Perkin-Elmer MultiScope System, User Reference

Page: 79 / 142

Sample Preparation
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79
Separating by aperturing
Powders and other particulate solids may contain several different components.
Instead of separating them, use the variable knife-edge aperture to isolate the
component you want to sample:
1. Spread the sample out with a probe so that you can visually distinguish the
components.
2. Looking through the microscope, find a particle of the component you want to
sample.
3. Center this particle in the field of view.
4. Adjust the variable knife-edge aperture until only the particle that is of
interest is visible.
Extremely small particles are easy to pick up and transfer with a very fine-pointed
tungsten needle. Scoring the surface of the salt plate with the needle makes a
simple map to help you positively identify the particles under the microscope.
Transferring w ith a tungsten needle
When necessary, sharpen the tungsten needle as described in
Tools You Can Make
Yourself
(see page 69).
Nujol or fluorolube mulls
Suspending fine particles of a solid sample in nujol or fluorolube reduces or
eliminates the surface reflections that can distort absorption measurements. These
oils also reduce the amount of radiation lost to reflection or scattering.
If the film is thin enough, you can correct the spectrum for the presence of the oil
by subtracting a spectrum of the pure liquid. It is difficult, however, to obtain the
correct thickness for a good subtraction.
Fibers
Fibers can be rolled to flatten them (see Flattening Solids on page 72), or they can
be pressed in a diamond anvil cell (see Polymers on page 76). The following is
another approach.
Fibrous Solids
If a fibrous sample, such as paper, is too thick, tear it and examine the torn edges.
The edges contain single fibers and thin clumps of fibers.