VESICLE SIZE DISTRIBUTIONS MEASURED BY FLOW FIELD-FLOW FRACTIONATION COUPLED WITH MULTIANGLE LIGHT-SCATTERING

The separation method, flow field-flow fractionation (flow FFF), is co upled on-line with multiangle laser light scattering (MALLS) for simul taneous measurement of the size and concentration of vesicles eluting continuously from the fractionator. These size and concentration data, gathered as a function of elution time, may be used to construct both number-and mass-weighted vesicle size distributions. Unlike most comp eting, noninvasive methods, this flow FFF/MALLS technique enables meas urement of vesicle size distributions without a separate refractive in dex detector, calibration using particle size standards, or prior assu mptions about the shape of the size distribution. Experimentally measu red size distributions of vesicles formed by extrusion and detergent r emoval are non-Gaussian and are fit well by the Weibull distribution. Flow FFF/MALLS reveals that both the extrusion and detergent dialysis vesicle formation methods can yield nearly size monodisperse populatio ns with standard deviations of similar to 8% about the mean diameter. In contrast to the rather low resolution of dynamic light scattering i n analyzing bimodal systems, flow FFF/MALLS is shown to resolve vesicl e subpopulations that differ by much less than a factor of two in mean size.