backflush helium line is removed and the corresponding opening at the cross-fitting is sealed with a nut. The manometer serves to detect leaks in the system and to monitor for pressure stabilization. The eccentric cam is operated to withdraw 1 ml of helium from the gas chromatograph into the bellows. The sample injection is effected by twisting the injection device’s knob and actuating the bellows motor. This moves the cold copper blocks away from the injector while the preheated (to 25OOC) copper blocks move vertically to clamp the injector for 10 sec. The bellows movement returns the 1 ml of helium through the injector, carrying the vaporized sample into the chromatograph. The injector is then reclamped between the cold blocks. An important feature of the injector is a restriction at its downstream end. When the injector is flash-heated to inject the sample into the chromatograph, only a negligible fraction of the sample can travel through the restricted end. The injection of the sample into the gc port is 95 to 98 complete. The entire procedure of sampling and sample transfer is quite reproducible. In sampling from synthetic mixtures of nine components in air, the reproducibility of the gc peak areas was within + 3 A blank and an air analysis are shown in Figure 4.
z
z.
I
,
,
,
,
,
1
,
Figure 4. Blank analysis (A) and analysis of air (B) from an urban expressway
Literature Cited Dravnieks, A,, Krotoszynski, B. K., J. Gas Chromat. 6 , 144 (1968). Johns-Manville Celite Division, Sales Bull. FF-l57B, “Chromosorb 102,” New York, N.Y., 1967.
Column: 100 ft, support-coated Carbowax ZOM column programmed 60-180°C at Z”C/min
Receiued for review July 20, 1970. Accepted June 25, 1971
30
24
18
12 Time,min
6
0
Correction Floyd D. Sutterfield points out that in the Altshuller et al. paper [ES&T, 5, 1009 (1971)], his first name appears incorrectly as Frank. 1222 Environmental Science & Technology
