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Uses for Flexible Collodion in the Analysis of Small Particles
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Anna S. Teetsov, McCrone Associates, Westmont, IL |
Flexible collodion is a name given to a solution
of 4 g of nitrocellulose in 100 mL of a mixture of 25 mL of ethanol and
75 mL of ether, with 2% camphor and 3% castor oil (by wt.); the camphor
and castor oil impart the flexibility. It can be found in ˝ liter bottles
in most chemical supply catalogs. Flexible collodion solution should not
be confused with plain collodion solution; collodion solution does not
contain the camphor and castor oil, and is not flexible. This formulation
was first used as a glue (Greek Kolla glue).
click image to enlarge (69K) 
Figure 1 |
About 0.5 mL of the lightly-viscous
solution spread over 2/3 of a microscope slide will form a 25 µm
thick film of nitrocellulose with a trace of castor oil, when the
solvents evaporate. This film is referred to in this article as
collodion film. In a well-ventilated area, a number of these
slides should be made at one time, and stored in petri dishes.
Collodion film is a very popular sample preparation
medium. It is conveniently available on a microscope slide and can
be reconstituted instantly (made lightly viscous) with a single
drop of amyl acetate. Small drops of the reconstituted sample on
the end of a tungsten needle are used for isolating, characterizing
and preparing small particles for further analysis. The reconstituted
sample will remain lightly viscous for up to 15 minutes. The slide
can be reused many times and stored indefinitely (see Figure 1).
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If the particles or substrate dissolve in amyl acetate,
the following options are available: drops of the flexible collodion solution
as received, which contain ether and ethanol, can be used instead.
If ether reacts with the
substrate or particles on which flexible collodion solution is to be used, then
the ether can be replaced with additional ethanol as follows:
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A 1:1 flexible collodion solution and ethanol
are heated in a water bath at about 40°C with constant stirring
until no more bubbles of ether are coming off. The resulting solution
should be used within the next few hours because the solution does
not keep. |
When larger quantities of
nitrocellulose in amyl acetate solution than those picked up with a tungsten
needle from a microscope slide are required, then the flexible collodion
solution in the pint bottle is treated as follows:
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In a well-ventilated area, 6 mL of the collodion
solution and 3 mL of amyl acetate are poured into a 15 mL test tube. The
tube is placed in a water bath at about 40°C and stirred constantly
with a disposable pipette. It will bubble vigorously for 1 to 2
minutes or until almost all of the ether and some of the ethanol
have evaporated. This solution can be stored in Teflon™ stoppered
vials for up to two years. |
Two examples of how the reconstituted solution is
used are explained in the pages that follow:
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