← Lab Calculator Free · No sign up · Instant

🧬 TLC to Flash Method Converter

Estimate flash chromatography elution volume from a TLC Rf value, and check separation from a nearby impurity.

TLC Rf of Target Compound

Rf of Nearest Impurity optional

Estimated Elution Volume

— CV

💡 Note: This uses the classical rule of thumb (Still, Kahn & Mitra, 1978) that a compound elutes from a flash column at roughly 1/Rf column volumes under the same solvent system used on TLC. Actual elution volume varies with silica batch, loading, and flow rate — always confirm with fraction TLC during the run.

📖 Example: TLC Rf = 0.35 in the chosen solvent system → elutes at approximately 1/0.35 ≈ 2.9 column volumes. If the nearest impurity has Rf = 0.20, ΔRf = 0.15 — right at the minimum recommended for clean separation.

Frequently asked questions

Why does a lower Rf mean a higher elution volume?

Rf measures how far a compound travels relative to the solvent front on TLC — a low Rf means the compound is strongly retained by the stationary phase. The same retention behavior on a flash column means the compound needs more column volumes of solvent to elute, hence the inverse relationship (1/Rf).

What ΔRf do I need for a clean separation?

The classical Still, Kahn and Mitra (1978) guideline recommends a minimum ΔRf of 0.15 between the target compound and its nearest impurity on TLC to achieve clean baseline separation on a flash column using the same solvent system.

Does this work for gradient flash runs, or only isocratic?

This estimate is based on a single, fixed solvent system (isocratic), matching the TLC conditions used to measure Rf. For gradient runs, the elution point will differ from this static estimate since solvent strength changes during the run — use this as a starting isocratic reference point instead.

Accuracy & how this is derived

Derivation: Classical flash chromatography elution approximation (Still, Kahn, Mitra, 1978): elution volume in column volumes is approximately the reciprocal of the compound's TLC Rf under the same solvent system.

Validated against: Still, W. C.; Kahn, M.; Mitra, A. J. Org. Chem. 1978, 43, 2923 — the original flash chromatography methodology paper.

⚠️ For educational and research support only — verify critical results independently before use in regulated, clinical, or publication-bound work.

✔ Last updated: July 2026 · Report an error

From TLC to flash chromatography: predicting elution volume

Flash chromatography purification is typically planned from a TLC Rf value determined in the same solvent system, using the classical approximation that a compound elutes from a silica column at roughly the reciprocal of its Rf in column volumes. This simple rule, introduced by Still, Kahn and Mitra in their original 1978 flash chromatography paper, provides chemists a fast way to estimate roughly when a compound of interest will come off the column and to check whether a nearby impurity is likely to co-elute, without needing to run the full purification blind.