Why does the Amide I band region in my spectrum present a shift towards lower wavenumbers?

30 November 2019 0 2K Report

I have several ATR FT-IR spectra of different proteins and amyloids that present a total shift in the Amide I band region towards lower wavenumbers. The maximum at 1620 cm-1 is currently at 1600 cm-1. Therefore my Amide I band region goes from 1650 to 1550 cm-1 instead of 1700 to 1600 cm -1. Can anyone help me with that?

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