Magnetic Beads

medimag at my-deja.com medimag at my-deja.com
Wed Dec 8 12:11:59 EST 1999


In article <82jt8n$9sq$1 at scream.auckland.ac.nz>,
  "Klaus Lehnert" <k.lehnert at auckland.ac.nz> wrote:
> 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
>
>

I think I have good news for you guys.  Every country with a
little bit of industry has some distributors of magnets for
industrial purposes.  They are not only used in things like
electric motors, but they are used a lot an assembly processes.

In the U.S. there are some large multi outlet companies in thsi
field, and a logical place would be to go to the Thomas
Register, or, if you live in a large city, the Yellow Pages.

I use Bunting Magnetics.  But surely in NZ there are various
companies which sell magnets for industrial purposes.  Re. Radio
Shack, this is a marginal product for the store owner, and not
all stores in the U.S. have magnets.   We talk about them
because it is a place where you can walk in and buy one or a
small package, and get a lot of change back from your $5. But in
quantity the ind. distributors are a good deal cheaper.  With
Bunting you need to spend $40.  Shipping charges are reasonable.

With Bunting you can buy a 1" x 1/4" disc neo. magnet for $10.
They have smaler ones that are chrome plated, and the smaller
ones are a lot less and the larger ones go up in price
geometrically. I mention the $10 one because that is the last
size, going up, that does not start to get expensive.

Another distributor is Decker.  Their flex. material is better,
but a lot more expensive.  In fact, I use a mag. health products
distributor, Amer. Health Service a lot, and they have a pretty
full line, including good quality flex mag. material.

I still get most mof my flex material at Bunting though, but I
have to make sure they magnetize it conventionally. (Assuming
that you want one polarity to each side). You really have to
emphasize it and double check when you get it.  I sometimes back
up the flex. material with ferrite or neo magnets.

I think the geologist can find a good solution with an ind.
magnet distributor too.

Hope this helps.


Bob Johnson. 9 yrs. biomagnetic study.  No products to sell.



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