There are 4 things to control when sorting - drop drive frequency,
drop drive amplitude, delay time for drop charge, and drop charge
phase (wrt drop drive).
>From the brief information you have given, it appears that your
sorted stream is "fanning" - that is, all sorted drops for a single
event are not getting equivalent charge. You can check if this is so
by viewing the deflected stream during a test sort - backlighting is
best. The fanning can be minimized/eliminated by adjusting the
phase.
Good luck!
-Marty Bigos
Stanford Shared FACS Facility