Na2-EDTA as anticoagulant -how to prepare solution

[weirdo]

Hello to all!

I'm a newcomer here, please keep in mind: my English is far from good, so be patient ! All suggestions appreciated!

I didn't find answer searching the forum, so I'm asking here:
It is about EDTA (disodium-EDTA-dihydrate salt). I need help - how to make solution of that chemical for use as human blood (peripheral whole blood) anticoagulant (in vitro), and then, how to make working solution for dilution of blood sample so I can use it in hemacytometer! I mean: to make EDTA sol. first, and then use that solution for diluting blood sample. Should I add something to EDTA sol. before blood dilution (wrong pH for example)?

I can only find Na2-EDTA and "EDTA free acid" (both in pulver form) from ebay! Which is better?
Also I can find regular 0,85 (or 0,9)% saline sol. in local pharmacy.

I am NOT a biologist (but physicist), (micro)biology is my hobby, so I'm not a total "beginner" in natural sciences.

Thank you in advance!
Sorry if I posted this at a wrong place!

Regards!