- Acetone/Acetonitrile precipitation
- Cation Exchange chromatographic techniques (disposable SCX spintip for example)
- Centrifugal Ultrafiltration and/or dialysis
Something else to consider... Is the Popculture reagent compatible with tryptic digestion? Make sure the pH is buffered properly and that the detergent concentration isn't too high. A relatively low detergent concentration won't low digestion efficiency (in fact it could increase the efficiency), but extremely high surfactant concentration could inhibit digestion.