TIC Negative Spike - Momentary Ref Spray Drop

[Chris]

I have a TOF instrument with the negative spike issue that Brett
experienced, however it only appears to occur when the reference
solution gets low. On my system the dip tube only goes about 2/3 of
the way down (someone go carried away with their tubing cutter :) so
my "low" is equivalent to a 1/3 full bottle. Today I re-filled the
reference solution bottle and almost immediately the negative spikes
in the TIC were gone. Any ideas why the negative spiking is occuring
only when the reference solution level gets low?

Thanks.
Chris