Metrohm 940 Professional IC Vario ONE/ChS/LPG - Manual (Page 49)

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3 Installation
940 Professional IC Vario ONE/ChS/LPG (2.940.1250)
￭￭￭￭￭￭￭￭ 41
3.16 Low-pressure gradient
Up to three different eluents can be mixed using the low-pressure gradi-
ent. The three valves are normally closed. The valves are opened long
enough during each pump cycle so that the desired portion of eluent
flows and then the valves are closed again. This also results in all of the
valves audibly opening and closing if 100% of a solution is being pumped.
The eluent gradient generated in the mixing valve is aspirated by the high-
pressure pump and led into the IC system. Due to the physical limitations
of the mixing valve, the flow cannot exceed 3 mL/min when using a low-
pressure gradient.
We recommend using the low-pressure gradient for eluent portions of 10
to 90%. The smallest possible portion of eluent can change, however,
depending on the pump head being used and the selected flow rate (see
Table 2, page 41).
Table 2 Smallest possible portion of eluent based on the pump head in
use and the configured flow
Flow Standard pump head Macro pump head
1 mL/min 10% 2.5%
2 mL/min 20% 5%
3 mL/min Not recommended 7.5%
The optimal assignment of eluents to the valves depends on the applica-
tion and is outlined in the Application Notes. You can only achieve a
reproducible gradient profile if this eluent-valve assignment remains
unchanged.
Gas is removed from each eluent via a separate eluent degasser.