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80 . MultiScope System Microscope User's Reference
Coatings on Substrates
If the sample is coated on a substrate, the method for collecting its spectrum
depends on the nature of the substrate:
•
If the substrate is reflective, you can analyze the sample in reflectance.
• If the substrate is opaque, scrape off a sample of the coating; use the roller
knife to scrape a small piece on to a KBr or BaF
2
disk.
Liquids
Solutions of samples
Although liquids are seldom analyzed with the microscope, sometimes the sample
of interest is in solution.
1. Transfer the solution on to a salt plate.
2. Allow the solvent to evaporate, leaving the sample on the plate.
Micropipettes
You can use a micropipette to apply liquid to the surface of a salt plate, or to the
edge of the junction between two salt plates. In the latter case, the liquid flows
between the plates by capillary action.
Preventing liquids from spreading
If the amount of liquid being transferred to the salt plate is very small, restrict it to
a small area of the plate. There are several ways to do this:
• Use a microbrush to transfer solutions. The bristles of the microbrush hold the
liquid in a small region of the salt plate until the solvent evaporates (see
Tools
You Can Make Yourself
on page 69 for a procedure for making microbrushes).
• Repeatedly jab a small area of the salt plate with a tungsten probe. Leave the
resulting small salt particles in the well that is produced.
The capillary spaces between the salt particles retain the liquid and minimize
spreading.
• Place the salt plate on a small metal washer that is being gently heated.
Because there is more heat at the outside of the salt plate than near the center
(over the hole in the washer), the droplet of liquid is forced toward the center.