Optimized field-flow fractionation system based on dual stream splitters.
Optimized field-flow fractionation system based on dual stream splitters.
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基于双流分流器的优化场流分馏系统。
DOI：
10.1021/ac00281a037
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发表时间：
1985
影响因子：
7.4
通讯作者：
Giddings,JC
中科院分区：
文献类型：
--
作者：
Giddings,JC
先生：提高场流分离（FFF）的分离速度（以及分辨率）的基本原则是尽可能地减小压靠在FFF通道积聚壁上的颗粒云的平均厚度l。这一规则自1973年（1）以来就已为人所知，可从以下关于产生一个理论塔板所需时间tp的极限方程推导出，其中ip= 4 P/D（1），其中D是颗粒扩散系数。因此，需要N个板以获得足够分辨率的分离需要Ntp的时间，其等于t= 4 NP/D（2），显示t对l的二次依赖性，并证明最小化l（1，2）的可取性。根据这一结论，实验FFF通常在1-10 pm范围内的l值下操作。对于厚度约为0.25 mm（250 µ）的典型通道，这意味着样品层与通道相比非常薄，因此样品仅占通道横截面的一小部分，如图1所示。为了避免分离度的显著降低，运行的总实验时间通常包括沿着上述分离时间Ntp（参见等式2）的一段时间，在该时间内，流动停止以允许在运行开始时样品松弛（3）。该停流时间由弛豫时间r控制，弛豫时间r可以表示为颗粒必须穿过以形成稳态云的最长距离（通常为通道厚度w）除以场诱导速度U
Sir: The cardinal rule for increasing separation speed (as well as resolution) in field-flow fractionation (FFF) is to reduce as far as possible the mean thickness l of the cloud of particles compressed against the accumulationwall of the FFF channel. This rule, known since 1973 (1), can be deduced from the following limiting equation for the time, tp, needed to generate one theoretical plate ip= 4 P/D(1) where D is the particle diffusion coefficient. A separation requiring N plates for adequate resolution therefore requires a time of Ntp, which equals t= 4 NP/D(2) showing a quadratic dependence of t on l and demonstrating the desirability of minimizing l (1, 2). In response tothis conclusion, experimental FFF is often operated with l values in the range 1-10 pm. For typical channels of about 0.25 mm(250 µ) thickness, this means that the sample layer is very thin compared to the channel, and that the sample therefore occupies only a small fraction of channel cross section, as illustrated in Figure 1. In order to avoid a substantial degradation of resolution, the total experimental time for a run usually includes, along with the above time Ntp (see eq 2) for separation, a period in which flow is halted to allow for sample relaxation at the beginning of the run(3). This stop-flow time is governed by the relaxation time r, which can be expressed as the longest distance (usually channel thickness w) the particles must traverse to form the steady-state cloud divided by the fieldinduced velocity U