Schure Mark R, Palkar Saurabh A
Theoretical Separation Science Laboratory, Rohm and Haas Company, Spring House, Pennsylvania 19477, USA.
Anal Chem. 2002 Feb 1;74(3):684-95. doi: 10.1021/ac011006p.
The coupling of field-flow fractionation (FFF) and multiangle light scattering (MAIS) detectors is complementary in that the MALS system allows particle characterization when a narrow dispersity particle population is present in the detector. The fractionation process provides this narrow dispersity. Utilizing discrete particle simulations of FFF and optical calculations based on both the Mie theory of particle scattering and Rayleigh-Gans-Debye (RGD) scattering theory, the extent of polydispersity that can be tolerated for accurate particle quantitation is explored. It is found that flow, electrical, and sedimentation FFF provide adequate separation for accurate particle quantitation by MALS. The Mie theory is more accurate than the RGD theory, which is known to deviate at higher particle size. Low error in the measurement of mean diameters is found when only the particle diameter is of interest. It is shown that the reconstruction of the particle size distribution from time slice data is distorted due to errors in concentration, which result from finite polydispersity and other effects. A number of procedures are evaluated in restoring the size distribution to higher accuracy. None of these procedures is deemed of general purpose and none of these is reliable. The best results are obtained when fractionation is conducted under the minimal possible outlet polydispersity and when steric effects are minimized. In addition, best results are had for inherently narrow dispersity colloidal materials.
场流分级（FFF）与多角度光散射（MAIS）检测器的联用具有互补性，因为当检测器中存在窄分散度的粒子群体时，多角度光散射系统能够对粒子进行表征。分级过程可提供这种窄分散度。利用场流分级的离散粒子模拟以及基于粒子散射的米氏理论和瑞利 - 甘斯 - 德拜（RGD）散射理论的光学计算，探讨了准确进行粒子定量分析时可容忍的多分散度范围。研究发现，流动场流分级、电场流分级和沉降场流分级为多角度光散射进行准确的粒子定量分析提供了充分的分离效果。米氏理论比RGD理论更准确，已知RGD理论在较大粒径时会出现偏差。当仅关注粒子直径时，发现平均直径测量的误差较小。结果表明，由于有限多分散度和其他效应导致的浓度误差，会使从时间切片数据重建的粒度分布产生畸变。对多种恢复粒度分布更高精度的方法进行了评估。这些方法均不具有通用性，也不可靠。当在尽可能小的出口多分散度下进行分级且空间位阻效应最小化时，可获得最佳结果。此外，对于固有窄分散度的胶体材料可得到最佳结果。
