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28 Installation and Operation Guide
3 Splitter Configurations
For constant pressure methods, first find the maximum flow as above. Use the
GC, ChemStation, Flow Calculator Software or the Method Translation
Software to find the inlet pressure that gives the maximum flow at the upper
temperature of the method (make sure the column outlet pressure is set to
3.8 psig for the calculation).
For example, if a 30 m × 0.32-mm id column is used with Configuration 1, using
helium carrier and programming to 300 °C, the pressure that gives a flow of
9.4 mL/min ([5.2 + 5.2] – 1 = 9.4) is 56.3 psig. This is the maximum pressure at
which the inlet should be set. The inlet should not be set at or below 3.8 psig.
If you decide to use a typical configuration, note the restrictor dimensions
from Table 2 and proceed to “Restrictor and Column Installation" on page 35.
Splitting to an MSD
Note that the maximum column flows for an MSD are quite low. This limit is
imposed by the rating of the turbo or diffusion pump. Configurations with
split ratios greater than 1 can be used but peak broadening and/or tailing
should be expected. They are shown in the configuration tables more as a
caution than as a recommendation.
In practice, the column flow can be set to within 0.5 mL/min of the total flow
if necessary. For example, the 1:1 split to an MSD with a performance turbo
pump running a method programmed to 300 °C should have a column flow of
no more than 2.3 mL/min ([1.4 + 1.4] – 0.5) at 300 °C.
Split ratios to the MSD greater than 1 are very limited due to these flow
considerations and should be avoided if possible.