lesson
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A black marker line looks like one single ink, but drop a splash of water on it and you will see bands of vibrant blue, pink, and yellow spread across the page.
Chromatography is an analytical technique used to separate and identify the individual chemical substances that make up a mixture (a blend of two or more substances that are not chemically bonded).
In 1900, botanist Mikhail Tsvet invented the technique while trying to separate colorful plant pigments like chlorophyll and carotene from crushed leaves.
📊An interactive side-by-side illustration showing a black ink spot before and after chromatography. On the left: a strip of paper with a single dark spot labeled 'Black Ink Mixture'. On the right: the same strip after development showing three separated colored spots (blue at top, magenta in middle, yellow near bottom). An animated toggle switch 'Run Separation' animates the liquid rising up the paper strip, carrying and separating the colored dyes at different speeds.
How does a strip of paper pull apart chemicals that are already thoroughly dissolved together?
The Two Phases
Every chromatography setup relies on two competing components: a stationary phase that does not move, and a mobile phase that moves through or across it.
In paper chromatography, the stationary phase is the solid strip of chromatography paper (made of cellulose fibers), while the mobile phase is a liquid solvent such as water or ethanol that travels up the paper by capillary action.
📊A clear labeled diagram of a paper chromatography chamber. A glass beaker with a lid contains a hanging strip of white chromatography paper clipped at the top. The bottom 1cm sits in shallow liquid solvent. Labels clearly point to: 'Stationary Phase (Chromatography Paper)', 'Mobile Phase (Solvent)', 'Baseline (Pencil Line)', and 'Solvent Front (Leading Edge)'. Animated upward arrows show the mobile phase climbing past the pencil baseline.
Substances separate because each compound divides its time between dissolving in the moving mobile phase and clinging to the stationary phase.
A dye with high solubility in the solvent and weak attraction to the paper travels fast and far, whereas a dye that binds strongly to the paper stays closer to the starting line.
Why do lab practicals always insist on very specific rules when drawing the starting line and pouring the solvent?