INTRODUCTION

Mid-infrared (mid-IR) spectroscopy is an instrumental method used to measure the absorption of electromagnetic radiation over the wavenumber range between 4000 and 400 cm⁻¹ (corresponding to wavelengths between 2.5 and 25 µm). Unless otherwise specified in a monograph or other validated procedure, the region from 3800 to 650 cm⁻¹ (corresponding to wavelengths from 2.6 to 15 µm) should be used to ensure compliance with monograph specifications for IR absorption. The absorption of photons causes the promotion of molecules from a ground state of their vibrational mode to an excited vibrational state.