[RASMB] 20 mm path cells [was: peptide in DMSO]

[Kristian Schilling]

John,

I have been planning for years to post some information on our centerpieces 
on the website. Perhaps I should eventually get back to that...

The initial point about our centerpieces was Dr. Mueller's (Bayer) efforts 
years ago to persuade Beckman to offer titanium centerpieces, inert to 
acids, bases, and organic solvents. After this did get nowhere for years, 
it was him and Helmut Coelfen who eventually found workshops here in 
Germany capable of manufacturing standard 12 mm centerpieces with 
sufficient surface smoothness.

When I opened up this business in 2000 I was in need of these centerpieces 
as well (I encountered them in Helmut's lab during my PhD work) which made 
three of us. We then agreed that for the future I coordinate the making of 
centerpieces and gradually I have been providing them to other users as well.

In the course of the recent years, I have been extending the scope to 20mm, 
3mm and 1.5mm centerpieces; we have also made six channel but I was not 
really happy with those - they tended to leak from one sector to the other. 
While we were at it, I have also been making housings, window holders, 
screw rings, and plug screws. One motivation was to switch to metric plug 
screws that do not wear off as quickly as the brass inch screws made by 
Beckman. Another was to have suitable housings for longer and shorter 
centerpieces. A third was to save money.

It is correct that there is a balance issue. It is already with 
12-mm-centerpieces that the Beckman weight set cannot balance the 
additional weight. It has been attempted to make screws from heavy metals 
but those are still too long and may stand proud of the thread. So we make 
titanium counterbalances as well, and they can be balanced with the Beckman 
weight set. They have the slit masks for radial calibration.

Beckman once stated (in the course of Dr. Mueller's correspondence) that 
they see no security issue concerning the rotor - the additional weight is 
no problem. However, their policy is that their warranty does not cover 
rotors and instruments if any non Beckman cell material is used. I tell 
this all users that have purchased cell components from us. I might add 
that we give no warranty either, but we have been using these cells at full 
rated speed for years.

One point you asked about the 20-mm-cells (where our housings are required, 
of course): No, they do not protude from the rotor hole. But there is not 
much left. For sure, we would have come to yet longer cells, as low 
concentrated samples are frequent. 20 mm is the best one can do.

And yes, the standard centerpieces fit into the Beckman cell housings, and 
they require the same gaskets as do the aluminum centerpieces. Needless to 
say that we have found a workshop for the gaskets as well.

Best wishes,
Kristian


At 08:30 29.04.2008 -0700, John Philo wrote:
>Steve (or Kristian)
>
>I for one had not heard about these 20 mm pathlength cells, and I could find
>nothing about them on the Nanolytics web site. Could you elaborate a bit
>about the configuration? Do the housings actually project out of the rotor?
>Other than a special housing and centerpiece, are other parts (centerpiece
>gaskets, screw rings, windows, window holders, etc.) the same? Is a
>different counterbalance required to achieve balance?
>
>John



=================================
Nanolytics
Gesellschaft fuer Kolloidanalytik mbH
Dr. Kristian Schilling

Am Muehlenberg 11
14476 Potsdam
Tel.:	+49 331 5818360
Fax:	+49 331 5818361

e-mail:	schilling at nanolytics.de
Internet:	www.nanolytics.de