Quantitative Analysis of Organic Liquid Three-Component Systems: Near-Infrared Transmission versus Raman Spectroscopy, Partial Least Squares versus Classical Least Squares Regression Evaluation and Volume versus Weight Percent Concentration Units.

Yan Yan,Zhang Zhang,Xiong Xiong,Qi Qi,Ma Ma,Siesler Siesler

doi:10.3390/molecules24193564

Abstract

The band shapes and band positions of near-infrared (NIR) and Raman spectra change depending on the concentrations of specific chemical functionalities in a multicomponent system. To elucidate these effects in more detail and clarify their impact on the analytical measurement techniques and evaluation procedures, NIR transmission spectra and Raman spectra of two organic liquid three-component systems with variable compositions were analyzed by two different multivariate calibration procedures, partial least squares (PLS) and classical least-squares (CLS) regression. Furthermore, the effect of applying different concentration units (volume percent (%V) and weight percent (%W) on the performance of the two calibration procedures have been tested. While the mixtures of benzene/cyclohexane/ethylbenzene (system 1) can be regarded as a blended system with comparatively low molecular interactions, hydrogen bonding plays a dominant role in the blends of ethyl acetate/1-heptanol/1,4-dioxane (system 2). Whereas system 1 yielded equally good calibrations by PLS and CLS regression, for system 2 acceptable results were only obtained by PLS regression. Additionally, for both sample systems, Raman spectra generally led to lower calibration performance than NIR spectra. Finally, volume and weight percent concentration units yielded comparable results for both chemometric evaluation procedures.

Highlights

Due to the different physical excitation mechanisms of mid-infrared (MIR)/NIR and Raman spectra, molecular interaction in multicomponent systems can affect these types of vibrational spectra to different extents
In this work, apart from comparing the impact of molecular interactions in liquid multicomponent systems on the results obtained by the two different types of spectroscopies, a further topic of this publication are the effects of these structural phenomena on the performance of two different multivariate evaluation routines (PLS and CLS regression) for the quantitative analysis of the investigated liquid three-component systems
The mixtures of benzene/cyclohexane/ethylbenzene can be regarded as a blended system with comparatively low molecular interactions, whereas hydrogen bonding plays a dominant role in the blends of ethyl acetate/1-heptanol/1,4-dioxane

Summary

Introduction

Due to the different physical excitation mechanisms of mid-infrared (MIR)/NIR and Raman spectra, molecular interaction in multicomponent systems (e.g., hydrogen bonding) can affect these types of vibrational spectra to different extents. Hydrogen bonding plays a vital role in the molecular interaction of OH and NH groups with carbonyl or ether functionalities and has significant footprints in the MIR spectra of multicomponent systems with relevant chemistry [1,2,3,4,5]. These spectral effects, Molecules 2019, 24, 3564; doi:10.3390/molecules24193564 www.mdpi.com/journal/molecules. Last but not least—and with reference to previous studies by Mark et al [10,11,12,13]—we have tried to shed light on the consequences of using different concentration units (%V and %W) for the quantitative analysis of the described multicomponent systems

Methods

Results

Conclusion