ELECTRICAL FIELD-FLOW FRACTIONATION IN PARTICLE SEPARATION .1. MONODISPERSE STANDARDS
ELECTRICAL FIELD-FLOW FRACTIONATION IN PARTICLE SEPARATION .1. MONODISPERSE STANDARDS
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DOI：
10.1021/ac00061a021
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发表时间：
1993-07-01
影响因子：
7.4
通讯作者：
GAO, YS
中科院分区：
文献类型：
--
作者：
CALDWELL, KD;GAO, YS
在最初的实施中，电场流分级（EFFF）是在膜壁通道中进行的，电极放置在流道外部。该系统分离效率低下，导致该技术在大约二十年的时间里基本上无人看管。在本研究中，我们描述了一种新的简单的 EFFF 方法，该方法证明了该技术能够对水悬浮液中的胶体样品进行快速、高分辨率的分离。目前的通道以光滑且刚性的石墨电极为界，允许在由聚酯薄膜垫片限定的薄（178μm）分离空间上施加小电压（通常小于2V）。尽管这种布置产生了 100 V/cm 量级的标称场，但电极的极化极大地将整个通道的有效场降低到标称值的 1% 以下。然而，在低离子强度条件下，该系统能够保留并分离尺寸范围为 60 至 10 000 nm 的聚苯乙烯 (PS) 乳胶标准品。对于具有可比较 zeta 电位的小颗粒，在 EFFF 的“正常”模式下分离，尺寸选择性 S(d) 约为 0.7。与其他 FFF 技术一样，EFFF 显示出从“正常”行为到“空间”行为的转变；这种转变的临界直径高度依赖于离子强度，在施加电压为 1.37 V、流速为 1 mL/min 的情况下，值范围从去离子水中的约 500 nm 到 133 muM 氯化钠水溶液中的约 1200 nm。尽管通常在样品注射后立即观察到的停流期会扰乱磁场，但在大多数情况下它仍然对分辨率产生积极影响。因此，大约 5 分钟的停流时间将允许在 2 分钟的分离步骤中从可溶性污染物中分离出 272 nm 乳胶的基线。
In its original implementation, electrical field-flow fractionation (EFFF) was carried out in membrane-walled channels with the electrodes placed externally to the flow channel. The poor separation efficiency of this system left the technique largely unattended for about two decades. In the present study, we describe a new and simple approach to EFFF, which demonstrates the technique's ability to carry out rapid, high-resolution separations of colloidal samples in aqueous suspensions. The present channels are bounded by the smooth and rigid graphite electrodes which allow for the application of small voltages, typically less than 2 V, across the thin (178 mum) separation space defined by a Mylar spacer. Although this arrangement generates nominal fields of the order of 100 V/cm, polarization of the electrodes considerably reduces the effective field across the bulk of the channel to less than 1% of the nominal value. Nevertheless, under conditions of low ionic strength the system is shown to retain and separate polystyrene (PS) latex standards with sizes ranging from 60 to 10 000 nm. For small particles of comparable zeta-potential, separating in the ''normal'' mode of EFFF, the size selectivity S(d), is approximately 0.7. As with other FFF techniques, EFFF displays a transition from ''normal'' to ''steric'' behavior; the critical diameter for this transition is highly dependent on ionic strength, with values ranging from approximately 500 nm in deionized water to approximately 1200 nm in 133 muM aqueous NaCl under an applied voltage of 1.37 V and a flow of 1 mL/min. Although the stop-flow period customarily observed immediately after sample injection is shown to perturb the field, it still has a positive effect on resolution under most conditions. Thus, stop-flow times of approximately 5 min will permit the baseline resolution of a 272-nm latex from soluble contaminants in a 2-min separation step.