12.3 Chromatography

LEARNING GOALS

After   Chapter 12.3,   you will    be  able    to:

Identify    the properties  that    can be  used    to  separate    compounds   through chromatography

Differentiate   between thin-layer, paper,  column, gas,    and high-performance    liquid

chromatography

Describe    the three   main    specialized types   of  columns used    in  column  chromatography,

and their   methods for separation

Predict the best    chromatography  method  for a   given   mixture

Chromatography is another tool that uses physical and chemical properties to separate and
identify compounds from a complex mixture. In all forms of chromatography discussed here, the
concept is identical: the more similar a compound is to its surroundings (whether by polarity,
charge, or other characteristics), the more it will stick to and move slowly through its surroundings.

KEY CONCEPT

Chromatography  separates   compounds   based   on  how strongly    they    adhere  to  the solid,  or

stationary, phase   (or in  other   words,  how easily  they    come    off into    the mobile  phase).

The process begins by placing the sample onto a solid medium called the stationary phase, or
adsorbent. We then run the mobile phase, usually a liquid (or a gas in gas chromatography)
through the stationary phase. This will displace (elute) the sample and carry it through the
stationary phase. Depending on the characteristics of the substances in the sample and the polarity
of the mobile phase, it will adhere to the stationary phase with differing strengths, causing the