TABLE 3.

Calibration constant K (glucose/internal standard) (n = 4)

Internal standard	MW	pH 8.5 + 30 mM NaCl	pH 8.5 + 30 mM NaCl + 10 mM EDTA	pH 8.5 + 100 mM CaCl2*	pH 6.3 + 30 mM NaCl*
Na+	23	0.064 ± 0.007	-	-	0.045 ± 0.014
Urea	60	0.61 ± 0.04	0.71 ± 0.05	0.51 ± 0.11	0.47 ± 0.03
Glycerol	92	0.75 ± 0.05	0.79 ± 0.05	0.71 ± 0.06	0.74 ± 0.03
Mannitol	182	0.92 ± 0.01	0.92 ± 0.02	0.95 ± 0.04	0.95 ± 0.03
Sucrose	342	0.98 ± 0.02	1.00 ± 0.06	1.19 ± 0.12	1.20 ± 0.15

^*The extraction fluxes at pH 8.5 + 100 mM CaCl₂ were not significantly different, for any solute, from those at pH 6.3 + 30 mM NaCl.