[RASMB] Cell Leak

[Borries Demeler]

Those are all good suggestions. And I think we are apparently not the
only ones using epon centerpieces at 60k :-) In my opinion the cps
will survive short times at 60k with differential column loadings, but of
course you want to minimize the time as much as possible. So aside from
the somewhat cumbersome methods suggested by Peter I would recommend to
just closely watch the menisci of both channels for every scan, even in
the slower absorbance scanning mode.  If you see them change position,
it is early enough to shut down the machine right away and save your cell.
Prolonged exposure to different column heights will most certainly damage
the septum.

Regards, -Borries

> 
> Hi all,
> 
> We've also seen a few times breakage of the center divider in the charcoal 
> filled epon centerpieces from single-sector leaks.  I agree that using 
> centerpieces that are rated higher is in principle a good idea.  However, 
> we found that not really essential so far.
> 
> Since we regularly have to sediment at 60,000 rpm, we've implemented a 
> protocol where we check the cells for leakage by sedimenting them briefly 
> at a lower rotor speed, first, maybe 10,000 or 20,000 rpm.  After verifying 
> that there's no leak (if there was it wouldn't destroy the cell at the low 
> speed), we take the rotor out, shake it up, and start with the temperature 
> equilibration at 0 rpm, followed by starting the run and acceleration to 
> 60,000 rpm.  In principle, that would not completely eliminate the 
> possibility of leakage starting to develop at the high rotor speed, but at 
> least we have not seen that happening so far.
> 
> This procedure is a bit cumbersome, and we don't always do it that 
> way.  Alternatively, when using the interference optics it is usually 
> possible to observe the status of all the cells during the time the rotor 
> accelerates, which gives a chance to abort the run before it gets to a too 
> high speed.  One can recognize one-sided leaks by diagonal fringe pattern, 
> moving meniscii, or simply from the lack fringes due to scattering on 
> deposits on the window.
> 
> So far that gave good results.
> 
> Peter 
> 
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