柱色谱Column chromatography

根据薄层色谱结果选择洗脱剂，使目标物 R_f 约为 0.2–0.35。硅胶用量一般为样品量的 30–100 倍；可湿法装柱（硅胶与洗脱剂调成匀浆倒入）或干法装柱，柱床须均匀、无气泡和裂缝。上样可用少量溶剂溶解后加入，或预先把样品吸附在少量硅胶上干法上样。洗脱时可用梯度洗脱（逐渐提高极性，如石油醚/乙酸乙酯从 20:1 到 5:1），分管收集并用 TLC 检测合并。

Choose the eluent from TLC so the target has an R_f of about 0.2–0.35. Use roughly 30–100 times as much silica as sample, and pack the column wet as a slurry or dry, with an even bed free of bubbles and cracks. Load the sample dissolved in a little solvent, or dry-loaded on a small amount of silica. Elute isocratically or with a gradient of rising polarity, such as petroleum ether–ethyl acetate from 20:1 to 5:1, collecting fractions and combining them after TLC.

茨维特 1906 年的色素分离就是柱色谱。传统重力柱速度慢，1978 年美国化学家克拉克·斯蒂尔发表“快速柱色谱”（flash chromatography）方法，用压缩空气或氮气加压，配合细颗粒硅胶（40–63 μm），使一次分离只需 10–20 分钟，这篇论文成为化学领域引用最多的论文之一。现在自动快速色谱仪可在线紫外检测并自动收集。

Tsvet's 1906 pigment separation was column chromatography. Gravity columns are slow, and in 1978 the American chemist W. Clark Still published flash chromatography, pushing eluent with compressed air or nitrogen through fine silica (40–63 μm) so that a separation took only 10–20 minutes; the paper became one of the most cited in chemistry. Automated flash systems now detect by UV and collect fractions automatically.

正相柱：硅胶（弱酸性，最常用）、氧化铝（有酸性、中性、碱性，适合对酸敏感的化合物或胺）；反相柱：C18 键合硅胶，用水/甲醇或水/乙腈洗脱，适合极性化合物；此外还有离子交换树脂、凝胶过滤介质（葡聚糖凝胶）和亲和介质，多用于生化分离。

Normal-phase media include silica gel (weakly acidic, the most common) and alumina (acidic, neutral or basic, for acid-sensitive compounds or amines); reversed-phase media are C18-bonded silica eluted with water–methanol or water–acetonitrile for polar compounds; and ion-exchange resins, gel-filtration media such as dextran gels and affinity media serve mostly in biochemical separations.