📚 A-Level CCEA Chemistry: Chromatography Essentials | A-Level CCEA 化学：色谱考点精讲
Chromatography is one of the most versatile separation techniques you will study in CCEA A-Level Chemistry. From identifying amino acids in a mixture to testing the purity of a pharmaceutical compound, chromatography finds applications across organic, inorganic and analytical chemistry. This article covers all the essential theory, practical techniques and common exam questions, helping you build a confident understanding of the topic.
色谱是 CCEA A-Level 化学课程中最通用的分离技术之一。无论是鉴定混合物中的氨基酸，还是检测药物化合物的纯度，色谱在有机、无机和分析化学中都有广泛应用。本文涵盖所有关键理论、实验操作以及常见考题，帮助你扎实掌握这一考点。
1. What Is Chromatography? | 什么是色谱？
Chromatography is a physical method of separation in which the components of a mixture are distributed between two phases: a stationary phase and a mobile phase. The name originates from the Greek words ‘chroma’ (colour) and ‘graphein’ (to write), as the technique was first used to separate coloured plant pigments by the Russian botanist Mikhail Tswett in 1903. Today, chromatography is widely employed to separate, identify and quantify components in complex mixtures, from drug detection to environmental analysis.
色谱是一种物理分离方法，混合物中各组分在固定相和流动相两相之间分配。该名称源自希腊语“颜色”和“书写”，因为俄国植物学家茨维特于1903年首次用此技术分离有色植物色素。如今，色谱被广泛用于复杂混合物中组分的分离、鉴定与定量分析，涵盖从药物检测到环境分析等领域。
2. Basic Principle: Mobile and Stationary Phases | 基本原理：流动相与固定相
All chromatographic separations rely on the differential partitioning of solutes between a mobile phase and a stationary phase. The mobile phase is a fluid (liquid or gas) that carries the sample through the system. The stationary phase is a solid or a liquid held on a solid support that does not move. Solutes that interact more strongly with the stationary phase travel more slowly; those that spend more time in the mobile phase move faster. This difference in migration rates leads to separation.
所有色谱分离都依赖于溶质在流动相和固定相之间的分配差异。流动相是携带样品通过系统的流体（液体或气体）。固定相是保持不动的固体或固体支持物上的液体。与固定相作用更强的溶质移动较慢；在流动相中停留时间更长的溶质移动较快。这种迁移速率差异导致分离。
3. Adsorption Chromatography vs Partition Chromatography | 吸附色谱与分配色谱
Chromatography can be classified by the primary mechanism of separation. In adsorption chromatography, the stationary phase is a finely divided solid (e.g. silica gel or alumina), and solute molecules compete for binding sites on its surface. Thin layer chromatography (TLC) and column chromatography with solid adsorbents are common examples. In partition chromatography, the stationary phase is a thin liquid film coated on an inert solid support, and separation occurs due to differences in solubility of solutes between the two liquid phases. Paper chromatography (where water held in the cellulose acts as the stationary phase) and many forms of gas-liquid chromatography are partition processes.
色谱可按主要分离机理分类。吸附色谱中，固定相是细分固体（如硅胶或氧化铝），溶质分子竞争其表面结合位点。薄层色谱（TLC）和用固体吸附剂的柱色谱是常见例子。分配色谱中，固定相是涂覆在惰性固体载体上的薄层液膜，分离因溶质在两液相间的溶解度差异而发生。纸色谱（纤维素中持有的水作为固定相）及许多气液色谱形式都属于分配过程。
4. Paper Chromatography | 纸色谱
Paper chromatography is a simple, low-cost technique often used to separate small polar molecules like amino acids and sugars. A spot of the mixture is placed near the bottom of a strip of chromatography paper. The paper is then placed in a sealed container with a suitable solvent (the mobile phase) so that the solvent level is below the spot. As the solvent rises up the paper by capillary action, components move at different rates. The paper acts as a support, with water adsorbed to the cellulose fibres serving as the stationary phase; this makes paper chromatography an example of partition chromatography.
纸色谱是一种简单、低成本的分离技术，常用于分离氨基酸和糖类等小极性分子。将混合物点样于色谱纸条底部附近，然后把纸条放入密封容器，其中盛有适当溶剂（流动相），溶剂液面须低于点样处。溶剂通过毛细作用沿纸上升，各组分以不同速率移动。纸作为载体，吸附在纤维素纤维上的水充当固定相；因此纸色谱为一例分配色谱。
The separated components may be invisible; locating agents such as ninhydrin (for amino acids) or UV light can be used to visualise them. The retention factor, Rf, is calculated for each spot and compared to known standards for identification.
分离后的组分可能不可见；可使用茚三酮（用于氨基酸）或紫外灯等显色剂使其显现。计算各斑点的比移值 Rf，并与已知标准品对比进行鉴定。
5. Thin Layer Chromatography (TLC) | 薄层色谱
TLC uses a plate coated with a thin layer of a solid adsorbent such as silica gel (SiO₂) or alumina (Al₂O₃) as the stationary phase. The sample is spotted near the bottom, and the plate is placed in a developing chamber with a small depth of solvent. Separation occurs primarily by adsorption, because the solid stationary phase has active sites that bind solute molecules. TLC provides faster runs, sharper spots and better resolution than paper chromatography. It is widely used for monitoring the progress of organic reactions and checking the purity of products.
薄层色谱用涂有硅胶（SiO₂）或氧化铝（Al₂O₃）等固体吸附剂薄层的板作固定相。将样品点于板底部附近，然后将板放入盛有少量溶剂的展开缸中。分离主要通过吸附发生，因为固体固定相具有可结合溶质分子的活性位点。TLC 运行更快、斑点更清晰且分离度优于纸色谱。它广泛用于监测有机反应进程和检查产品纯度。
6. Column Chromatography | 柱色谱
Column chromatography is a preparative technique used to separate and collect larger quantities of mixture components. A glass column is packed with a solid stationary phase (often silica or alumina). The mixture is loaded at the top, and a suitable solvent (the eluent) is continuously passed through the column. Components move down the column at different speeds depending on their affinity for the stationary phase. Fractions are collected at the bottom, and the solvent can be evaporated to recover the separated substances. This technique is particularly valuable in organic synthesis for purifying reaction products.
柱色谱是一种制备技术，用于分离和收集较大量混合物组分。玻璃柱中装填固体固定相（常为硅胶或氧化铝）。混合物从柱顶加入，适当溶剂（洗脱液）连续通过柱体。组分根据与固定相亲和力的不同以不同速度向下移动。在柱底收集流分，蒸去溶剂即可回收分离出的物质。此技术在有机合成中纯化反应产物极具价值。
7. Gas Chromatography (GC) | 气相色谱
Gas chromatography is a highly sensitive instrumental method for separating and analysing volatile, thermally stable mixtures. The mobile phase is an inert carrier gas (e.g. helium or nitrogen). The sample is injected, vaporised, and swept through a long, narrow column containing either a solid stationary phase (gas-solid chromatography) or a liquid stationary phase coated on the column walls or on a solid support (gas-liquid chromatography). Components separate based on their boiling points and their solubility in the stationary phase. A detector (commonly a flame ionisation detector, FID) records a chromatogram: a plot of detector response versus time. Each separated substance produces a peak; the retention time (the time taken for a substance to pass through the column) is used for qualitative identification, while the peak area (or height) is used for quantitative analysis.
气相色谱是一种高灵敏度的仪器方法，用于分离和分析挥发性、热稳定的混合物。流动相为惰性载气（如氦气或氮气）。样品注入后气化，并被载气带入细长的色谱柱；柱内可为固体固定相（气-固色谱）或涂覆在柱壁或固体载体上的液体固定相（气-液色谱）。组分根据其沸点及在固定相中的溶解度实现分离。检测器（常用火焰离子化检测器 FID）记录色谱图：即检测器响应随时间的变化。每种分离物质产生一个峰；保留时间（物质通过色谱柱所需时间）用于定性鉴定，而峰面积（或峰高）用于定量分析。
8. High Performance Liquid Chromatography (HPLC) | 高效液相色谱
HPLC is an advanced form of column chromatography in which the mobile phase is pumped through a column packed with very fine stationary-phase particles under high pressure. This technique achieves fast, high-resolution separations for a wide range of substances, including those that are non-volatile or thermally labile. In normal-phase HPLC, the stationary phase is polar (e.g. silica) and the mobile phase is non-polar. In reverse-phase HPLC, the stationary phase is non-polar (e.g. C18 hydrocarbon chains bonded to silica) and the mobile phase is polar (e.g. water-methanol mixtures); reverse-phase HPLC is the most common mode. As in GC, a chromatogram is obtained with retention times and peak areas. HPLC is extensively used in pharmaceutical, forensic and environmental analysis.
高效液相色谱是柱色谱的先进形式，其流动相在高压下泵送通过填充有极细固定相颗粒的色谱柱。该技术可对包括非挥发性和热不稳定物质在内的多种成分实现快速、高分辨分离。在正相 HPLC 中，固定相为极性（如硅胶），流动相为非极性。在反相 HPLC 中，固定相为非极性（如键合在硅胶上的 C18 烃链），流动相为极性（如水-甲醇混合物）；反相 HPLC 是最常见的模式。与 GC 类似，可得到包含保留时间和峰面积的色谱图。HPLC 广泛用于药物、法医和环境分析中。
9. Calculating and Interpreting Rf Values | Rf 值的计算与解读
The retention factor, Rf, is a crucial parameter in planar chromatography (paper and TLC). It is defined as the ratio of the distance travelled by the centre of a solute spot to the distance travelled by the solvent front, both measured from the origin line.
比移值 Rf 是平面色谱（纸色谱与 TLC）中的一个关键参数。其定义为溶质点中心移动的距离与溶剂前沿移动的距离之比，两者均从原点线测量。
Rf = distance moved by substance / distance moved by solvent front
Rf values are always between 0 and 1. Under identical conditions (same stationary phase, mobile phase, temperature), each substance has a characteristic Rf value, allowing for identification by comparison with known standards. A single spot on a chromatogram suggests a pure substance; multiple spots indicate a mixture or impurity. It is essential to apply the spot small and concentrated to avoid tailing and inaccurate Rf measurement.
Rf 值总是介于 0 与 1 之间。在相同条件下（相同固定相、流动相、温度），每种物质具有特征 Rf 值，通过对比已知标准品可进行鉴定。色谱图上单一点表明纯物质；多个斑点则表明混合物或存在杂质。点样应小而浓，以避免拖尾和 Rf 测量不准。
10. Two-Way Chromatography | 双向色谱
When a mixture contains substances with very similar Rf values in a given solvent, one-dimensional chromatography may not separate them adequately. Two-way chromatography solves this problem. A sample is spotted at one corner of a square plate or paper and developed with a first solvent. After drying, the plate is turned 90°, and a second, different solvent is used for development in the perpendicular direction. Components that did not separate in the first solvent may separate in the second, spreading out across the two-dimensional plane. This technique is especially useful for amino acid analysis in protein hydrolysates.
当混合物中含有在给定溶剂中 Rf 值非常相近的物质时，一维色谱可能无法将其充分分离。双向色谱解决了这一问题。样品点于方形薄层板或纸的一角，用第一种溶剂展开。干燥后，将板旋转 90°，用另一种不同的溶剂沿垂直方向展开。在第一种溶剂中未能分离的组分可能在第二种溶剂中得到分离，在二维平面上分散开来。该技术特别适用于蛋白质水解液中氨基酸的分析。
11. Factors Affecting Chromatographic Separation | 影响色谱分离的因素
Several experimental variables influence the quality of separation. The choice of stationary and mobile phases is paramount. In adsorption chromatography, the polarity of solvents and activity of the adsorbent determine the relative migration rates. A more polar solvent competes more effectively for binding sites, carrying polar solutes further. Temperature affects the solubility and vapour pressure of solutes, especially in GC and partition systems. The particle size of the stationary phase and the column length (in column chromatography, GC and HPLC) directly affect the number of theoretical plates and thus the resolution. Evenness of application, saturation of the chamber with solvent vapour, and avoiding overloading are critical for reproducible planar chromatography.
多个实验变量影响分离质量。固定相和流动相的选择至关重要。在吸附色谱中，溶剂的极性和吸附剂的活性决定相对迁移速率。极性更强的溶剂更有效地竞争结合位点，将极性溶质带得更远。温度影响溶质的溶解度和蒸气压，尤其在 GC 和分配系统中。固定相颗粒大小及柱长（在柱色谱、GC 和 HPLC 中）直接影响理论板数，从而影响分离度。均匀点样、用溶剂蒸气饱和展开缸以及避免超载对实现可重复的平面色谱至关重要。
12. Exam Tips and Common Pitfalls | 应试技巧与常见误区
In CCEA examination questions on chromatography, candidates often lose marks by failing to define Rf clearly or by measuring distances imprecisely. Always state the formula and indicate that both measurements are taken from the origin. When describing a GC or HPLC chromatogram, distinguish between the use of retention time (qualitative) and peak area (quantitative). Be prepared to compare techniques: for example, explain why HPLC is preferred over GC for heat-sensitive compounds, or why TLC gives better resolution than paper chromatography. Diagrams are frequently awarded marks: practise drawing a labelled chromatogram or a schematic of a GC system, showing the injector, column, oven, detector and recorder. Finally, always relate the principle of separation to the relative affinity for stationary and mobile phases – this is at the heart of every chromatography question.
在 CCEA 涉及色谱的考题中，考生常因未能清晰定义 Rf 或距离测量不准确而失分。务必写出公式并指出两项测量值均从原点起计。描述 GC 或 HPLC 色谱图时，要区分保留时间（定性）与峰面积（定量）的用途。准备好比较不同技术的优缺点：例如，说明为何 HPLC 比 GC 更适用于热敏化合物，或为何 TLC 的分辨率优于纸色谱。画图常常能得分：练习绘制标注完善的色谱图或 GC 系统示意图，标明进样器、色谱柱、柱温箱、检测器和记录仪。最后，始终将分离原理与各组分对固定相和流动相的相对亲和力联系起来——这是每个色谱考题的核心。
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