I've used water as a sheath in a FACS440, and also in a FACScan. It had no effect on immunofluorescence, although I noted a slight increase in % c.v. for DNA histograms -- usually only a fraction of a percent. Obviously, one cannot use water as sheath in a charge-based sorter (I have used as little as 0.009% saline and still gotten reasonable droplet charging, however). One drawback might be that the possibility of back-flow into the sample, thus changing osmolality and possibly affecting viable cells adversely, assuming one runs cells viably. I currently run an isotonic diluent from a commercial source ($13 / 20 liter), -- I filter it on-site through a 0.2um cartridge before using -- in my Coulter sorters and my XL. Haven't had a need to try water. I suppost a good question might be . . . why do you want to use water? MAK. Mark A. KuKuruga University of Michigan Flow Cytometry kukuruga@medmail.med.umich.edu
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