How much of my purified protein is necessary to perform 2D-PAGE?

My sample is a purified protein and I need a two-dimensional electrophoresis to show at least two isoforms. The strips I can use are pH 3-10, 7cm or 17cm. I don't know the protein quantity I have to use. My group doesn't have experience with purified proteins, but we thought 10ug on both strips are sufficient. What do you think?