Hi, I've gottta have a stab at this one... Its a few years since I ran a
sorter in my pevious life, but this sounds to me like a case of uncharged
"satellite drops" merging with one of your charged drops. Someone will
tell me if I'm off on a tangent :-)
I'm guessing 3 drop sorts here. When the drops breakoff the joining neck
forms a small "satellite droplet" , which depending upon phasing and
frequency tends to merge either with the cell above or below it.
(this is from deep memory, but there is a good discussion in Flow Cyt and
cell sorting 2nd ed,... The Yellow one... by Myron Melamid (sp) and others)
You can see all of this through the observation microscope, have a look
to see which cell the satellite merges with when all is well, and I'll
bet it goes the other way when you see the "doublet". I think you have
an uncharged droplet merging with a charged cell, reducing the effective
charge, causing less deflection and the appearance of the second spot.
I think its a pressure/frequency thing, but check in the old yellow bible
as its well covered.
Best of luck
--Daryl Webb (dwebb@waite.adelaide.edu.au) Dept. of Plant Science, Waite Institute University of Adelaide, Glen Osmond S.A. 5064 Australia. Voice:61_8 8303 7426 Fax:61_8 8303 7102