Frans_M_Everaerts_Isotachophoresis_378342.pdf

INJECTION SYSTEMS
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Fig.7.1. Principle of the four-way tap for rinsing and re-filling the electrophoretic equipment and for
sample introduction. Position 1: the narrow-bore tube can be rinsed and re-fiied. Position 2: the
reservoir with terminating electrolyte can be rinsed and re-fiied. Position 3: the sample can be
introduced. Position 4: the analysis can be performed.
7.2.3. Six-way valve
Fig.7.2 shows the way a six-way valve is used, while Fig.7.3 shows an exploded view
of this valve in order to demonstrate its construction. The conical plunger is made of
Amite, while the plunger housing is made of Kel-F. This plunger housing is surrounded by
a brass hexagon for mechanical stability. Moreover, this hexagon prevents any shift of
the plunger and the plunger housing due to the weakness of the Kel-F and the forces
on the plunger so that a liquid-tight connection is obtained. Holes are drilled in the brass
hexagon for connection of the various components via the holes drilled in the plunger
housing and the plunger. In each of these holes in the hexagon, a threaded base is soldered,
so that with screw-caps and collars liquid-tight connections can be made, as shown in
Fig.7.4. It does not need further explanation that the liquid inside the various bores may
not have any electrical contact with the brass hexagon. By means of the special construc-
tion shown in Fig.7.3 (parts 5 and 6), the six-way valve can be turned only through 60°,
so that the three canals inside the plunger are always connected with the bores inside the
plunger housing. The connections with the narrow-bore tube and the piece of insulating
material that provides the connection with the injection block or directly with the
reservoir filled with the terminating electrolyte must fit exactly, otherwise a dead volume
will occur that will decrease the effective length for separation enormously.
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