I have a question about the solvent used to preparation of the mobile phase for HPLC test. We use purified water passed through 0.45um membrane as the solvent. However, a inspector said it was not allowed to use. We must use ultrapure water. But I didn't find this requirement in the USP.
SO I want to know if it is necessary to use ultrapure water as the solvent in HPLC test.