matrix for spin columns

Darren Natale dnatale at
Wed Mar 26 16:58:45 EST 1997

David Micklem wrote:
> In article <5hbmpr$i6i15 at>, pnh at (Paul N
> Hengen) wrote:
> >
> >Try Sephadex G-50 (cut-off is ~ 30,000 MW). The MW of a 50 nt PCR product will
> >be close to 30,000 if it is 0% CG or 100% GC (all A's or all C's).  If you find
> >it too close for the cut-off try Sephadex G-25. You can get it from Sigma (see
> >page 1813), or you can buy pre-loaded push columns from other biotech companies
> >like Stratagene...very convenient.

> <snip!>

> Is this approach OK for DNA?  I'd always assumed that the cut-offs were for
> roughly spherical molecules, which PCR products/oligos probably aren't...

This is correct.  The DNA exclusion limit (according to Pharmacia) is:

 10 bp for G-25
 20 bp for G-50
 25 bp for G-100

Unfortunately, you cannot simply double the lengths for ssDNA:

 10 bases for G-25
 20 bases for G-50
 27 bases for G-100

D. Natale
dnatale at

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