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December 3, 2002
A: FROM MENTOR SHEILA ENGLAND
IN PA
This response to Chromatography question is from my son-in-law
who is a Lead
Chemist with PPG Industries.
Sheila-
There are a number of things that can be used to do this.
Almost any kind
of paper would work, however very porous papers are best,
try tissue paper
or paper towels. Also you can do column chromatography with
powders that do
not dissolve in your solvent. Depending on your experiment
for example you
may want to see how using flour as a solid phase differs from
using a
standard material like silica. Something like a talc may give
different
results, however I have never tried. almost any non-soluble
powder or paper
could be used. Keep in mind however that some may hold very
tightly onto
the compound you are analyzing so that it doesn't move at
all, others may
not be held at all and it may move with the solvent front.
It also may be
of interest depending on your experiment to see how using
a material like
water as your solvent gives different results from using rubbing
alcohol.
You could also try to change the pH of your water. Varying
temperature is
another way to change your
separation. The key to chromatography is to find a set of
conditions
(solvent, solid phase, temperature, etc.) that allows you
to separate the
various components of your mixture in a reasonable amount
of time.
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December 2, 2002
A: FROM MENTOR ROSE CLARK
IN PA
Chromatography is the separation of molecules and comes in
many forms.
Thin layer chromatography is typically done with paper or
a thin layer
of silica on plastic and can be used to separate different
dyes or
organic molecules. I am not sure from your question what the
main point
of the science project is but we have used coffee filter paper,
cloth
(tie-dying), and various materials for column chromatography
for
separation of organic dyes. For separation of dyes, the best
markers to
use are felt-tip black markers that are not permanent since
they will
contain many colors. For column chromatography, Carolina biological
supply sells kits for teaching that any H.S. teacher could
order. The
following is from there web-site: " Kemtec®. Separation
of plant
pigments using ion exchange. Students extract pigments from
fresh plant
materials and then separate them on the basis of molecular
charge and
structure utilizing ion exchange column chromatography. Students
pack
and calibrate the column then separate colorful anthocyanin,
carotene,
chlorophyll, and xanthophyll pigments from plant extracts."
The website
is: http://www.carolina.com/
If you have more questions please ask.
Thanks, Dr. Rose Clark
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December 2, 2002
A: FROM MENTOR JOAN LUSK IN
RI
Paper is definitely the simplest, cheapest, and most readily
available outside of scientific supply companies. the next
simplest
medium is a thin layer of an absorbent material like silica
gel,
supported on a glass plate or a plastic sheet. You can buy
these and
use them pretty much the same way you'd use paper. The process
is
known as "thin layer chromatography" or TLC.
For separating materials in greater quantity, the absorbent
material
is packed into a glass tube, the sample applied to the top,
and a
stream of solvent slowly moves the components to be separated
down
the tube at different rates, depending on how well they stick
to the
absorbent. This method is called "column chromatography."
The
principles are the same as for TLC.
http://www.rohmhaas.com/company/plabs.dir/htmldocs/straw.htm
describes doing column chromatography in soda straws.
There is also "gas chromatography", in which more
volatile compounds
are separated by being carried by a stream of a gas along
a thin tube
of absorbent material. The apparatus for doing this is more
elaborate than for the methods above, but the principles are
the same.
I think you might have more success sticking with paper as
the
supporting medium and varying the solvents and samples that
you use.
What solvents move the same compounds faster or slower? You
can vary
the proportions in an alcohol/water mixture, for example.
Can you
make any generalizations? What different mixtures can you
separate,
either mixtures you make yourself or natural mixtures like
the
different pigments in leaves. You can also explore how to
make
colorless compounds visible on the chromatogram.
There's a lot more about different kinds of chromatography
at
http://groups.yahoo.com/group/chrom-L/links/School_Project_Chemi_000963152786/
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