Metrohm 850 Professional IC Anion MSM-HC - LP-Gradient - Manual (Page 45)

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3 Installation
850 Professional IC Anion MSM-HC LP Gradient
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3.11 Low pressure gradient
Up to three different eluents can be mixed with the low pressure gradient.
The three "normally closed" valves are usually closed. With each pumping
cycle, the valves are kept open until the desired percentage of eluent has
flowed, after which they are closed again. This results in a situation where
the valves also open and close audibly when 100% of a solution is con-
veyed.
The eluent gradient generated in the mixing valve is aspirated by the high
pressure pump and conveyed into the IC system. Because of the physical
restrictions of the mixing valve, the flow must not exceed 3 mL/min. when
using a low-pressure gradient.
In general, the use of the low pressure gradient is recommended for elu-
ent percentages ranging from 10…90%. However, depending on the
installed pump head and the set flow, the smallest possible eluent per-
centage can vary (see Table 1, page 35).
Table 1 Smallest possible eluent percentage depending on installed
pump head and set 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 %
Depending on the application, an optimal assignment of each eluent to a
valve is documented in the Application Notes. To obtain a reproducible
gradient profile, this eluent-valve assignment must remain unchanged.
Each eluent is degassed by means of its own eluent degasser (see Chapter
3.10, page 33).