I am looking to purchase appropriate filters (.22 or .45 micrometer) for filtering DMF (dimethylformamide) solutions. It was suggested I use PVDF filters. But I found that the membrane almost melted/dissolved after a few uses (2-3). Can anyone recommend the correct type of filters? Are there any companies that can give a few filters for trials? I am not sure which (.25 or .45) would work best?