Page 35 - Illustrated Pocket Dictionary of Chromatography

30 CHEMICAL IONIZATION (CI)

Three different manufacturers’ check valves. Note that they all have a different
sealing mechanism on the bottoms. Left, a hard plastic disk; center, a flexible
plastic O ring; right, a metal disk. Also note that the threading is different, thereby
preventing use in more than one type of pump.

An exploded view of a check valve. From left to right: housing, upper seat, ball,
retaining disk. Not seen is the second seat recessed into the disk.

chemical ionization (CI) In chemical ionization the source
produces accelerated electrons that pass through the volatilized
sample. A reagent gas is also bled into the source along with the
sample. The reagent gas is present at a high concentration compared
with the sample such that it is preferentially ionized. The resulting
reagent gas ions then chemically react with the sample to produce
ions that are then analyzed by their mass-to-charge ratio. A typical
reagent gas is methane, which reacts with a sample molecule, S, as
follows:

+
-
CH 4 + e Æ CH 4 + Æ CH 4 + SH +
S