Quantitative evaluation of models for solvent-based, on-column focusing in liquid chromatography.
Quantitative evaluation of models for solvent-based, on-column focusing in liquid chromatography.
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DOI：
10.1016/j.chroma.2015.07.038
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发表时间：
2015-08-28
期刊：
影响因子：
--
通讯作者：
Weber SG
中科院分区：
文献类型：
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作者：
Groskreutz SR;Weber SG
柱上聚焦或预浓缩是一种众所周知的方法，通过在进样过程中产生导致高溶质保留的瞬变条件来提高浓度灵敏度。预富集产生于两个现象：1)溶质进入色谱柱时被保留。它们的速度是k‘相关的，并且低于流动相速度；2)由于较高的淋洗强度流动相穿过溶质区而产生的阶跃梯度，区域被压缩。几位工作人员得出的结果是，洗脱区宽度(时间)与进样时间宽度的比率为K2/K1，其中K1是溶质在样品溶剂中的保留因子，K2是流动相(等规度)中的保留因子。米尔斯等人。提出了一个不同的因素。到目前为止，这两种模型都没有经过充分的测试。这项工作的目标是对这两个模型进行定量评估。我们使用对羟基苯甲酸的正构烷基酯(对羟基苯甲酸酯)作为溶质。通过进行大量进样以产生明显的体积过载，我们可以准确地测量K1和K2范围内的宽度比(洗脱/进样)。米尔斯等人。模型与数据不匹配。数据与因子K2/K1基本一致，但聚焦比预测值高出约10%。我们将这种额外的聚焦归因于这样一个事实，即第二种压缩现象提供的区域比阶跃梯度通过该区域时的预期区域窄。
On-column focusing or preconcentration is a well-known approach to increase concentration sensitivity by generating transient conditions during the injection that result in high solute retention. Preconcentration results from two phenomena: 1) solutes are retained as they enter the column. Their velocities are k′-dependent and lower than the mobile phase velocity and 2) zones are compressed due to the step-gradient resulting from the higher elution strength mobile phase passing through the solute zones. Several workers have derived the result that the ratio of the eluted zone width (in time) to the injected time width is the ratio k2/k1 where k1 is the retention factor of a solute in the sample solvent and k2 is the retention factor in the mobile phase (isocratic). Mills et al. proposed a different factor. To date, neither of the models has been adequately tested. The goal of this work was to evaluate quantitatively these two models. We used n-alkyl esters of p-hydroxybenzoic acid (parabens) as solutes. By making large injections to create obvious volume overload, we could measure accurately the ratio of widths (eluted/injected) over a range of values of k1 and k2. The Mills et al. model does not fit the data. The data are in general agreement with the factor k2/k1, but focusing is about 10% better than the prediction. We attribute the extra focusing to the fact that the second, compression, phenomenon provides a narrower zone than that expected for the passage of a step gradient through the zone.