Single-Path Supercontinuum Near- to Mid-Infrared Correlation Spectroscopy of Aqueous Samples

Abstract

Combining near-infrared (NIR) and mid-infrared (MIR) spectroscopy to cover both the fundamental and overtone combination molecular vibrational resonances allows more robust analytical methods to be used, such as two-dimensional correlation spectroscopy. However, due to the strong differences in molar absorption coefficients and transparency of the optical material, it is inherently difficult to perform NIR and MIR spectroscopy on aqueous samples using a single instrument. Combining spectra from different instruments and sample presentations can result in unwanted spectral variations, which can influence the prediction models and mitigate the advantages of the combination approaches. In this work, a more consistent instrument response is achieved by combining a single supercontinuum (SC) laser spanning from 1000 to 4000 nm as the light source, with an attenuated total reflection crystal and a transmission cuvette in a single-path configuration. Using this approach, NIR–MIR correlation spectroscopy is demonstrated using a set of 22 aqueous samples with varying concentrations of ethanol, sucrose, and ʟ-proline.