1. Phase Components: Most large-scale applications of ATPS are based on polymer-salt systems. Poly(ethylene glycol) (PEG) (Sigma, St. Louis, MO) is the top phase polymer and the salt, namely phosphate, sulfate, or citrate, is the bottom phase component. As an alternative to salt, commercial hydroxypropyl starch (Reppal, Carbamyl AB, Kristianstad, Sweden), or crude dextran (Sigma), can be used as the bottom phase rich polymer (see Notes 1-3) (see also Chapter 3).
2. Salts: In case of polymer-polymer systems, the addition of salts may be needed as buffer components to maintain the pH, or to direct the partitioning of target biomolecule.
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