108 DIY Science: Illustrated Guide to Home Chemistry Experiments
SBSTITUTIU oNS ANd modIfICATIoNS- You may substitute any wide-mouth containers
of appropriate size for the chromatography jars.
Ideally, use transparent jars that are large enough
for a 15 cm paper square. Use containers made
of glass or another material that is impervious to
acetone and petroleum ether. To minimize problems
caused by evaporation of the solvent, cover the
containers while they are in use. - Although chromatography paper gives the best
results, you may substitute filter paper if chroma-
tography paper is unavailable. Whatever paper
you use, you’ll need strips about as long as your
chromatography jars are tall. The squares should
be as large as possible, but small enough to fit the
chromatography jar without contacting the side. - You may substitute marking pens in colors other than
brown and black. I chose those colors because the
inks used in them are usually a mix of two or more
different dyes. (continues ... )
LABORATORY 6 .5:
CHRomAToGRApHy: Two-pHASE SEpARATIoN of mIxTURES
Chromatography (from the Greek for
“color-writing”) is a method for separating
mixtures. In chromatography, a mixture
(called the analyte or sample) dissolved in a
mobile phase (sometimes called the solvent
or carrier) passes through a stationary phase
(sometimes called the substrate). During
the passage, various components of the
analyte carried by the mobile phase
selectively adhere to the stationary phase
with greater or less affinity, separating
the components physically across the
stationary phase.
RIREEqU d EqUIpmENT ANd SUppLIES£ goggles, gloves, and protective clothing£ chromatography jar and cover (3)£ chromatography paper strips (12)£ chromatography paper squares (6)£ black and brown permanent and water-soluble
marking pens£ pencil£ ruler (mm scale)£ paper clips (12)£ stiff wire (3 segments)£ water£ acetone (as required)£ petroleum ether (as required)The Russian botanist Mikhail Semyonovich Tsvet invented
chromatography in 1900, and used it to separate chlorophyll
and other plant pigments. Tsvet named his new procedure
“chromatography” because his chromatograms were literally
colorful. Nowadays, chromatography is often used to separate
colorless compounds, so the original rationale for the name no
longer applies.
The simplest chromatography method—the one we explore
in this laboratory—is called paper chromatography. Unlike
other chromatography methods, paper chromatography
requires no expensive equipment or special materials. In paper
chromatography, the mobile phase is water or another solvent,
and the stationary phase is paper. The solvent is absorbed by
the paper, and dissolves a spot of the analyte. As the solvent is
drawn up the paper by capillary action, the various dissolved
components of the mixture are deposited on the paper at
different distances from the original spot.
Other chromatography methods—including thin-layer
chromatography (TLC), gas chromatography, and liquid
chromatography—are often used in laboratories and industrial
processes. These other methods have various advantages
compared with paper chromatography, including faster
throughput, sharper separations, higher sensitivity, and smaller
required analyte amounts. Most chromatography done in
laboratories is analytical chromatography, which requires only
small amounts of analyte and is used to separate mixtures
for subsequent instrumental or wet analyses and to follow
reactions to completion or equilibration. Conversely, industrial
chromatography is preparative chromatography, which uses