Making miniprep solutions for spin columns - Now that we can reuse the columns... (May/04/2007 )

The old Qiagen handbook should have the exact composition. I dont have it. Anyone has the old handbooks?

I doubt it would. That was quote from the Qiagen website, describing buffer N3 as 'confidential' and 'proprietary'.

Given that the Qiagen kit and pretty much every other miniprep kit is based on the old alkaline lysis method, I reckon there's a strong chance that N3 would be mostly potassium acetate...

How about an some guesswork

It is a known fact that the solution used in a spin column are basically alkaline lysis solutions. The N3 solution corresponds to Solution III (alkaline lysis) with addition of guanidine hydrochloride to make the DNA bind to the column.

The formulation for solution III:
3M KOAc
2M HOAc

And the amount of guanidine hydrochloride used in DNA extraction is:
4M Guanidine hydrochloride

Thus guessworks says
3M KOAc
2M HOAc
4M Guanidine hydrochloride

Give a try and report back if this works.

Is it possible to reuse gel extraction columns also? If so then is the same method applied as is for miniprep columns?

Yes. both silicon based DNA binding columns use the same principle and more or less the same material.

Recent manuals suggest a wash with 35% guanidinium HCl, which is 350 g/l. 4M GuHCl is only 282 g/l. You might want to try 4.5 - 5 Molar.

Ahh, so we've narrowed it down to a few different concentrations!
Now I'm wondering, the original chaotropic salt principle used guanidinium isothiocyanate which is more expensive, and I think I read somewhere on this forum that it's a more effective chaotropic agent than GuHCl so presumably less of it is needed.

If I have time to try it I will! But if anyone else can try it, I'm very interested to hear your results...