19
Clue: Some components are not gated correctly.
Possibility:
•
Carrier Pressure Set Point may be too high or too low.
See Carrier Pressure Set Point.
•
Gate times may be incorrect. See Gating Peaks.
Clue: NGC is “processing” unused streams.
Possibility:
•
Unused streams need to be disabled. See Stream
Sequencing-Enable or Disable Streams.
Troubleshooting Solutions
Oven Temperature Stabilization
The oven temperature must be stabilized to receive good, repeatable
data. The oven temperature is typically stable enough in 30 to 60
minutes to pass diagnostics. This allows the user to proceed with all the
required setup information. Despite this, for the oven and other
components to fully stabilized, Totalflow recommends that the unit be
allowed a burn-in period of eight (8) hours. The end caps should be
installed during this period and during normal processing. Ambient
temperatures and not having the end caps installed could impede the
oven temperature from stabilizing at 60
°
C (140° F).
Carrier Pressure Set Point
The NGC has two column trains that have their own carrier pressure
regulator. Tests show that if nC5 on Column 1 elutes at approximately 160
seconds and C2 on Column 2 elutes at approximately 220 seconds, the
unit performs optimally. This is not to say that there may be special
applications which can cause these times to be different.
If nC5 and C2 are not within 3 - 4 seconds of these ranges, the user may
want to change the carrier pressures. It should be noted that changing the
carrier pressures will move the other peaks. As such, the user may want to
perform an Auto Peak Find.
To change carrier pressures, the user must be in Hold mode. Click the Hold
button on the Operation screen, and wait until the end of the cycle. When
the unit enters Hold mode, click on the Peak Find button. If the Manual
check box at the top of the screen is grayed out, close the Peak Find
screen, and click on the View option from the main toolbar. Select Expert
from the drop-down. Return to the Analyzer Operation screen, and click
the Peak Find button again. Manual mode will now be selectable.
While units vary from one to the other, it should be noted that one PSI
change will move the nC5 or C2 peak by 10-12 seconds. Increase pressure
to decrease the time that the components elute, and decrease pressure to
increase the time they elute. After making a pressure change, click Send
Setup and then Run Single Cycle. The chromatograms will update at the
end of the cycle (typically, 5 minutes). The user should repeat this process
until they receive the preferred results.
Troublesh
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