Faults which may occur
during startup
With
Straight
: Peak on monitor detector and
preliminary peak on main detector even though the
differential pressure is very low and P
A
this greatly
reduced
Cause Remedy
The annular clearance is too
large
Use a column with a smaller
internal diameter
or
use a coupling capillary with
a larger outer diameter
With
Straight
: No peak or too small peak on main
detector
Cause Remedy
The input of column B is
blocked
Check flow through
column B, possibly break off
approx. 15 mm from
beginning of column B
With
Straight
: Differential pressure required during
adjustment is very high
Cause Remedy
The coupling capillary is
squashed or blocked
Blow through coupling capil-
lary
or
replace live T-piece
Straight
can be adjusted well, but
Cut
and
Backflush
poor:
In
Cut operating mode
: Peak on main detector although
the differential pressure is very high
Cause Remedy
The annular clearance
between the coupling
capillary and the column
internal diameter is too
small. A smaller differential
pressure is present at the
ends of the coupling
capillary than the measured
differential pressure
Use column with larger
internal diameter
or
use coupling capillary with
smaller outer diameter
Column A has been inserted
too far into the live T-piece.
The internal gasket does not
seal the column outlet
Pull back column A by 1 to
1.5 mm
Contamination from the
stationary phase may reduce
the annular clearance with
plot columns
Scratch end of column free
using a drill
Live switching: troubleshooting
NOTE
The needle valves NV
Cut outlet
and NV
Purge outlet
can be re-
placed in the case of critical components or laboratory oper-
ation by capillaries with a corresponding flow resistance.
The differential pressure is reduced at high
temperatures.
Cause Remedy
The flow is reduced in the
capillaries because the
viscosity of the gas
increases with temperature.
The pressure drop across
the currently selected needle
valve NV
Cut
or NV
Straight
is
reduced, the differential
pressure becomes smaller,
and the flow in the capillary
as well
Adjust the differential
pressure in position
Cut
at a
higher temperature
Adjust the differential
pressure in position
Straight
at a lower temperature
FID response factors are changed during the
temperature program, the baseline drifts downwards
Cause Remedy
The flows via the capillaries
act like a make-up gas. The
flow changes during the
temperature program
because the viscosity of the
gas changes
Use an additional constant
flow as the make-up gas,
and keep the flows through
the capillaries as low as
possible, e.g. using
temperature-independent
auxiliary flows
With
Cut operating mode
: Peak tailing on monitor
detector
Cause Remedy
Tailing is caused by the
sample injection or by
column A
Connect column A directly to
a detector. If the tailing
disappears, check the
live T-piece
Graphite particles are
present in the ducts of the
live T-piece. The flow in the
capillary
Cut outlet
is then
too low
If the tailing is reduced at
higher temperatures, the
cause is adsorption on the
graphite in the live T-piece
- in the ducts of the
live T-piece
- or on the gaskets
Column A has been inserted
too far into the live T-piece
Pull back column A a little
The capillary
Cut outlet
has
been inserted too far or not
far enough into the live T-
piece
Shift the capillary
Cut outlet
With
Cut operating mode
: Some of the main
components arrive at the main detector, the smaller
peaks are cut directly to the monitor detector
Cause Remedy
The flow in the capillary
Cut
outlet
changes because the
carrier gas with sample has
a different viscosity to pure
carrier gas
Increase differential pressure
in position
Cut
. This
increases the flow in the
capillary, and the main
component is diluted
Live switching: troubleshooting
6 - 10
live.chp, Issue August 17, 1999
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