SDS-PAGE for purity

S.Ballal ballal_sv at hotmail.com
Mon Jul 22 01:15:33 EST 2002

You are absolutely right Frank, 99% by SDS does not mean anything much
untill the limits of assay and limits and method of detection are
completely defined.

This is true for any assay, for example HPLC where 99% pure by HPLC
will not mean much untill all the parameters for detection and
criteria for integration etc. are completely defined.


ffrank at rz.uni-potsdam.de (Frank Fürst wrote in message news:<87k7nttp4f.fsf at pc201-37.biochem.uni-potsdam.de>...
> ballal_sv at hotmail.com (S.Ballal) schrieb:
> > You will need a scanner/ densitometer for "percent area
> > determination:. This is something which should not be done with
> > "eyeing".
> I agree, however:
> > In case you know the minimum quantity of contaminant you want to
> > detect( say 0.1%), then you can load the same amount of the same
> > protein in another lane (say 0.1% of the loaded protein) and ensure
> > that same is visible during staining and destaining. This you you can
> > always prove that you have not understained your silver and
> > overdestained your CBB stains.
> That only assures that you don't have more than 0.1% of one particular
> contaminant. However, you can still have 30 proteins, each with just
> below 0.1%, and you won't get 99.9% purity, but rather 97.x%
> In fact it is questionable how relevant such a contamination is - but
> then it is equally questionable how sensible a statement is that a
> protein "is 99% pure by SDS-PAGE".
> Bye, Frank

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