What Is Chromatography Paper? How Paper Chromatography Works

Chromatography paper is a plain-looking sheet of absorbent cotton paper with one job: separating a mixture into its individual components so you can see what it's actually made of. Dip one end in a coloured ink and it will pull that ink apart into a small rainbow of pigments in a matter of minutes.

It still shows up in school laboratories across South Africa, in forensic ink analysis, and in food and pharmaceutical testing, even though more advanced lab techniques exist. This guide covers what it is, how the separation actually works, how to run the experiment safely, and how to read your results.

What Is Chromatography Paper?

Chromatography paper is a highly absorbent, uniform sheet made from pure cotton cellulose. SmartLabs stocks paper equivalent to Whatman Grade 1CHR, a long-standing industry reference grade, made by Ahlstrom-Munksjö from 100% alpha cotton cellulose with no added sizing or fillers. That purity matters: any contaminants in the paper itself would show up as extra bands in your results and ruin the separation.

It's a physical separation technique, not a chemical reaction. Nothing in the sample changes composition. The paper simply lets you see substances that are normally mixed together, moving apart at different speeds.

How Does Paper Chromatography Work?

Paper chromatography relies on two things moving at different rates: a stationary phase and a mobile phase.

• The stationary phase is the chromatography paper itself. It stays put and holds onto the substances in your sample to varying degrees.
• The mobile phase is the solvent, usually water or alcohol, that travels up the paper by capillary action, carrying the sample's components along with it.

Different substances in a mixture are attracted to the paper (and to the solvent) by different amounts. A component that clings more tightly to the paper moves slowly. A component that dissolves more readily in the solvent gets carried further, faster. Over a few minutes, one spot of ink separates into several distinct bands of colour, each travelling a different distance up the paper.

Types of Chromatography Paper

Not all chromatography paper is the same, and the differences affect how clean your results are.

• Grade and purity. SmartLabs supplies chromatography paper equivalent to Whatman Grade 1CHR, made from 100% alpha cotton cellulose at 0.19mm thickness, with controlled and uniform absorption across the sheet. This consistency is what gives you a clean, repeatable separation instead of smudged or uneven bands.
• Sheet size. We stock two standard sizes: 200mm x 200mm and 100mm x 300mm, both supplied in packs of 100 sheets. The larger square sheets suit multiple samples run side by side, while the narrower strips are convenient for single-sample classroom demonstrations.
• General purpose vs specialised grades. Standard chromatography paper, like the grade SmartLabs supplies, covers classroom paper chromatography, ink analysis, and general separation work. More specialised electrophoresis and blotting papers exist for research applications such as Southern, Northern, and Western blotting, which use similar high-purity cotton cellulose but are optimised for different techniques.

How to Run a Paper Chromatography Experiment: Step by Step

1. Cut a strip of chromatography paper. A strip roughly 2 to 3cm wide and long enough to hang into your container without the bottom edge touching the base works well.
2. Draw a pencil line near the bottom. About 2cm from the bottom edge, draw a faint pencil line across the strip. Use pencil, not pen, since ink from a marker would dissolve and interfere with your results.
3. Add your sample spot. Place a small, concentrated dot of ink, food dye, or crushed plant pigment on the pencil line. Keep it small. A large, spread-out spot gives blurry, overlapping bands.
4. Let the spot dry. Give it a minute before continuing, so the sample doesn't wash straight off the paper once it touches the solvent.
5. Suspend the strip in solvent. Pour a shallow layer of solvent into a beaker, enough to sit just below your pencil line, and hang the strip so only the very bottom touches the liquid. The sample spot itself must stay above the solvent line.
6. Wait for the solvent to rise. Capillary action draws the solvent up the paper, carrying the separating pigments with it. This typically takes several minutes, depending on the paper and solvent.
7. Remove and mark the solvent front. Take the strip out before the solvent reaches the top, and immediately draw a pencil line at the highest point the solvent reached. This is your solvent front, and you'll need it to calculate Rf values.
8. Let it dry and compare your bands. Once dry, you should see your original sample separated into distinct coloured bands at different heights up the strip.

Reading Your Results: What Is an Rf Value?

Once you have a finished chromatogram, you can describe each band numerically using its Rf value, short for retention factor.

Rf = distance travelled by the substance ÷ distance travelled by the solvent

Measure from the original pencil line (not the bottom of the paper) to the centre of each coloured band, then divide that by the distance from the same pencil line to your solvent front mark. Rf values always fall between 0 and 1. A value close to 1 means the substance travelled almost as far as the solvent, meaning it had a low attraction to the paper. A value close to 0 means it barely moved, staying close to the paper.

Rf values are specific to a particular paper, solvent, and temperature. They're most useful for comparing an unknown sample against a known reference run under the same conditions, which is exactly how forensic labs use chromatography to match an ink sample to a suspect pen or document.

Common Solvents Used in Paper Chromatography

The solvent you choose has a big effect on how well your sample separates. Here's a starting reference for common school and general lab use.

If you're separating plant pigments such as chlorophyll for a biology practical, note that water and isopropyl alcohol alone often won't separate them well. That separation typically needs a less polar solvent mixture, run under proper lab supervision because of the fire and fume risk.

Where Chromatography Paper Is Used in Real Life

• Education. Grade 10 to 12 practicals on separating mixtures, plant pigment analysis, and ink analysis, mapped to the CAPS curriculum.
• Forensic science. Comparing ink from a questioned document against a suspect pen, or analysing dyes and other trace evidence.
• Food and beverage testing. Checking food dyes for authenticity or detecting undeclared colourants.
• Pharmaceutical quality control. Confirming that a compound is present and reasonably pure before more precise instrumental testing.
• Molecular biology research. High-purity cotton cellulose papers of this type are also used in blotting and electrophoresis techniques such as Southern, Northern, and Western blots.
• Environmental testing. Basic screening of water samples for certain dissolved dyes and contaminants.

Chromatography Paper vs Filter Paper: What's the Difference?

These two often get confused, since both are plain-looking sheets of absorbent paper, and some suppliers even use the terms loosely.

• Choose chromatography paper when you need to separate a mixture into its components, based on differences in how strongly each one clings to the paper versus the solvent.
• Choose qualitative filter paper when you need to physically separate a solid from a liquid, such as removing precipitate from a solution. Filter paper works by trapping solid particles as liquid passes through, not by separating dissolved substances from each other.

Chromatography paper is manufactured to a tighter, more uniform standard specifically so that the rate of solvent movement is controlled and consistent across the sheet. Ordinary filter paper isn't held to that same standard, so results from using it for chromatography tend to be less reliable.

Tips for Better Chromatography Results

• Use pencil, never pen, for your baseline. Ink from a pen or marker will dissolve in the solvent and add noise to your results.
• Keep the sample spot small and concentrated. A large or diluted spot spreads into blurry, overlapping bands instead of clean, distinct ones.
• Keep the solvent level below the sample spot. If the spot itself sits in the solvent, it will simply dissolve away into the liquid instead of travelling up the paper.
• Use a covered container where possible. An open beaker lets the solvent evaporate unevenly and can slow or distort the separation. A jar with a loose lid works better.
• Mark your solvent front immediately. Once you remove the strip, the solvent keeps evaporating and spreading, so mark the front line right away or your Rf calculations will be off.
• Handle dry strips carefully. Finished chromatograms are fragile and the colour bands can smudge if touched. Handle them by the edges.

Frequently Asked Questions About Chromatography Paper

What is chromatography paper used for?

Chromatography paper is used to separate a mixture into its individual components, most commonly to separate the dyes in ink or the pigments in plant material. It's used in school science practicals, forensic ink analysis, food testing, and pharmaceutical quality control.

How does paper chromatography separate substances?

A solvent moves up the paper by capillary action, carrying the sample with it. Substances that cling more tightly to the paper move slowly, while substances that dissolve more readily in the solvent are carried further and faster, which separates a mixture into distinct bands.

What is an Rf value in chromatography?

The Rf value, or retention factor, is the distance a substance travels divided by the distance the solvent travels, measured from the same starting line. It's always between 0 and 1, and it's used to help identify or compare substances run under the same conditions.

Can you reuse chromatography paper?

No. Chromatography paper is single use. Once a sample has been run through it, the paper holds the separated pigments permanently and can't be reset for another test.

What is the difference between chromatography paper and filter paper?

Chromatography paper is manufactured to a controlled, uniform standard for separating dissolved substances by how they move with a solvent. Filter paper is designed to physically trap solid particles while liquid passes through it. They serve different purposes, even though both are absorbent paper sheets.

Where can I buy chromatography paper in South Africa?

SmartLabs supplies chromatography paper equivalent to Whatman Grade 1CHR to schools, universities, and industrial customers across South Africa. We ship nationwide from Johannesburg with traceable courier delivery.

Final Word

Paper chromatography has stayed in classrooms and labs for one simple reason: it turns an invisible mixture into something you can actually see, using nothing more exotic than paper and a solvent. Whether you're running a Grade 10 separating mixtures practical, checking a food dye, or comparing ink samples, a strip of chromatography paper still gets you a clear, visible answer.

If you supply a school, run a lab, or just need a reliable source of chromatography and separation supplies, browse the full SmartLabs range or get in touch. We're always happy to help you choose the right tool for the job.