📚 Chromatography: Separating Mixtures | 色谱法：分离混合物
Chromatography is a powerful separation technique used to separate mixtures of dissolved substances, especially coloured ones such as inks, dyes and food colourings. Instead of using evaporation or filtration, chromatography separates components by making them move at different speeds across a surface.
色谱法是一种重要的分离技术，用于分离溶解在水中的混合物，尤其是墨水、染料和食用色素等有色物质。它不依靠蒸发或过滤，而是让各组分在一种表面上以不同速度移动，从而将它们分开。
1. What Is Chromatography? | 什么是色谱法？
In chemistry, a mixture contains two or more substances that are not chemically joined. Some mixtures can be separated by simple physical methods such as filtration or distillation. Chromatography is used when you need to separate several dissolved substances that are all mixed together, particularly when they are coloured.
在化学中，混合物含有两种或两种以上没有化学结合的物质。有些混合物可以通过过滤或蒸馏等简单物理方法分离。当你需要分离几种混合在一起的溶解物质，特别是它们有颜色时，就要用到色谱法。
The name 'chromatography' comes from the Greek words 'chroma' meaning colour and 'graphein' meaning to write. Early scientists used it to separate plant pigments, but today it works for both coloured and colourless substances.
色谱法这个名字源自希腊语 'chroma'（颜色）和 'graphein'（书写）。早期科学家用它来分离植物色素，但如今它既能分离有色物质，也能分离无色物质。
2. Why Do We Need Chromatography? | 为什么需要色谱法？
Filtration is only able to separate an insoluble solid from a liquid, such as sand from water. Distillation can separate a solvent from a dissolved solid, such as pure water from salt solution. However, when several soluble dyes are mixed together in one solution, neither filtration nor distillation can show how many dyes are present.
过滤只能把不溶性固体从液体中分离，例如将沙子从水中分离。蒸馏可以把溶剂从溶解的固体中分离，例如从盐水中得到纯水。然而，当多种可溶性染料混合在同一种溶液中时，过滤和蒸馏都无法显示其中有多少种染料。
Chromatography solves this problem because the different dyes move through a medium at different rates. This allows scientists to separate and identify each dye in the mixture.
色谱法解决了这个问题，因为不同的染料在介质中移动的速率不同。这使得科学家能够分离并鉴定混合物中的每一种染料。
3. Mobile Phase and Stationary Phase | 流动相和固定相
All chromatographic techniques rely on two phases. The stationary phase stays still, and the mobile phase moves through it. In paper chromatography the paper is the stationary phase and the solvent is the mobile phase.
所有色谱技术都依赖两个相。固定相保持不动，流动相从中流过。在纸色谱法中，纸是固定相，溶剂是流动相。
A component's movement depends on how strongly it is attracted to the stationary phase compared with the mobile phase. Substances that are more attracted to the mobile phase travel further; substances that are more attracted to the stationary phase stay closer to the baseline.
组分的移动取决于它对固定相和流动相的相对吸引力。对流动相吸引力更强的物质移动得更远；对固定相吸引力更强的物质停留在离基线更近的位置。
| Phase (相) | In paper chromatography (在纸色谱中) | Role (作用) |
|---|---|---|
| Stationary phase (固定相) | Chromatography paper (色谱纸) | Stays fixed and interacts with the components (保持固定，与组分相互作用) |
| Mobile phase (流动相) | Solvent such as water or ethanol (水或乙醇等溶剂) | Moves upwards and carries the components (向上移动并携带组分) |
4. Paper Chromatography: The Basic Setup | 纸色谱法：基本装置
A simple paper chromatography experiment requires a strip of chromatography paper, a beaker, a suitable solvent, a pencil, a capillary tube or splint, and the mixture to be tested. The paper must be able to absorb the solvent without disintegrating.
一个简单的纸色谱实验需要一条色谱纸、一个烧杯、合适的溶剂、一支铅笔、一根毛细管或细木条，以及待测混合物。纸必须能吸收溶剂且不变形。
It is important to use a pencil to draw the baseline, not a pen. Ink from a pen would dissolve in the solvent and move up the paper, contaminating the results.
用铅笔画基线很重要，不能使用钢笔。钢笔的墨水会溶解在溶剂中并沿纸上移，从而污染实验结果。
The baseline should be drawn in pencil above the level of the solvent. If the baseline is below the solvent surface, the sample spot will wash off into the solvent.
基线应用铅笔绘制，并位于溶剂液面之上。如果基线低于溶剂表面，样品点会被洗入溶剂中。
5. Step-by-Step Method | 分步实验方法
Step 1: Draw a pencil line across the paper about 2 cm from one end.
步骤1：在距纸一端约2厘米处用铅笔画一条线。
Step 2: Place a small spot of the mixture on the centre of the pencil line using a capillary tube.
步骤2：用毛细管将少量混合物点在铅笔线中央。
Step 3: Pour solvent into a beaker to a depth below the pencil line.
步骤3：往烧杯中倒入溶剂，液面低于铅笔线。
Step 4: Suspend the paper so the bottom dips into the solvent but the spot remains above the liquid.
步骤4：悬挂纸张，使底部浸入溶剂，但样品点保持在液面以上。
Step 5: Allow the solvent to rise up the paper and carry the mixture components.
步骤5：让溶剂沿纸上移并携带混合物各组分。
Step 6: Before the solvent reaches the top,
Published by TutorHao | KS3 Chemistry Revision Series | aleveler.com
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