Mixed-mode cation-exchange stationary phases are useful for the separation of mixtures containing hydrophobic, acidic, and basic molecules. To ensure that weak organic bases are protonated and carboxylic acids are neutral low pH mobile phases are required. Mixed-mode stationary phases that are stable at pH < 3 are needed. We synthesized a crosslinked structure along the surface of thiol functionalized silica gel particles using the thiol-yne click reaction. The alkyne, 1,7-octadiyne, was added to the 3-mercaptopropyl silica gel, then crosslinked using 1,6-hexanedithiol. Elemental analysis showed low octadiyne ligand surface coverage, but, stoichiometrically, three sulfurs were added to each octadiyne ligand during the crosslinking step, indicating that crosslinking occurred. The effect of the crosslinking on the stability was tested with a 50:50 (v/v) pH 0.50 5% TFA aqueous:acetonitrile mobile phase at 70 °C for six days, over 35,000 column volumes. The stationary phase showed good stability with the retention of triphenylene decreasing only 20% during that time. The Tanaka test showed that the phase has a methylene selectivity of 1.20 ± 0.04, a high shape selectivity of 2.71 ± 0.03, and a 3.98 ± 0.05 cation-exchange factor at pH 2.70. The phase has a selectivity factor for nitrobenzene and benzene of 1.41 ± 0.01, indicating the electron donating charge transfer characteristic of the phase. The mixed-mode characteristics of the phase were investigated using a mixture of the monoamine neurotransmitters norepinephrine, dopamine, and serotonin. Baseline resolution of the monoamines could be obtained using a simple 20 mM potassium phosphate (pH 2.70)/methanol mobile phase. Altering both the methanol content and the potassium ion concentration altered the retention of the monoamines indicating mixed-mode cation exchange characteristic of the crosslinked stationary phase.

中文翻译：

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使用硫醇-炔单击反应制备的交联的，低pH稳定的混合模式阳离子交换固定相。

混合模式阳离子交换固定相可用于分离包含疏水，酸性和碱性分子的混合物。为确保弱有机碱被质子化且羧酸为中性，需要低pH流动相。需要在pH <3下稳定的混合模式固定相。我们使用硫醇炔键单击反应沿硫醇官能化硅胶颗粒的表面合成了交联结构。将炔1，7-辛二炔添加到3-巯基丙基硅胶中，然后使用1，6-己二硫醇交联。元素分析显示低的辛二炔配体表面覆盖率低，但化学计量上，在交联步骤中向每种辛二炔配体添加了三种硫，表明发生了交联。交联对稳定性的影响用50：50（v / v）pH 0.50 5％TFA水：乙腈流动相在70°C下连续六天，色谱柱体积超过35,000。固定相显示出良好的稳定性，在此期间三苯撑的保留仅降低了20％。田中试验表明，该相的亚甲基选择性为1.20±0.04，高形状选择性为2.71±0.03，在pH 2.70时的阳离子交换因子为3.98±0.05。该相对硝基苯和苯的选择性系数为1.41±0.01，表明该相的给电子电荷转移特性。使用单胺神经递质去甲肾上腺素，多巴胺和5-羟色胺的混合物研究了相的混合模式特性。可以使用简单的20 mM磷酸钾（pH 2.70）/甲醇流动相获得单胺的基线拆分值。