Is it palmitate (as sodium palmitate) or as the free palmitatic acid? What concentration do you need?

Sodium palmitate is soluble in water; the free acid is much less polar ( see http://pubs.acs.org/doi/pdf/10.1021/je8005979 )

It is sodium palmitate, but it is not dissolved in water, we tried everything. We need almost 5mM.

Hi there, for my experiments I used the protocol described in this paper (free in PubMed central):

Coleman DT, Bigelow R, Cardelli JA  - Mol Cancer Ther January 2009 8;214

Making the solution is a bit tricky you need to keep the solution stirring at 50°C.

Hope it will work for you and let me know if you need other help.