Page 248 - Tandem Techniques

Page 230

gas supplies. The central assembly is built round a union which is held by a threaded collar that seals it
against the polyimide ferrule on the discharge tube. The ferrule is tapered at both ends, and seals the gas
union to the discharge tube and excludes water from the heated area. The column is fed through the end
of the union, and extends into the discharge tube terminating at a point, 5 mm from the ferrule. The
column is sealed with a standard capillary column fitting and a graphite ferrule. The makeup gas and
reagent gas enter the center connection to the union, and the other two connections are used for purge
flow. The threaded collar of the union fits into a stainless steel plate, which is mounted to the cavity
with stand-offs that prevent heat from the gas-union passing to the cavity. Heat is provided by two
stainless steel blocks, containing cartridge heaters, that fit over the union. Temperature monitoring
sensors are appropriately situated in the block. The sampling procedure utilizes a valveless venting
system which is shown in Figure 6.2.

Figure 6.2
The Venting System
Reprinted with permission from D. Quimby and J. J. Sulllivan, Anal.
Chem., 62(10)(1990)1027, Copyright 1990 American Chemical Society