📚 Chromatography: Key Points for IB and OCR Chemistry | 色谱：IB和OCR化学考点精讲
Chromatography is an essential analytical technique in IB and OCR chemistry, used to separate, identify, and quantify components in complex mixtures. Understanding its principles, types, and calculations is critical for exam success, as questions often involve interpreting chromatograms, calculating Rf values, and explaining separation mechanisms. This guide covers the core concepts, instrumental methods, and common pitfalls for chromatography, tailored to both IB and OCR specifications.
色谱是IB和OCR化学中一种重要的分析技术，用于分离、鉴定和定量复杂混合物中的组分。掌握其原理、类型和计算对于考试成功至关重要，因为考题往往涉及解读色谱图、计算Rf值以及解释分离机理。本指南涵盖了色谱的核心概念、仪器方法以及常见易错点，贴合IB和OCR的考试大纲要求。
1. Introduction to Chromatography | 色谱导论
The term ‘chromatography’ originates from Greek meaning ‘colour writing’, although colour is not required for modern applications. Any chromatographic system consists of a stationary phase and a mobile phase. The mobile phase moves through or over the stationary phase, carrying the components of the mixture. Differential partitioning or adsorption between the two phases causes separation. In IB and OCR contexts, candidates must be able to describe how the balance between intermolecular forces and phase affinities drives separation.
“色谱”一词源自希腊语，意为“用颜色书写”，但在现代应用中不一定需要颜色。所有色谱系统都包含固定相和流动相。流动相穿过或在固定相上方移动，携带混合物中的组分。组分在两相之间的差异分配或吸附导致了分离。在IB和OCR化学中，考生需要描述分子间作用力与相亲和力之间的平衡如何驱动分离。
The fundamental principle is that components with a stronger interaction with the stationary phase move more slowly, while those more soluble in the mobile phase or having a higher vapour pressure (in GC) move faster. Key intermolecular forces include hydrogen bonding, dipole-dipole interactions, and London dispersion forces. The separation efficiency depends on temperature, solvent polarity, and the nature of the stationary phase.
基本原理是：与固定相作用更强的组分移动较慢，而在流动相中溶解度更高或蒸气压更高（在气相色谱中）的组分移动较快。关键的分子间作用力包括氢键、偶极-偶极作用和伦敦色散力。分离效率取决于温度、溶剂极性以及固定相的性质。
2. Principles of Separation | 分离原理
Chromatography relies on the distribution of a solute between two immiscible phases. This distribution is described by the partition coefficient K, defined as the ratio of the concentration of the component in the stationary phase to its concentration in the mobile phase. In adsorption chromatography, the stationary phase is a solid on which solute molecules are adsorbed; in partition chromatography, the stationary phase is a liquid coated on an inert solid support.
色谱法依赖溶质在两个不混溶相之间的分配。这种分配通过分配系数K来描述，K定义为组分在固定相中的浓度与其在流动相中浓度的比值。在吸附色谱中，固定相是一种固体，溶质分子吸附在其表面；在分配色谱中，固定相是涂覆在惰性固体载体上的液体。
The mobile phase can be a liquid, a gas, or a supercritical fluid. During separation, components repeatedly transfer between the mobile and stationary phases; this is called multiple equilibria. The more time a component spends in the mobile phase, the faster it migrates. This dynamic equilibrium distinguishes chromatography from simple extraction techniques.
流动相可以是液体、气体或超临界流体。在分离过程中，组分反复在流动相和固定相之间转移，这称为多重平衡。一种组分在流动相中停留的时间越多，其迁移速度就越快。这种动态平衡使色谱区别于简单的萃取技术。
3. Paper Chromatography | 纸色谱
Paper chromatography is a simple planar technique commonly used in school laboratories. The stationary phase is water adsorbed on cellulose paper fibres, and the mobile phase is a suitable solvent or solvent mixture. The paper acts as support for the stationary liquid; separation is primarily due to partition between the liquid phases. It is excellent for separating polar compounds such as amino acids, dyes, and sugars.
纸色谱是一种简单的平面色谱技术，常用于中学实验室。固定相是吸附在纤维素纸纤维上的水，流动相是合适的溶剂或混合溶剂。滤纸充当固定液体的支撑体；分离主要是基于两液相之间的分配。纸色谱非常适合分离氨基酸、染料和糖类等极性化合物。
To set up, a small spot of the sample is placed above the solvent level in a sealed chamber. The solvent rises by capillary action, carrying components at different rates. After the solvent front has moved approximately 80% up the paper, the chromatogram is removed, dried, and visualised, often under UV light or by staining (e.g., ninhydrin for amino acids).
实验步骤：将少量样品点在铅笔标记的原点线上，原点须高于展开剂液面。在密闭层析缸中，溶剂通过毛细作用上升，以不同速率携带各组分。当溶剂前沿移动约纸张高度的80%时，取出色谱图晾干，并用紫外灯或染色剂（如用于氨基酸的茚三酮）显色。
4. Thin-Layer Chromatography (TLC) | 薄层色谱 (TLC)
TLC uses a glass, plastic, or aluminium plate coated with a thin layer of adsorbent such as silica gel (SiO₂) or alumina (Al₂O₃). The stationary phase is the solid adsorbent, and separation is based on adsorption and desorption of components. A small drop of the sample is spotted at the bottom, and the plate is placed in a developing chamber containing a shallow layer of mobile phase.
薄层色谱使用涂有薄层吸附剂（如硅胶SiO₂或氧化铝Al₂O₃）的玻璃、塑料或铝板。固定相为固体吸附剂，分离基于组分的吸附与解吸。将一小滴样品点在板的下端，然后将板放入盛有少量流动相的展开缸中。
TLC offers faster runs, better resolution, and greater flexibility than paper chromatography because the particle size of the stationary phase can be controlled. It is widely used in organic synthesis to monitor reaction progress, check purity, and compare unknown substances against reference standards. Visualisation is often done with iodine vapour, UV fluorescence quenching, or specific spray reagents.
TLC比纸色谱运行更快、分辨率更好且更灵活，因为可以控制固定相的粒径。它广泛用于有机合成中监测反应进程、检查纯度以及将未知物与标准品进行比对。显色常采用碘蒸气、紫外荧光猝灭或特定喷雾显色剂。
5. Column Chromatography | 柱色谱
Column chromatography is a preparative technique used to separate and collect individual components from a mixture. A vertical glass column is packed with a stationary phase (e.g., silica or alumina) and equilibrated with the mobile phase. The sample is introduced at the top, and the mobile phase (eluent) is passed through continuously. Fractions are collected at timed intervals.
柱色谱是一种制备技术，用于从混合物中分离并收集各个组分。垂直的玻璃柱中填充固定相（如硅胶或氧化铝），并以流动相平衡。将样品从柱顶加入，然后连续加入流动相（洗脱液），并在不同时间段收集流出组分。
The separation mechanism is similar to TLC but on a larger scale. Components that interact weakly with the stationary phase elute first, while those that adsorb strongly elute later. Changing the solvent polarity during elution (gradient elution) can improve separation of complex samples. This technique is widely used in organic laboratories to purify reaction products.
分离机理与TLC相似，但规模更大。与固定相作用弱的组分首先被洗脱，而吸附力强的组分后被洗脱。在洗脱过程中改变溶剂极性（梯度洗脱）可以改善复杂样品的分离效果。该技术广泛用于有机实验室中提纯反应产物。
6. Gas Chromatography (GC) | 气相色谱 (GC)
Gas chromatography is an instrumental method that separates volatile, thermally stable compounds. The mobile phase is an inert carrier gas (e.g., helium, nitrogen). The mixture is injected into a heated injector, vaporised, and swept onto a capillary column containing a liquid stationary phase coated on the inner wall (or a solid stationary phase in gas-solid chromatography). Separation occurs as components partition between the gas phase and the liquid stationary phase.
气相色谱是一种仪器分析方法，用于分离挥发性且热稳定的化合物。流动相为惰性载气（如氦气、氮气）。混合物注入加热的进样口后被气化，并被带入毛细管柱，柱内壁涂有液体固定相（气-固色谱中则为固体固定相）。当组分在气相与液体固定相之间分配时，即实现分离。
The column is housed in a temperature-controlled oven. Components are detected as they exit the column by a detector, such as a flame ionisation detector (FID) or a thermal conductivity detector (TCD). The resulting gas chromatogram displays a series of peaks; the retention time tᵣ is characteristic of each compound under fixed conditions. Peak area is proportional to the amount of the component, enabling quantitative analysis.
色谱柱置于温控炉中。组分从柱中流出后被检测器（如火焰离子化检测器FID或热导检测器TCD）检测。所得气相色谱图显示一系列色谱峰；在固定条件下，保留时间tᵣ是每种化合物的特征参数。峰面积与组分的含量成正比，可用于定量分析。
7. High-Performance Liquid Chromatography (HPLC) | 高效液相色谱 (HPLC)
HPLC is a powerful technique that uses high-pressure pumps to force the mobile phase through a column packed with very fine, uniform particles of stationary phase (typically 3–10 µm). This improves separation efficiency and speed compared to traditional column chromatography. It is suitable for non-volatile, thermally labile, or polar compounds that cannot be analysed by GC.
高效液相色谱（HPLC）使用高压泵迫使流动相通过填充有非常细小且均匀的固定相颗粒（通常3–10µm）的色谱柱，与传统柱色谱相比，这大大提高了分离效率和速度。HPLC适用于不能通过GC分析的非挥发性、热不稳定或极性化合物。
The most common mode is reversed-phase HPLC, where the stationary phase is non-polar (e.g., C₁₈ hydrocarbon chains bonded to silica) and the mobile phase is polar (e.g., water–methanol or water–acetonitrile mixtures). In normal-phase HPLC, the stationary phase is polar. A UV–vis detector is often used. Retention time and peak area serve the same diagnostic roles as in GC.
最常见的模式是反相高效液相色谱，其中固定相为非极性（例如键合在硅胶上的C₁₈烃链），流动相为极性（例如水-甲醇或水-乙腈混合物）。在正相高效液相色谱中，固定相为极性。通常使用紫外-可见检测器。保留时间和峰面积的作用与气相色谱中相同。
8. Retention Factor (Rf) Calculations | 保留因子 (Rf) 计算
For planar methods (paper and TLC), the retention factor Rf is a dimensionless number used to identify a substance. It is defined as the distance moved by the centre of the spot divided by the distance moved by the solvent front, both measured from the origin.
对于平面色谱法（纸色谱和薄层色谱），保留因子Rf是一个无量纲的数值，用于鉴定物质。它的定义是斑点中心移动的距离除以溶剂前沿移动的距离，两者均从原点开始测量。
Rf = dₛₚₒₜ / dₛₒₗᵥₑₙₜ
This value always lies between 0 and 1. An Rf of 0 means the component did not move, while an Rf close to 1 indicates it moved almost with the solvent front. Rf values are reproducible only if conditions (temperature, solvent, stationary phase) are kept constant. Always measure to the centre of the spot and label all distances clearly on diagrams in exams.
该值始终在0与1之间。Rf为0表示组分未移动，而Rf接近1表示其几乎随溶剂前沿一起移动。仅当条件（温度、溶剂、固定相）保持一致时，Rf值才具有重现性。务必测量至斑点中心，并在考试的图表上清晰地标示所有距离。
In instrumental chromatography (GC and HPLC), retention time tᵣ is used instead. The adjusted retention time t’ᵣ = tᵣ – tₘ, where tₘ is the time taken for an unretained solute to pass through the column (dead time). The relative retention (separation factor α) can be calculated as the ratio of adjusted retention times for two neighbouring peaks.
在仪器色谱法（气相色谱和高效液相色谱）中，改用保留时间tᵣ。调整保留时间t’ᵣ = tᵣ – tₘ，其中tₘ是非滞留溶质穿过色谱柱所需的时间（死时间）。相对保留值（分离因子α）可计算为相邻两峰调整保留时间之比。
9. Interpreting Chromatograms | 色谱图解读
A chromatogram is the visual output of a separation. In planar chromatography, it shows spots at specific distances; in instrumental methods, it is a plot of detector response against time. The number of peaks corresponds to the number of separable components in the mixture. Peak height or area is related to the quantity present, while the position (Rf or tᵣ) gives qualitative identification when compared with standards.
色谱图是分离的可视化输出结果。在平面色谱中，它表现为特定距离上的斑点；在仪器方法中，它是检测器响应值对时间所作的图。峰的数量对应于混合物中可分离组分的数量。峰高或峰面积与存在量相关，而峰的位置（Rf或tᵣ）在与标准品比较时可给出定性鉴定信息。
Peak symmetry is important: tailing (asymmetric peaks) can indicate overloading, strong adsorption sites, or dead volumes in the system. Resolution between two adjacent peaks must be sufficient for accurate quantification. A common criterion is baseline resolution, where the valleys between peaks return to the baseline. The efficiency of a column is expressed as the number of theoretical plates N, calculated from peak width and retention time.
峰对称性非常重要：拖尾（不对称峰）可能表示过载、强吸附位点或系统死体积。相邻两峰之间的分离度必须足以进行精确定量。一个常用标准是基线分离，即峰间凹槽回到基线。色谱柱的柱效以理论塔板数N表示，通过峰宽和保留时间计算。
10. Factors Affecting Separation | 影响分离的因素
Separation quality is influenced by the nature of the mobile phase, the stationary phase, temperature, flow rate, and sample size. In liquid chromatography (paper, TLC, column, HPLC), the polarity of the solvent system determines how strongly it competes with the stationary phase for solute molecules. A more polar mobile phase in normal-phase systems reduces retention, while in reversed-phase it increases retention.
分离质量受流动相性质、固定相、温度、流速和进样量的影响。在液相色谱（纸色谱、薄层色谱、柱色谱、高效液相色谱）中，溶剂体系的极性决定了它与固定相争夺溶质分子的能力。在正相体系中，极性更强的流动相会降低保留，而在反相体系中则会增加保留。
Temperature affects solubility, vapour pressure (in GC), and the kinetics of mass transfer. Higher temperatures typically decrease retention times in GC and LC but may also degrade thermally labile samples. In GC, the oven temperature is often programmed to ramp up during the run, which sharpens peaks and reduces analysis time. Column length and stationary-phase film thickness also directly impact separation.
温度会影响溶解度、蒸气压（气相色谱中）以及传质动力学。较高的温度通常会缩短气相色谱和液相色谱中的保留时间，但也可能导致热不稳定样品的降解。在气相色谱中，常常采用程序升温，在运行过程中逐渐升高温度，这可以使峰形变尖锐并缩短分析时间。柱长和固定相液膜厚度也直接影响分离效果。
11. Applications and Experimental Tips | 应用与实验技巧
Chromatography is used across forensic science, pharmaceuticals, environmental monitoring, and food analysis. In IB and OCR exams, you may be asked to suggest a suitable chromatographic method for a given scenario, interpret food dye or ink separations, or explain how chromatography can test the purity of aspirin synthesised in the lab. HPLC is routinely used to determine drug concentrations in blood, while GC is used to analyse alcohol levels in breath or fermentation products.
色谱法广泛应用于法医学、制药、环境监测和食品分析等领域。在IB和OCR考试中，你可能会被要求为某个给定情境建议合适的色谱方法、解释食用色素或墨水的分离，或说明如何利用色谱检验实验室合成的阿司匹林的纯度。HPLC常用于测定血液中的药物浓度，而GC则用于分析呼吸中的酒精含量或发酵产物。
Key experimental tips: always wear PPE; spot samples using a fine capillary tube to keep spots small and concentrated; never let the solvent level touch the spot on a TLC plate or paper; allow the solvent front to run to within 1 cm of the top; mark the solvent front immediately after removal; and dry plates in a fume cupboard when using organic solvents. For column chromatography, do not let the column run dry.
关键的实验技巧包括：始终穿着个人防护装备；使用内径小的毛细管点样，保持斑点小且浓；切勿让溶剂液面触及薄层板或色谱纸上的点样处；让溶剂前沿运行至距顶端约1厘米处停止；取出后立即标记溶剂前沿；使用有机溶剂时在通风橱内干燥薄层板。对于柱色谱，切勿让色谱柱流干。
12. Common Exam Questions and Mistakes | 常见考题与易错点
Exam questions frequently ask students to calculate Rf values from a diagram, identify which component has the strongest adsorption to the stationary phase (lowest Rf or longest tᵣ), or explain why a particular solvent mixture is chosen. Another typical task is to deduce the composition of an unknown mixture by comparing its chromatogram with those of standards. In GCSE/IGCSE style questions, marking the origin and solvent front correctly is essential.
考题常常要求学生根据图表计算Rf值、识别哪个组分对固定相的吸附最强（Rf最小或tᵣ最长），或解释为何选择某种溶剂混合物。另一典型任务是，通过将未知混合物色谱图与标准品色谱图进行对比，推断其组成。在GCSE/IGCSE风格的试题中，正确标注原点与溶剂前沿至关重要。
Common mistakes include failing to measure Rf from the centre of the spot, confusing adsorption with absorption, reversing the order of elution in normal and reversed-phase systems, and assuming that a peak with the largest area always corresponds to the highest concentration without considering detector response factors. Also, students often forget that Rf is unitless and must be reported without units. In TLC, using ink to draw the baseline can introduce contamination; always use pencil.
常见错误包括：未从斑点中心测量Rf；混淆吸附与吸收；颠倒了正相和反相体系中的洗脱顺序；在未考虑检测器响应因子的情况下，认为面积最大的峰总是对应于最高浓度。此外，学生常忘记Rf是一个无量纲量，报告时不应带有单位。在薄层色谱中，使用墨水绘制基线可能引入污染，应始终使用铅笔。
Published by TutorHao | Chemistry Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
屏轩国际教育cambridge primary/secondary checkpoint, cat4, ukiset,ukcat,igcse,alevel,PAT,STEP,MAT, ibdp,ap,ssat,sat,sat2课程辅导，国外大学本科硕士研究生博士课程论文辅导