Chromatography Simulator
Equations in this simulation
| R_f | retention factor on a plate | between 0 (stays on the baseline) and 1 (runs with the front); both distances are measured from the baseline | |
|---|---|---|---|
| d_front | distance moved by the solvent | grows like the square root of time as the solvent soaks up the plate |
With the current values:
| k | retention factor: time stuck to the plate or packing ÷ time in the solvent | the more polar the compound compared with the solvent, the larger k | |
|---|---|---|---|
| p | polarity of the compound | on a scale running roughly from 0 to 1 (very nonpolar compounds fall below 0), set so the Rf values match published ones in a reference solvent | |
| s | polarity of the solvent | set by the Solvent menu; a more polar solvent carries polar compounds further |
With the current values:
| t_R | retention time of a peak in the column | t₀ is the time the solvent itself takes, set by Flow rate (mL per minute, column) | |
|---|---|---|---|
| N | Column efficiency N (theoretical plates) | a better packed or longer column gives narrower peaks |
With the current values:
| R_s | resolution of the two closest spots or peaks | about 1.5 or more is a clean separation; below 1 they overlap |
|---|
With the current values:
How to use the chromatography simulator
- Choose a plate, a mixture and a solvent. The solvent soaks up the plate from the bottom, the front marked by a blue line, and each compound travels a fixed fraction of the distance the front has moved, set by how strongly it sticks to the polar plate compared with how well the solvent carries it. When the front reaches the top the plate is taken out; the results list each spot's distance and Rf value.
- Try the leaf pigments in hexane and acetone, then in pure hexane or ethyl acetate, and watch the separation change; amino acids are colorless until you tick the ninhydrin stain. The chart is a scan of color intensity up the lane, and the resolution tells you whether the two closest spots overlap. Tick Solvent above the baseline to see what happens when the spots are dipped into the solvent.
- Switch to the column: the bands move down at different speeds and come out into a detector, which draws a chromatogram of peaks. Raise the efficiency N for narrower peaks, change the flow rate to change the dead time t₀, and compare the retention times and the resolution. The Gel Electrophoresis Simulator separates DNA by size instead.
Frequently asked questions
What is an Rf value?
The retention factor on a plate: the distance moved by a spot divided by the distance moved by the solvent front, both measured from the baseline where the sample was put. It runs from 0 (the compound does not move) to 1 (it moves with the solvent). For a given plate, solvent and temperature, a compound always has about the same Rf, which is how spots are identified.
Why do the compounds separate?
Each compound spends part of its time stuck to the stationary phase (the paper, the silica of a TLC plate or the packing of a column) and part dissolved in the moving solvent. The ratio is its retention factor k, and Rf = 1 ÷ (1 + k). Compounds that stick more move more slowly. On a polar plate, polar compounds stick most, so a more polar solvent moves them further.
Why must the baseline be above the solvent?
If the spots sit below the surface of the solvent in the tank, they dissolve straight into it instead of being carried up the plate. Draw the baseline in pencil (ink would itself separate) about 1 cm from the bottom, with the solvent below it.
What does resolution mean in chromatography?
How well two neighboring peaks or spots are separated: Rs = 2 × the difference in retention time ÷ the sum of the peak widths. At Rs = 1 they overlap by about 2%; at 1.5 they are separated down to the baseline. Narrower peaks (higher efficiency N) or a bigger difference in k improve it.
It says WebGL is turned off.
The 3D view needs WebGL, which every current browser has. It can be switched off by hardware acceleration being disabled in the browser settings, or by a very old graphics driver. Turn hardware acceleration on, or try another browser.
Is anything uploaded?
No. The simulation is drawn by your own browser with WebGL; nothing is sent anywhere, and it keeps working offline once the page has loaded.