Illustrated Guide to Home Chemistry Experiments

112 DIY Science: Illustrated Guide to Home Chemistry Experiments

pARTII: Two- dImENSIoNAL CHRomAToGRApHy
If an analyte contains several different compounds, it
sometimes happens that a particular solvent achieves
better separation for some of the compounds than for others.
Another solvent might provide better separation of those
problem compounds, but poorer separation of the compounds
that were well separated by the first solvent. One way to
separate such analyte mixtures is to use two passes with
different solvents, reorienting the substrate by 90° between
the runs. The solvent used in the first pass achieves good
separation of some of the components. Those components that
are not well separated by the first solvent are separated by the
second solvent. Because the new solvent front moves at 90°
relative to the first solvent front, the resulting chromatogram is
two-dimensional. Such two-dimensional chromatograms yield
characteristic (and often colorful) patterns even with complex
mixtures of analytes.

1. If you have not already done so, put on your splash
   goggles, gloves, and protective clothing.


2. Prepare six squares of chromatography paper and label
   them A through F.


3. Draw a pencil line parallel to and about 4 cm from one
   edge of each square, and label that line 1. Draw a second
   perpendicular pencil line about 4 cm from an adjoining
   edge, and label that line 2.


4. Spot each square at the intersection of the lines, as
   described in Part I. Spot squares A, B, and C with both

the brown and black permanent marking pens, at least

five times each. Spot squares D, E, and F with both the

brown and black water-soluble marking pens, at least

five times each. Record the analyte for each square in

Table 6-6.

5. Using the stiff wire and two paper clips, suspend square
   A in the first chromatography jar, square B in the second
   jar, and square C in the third jar.


6. When the solvent front approaches the top of each
   square, remove the square from the chromatography jar,
   mark the highest point reached by the solvent front, and
   suspend the square to dry.


7. While the first set of squares is drying, suspend square
   D in the first chromatography jar, square E in the second
   jar, and square F in the third jar. When the solvent front
   approaches the top of each square, remove the square
   from the chromatography jar, mark the highest point
   reached by the solvent front, and suspend the square
   to dry.


8. When the first set of squares is dry, rotate square A 90°
   to put the second pencil line parallel with the bottom
   of the chromatography jar and suspend square A in the
   second chromatography jar. Repeat this procedure to
   put square B in the third jar and square C in the first
   jar. When the solvent front approaches the top of each
   square, remove the square from the chromatography jar,
   mark the highest point reached by the solvent front, and
   suspend the square to dry.

TABLE 6-6: Two-dimensional chromatography—observed data

SquareAnalyte Solvent 1 Solvent front 1Solvent 2 Solvent front 2

ExamplePermanent pensAcetone 8.85 cm Petroleum ether 9.20 cm

A.

B.

C.

d.

E.

f.