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2.5 OMNIC Software Overview

OMNIC is the application software used to operate the Nicolet Impact 410 Fourier Transform Infrared Spectrometer in the laboratory. Some of the operations are counterintuitive, so the Intern is encouraged to read the HELP files and consult the Quick Guide kept near the instrument. To collect data:

  1. A background spectrum must be collected before any samples are collected. Only one background spectrum is required for a group of sample data collected in one session.

    1. If diffuse reflectance spectra are being collected, the background spectrum is collected with neat, finely ground anhydrous KBr in the sample cup.
    2. If ATR is being used, the background is collected using the empty, clean ATR cell. Please note that the ATR cell is fragile, and is quite susceptable to thermal shock.

  2. The sample data can be collected after the background run. However, one must examine the data to insure the spectrum contains good data. Diffuse reflectance spectra especially must be carefully watched for two possible sources of problems. Both are manifested as spectra with very weak signals.

    1. the sample is overly diluted in KBr - a technique I've found that works well to eliminate this (and is useful when only very small samples are available) is to fill the sample cup with KBr. A small amount of sample is ground with minimal amount of KBr, and this is sprinkled on the top of the KBr already in the cup. This 'concentrates' the sample at the top of the sample cup, rather than having sample 'wasted' sitting at the bottom of the cup where no light reaches it anyway.
    2. the sample/KBr is not ground to a uniform particle size. This is much more important, and a bit harder to achieve, than when grinding for KBr pellets. The trick here until you get used to how to do it is to grind until you think the powder is ready, then grind some more.

  3. After a good spectrum is collected, the data file must be saved.

    1. Spectra of reference standards should be saved into the directory for standards as indicated by the Lab Manager. Standard spectra may also need to be placed into the local library (ie, we do not add to the commercial libraries that were purchased with the instrument).
    2. Spectra of samples should be saved into the 'samples' directory.

  4. After saving the data, a library search can be conducted. The results, positive or negative, of a library search are never considered conclusive, but are used only as a guide.

next up previous contents
Next: 2.6 Links to IR Up: 2. Introduction to Infrared Previous: 2.4.3 Units for Reflectance   Contents
John S. Riley, DSB Scientific Consulting