PerkinElmer Spotlight 150, User Manual

Page: 57 / 107

Preparing Samples . 57
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.
• Coatings on reflective or opaque substrates can be measured using the micro-ATR
objective. See
Collecting Spectra With the ATR Objective
on page 70 for details.
Liquids
Solutions of samples
Although liquids are seldom analyzed with the Spotlight 150, 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.
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.