I wouldn't no about the excitation level of APC at UV wavelengths,
tails can reach far. Another check you should do is running
non fluorescence beads of same size as the APC beads. Just a double
check for scatter light penetration through your filters.
Robbert van Leeuwen
Flowcytometry / Applied Optics Group
University of Twente
The Netherlands
Robbert@top.tn.utwente.nl