A Method to Prevent Septum Blee iing in High Temperature Gas Chromatography Gas chromatography of high boiling compou d s requires high injection port temperatures (35040ODC),and the ideal septum fw these temperatures still does not exist. T h e basic material oi'septa is silicone ruhher r ith plasticizers added to increase c -e elasticity. But these low molecular weight plasticir rs will elute fmm the septum if elevated injection port temperatures are employed. T minimize hleed from the septum b -entering the system some manufacturersset u p a ha rier hetween the septum and the column like that used in high performance liquid ehr matography and sample storage: Injector port: a, polyimide coated sepa silicone ruhher septa with a thin layer of a h m i n t n foil, a Teflon-coated septa, or tum; b, septum cap; c, d, a polyimide coated septa (see figure, a ) . R u t the soh inner layer deteriorates with the Carrier gas; and e, Column. hot septum cap ( b ) ,and, after several puncturings, t e silicone ruhher adheres closely to the cap, and the diaphragm swells and cracks. Sr$um exchange is difficult because it is recovered in swelled hits. Therefore, between the septum cap and the inner layer of polyimidecoated septa, we put a pomus Teflm frit ( c ) . These Teflon frits are used in high performance liquid chromatography hefore packing to prevent the microparticles from escaping from the column. In gas chnmatography, these porous discs increase septa life time and exchange is very rapid. This home-made method is inexpensive and more simple than the injector port developed hy Purcell.' 'Purcell, J. E., Downs, H. D., and Ettre, L. S., Chrornotographio, 8,605 (1975)
M. Lafosse L a h o r a t o i r e Chimie O r g a n i q u e Physique e t Chromatographie U.E.R. d e Sciences F.45045 O r l e a n s Cedex, F r a n c e
202 / Journal of Chemical Education
