Factors influencing accuracy of colloidal and macromolecular properties measured by field flow fractionation

Although it is widely recognized that field-flow fractionation (FFF) can be used to measure numerous properties of macromolecular and colloidal components (as well as to separate the components), no systematic work has been done to evaluate the factors controlling the accuracy of FFF measurement. To hU the void, measurement errors are first divided into two basic classes: (1) those arising from shortcomings in the theoretical retention models that allow properties to be deduced from measured retention times and (2) experimental errors in retention time measurements and in system parameters that enter the final calculations of properties, with regard to (1), progress is outlined in improving retention models to account for steric effects, particle-wall interactions, viscosity gradients, and so on, For (2), equations are derived for estimating the relative error delta p/p in arbitrary property p resulting from a given error in experimental parameter E(i). It is found that delta p/p is inversely proportional to the selectivity of the separation relative top, thus formally linking error generation and intrinsic separability. A number of examples are given, including the effects of error in the measurement of retention time, now rate, channel thickness, and experimental temperature on the accuracy of determination of particle size and mass (molecular weight) by different FFF techniques.