What are the causes of poor results on the IlluminatIR?

Applies to: Chemical and Gas IlluminatIR (FTIR) | Tickets Solved: 0 | Rank: 7

What are the causes of poor results on the IlluminatIR?


Sample Thickness - Too thin of a sample will look very “grassy” or noisy. A different particle needs to be analyzed or more scans should be performed. A thick sample will have an absorbance greater than 0.8 and top out the peaks. The sample should be flattened or the operator should move to a different part of the slide.

Sample Flatness:

The sample must be flat on the slide. If the sample is not flat the baseline will not be flat. If the sample is not pressed flat on the slide, a baseline correct can be used in post processing, or another particle should be analyzed.


Sample not centered in aperture - If the sample is not centered the result will again be “grassy” or noisy. The sample should be centered and re-analyzed.

Aperture size incorrect:

The aperture selected should not be greater than 20% of the particle being analyzed. A baseline that tilts upward from right to left is considered to be a result of scatter. A smaller aperture should be selected and a new background and sample analyzed.

Old Background:

Upward- or downward -pointing peaks near 3800, 2300 and 1600 cm-1 in sample absorbance spectrum indicates high abundance of H2O and CO2. A new background should be conducted and the sample should be re-analyzed.


Granular - Move to a different part of the slide and re-analyze the sample.

Reflective - When a sample is reflective negative peaks are observed in the results. Prepare a thinner sample or move to a different particle and re-analyze.

Too Small - Too small of a sample will look very “grassy” or noisy. Find a larger particle with same spectral features.

For detailed instructions please see attached document.

For further questions or troubleshooting please contact technical support.

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Keywords: size, focus, preparation, thickness, flat, centered, aperature, baseline, uneven, tilt, background, CO2, bad results