Berthod A, Hassoun M, Ruiz-Angel M J
Laboratoire des Sciences Analytiques, Université Claude-Bernard, Lyon 1, 69622, Villeurbanne, France.
Anal Bioanal Chem. 2005 Sep;383(2):327-40. doi: 10.1007/s00216-005-0016-7. Epub 2005 Oct 12.
Countercurrent chromatography (CCC) is a separation technique that uses a biphasic liquid system; one liquid phase is the mobile phase, the other liquid phase is the stationary phase. Selection of the appropriate liquid system can be a problem in CCC, since it is necessary to select both the "column" and the mobile phase at the same time as the first is completely dependent on the second. A range of systems with various proportions of solvents were developed to ease this choice; 23 variations of the heptane/ethyl acetate/methanol/water biphasic liquid system were labeled A to Z. This range proved to be extremely useful and became the popular Arizona (AZ) liquid system. However, authors often replace the heptane with hexane. In this work, the chemical compositions of the upper phases and the lower phases of 55 Arizona systems made with various alkanes (pentane, hexane, heptane, isooctane and cyclohexane) were determined by gas chromatography and Karl Fischer titration. The test mixture separated consisted of five steroid compounds. The lower phases were found to have similar compositions when different alkanes were used, but the upper phases were found to change. Exchanging heptane for hexane or isooctane produced minimal changes in the CCC chromatogram, while changing the proportions of the solvents resulted in an exponential change in the retention volumes. The high density of cyclohexane made liquid stationary phase retention difficult. All Arizona systems equilibrated within 30 min, but were not stable: water slowly hydrolyzed the ethyl acetate (as shown by a continuous decrease in the pH of the lower aqueous phase), especially in the water-rich systems (early alphabet letters).
逆流色谱法（CCC）是一种利用双相液体系统的分离技术；一个液相是流动相，另一个液相是固定相。在逆流色谱法中，选择合适的液体系统可能是个问题，因为必须同时选择“柱”和流动相，因为前者完全依赖于后者。人们开发了一系列具有不同溶剂比例的系统来简化这种选择；庚烷/乙酸乙酯/甲醇/水双相液体系统的23种变体被标记为A到Z。这一系列系统被证明非常有用，并成为广受欢迎的亚利桑那（AZ）液体系统。然而，作者们经常用己烷代替庚烷。在这项工作中，通过气相色谱法和卡尔费休滴定法测定了由各种烷烃（戊烷、己烷、庚烷、异辛烷和环己烷）制成的55种亚利桑那系统的上相和下相的化学成分。所分离的测试混合物由五种甾体化合物组成。发现当使用不同的烷烃时，下相具有相似的组成，但上相发生了变化。用己烷或异辛烷代替庚烷在逆流色谱图中产生的变化最小，而改变溶剂比例则导致保留体积呈指数变化。环己烷的高密度使得液体固定相难以保留。所有亚利桑那系统在30分钟内达到平衡，但不稳定：水会缓慢水解乙酸乙酯（如较低水相的pH值持续下降所示），尤其是在富水系统（字母表靠前的字母）中。
