PerkinElmer Spotlight 400 Series, User Manual

Page: 59 / 120

Preparing Samples . 59
Particles
Crushing
Crushing enables you to thin samples such as large particles that cannot be sliced. This can
be done in various ways:
• If the sample is small, crush it with the roller end of the roller knife.
•
If the sample is larger, use a pestle and mortar.
Separating by aperturing
Powders and other particulate solids may contain several different components. Instead of
separating them, use the infrared 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 at the Monitor Visible window, find a particle of the component you want to
sample.
3. Center this particle in the field of view.
4. Adjust the infrared aperture until only the particle that is of interest is visible.
You can easily pick up extremely small particles and transfer them 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 imager.
Transferring with a tungsten needle
When necessary, sharpen the tungsten needle.
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.