Dear colleagues:

I have two questions related to quantitative extraction of lipids (from
complex systems).

First, Folch method sets a the final proportion chloroform: methanol :
water of 8:4:3 as (cuasi-)optimum. As a result, the contents of these
solvents in the lower phase, which contains nearly all lipids, is 86:14:1
(per volume unit) but:
Which is the ratio between the volumes of the lower phase and the upper
phase? This is essential to quantify the content of lipids extracted, so
that it is not affected by sources of error related to the great difficulty
of siphoning the upper phase without removing any volume of the lower phase.

Secondly, there are several reasons to replace chloroform with
dichloromethane in lipid extraction. We have found that the volume of the
lower phase collected is lower when dichloromethane is used and
consequently the lipid content was found to be higher. But again
calculations are affected by sources of error associated to siphoning the
upper phase. It is not difficult to get rid of them, but we would need to
know:
Again, which is the ratio between the volumes of the lower phase and the
upper phase?
And, which is the proportion of dichloromethane: methanol : water in the
lower phase?

Additionally, does dichloromethane have the same capacity than chloroform
to exclude non-lipid contaminants from the enriched-lipid phase?

Thanks in advance for your help.

Yours sincerely.

Juan José Rodríguez Herrera
Dpto. Química y Tecnología de Productos Pesqueros
(Dpt. of Chemistry and Technology of Fish Products)
Instituto de Investigaciones Marinas
(Institute of Marine Research)
Consejo Superior de Investigaciones Científicas (C.S.I.C)
36208 VIGO
ESPAÑA (SPAIN)