I'm doing some work on mixing hydrophilic ionic liquids with an aqueous buffer as biocatalytic reaction media. As I read the papers, I was aware of some commercial ILs mentioned in the papers were solid (or powder), although these ILs were mixed with water (or buffer) by v/v without further operation based on the papers.

I'm now feeling confused about the way to mix ILs with buffer. If I mix them by wt% the result might be influenced by the distinct molecular weight of different ILs, while if I mix them by v/v there are not so many ILs to test.

I'd appreciate it if you could tell me how you make ILs like [TBA][SO4] or [BMIM][Br] which are sold as solid be liquid. Also, it's better if you could tell me which way you would choose to mix ILs with buffer.