Hi, I'm trying to concentrate dilute protein mixtures in my tandem
affinity purification eluates for mass spec analysis. Specifically, I
need to get rid of the EDTA and EGTA as well as the 0.1% tween or
NP-40 that is in my elution buffer.
I saw that some people use the Wessel-Flugge method (Anal Biochem
1974) for this application (Methanol, Chloroform precipitation).
However, in my hands I found it didn't seem to work great, at least I
don't see a nice pellet.
I've had some success in the past with TCA but often end up with some
residual acidity even after many acetone washes. Anyway, at least
with TCA I got a nice pellet every time.
My question re: Wessel-Flugge is, HOW MUCH OF THE UPPER LAYER ARE YOU
SUPPOSED TO REMOVE??? Should I get rid of the upper phase all the way
down to the chloroform layer, or leave a bit above of the chloroform??
The original publication says to remove the upper layer above the
chloroform and interphase. But I don't see much of an interphase,
except in some samples where I saw a diffuse band of white above the
chloroform layer on the bottom. so, in case that diffuse white stuff
was my protein, I left maybe 150 uL on top of the chloroform. In the
end I did not see much, if any, precipitate and was pretty
disappointed since the method seemed so promising.
any advice would be very much appreciated. I found the description by
Wessel and Flugge pretty cursory.