Peak Shape-analysis In Sedimentation Field-flow Fractionation

Peak shape effects in sedimentation field-flow fractionation (SFFF) are investigated by Edgeworth-Cramer (EC) least-squares peak profile fitting, numerical integration, and graphical analysis. The use of an EC series expansion procedure with regard to the description of an SFFF process is discussed. The onset of nonlinear effects and secondary-order phenomena such as steric contributions in the normal SFFF elution mode and injected sample overloading are detected by means of the EC series expansions through fitting patterns and statistical peak shape parameter analysis. It has been found that, under ideal conditions of monodisperse sample analysis, current SFFF instrumentation produce symmetric peaks with skewness values as low as 0.2, leading to accurate particle parameter estimations. Therefore, peak shape markers are a complementary check for detecting mixed elution processes, overloading effects, or polydispersity contributions that could affect the accuracy of particle parameter estimations. Peak shape analysis is generally able to allow for the unbiased determination of peak parameters at the onset of a steric contribution in the normal elution mode. Fast, handy rules are given for checking "pure" normal elution modes and the extent of bias on retention parameters.