Varian 450-GC, User Manual

Page: 117 / 205

1079 PTV Injector - Injectors
Varian, Inc. User Manual 450-GC Page: 179
Split Mode
The split injection mode is preferred for the analysis of relatively concentrated
samples. The sample is split in the Injector with a representative portion
entering the column. The split injection mode provides the shortest sampling
time which leads to sharp chromatographic peaks. Use the 3.4 mm open insert,
the 3.4 mm ID fritted insert, or the packed 3.4 mm ID insert when operating in
the split mode.
In the split injection mode, the sample volume is typically 1 µL or less. Early
eluting compounds usually appear as very sharp peaks. In some cases, the
peak width is less than one second. Thus, it is important that you inject the
sample as quickly as possible. If the sample injection time, (time between the
insertion and removal of the syringe needle from the Injector) exceeds the peak
width, peaks can broaden, tail or chromatographic performance will be
degraded. With broader, later eluting peaks, it is less important that you inject
the sample quickly. The split ratio (fr action of sample that enters the column) is
the ratio of the flow of carrier gas out the split vent to the flow through the
column. The 1177 Split/Splitless Injector on page 153 is optimized for Split
application.
Isothermal Splitless Mode
The 3.4 mm insert packed with glass wool is typically used for isothermal
splitless injection. The small capillary section of the glass insert fits snugly
around the syringe needle and restricts backflush of the sample vapor during
injection. In the splitless injection mode, the sample enters the column during a
variable sampling time at the beginning of the analysis. This period is typically
30 - 90 seconds during which there is no flow from the Injector to the split vent.
After the sampling time, the Injector is vented to clean any residual sample out
of the Injector. The 1177 Split/Splitless Injector on page 153 is optimized for
Splitless application.
On-Column Modes
In the on-column modes the column is sealed to the glass insert (0.18 - 0.53
mm columns). This ensures that there is maximum transfer of sample to the
column. In the on-column modes the sample is normally injected at or below
the solvent boiling point and then the Injector is ramped to transfer the sample
onto the column. The 1093 OC Injector , on page 231 is optimized for On-
Column applications. Especially for applications operating at an oven
temperature range that require short wire-bore columns.