we purchased 37% Formaldehyde solution, which is ready to use and storable for a long time from Carl Roth (Art. No. 7398.1). We also used this for mRNA Gel electrophoresis and it is not expensive.
Hi, formaldehyde is just a liquid form of paraformaldehyde, Proceed as you would for any other reagent (w/v), add 37 grams for every 100 ml of the solution (Phosphate buffer saline instead of Deionised water is used only for histological purposes, commercially available are in Deionised water). However this concentration seems way too high, so you might have to warm the Deionised water before, make sure you perform the whole process in a hood with airflow, as formaldehyde fumes are quite dangerous.