Yes, you can store Ficoll soultion but do not pure ficoll, because its shelf half life is only five years,  If the Ficoll is too cold or too hot the isolation will not work right.It is temperature and cold sensitive chemical.Ficoll-Paque media products are aqueous solutions containing Ficoll PM400 and sodium diatrizoate with calcium disodium

ethylenediamine-tetraacetic acid. Ficoll PM400 is a synthetic high molecular weight (Mr 400 000) polymer of sucrose and epichlorohydrin which is readily soluble in water. The molecules of Ficoll PM400 are highly branched, approximately spherical, and compactly coiled with a Stokes’ radius of about 10 nm. Ficoll PM400 has a low intrinsic viscosity (17 ml/g) compared with linear polysaccharides of the same molecular weight (cf. dextran Mr 400 000:/intrinsic viscosity (η)/49 ml/g) and solutions of Ficoll PM400 have low osmotic pressures. Sodium diatrizoate is a convenient compound to use with Ficoll PM400 since it forms solutions of low viscosity with high density. Sodium diatrizoate (Mr 635.92) is the sodium salt of 3,5-diacetamido-2,4,6-triiodobenzoic acid.To maintain the Ficoll-Hypaque/blood interface, it is helpful to hold the centrifuge tube at a 45° angle.Keep it at 4 degree  room temperature prior to starting procedure  by manipulation in a hyperosmolar Ficoll solution.

Thanks Ravi Kant for all these informations. 

Very perfect answers!