A multimodal spectrometer for Raman scattering and near-infrared absorption measurement

Abstract

Raman and infrared (IR) spectroscopy are complementary spectroscopic techniques. However, measurement of Raman and IR spectra are commonly carried out on separate instruments. A dispersive system that enables both Raman spectroscopy and NIR spectroscopy was designed, built, and tested. The prototype system measures spectral ranges of 2600–300cm−1 and 752–987nm for Raman and NIR channels, respectively. A wavelength accuracy better than 0.6nm and spectral resolution better than 1nm (14.4cm−1 for Raman channel) could be achieved with our configuration. The linearity of spectral response was better than 99.8%. The intensity stability of the instrument was found to be 0.7% and 0.4% for Raman and NIR channels, respectively. The performance of the instrument was evaluated using binary aqueous solutions of ethanol and ovalbumin. It was found that ethanol concentrations (2–10%) could be predicted with a root mean squared error of prediction (RMSEP) of 0.45% using Raman peak height at 882.2cm−1. Quantification of ovalbumin concentration (8–16g/L) in aqueous solutions and in denatured states yielded RMSEP values of 1.05g/L and 0.74g/L, respectively. Using concentration as external perturbation in two-dimensional correlation spectroscopy (2DCOS), heterospectral correlation analysis revealed the relationship between NIR and Raman spectra.