Espinosa S, Bosch E, Roses M
Departament de Quimica Analitica, Universitat de Barcelona, Spain.
Anal Chem. 2000 Nov 1;72(21):5193-200. doi: 10.1021/ac000591b.
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: sspH and wspH (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 (wspH scale) to sspH 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 wwpH scale (pH measured in the aqueous buffer before mixing it with the organic modifier). The use of the rigorous sspH and wspH 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 wwpH scale.
讨论了在反相液相色谱中用作流动相的乙腈 - 水混合物中导致不同pH标度的pH校准程序。选择乙腈 - 水混合物中已知pH值的合适缓冲液，并用于建立两种严格的乙腈 - 水pH标度：sspH和wspH（分别在乙腈 - 水混合物中测量并以乙腈 - 水或水作为标准状态的pH）之间的关系（δ值）。这些δ值允许将用含水缓冲液校准的电极系统在乙腈 - 水中测量的pH值（wspH标度）转换为sspH值，sspH值与热力学酸碱常数直接相关。这提供了一种测量乙腈 - 水流动相pH值的简便方法，并通过热力学酸碱常数将该pH值与酸和碱的色谱保留相关联。在几种流动相组成下，测试了酸和碱的保留随流动相pH值的变化关系，并与用常见的wwpH标度（在与有机改性剂混合之前在含水缓冲液中测量的pH）获得的关系进行了有利比较。使用严格的sspH和wspH标度可以解释碱的保留行为，在许多情况下，从没有根据的wwpH标度中的pH测量无法证明这种行为。
