High-performance liquid chromatography (HPLC) was previously called high-pressure liquid
chromatography. As the name suggests, the eluent is a liquid, and it travels through a column of a
defined composition. There are a variety of stationary phases that can be chosen depending on the
target molecule and the quantity of material that needs to be purified. This is fairly similar to
column chromatography because the various compounds in solution will react differently with the
adsorbent material. In the past, very high pressures were used, but recent advances allow for much
lower pressures—hence the change in name. In HPLC, a small sample is injected into the column,
and separation occurs as it flows through. The compounds pass through a detector and are
collected as the solvent flows out of the end of the apparatus. The interface is similar to that used
for GC because the entire process is computerized, but uses liquid under pressure instead of gas.
Because the whole process is under computer control, sophisticated solvent gradients as well as
temperature can be applied to the column to help resolve the various compounds in the sample—
hence the higher performance of HPLC over regular column chromatography.
MCAT Concept Check 12.3:
Before you move on, assess your understanding of the material with these questions.What properties of molecules do thin-layer chromatography, paper chromatography, and
standard column chromatography take advantage of to separate compounds?What are the three specialized types of column chromatography? What does each use in
order to separate the sample?Type of Column Chromatography Method for Separating Sample