Pharmaceutical Analysis
TLC Rf Analyzer
Calculate Rf values from a TLC plate image — mark the baseline, solvent front and spots on your phone — or from distances you measured with a ruler.
Calculate Rf values from a TLC plate image
Photograph the developed plate square-on, against a plain background, with the solvent front still marked. Then mark the baseline, the front and the spots.
JPG, PNG or WEBP · or drop the file here
Image processing happens locally on your device. Your TLC image is not uploaded. The analyzer also works with no internet connection.
Rf = distance travelled by compound ÷ distance travelled by solvent front
Both distances are measured from the origin line, in the same unit — the unit cancels, so Rf has none. That is why the photo analyzer can work in image pixels: 210 px ÷ 350 px = 0.60, exactly as 4.2 cm ÷ 7.0 cm. A spot that stays on the origin has Rf 0; one that runs with the solvent front has Rf 1.
Sources: Merck TLC guide; Vogel's Textbook of Practical Organic Chemistry.
References
- Furniss BS, Hannaford AJ, Smith PWG, Tatchell AR. Vogel's Textbook of Practical Organic Chemistry. 5th ed. Harlow: Longman Scientific & Technical; 1989.
- International Union of Pure and Applied Chemistry. Compendium of Chemical Terminology (the 'Gold Book'). Source
Common questions
No. The image is opened, straightened, analysed and measured inside this page on your device. Nothing is sent to a server, and the analyzer works in airplane mode in the PharmaWallah app. A plate is only kept if you press Save analysis, and then only in this browser.
Rf is a ratio, so any unit works as long as both distances use the same one. Pixels are measured straight from the photo. If you also want centimetres, enter the solvent-front distance you measured on the plate under Physical distance calibration.
Detection is only a suggestion. Adjust the sensitivity, choose whether your spots are dark or bright under UV, and re-detect — or add, move and delete spots by hand. Only spots you confirm are used in the results.
Use Prepare plate → Perspective. Find plate places the four corners automatically when it can; otherwise drag them onto the plate's corners and press Correct perspective. Rotate and Crop cover the simpler cases.
From the origin line to the centre of the spot (or its densest point if it is streaked), and from the origin to the solvent front for the other distance.
Between about 0.2 and 0.8. Spots very near the origin or the solvent front are poorly separated; change the solvent polarity to move them into range.
Not reliably. Rf depends on the plate, solvent and conditions. Run the unknown next to a reference standard on the same plate and compare them directly.
Prepared by the PharmaWallah student team. Verify results with your textbook or instructor. Report an error · Editorial policy