CP-3800 GC Operator’s Manual
83
Note
: In many cases switching from one 1079 mode to another involves
changing the glass insert. A detailed stepwise procedure to carry out this task is
given in the Maintenance section of the 3800 Getting Started manual. In most
injection modes the insert is installed with a graphite ferrule. Use the special
fixture supplied with the 1079 accessory kit to install the ferrule correctly on the
insert.
Isothermal
Split
Injection
The split mode is used when samples are relatively concentrated and for
neat samples. This mode of injection involves rapid vaporization of the
sample followed by sample splitting. Splitting involves directing a portion of
the sample into the column while the remainder is vented. The split ratio is
defined as the proportion of sample vented to the sample entering the
column. With EFC carrier gas control this parameter can be set
automatically in the 1079 method.
Table 9 Split Injection Typical Conditions
Injector Insert
Install the fritted split insert (03-926119-46) or unpacked split insert (03-
926119-45). See instructions in the Maintenance section of the Getting
Started manual (03-914647-00) for changing the 1079 insert.
Column Installation
7.5 cm from the bottom of the column nut at the base of the injector
Injector Temperature
Isothermal 250
°
C.
Column Temperature
50
°
C initial for 0.1 min, ramp to 250
°
C at 20
°
C/min, hold 5 min.
Carrier Gas Control
Set the split mode to ON for the duration of the run in the 1079 method
section, and set the split ratio to 100. The sample will be split upon
injection and a representative portion representing 1/100
th
of the amount
injected will enter the column. Note that the split ratio is a method specific
parameter and should be set appropriately for individual analyses. In
addition the injector pressure or pressure ramp should be set to achieve
the desired column flow rate.
Isothermal
Splitless
Injection
The classical splitless injection technique involves vaporizing the sample in a
hot injector and slow transfer to the column. The split state is OFF during
the sampling period; therefore, all of the injected sample should enter the
column. The initial column temperature is maintained for at least the
sampling time to trap all sample components at the head of the column. At
the end of the sampling period (typically 0.5 to 1.5 minutes) the split state is
turned ON to vent any residual sample or solvent from the injector.
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