3
Column Modules
User Guide
59
To Connect the Column Using Valco ULM Unions
Use Valco Ultra Low Mass (ULM) fittings with reusable ferrules to minimize repeated trimming
of the GC column. The column leads exiting the transfer line to the union are very short by
design and cannot be trimmed repeatedly. The reusable ferrules allow disassembly of the
module assemblies without trimming the GC column in most cases. While the reusable
ferrules are not designed for use with the ULM fittings, the dead volume is adequately swept
for reasonable chromatography in most circumstances. Because of the reusable design of
this fitting, it is necessary to tighten the fitting after each temperature cycle in the GC oven.
A union bracket for the LTM system using the Valco ULM union is shown below. The union is
not removable from the bracket.
Start by observing the clamps with the mini-unions. The screw on each of these can be
loosened just enough that the brackets can slide along the rails projecting from the oven-side
of the transfer line module. It is not necessary to remove the screw; just loosening the screw
will allow the bracket to slide on and off of the rail.
With the screw toward the underside of the rail, note that there are two choices for how the
pair of brackets can be used: the unions can be away from the module; or the two brackets can
be exchanged on the rails, and the unions can instead be positioned between the bracket and
the module body.
The first position, with the unions pointed away, increases the distance between the unions
and the module and is recommended for the initial installation because this minimizes the
amount of column that must be trimmed. This leaves enough length of column past the ends
of the transfer lines to permit the column to be cut back several times if you want to change
columns and the ferrules cannot be separated from the column.
