Page 12 - An Inky Lead Questioned Documents

Chromatography

Chromatography is a method of separating the Additionally, a writer who is writing on an uneven
components of a mixture. Just as filtration separates surface or with a defective writing implement
components based on size, and centrifuging will produce writing that varies significantly from
separates components based on density, their normal writing. In these situations, the writer
chromatography separates components based on often produces writing that appears to come from
their solubility in a solvent and their adsorption to someone with a lower degree of graphic maturity
some medium, called the adsorbent. than they actually possess.

Chromatography was first used by the russian botanist mixture along with it. The amount of each
Mikhail Tsvet, during the turn of the last century, to component that dissolves into the solvent differs
separate plant pigments. Tsvet crushed leaves in a with each component, and each component has
solvent, then placed a calcium carbonate rod into different affinities for the solvent and adsorbent.
the solution. As the solution climbed the rod via These affinities are competitive — a component with
capillary action, the various colors of plant pigments a strong affinity for the solvent and weak affinity for
separated, giving a chromatograph, or, literally, a the adsorbent will move far along with the solvent; a
color chart. Over the last century, the methods used component with opposite affinities will move little.
in chromatography have changed, and now different
solvents and adsorbents are used. Currently, several This affinity is characteristic for each component,
types of chromatography exist, including paper however, the absolute distance along the adsorbent a
chromatography, thin layer chromatography (TLC), component moves depends on the amount of time the
high performance liquid chromatography (hPLC), and system is allowed to run. To account for this, the ratio
gas chromatography (GC). In most cases, the mixtures between the distance the component moved and the
being separated are not colored, but the name of the distance the solvent moved it used in comparisons:
technique is unchanged.

Chromatography works based on the affinities for
the solvent and the adsorbent of the component This ratio is referred to as the ‘retention factor’. It is
of a mixture. First, some of the mixture is placed useful for comparing substances analyzed together,
on the adsorbent. As the solvent travels along the for example, on the same TLC plate or paper slip. It
adsorbent and contacts the mixture, it carries the is also useful for comparing substances analyzed
acts that are quickly performed. using the same solvent and adsorbent under the
same environmental conditions, however, because
A given act of writing is also affected by the state environmental conditions do affect this ratio,
of the writer at the time. A writer who is tired, cold, the retention factor is not useful for comparing
under the influence of drugs, nervous, hurried, or substances analyzed at different laboratories or at
influenced by any number of other factors will write different times. To do this, the analyst must run known
differently than they will under ideal conditions. standards side-by-side with the mixtures of interest.

12 THE MYSTERY OF LYLE AND LOUISE