9.
Excessive pressure
If your system
back pressure exceed system suitability, the first thing to check is
the pump flow rate setting. If this is correct, then check to confirm
that the mobile phase was correctly prepared. In most cases, incorrect
mobile phase preparation will be accompanied by a change in retention
or selectivity.
If the onset of
excessive back pressure was "catastrophic" (i.e., a pressure well
above system suitability or even equipment limits) and "abrupt," the
most likely cause is a plug in a transfer line, valve, or other flow
passage. In most cases, this will be sufficiently high to trigger pump
shut-down. In this case, start disconnecting connections from the end
of the system and continue moving upstream (e.g., disconnect at:
detector outlet, column outlet, column inlet, guard column outlet, . .
.). When the pressure suddenly drops back down to normal, you have
pinpointed the source of the problem as just downstream from the last
connection you loosened.
If the onset of
excessive back pressure was gradual, possible causes include
plugging of the inlet frit/column head and contamination/deterioration
of the column. The former can often be remedied by simply back-flushing
the column; use your standard mobile phase and flow rate, but reverse
the column. The latter generally requires replacement of the
column.
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LC Resources, Inc. all rights reserved