= Thin-layer chromatography
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= TLC
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<Thin-layer chromatography> spreads a thin <chromatographic stationary phase> on a supporting plate. A small sample spot starts on a pencil origin line. The lower edge contacts the <eluent>, whose level must stay below that origin; <capillary action> draws the <chromatographic mobile phase> upward. Components exchange with the <chromatographic stationary phase> as the wet region advances. The leading wet edge is the solvent front. Mark it after removing the plate, before <solvent> evaporation erases it.<Thin-Layer Chromatography (University of Pittsburgh Chem0330)>[Thin-Layer Chromatography, Definition; Solvent; Process Overview, steps 1–4]{ref}
Juniata College's Science in Motion protocol grinds vegetable tissue with about $5\,\mathrm{mL}$ of <acetone>, transfers the extract, adds about $2\,\mathrm{mL}$ of <hexane>, and specifies sampling the upper layer after separation. It spots a <silica gel> plate with a capillary tube, drying between repeated applications; a reference <pigment> occupies another lane. A closed jar contains about $0.5\,\mathrm{cm}$ depth of 70:30 <hexane>–<acetone> <eluent>, below the pencil origin. The plate is removed before the front reaches the top; the front is marked immediately. Spot centres and front are measured from the origin.<Thin Layer Chromatography of Vegetable Pigments (Juniata College Science in Motion)>[Thin Layer Chromatography of Vegetable Pigments, pp. 2–3, steps 1–18]{ref}
The protocol's standard provides a comparison control. It specifies no added <water> in this extraction and reports no measured plate positions or <temperature>. Its tabulated <pigment> values are guidance, not observations from this run.<Thin Layer Chromatography of Vegetable Pigments (Juniata College Science in Motion)>[Introduction table; procedure; blank data tables]{ref}
A useful additional control is an <eluent> blank, checking contamination. Compare sample and standard on the same plate, and optionally apply both together at a third origin position. Agreement under identical conditions supports a proposed identity but cannot prove it: different substances can migrate together. A second <eluent> giving different selectivity strengthens the comparison. One spot cannot establish purity, and a missing visible spot can reflect poor detection rather than absence. Overloading, broad spots, or an uneven solvent front also weaken the readout. These are interpretation checks, not extra observations claimed for the protocol.
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