Re: ELITE drift
Robb Habbersett (robb@beatrice.LANL.GOV)
Mon, 20 Dec 93 16:34:19 MST
Larry-
In our 'home-brew' 3-laser machine, where I use silastic tubing
(250u id - .010 inch) which I think is the same as on at least
some of the commercial instruments, we have seen this problem
for as long as I remember. I don't think the tubing necessarily
has affinity for PI; I think its simply a matter of the velocity
of the fluid through the sample tubing, near the outside edge of
the tubing lumen, being nearly zero during sample analysis. In
between samples, when the tubing is back flushed with sheath fluid
(usually at a much higher flow rate than in the opposite direction
during sample analysis) the fluid in the sample tubing is completely
displaced with virgin sheath fluid rapidly. Then when analysis is
started on the new sample this fluid has to be completely replaced
with the sample fluid until there is no longer a diffusion gradient
from the center of the tubing lumen to the outside wall of the lumen. This process takes much longer (than back-flushing) since the total
flow of sample fluid is usually much lower. We either wait for this
replacement of fluid, before starting data acquisition, or, if we are
impatient, we run the sample at a high flow rate to fully displace
the sheath fluid in the sample line with sample fluid so there is no
longer a concentration gradient in the sample tubing to cause the PI
to diffuse out of the cells. Your interpretation may be valid as
well but I've always felt simple diffusion adequately explains this
observation.
Robb Habbersett
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