unstable FACScan readings

From: Snezna Rogelj (snezna@nmt.edu)
Date: Tue Oct 03 2000 - 22:16:50 EST


Hello, 

Could you please help us solve this horrifically frustrating and  incapacitating problem with our BD FACScan:

When we put a sample (beads or labeled cells) on for a reading, the fluorescence shows up as really bright and then progressively, over the next minute or even more,  drops by as much as 30%  to some final channel number. The populations on SSC and FSC do not shift at all, only the fluorescence (FL1 or 2 or 3). If we immediately reread the sample without taking it off the sipper, the fluorescence readings do not overshoot. 

What could possibly cause these artificially high initial readings?
How can we fix it?

We've been following a hunch that there may be a problem with the maintenance of pressure , but the sheath fluid tank stays pressurized overnight without a leak....the gaskets on the sipper are new....our proverbial rope is coming to an end...

Thank you for help,

Snezna
New Mexico Tech Biology Department



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