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🧪 Solvent System Selector

Predict the solvent ratio (%B) needed to achieve a target Rf, based on two known TLC test runs at different solvent strengths.

Two known test runs (solvent %B vs. observed Rf):

Test 1 — %B e.g. 20% EtOAc in hexane

Test 1 — Observed Rf

Test 2 — %B

Test 2 — Observed Rf

Target Rf typically 0.25-0.35 for flash

Predicted %B for Target Rf

—%

💡 Note: This linear interpolation is most reliable when your two test points bracket the target Rf and are reasonably close together (within ~20-30% B of each other) — solvent polarity vs. Rf is not perfectly linear over wide ranges. Always confirm the predicted ratio with a fresh TLC spot before committing to a full flash run.

📖 Example: 20% B → Rf 0.15; 40% B → Rf 0.55; target Rf = 0.30: %B = 20 + (40-20)×(0.30-0.15)/(0.55-0.15) = 20 + 20×0.375 = 27.5% B.

Frequently asked questions

Why do I need two test TLC runs first?

Predicting the solvent ratio for a target Rf requires knowing how Rf changes with solvent polarity for your specific compound and solvent system. Two test points let this calculator interpolate linearly between them, which is far more reliable than guessing a ratio from scratch.

What target Rf should I aim for in flash chromatography?

A target Rf of 0.25-0.35 is a common recommendation for flash purification — high enough to elute in a reasonable volume, low enough to allow good separation from impurities with different Rf values.

What if my target Rf is outside the range of my two test points?

This calculator performs linear interpolation, which is more reliable within the range bracketed by your two test points than when extrapolating outside it. If your target Rf falls outside that range, consider running a third test point closer to your target for a more reliable prediction.

Accuracy & how this is derived

Derivation: Linear interpolation between two known (%B, Rf) data points, solved for the %B corresponding to a target Rf value. Assumes an approximately linear relationship between solvent strength and Rf over the interpolated range.

Validated against: Standard linear interpolation approach; most reliable when the two test points are reasonably close together and bracket the target Rf, consistent with common TLC method development practice.

⚠️ 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

Predicting TLC solvent systems by interpolation

Selecting a solvent system for TLC or flash chromatography is often done by trial and error, running a compound at several solvent ratios until an Rf in the desired range is found. Linear interpolation between two test points offers a faster, more systematic route to that target: because Rf typically increases smoothly with solvent polarity over a moderate range, two known (percent B, Rf) data points bracketing the target allow the required solvent ratio to be estimated directly rather than guessed at through additional trial spots.