Figure 1

A-C. Residual vs. initial UCB concentrations in buffered DMSO/water systems. Measured residual [UCB] in supernatants of buffered DMSO/water systems, after centrifugation for 5 min at 14,000 g, are plotted against the pipetted, initial UCB concentrations before centrifugation. Mole fractions (N) of DMSO were 0.310 (A), 0.086 (B) and 0.025 (C). Panels B and C are log-log plots. The dashed unity line indicates complete retention of UCB in supernatant. The buffers used and the corrected pH values of the DMSO-buffer systems were: Panel A – (circle) Phosphate pH 8.4, (square) Tris pH 7.1, (diamond) Acetate pH 6.9, (triangle) Acetate pH 5.9; Panel B – (circle) Phosphate pH 7.6–7.7, (square) Tris pH 7.1, (triangle) Acetate pH 4.5; Panel C – (circle) Phosphate pH 7.2, (square) Tris pH 7.0, (triangle) Acetate pH 4.15. [UCB] in each supernatant was determined from A at 458 nm, using the extinction coefficient of 0.0634 μM^-1cm^-1.