Varian 450-GC, User Manual

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1177 Split/Splitless Capillary Injector - Injectors
Varian, Inc. User Manual 450-GC Page: 155
1177 Modes of Injection
The 1177 injection mode is defined by the Split Vent program and by the choice
of insert. The Split Vent is controlled differently based on the pneumatics
installed, if EFC the split valve is controlled from the Injector section, or in case
of manual pneumatics the split valve (is controlled from the valve table). The
following are brief descriptions of the various modes of injection. More detailed
information on each mode is given later in this section.
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 4.0 mm open insert,
or the packed 4.0 mm ID insert when operating in the split mode.
In the split injection mode, the sample volume is typically 2
μ
L or less. Early
eluting compounds usually appear as very sharp peaks. In some cases, the
peak width is less than one second. It is important that you inject the sample as
quickly as possible. If you are using the CP-8400 AutoSampler use the
Standard Split/Splitless mode of injection. If you are using a non-Varian
AutoSampler or you are using the User Defined Mode of operation on the
CP-8400 AutoSamplers, if the sample injection time (the 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 Splitvent flow to the column flow.
Splitless Mode
The 4 mm Goose-neck insert packed with glass wool is typically used for
isothermal splitless injection. The small capillary section of the glass insert fits
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 remove any residual solvent
and sample out of the Injector.