Williams P S, Giddings J C
Department of Chemistry, University of Utah, Salt Lake City 84112.
J Chromatogr. 1991 Jul 26;550(1-2):787-97. doi: 10.1016/s0021-9673(01)88582-4.
Field programming in field-flow fractionation has the purpose of expanding the molecular weight or particle diameter range subject to a single analytical run. The two most widely used field programs are those in which the field strength decays with time according to an exponential function and a power function, respectively. The performances of these two programming functions are compared by obtaining limiting equations showing how retention time tr, standard deviation in retention sigma t, and fractionating power Fd vary with particle diameter d. It is shown that uniform fractionating power (Fd independent of d) can be obtained with power programming but that in exponential programming Fd is always non-uniform, varying as d-1/2. In exponential programming a linear relationship arises between tr and log d. This particular relationship is impossible to realize in power programming but an alternative linear relationship can be obtained by plotting tr versus dt/3. These results are made more concrete by plotting and comparing field strength, relative field strength, Fd and tr for specific programming cases.
场流分级中的场编程目的在于扩展单次分析运行所涵盖的分子量或粒径范围。两种最常用的场程序分别是场强随时间按指数函数和幂函数衰减的程序。通过获得显示保留时间tr、保留标准偏差σt和分馏能力Fd如何随粒径d变化的极限方程，来比较这两种编程函数的性能。结果表明，幂编程可获得均匀的分馏能力（Fd与d无关），但在指数编程中，Fd总是不均匀的，随d-1/2变化。在指数编程中，tr与log d之间呈现线性关系。这种特定关系在幂编程中无法实现，但通过绘制tr与dt/3的关系图可得到另一种线性关系。通过绘制并比较特定编程情况下的场强、相对场强、Fd和tr，使这些结果更加具体。
