Solvent Exclusion Effect on Infrared Absorption Spectroscopy
Young Jong Lee1, Seong-Min Kim1, Sang Hak Lee1,2
1Biosystems and Biomaterials Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States.
Analytical Chemistry
|July 9, 2025
Summary
Accurate absorption spectroscopy requires correcting for the solvent exclusion effect, where solvent molecules are displaced by solute molecules. This study introduces a simple volumetric method using partial specific volume (PSV) to retrieve accurate solute-only spectra, crucial for molecular analysis.
Area of Science:
- Spectroscopy
- Analytical Chemistry
- Biophysics
Background:
- Absorption spectroscopy relies on solvent transmission as a reference, assuming no solvent light absorption.
- Solvent exclusion (SE) effect lowers absorbance, causing errors, especially with water's strong absorption peaks.
- Current methods for SE correction are limited by spectral breadth and laser source capabilities.
Purpose of the Study:
- To develop a simple volumetric method for correcting the solvent exclusion effect in absorption spectroscopy.
- To accurately retrieve solute-only absorption spectra, particularly for proteins in aqueous solutions.
- To validate the method's effectiveness for both globular and small-molecule solutes.
Main Methods:
- A volumetric solvent exclusion (SE) correction method utilizing partial specific volume (PSV) was developed.
- Spectra were acquired using a quantum cascade laser (QCL) spectroscopy system with solvent absorption compensation (SAC).
- The method was tested on globular proteins and small-molecule solutes in aqueous solutions.
Main Results:
- The PSV-based SE correction method successfully retrieved accurate solute-only absorption spectra.
- The method demonstrated effectiveness for globular proteins and small-molecule solutes.
- High molecular sensitivity was achieved with the QCL-SAC system and SE correction.
Conclusions:
- The simplified PSV-based SE correction is a robust method for accurate quantitation in absorption spectroscopy.
- This technique overcomes limitations of existing methods, especially near strong solvent absorption bands.
- The approach enhances the reliability of spectroscopic analysis for diverse solutes in solution.
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