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and this is the cause of the unstable spray. Otherwise, the flow from the nanopump may be
unstable. The spray will fluctuate if there is a leak in a connection or a bubble in the flow path
from the nanopump. Make sure the connections are leak-free, or purge the nanopump.
The air addition to the drying gas may not be at the optimum flow rate. Check that the
pressures and flows for the air and nitrogen supplies are set correctly. Remember that the air
addition is being added by a flow mass controller and not a regulator. The adjustment knob on
the air addition manifold controls flow. The bubble will always be at 100% with 1 l/min of flow.
At this rate, it is not enough to prevent charging of the chip.
Particulate matter in any of the flow paths or clogged gas traps will cause instability also.
O:
When I turn on the MS, the capillary current goes to a high level (several micro-amps)
and stays there. I see a spray (or may not see a spray), but no recognizable signal or spectrum.
A:
There is a leakage path from the spray cap to ground. This is most likely due to loose
bristles from the brushes or fibers from the previous top plate Put the instrument in Standby
mode, eject the Chip, remove the Chip cube, open the interface assembly, and inspect for and
clean off any loose bristles or fibers.
Another cause is contamination on the spray cap or spray cap insulator. Remove these, clean,
and reinstall.
O:
When I turn on the MS, I see flashes of light on the video display of the ionization
region.
A:
The instrument is arcing from the spray cap to ground. Do not continue to operate the
instrument under these conditions! Immediately set the instrument in Standby mode. The
cause is most likely the same as above, loose bristles or fibers near the spray cap, which need
to be removed from the instrument before continuing.
Also, remember to wait a few minutes for the ACN to evaporate after applying the IRM working
solution but before turning on the instrument.
O:
I have 2 million abundance counts for the internal reference mass ions and they have
flat-topped peaks.
A:
The signal for the reference mass ions is at complete saturation due to a large amount
of internal reference mass compound in the interface assembly. Complete saturation occurs at
256 * (number of transients per scan). Remove the Chip cube and clean the interface assembly
to remove most of the IRM compounds. Alternatively, eject the Chip, turn on the MS,
Page 29 of 33
18 July 2011
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