TLC vs Paper Chromatography

Paper chromatography and thin-layer chromatography (TLC) look almost identical: a spot of sample on a baseline, a solvent creeping upwards, and separated spots at the end. Both are measured with the same Rf value. So why do organic chemists almost always reach for TLC, while school labs often use paper? The differences lie in the stationary phase, and they have real practical consequences.

Quick comparison

Feature	Paper chromatography	Thin-layer chromatography (TLC)
Stationary phase	cellulose paper (with water bound to its fibres)	thin layer of silica gel or alumina on glass, plastic or aluminium
Main separation mechanism	mostly partition between water held on the paper and the moving solvent	mostly adsorption onto the polar surface of silica or alumina
Speed	slower (often 30–60 minutes or more)	faster (often 5–20 minutes)
Resolution (sharpness)	lower; spots spread more	higher; spots are tighter
Sensitivity	less sensitive	more sensitive; smaller samples
Solvent choice	mostly water or water-based mixtures	wide range, including many organic solvents
Visualising colourless compounds	locating agents (e.g. ninhydrin for amino acids)	UV light with fluorescent plates, iodine, many stains
Corrosive stains	can’t be used (they’d destroy the paper)	can be used on glass-backed plates
Cost	very cheap	cheap, but more than paper
Typical users	schools, simple dye and ink work	organic chemistry labs, pharmaceuticals, quality control

The stationary phase makes the difference

Paper

Chromatography paper is almost pure cellulose, a polymer covered in –OH groups. These hold a thin layer of water tightly. When a solvent moves up the paper, each substance divides itself between this bound water (the stationary phase) and the moving solvent. This is partition chromatography: substances that dissolve better in the mobile solvent travel further.

Paper is excellent for water-soluble, coloured substances such as inks, food dyes and plant pigments, and for amino acids.

TLC plates

A TLC plate is a sheet of glass, plastic or aluminium foil coated with a thin, even layer of fine particles, usually silica gel (SiO₂) or sometimes alumina (Al₂O₃). The silica surface is covered in polar Si–OH groups. Molecules separate mainly by adsorption: polar molecules stick more strongly to the surface, so they move more slowly; less polar molecules spend more time in the solvent and move further.

Because the particles are small and uniform, the solvent flows evenly and quickly, and spots stay compact.

Why TLC is faster and sharper

• Smaller, more uniform particles give more consistent flow and less spreading.
• Thinner layer: the sample occupies a small area, so spots start and stay small.
• Faster solvent movement: separations take minutes.

This means TLC can distinguish compounds with very similar Rf values that would merge on paper.

Seeing colourless compounds

Most organic compounds are colourless, so visualisation matters.

• TLC with UV: many commercial plates contain a fluorescent indicator that glows green under short-wave UV light (254 nm). Compounds that absorb UV block the glow and appear as dark spots. It’s quick and non-destructive.
• Iodine vapour: a plate placed in a jar with a few iodine crystals develops brown spots where organic compounds absorb iodine.
• Chemical stains: potassium permanganate, ninhydrin and many others react with specific functional groups. On glass or aluminium plates, even strongly acidic or oxidising stains can be used, followed by heating.
• Paper: locating agents can be used too (such as ninhydrin for amino acids), but harsh reagents would damage the paper.

Rf values

Both methods use the same calculation:

Rf = distance moved by substance ÷ distance moved by solvent front

But Rf values for the same compound are not interchangeable between paper and TLC, or even between different solvents or plate types. Always compare an unknown with a reference run on the same plate or paper, at the same time. See Rf value calculations.

Typical uses

Paper chromatography

• separating dyes in inks and food colourings
• identifying amino acids (with ninhydrin)
• separating plant pigments
• school practicals and introductory teaching

See paper chromatography.

TLC

• monitoring reactions: spotting the reaction mixture next to the starting material at intervals shows when the starting material has been used up
• checking purity of products after purification
• choosing a solvent system before running a column (a TLC Rf of about 0.2–0.4 for the target compound is a common guide)
• identifying compounds in pharmaceutical and forensic screening, and in food and herbal analysis

See thin-layer chromatography.

Worked example: choosing the method

Task A: A school class wants to find which dyes are in three brands of coloured sweets. → Paper chromatography. The dyes are coloured and water-soluble, water is a safe solvent, and paper is cheap enough for every group.

Task B: An organic chemist wants to know whether an esterification reaction has finished. → TLC. The compounds are colourless (UV visualisation needed), an organic solvent is required, and results are needed within minutes.

Task C: A student wants to identify amino acids in a hydrolysed protein. → Either works; paper is traditional and inexpensive, while TLC gives faster, sharper separation. Both use ninhydrin to reveal the spots.

Two-way chromatography

Both methods can be run in two dimensions to separate complex mixtures. The sample is spotted in one corner and run with one solvent. The paper or plate is dried, turned through 90°, and run again with a different solvent. Compounds that overlapped in the first direction usually separate in the second, spreading the mixture across the whole sheet. This was historically used to separate the amino acids from a hydrolysed protein on paper, and it works even better on TLC plates.

Cost and practicality in a school

Paper costs a few cents per strip and needs only a beaker and a lid. TLC plates cost more, often need a UV lamp to see the spots, and usually use organic solvents that must be handled in a fume cupboard. For younger students, paper is the obvious first choice; TLC is a natural next step in advanced courses where organic synthesis is taught.

Practical tips common to both

• Draw the baseline in pencil.
• Keep the baseline above the solvent level.
• Use small, concentrated spots.
• Cover the tank to keep it saturated with vapour.
• Mark the solvent front immediately.
• Handle TLC plates by the edges; fingerprints contain organic compounds that show up under stains.

A step up: HPTLC and instrumental methods

High-performance TLC uses even finer particles and automated application and scanning, giving quantitative results. For fully quantitative separation of complex mixtures, labs use gas chromatography or HPLC, which apply the same principles in a column. See gas chromatography vs HPLC.

Key takeaways

• Paper chromatography uses cellulose with bound water and separates mainly by partition; TLC uses silica or alumina and separates mainly by adsorption.
• TLC is faster, sharper and more sensitive, and works with a wider range of solvents and visualisation methods.
• Paper is cheap and ideal for coloured, water-soluble substances in teaching.
• TLC is the everyday tool of organic chemists for monitoring reactions and checking purity.
• Rf values depend on the system, so always run references alongside unknowns.