Author: John J. Manura
Affiliation: Scientific Instrument Services
In the original gold plated transfer line tip on the H.P. 5971 MSD (H.P. Part # 05971-20305), the GC capillary column is purged inside this fitting and diverted through side vents and then vented into the MSD source. This original H.P. design exposes the analytes being chromatographed to a hot metal surface before they enter the MSD source. Loss of sensitivity for some compounds can result from both the indirect transfer line path and also due to sample decomposition upon exposure of thermally labile compounds to the hot metal surfaces.
As a result we have redesigned the Transfer Line Tip for the H.P. 5971 MSD to permit the end of the fused silica capillary column to purge directly into the MSD source. The new S.I.S. design eliminates any metal contact with the sample - the GC capillary column protrudes directly through the Transfer Line Tip and into the MSD source. This new design should result in higher sensitivity due to this straight path for sample flow and the elimination of contact by the compounds being chromatographed to any metal surface in the transfer line.
When inserting the capillary column through the MSD interface and into the MSD source, it is necessary to remove the MSD interface in order to properly position the capillary column at the end of the Transfer Line Tip, since there is no physical stop at the end of this fitting. After the capillary column with accompanying nut and ferrule are attached to the MSD interface, the capillary column should be adjusted so that the capillary column protrudes past the end of the Transfer Line Tip between 0 and 1.0 mm. After this distance has been set the GC nut and ferrule should be tightened to seal the capillary column in the correct position and the MSD interface can be reattached to the MSD.
The new Transfer Line Tip is available from Scientific Instrument Services.
(Part # HP99, price $79.00 each.)
Yttria coated filament at start
Yttria coated filament after 16,000 cycles