A Guide to Establishing Water Potential of Aqueous Two-Phase Solutions (Polyethylene Glycol plus Dextran) by Amendment with Mannitol

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Abstract
A practical guide to calculating the mannitol (MAN) amendment required to achieve the desired water potential (.PSI.) of polyethylene glycol/dextran (PEG/DEX) aqueous 2-phase systems for protoplast purification is presented. The empirically generated equation .PSI. = 305[PEG'']2[MAN] + 0.74[PEG''][MAN]T - 103[PEG''][MAN] + 5.6[PEG'']2T - 623[PEG'']2 - 0.25[PEG'']T + 12.7[PEG''] - 0.078[MAN]T - 22.75[MAN]accurately predicts experimental .PSI. (in bars). [PEG''] indicates the presence of DEX where [DEX] = [PEG]/(0.6-0.4[PEG]). The equation is applicable for these ranges: [PEG''] from 0.047-0.13 g/g H2O; [MAN] from 0-0.7 M T [temperature] from 4.5.degree. to 40.degree. C. Actual .PSI. should differ from derived .PSI. by no more than 8% for the least negative values to 4% for the most negative values. The .PSI. for solutions of MAN, of PEG and of DEX were also determined. Equations to fit data for each were generated. Analyses indicated a significant synergistic effect on .PSI. when MAN is added to PEG/DEX and, at certain concentrations, between PEG and DEX.