CHARACTERIZATION OF SUBMICROMETER EMULSIONS USING SEDIMENTATION FIELD-FLOW FRACTIONATION WITH POWER FIELD PROGRAMMING

Sedimentation field-flow fractionation (SdFFF), operated with power-ba sed field programming, was shown to be effective in the characterizati on of submicrometer fat emulsions. Field programming, in which the dec rease of field strength with time gradually increases the average velo city of the sample components, extends the capabilities of sedimentati on field-flow fractionation in handling polydisperse samples. Submicro meter fat emulsions were analyzed by three different rates of field de cay and two different initial field strengths, using various stop-now times. Identical size distribution profiles were obtained under all ci rcumstances, using the appropriate stop-flow times. Fractions were col lected from the SdFFF eluting bands, and diameters were analyzed by ph oton correlation spectroscopy, showing good agreement with values give n by the FFF instrument. The agreement between the two methods indicat ed also that polydispersity of size dominated band broadening. Accurat e and highly reproducible size distribution profiles were obtained in all the cases studied. Sample loadability was examined by studying ove rloading effects and detection limits. The linearity of detector respo nse was also established, by injecting increasing loads of sample. The accuracy of the FFF peak shape was examined experimentally, by collec ting fractions, dissolving the emulsion in them, and measuring the UV absorption of the solutions. The profile formed by the fractions was r elatively close to the FFF band, proving that light scattering does no t seriously distort the size distribution profile.