Retention of ionizable compounds on HPLC.: 5.: pH scales and the retention of acids and bases with acetonitrile-water mobile phases
Retention of ionizable compounds on HPLC.: 5.: pH scales and the retention of acids and bases with acetonitrile-water mobile phases
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DOI：
10.1021/ac000591b
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发表时间：
2000-11-01
影响因子：
7.4
通讯作者：
Rosés, M
中科院分区：
文献类型：
--
作者：
Espinosa, S;Bosch, E;Rosés, M
讨论了在反相液相色谱中用作流动相的乙腈-水混合物中产生不同 pH 值的 pH 校准程序。选择乙腈-水混合物中已知 pH 值的适当缓冲液并用于建立两个严格的乙腈-水 pH 值之间的关系（δ 值）：(s)(s)pH 和 (s)(w)pH（在乙腈-水混合物中测量的 pH 值，分别称为标准状态下的乙腈-水或水）。这些 delta 值允许人们将使用水性缓冲液（(s)(w)pH 标度)校准的电极系统在乙腈-水中测量的 pH 值转换为 (s)(s)pH 值，这与热力学酸碱常数直接相关。这提供了一种简单的方法来测量乙腈-水流动相的 pH 值，并通过热力学酸碱常数将该 pH 值与酸和碱的色谱保留联系起来。测试了几种流动相组成下酸和碱的保留随流动相 pH 值变化的关系，并与使用常见 (w)(w)pH 标度（在与有机改性剂混合之前在水性缓冲液中测量的 pH 值）获得的关系进行了有利的比较。使用严格的 (s)(s)pH 和 (s)(w)pH 标度可以解释碱基的保留行为，但在许多情况下，无法通过毫无根据的 (w)(w)pH 标度中的 pH 测量来证明这一行为是合理的。
The pH calibration procedures that lead to the different pH scales in acetonitrile-water mixtures used as mobile phases in reversed-phase liquid chromatography are discussed. Appropriate buffers of known pH value in acetonitrile-water mixtures are selected and used to establish the relationship (delta values) between the two rigorous acetonitrile-water pH scales: (s)(s)pH and (s)(w)pH (pH measured in acetonitrile-water mixtures and referred to acetonitrile-water or water, respectively, as standard state). These delta values allow one to convert pH values measured in acetonitrile-water with electrode systems calibrated with aqueous buffers ((s)(w)pH scale) to (s)(s)pH values, which are directly related to the thermodynamic acid-base constants. This offers an easy way to measure the pH of acetonitrile-water mobile phases and to relate this pH to the chromatographic retention of acids and bases through the thermodynamic acid-base constants. The relationships are tested for the variation of the retention of acids and bases with the pH of the mobile phase at several mobile-phase compositions and favorably compared with the relationships obtained with the common (w)(w)pH scale (pH measured in the aqueous buffer before mixing it with the organic modifier). The use of the rigorous (s)(s)pH and (s)(w)pH scales allows one to explain the retention behavior of bases, which in many instances cannot be justified from the pH measurement in the ill-founded (w)(w)pH scale.