Magnetic Beads

[Klaus Lehnert]

Stephen,

the magnets in the commercial racks are rare earth magnets, which are much
"stronger" (whatever the correct physical term) than normal magnets of the
same size. I have used a normal magnet (U-shape, approx 20cm, size of foot
~1.5x3cm) with all sorts of magnetic beads. The big magnet works, but the
only way to get the beads onto a small area is to put the small foot of the
big magnet directly under the tube and then collect the beads in the bottom.
Washing seems less efficient that way, and they are much more difficult to
resuspend. The commercial racks collect the beads in a circular area (approx
3mm diam for eppendorf tubes) on the side of the tube, which makes washing
and resuspension much easier. So, compared to the normal magnets, the
commercial racks are much better.

I am not sure whether they are worth their money, or if we are ripped of by
the biotech companies. To find out, one could try rare earth magnets from
other sources. The "Lee Valley & Veritas" tool company ( www.leevalley.com ;
no affiliation, I only know because they are a woodworkers dream) sells
small rare earth magnets for virtually nothing (from  $ 0.28 for a
0.22"x0.1" magnet; Order-No. 99K31.01), and their "strength/force" could be
increased if they are stacked like coins, "focussing" it into the small
diameter area of the magnet's/coin's face. In fact, they claim they can't
sell the 0.75" diameter model in numbers less than five because they are
unable to separated them!) The only thing that has prevented me from trying
them is that I don't want to pay $40 for shipment of a 50 cent magnet to New
Zealand (and the fact that I already have a commercial rack ;-))

But hey, you're in the US of A, and they have bases in both the US and in
Canada, so shipment would only be US$ 4.00.

Maybe you can give them a try and let the rest of the world know.

Cheers from down under

Dr. Klaus Lehnert
University of Auckland
School of Medicine


----- Original Message -----
From: Stephen Snowdy <snowds at med.unc.edu>
Newsgroups: bionet.molbio.methds-reagnts
Sent: Wednesday, 8 December 1999 09:26
Subject: Magnetic Beads


> Does anyone know why the magnetic eppendorf holder costs so much?  It's
> over 200 dollars (Pierce) for a rack to hold 6 tubes.  I'm not a
> geologist so I must ask...is there any reason why one can't just use a
> regular Radio Shack magnet?
>
> Thanx.
>
> Stephen Snowdy
> UNC-Chapel Hill