Development of a Near-Infrared/Mid-Infrared Dual-Region Spectrometer for Online Process Analysis

Abstract

A near-infrared (NIR) and mid-infrared (mid-IR) dual-region spectrometer having two immersion probes, a transmission probe for NIR, and an attenuated total reflection (ATR) probe for mid-IR has been developed for highly reliable process monitoring and deep process understanding. This spectrometer facilitates sequential acquisition of both NIR (10,000-4000 cm(-1)) and mid-IR (5000-1200 cm(-1)) spectra by switching the light path leading to the probes without the need for probe replacement. The use of a single light source and a single beam splitter enables achievement of a permanent alignment of the optical system and sequential data acquisition. The transmission NIR and ATR mid-IR probes designed and developed in the present study facilitate the acquisition of NIR/mid-IR spectra with optimized absorption intensities in both regions by simply placing the probes into a sample solution. The performance of the developed spectrometer was demonstrated in monitoring the ethanol fermentation process. NIR/mid-IR spectra of the fermentation solution with multiplicative scatter correction (MSC) represent the relative changes in the concentrations of glucose and ethanol in both regions. Principal component analysis (PCA) was performed on the MSC-treated spectra in the regions 6300-5650 cm(-1), 4850-4300 cm(-1), and 3500-2880 cm(-1) to detect the end-point of the fermentation as an example of process monitoring. For all the regions, the score plot of the first principal component (PC) indicates that the fermentation progresses with the fermentation time and stops after 210 minutes and thus the end-point of the fermentation exists at around 210 minutes. The loading plot indicates that all of the first PCs are the relative changes in the concentrations of glucose and ethanol. This result reveals that the same chemical changes are observed in both transmission NIR and ATR mid-IR spectra. Multiple and simultaneous analysis was also performed, and intensity change in light scattering relating the growth of yeasts was monitored by the NIR spectra.

In‐situ monitoring of Saccharomyces cerevisiaeITV01 bioethanol process using near‐infrared spectroscopy NIRS and chemometrics

“…Genkawa et al in the development or construction of a dual‐region spectrometer (NIR‐MID IR), included an in‐situ NIR probe but by transmission and not transflection as in the case of this study. Although they stated that “the performance of the developed spectrometer was evaluated using monitoring of ethanol fermentation,” the coverage they present do not consider a detailed and specific monitoring of substrate‐metabolites (glucose, ethanol, glycerol) and biomass, nor the generation of robust calibration models, mainly because it was not the aim of their work.…”

Selection of the NIR Region for a Regression Model of the Ethanol Concentration in Fermentation Process by an Online NIR and Mid-IR Dual-Region Spectrometer and 2D Heterospectral Correlation Spectroscopy

“…7 This spectrometer consists of a halogen lamp, a Fourier transform NIR/mid-IR interferometer, a light-path switching device, a transmission immersion NIR probe with 1 mm optical pathlength, an ATR immersion mid-IR probe with ZnSe internal reflection element, and detectors for NIR mid-IR regions, facilitating the acquisition of time-dependent NIR/mid-IR spectra of a liquid sample during a reaction process by switching the light path leading to the probes. Details of this spectrometer were described in our previous paper.…”

“…Details of this spectrometer were described in our previous paper. 7 Firstly, both NIR and mid-IR probes were set in an empty beaker, and background spectra were measured in the NIR and mid-IR region by using air. The liquid culture medium was subsequently poured into the beaker.…”

“…The 2D NIR/mid-IR heterospectral correlation spectrum is subsequently calculated from the obtained spectral data set to explore an informative NIR region that includes bands of high positive correlation intensity with mid-IR bands assigned to the analyte. The online NIR/mid-IR dual-region spectrometer was recently developed, and facilitates the sequential measurement of both NIR (10000 -4000 cm -1 ) and mid-IR (5000 -1200 cm -1 ) spectra of a liquid sample, 7 which are required to calculate the 2D NIR/mid-IR heterospectral correlation spectrum. Generalized 2D correlation spectroscopy and its heterospectral correlation analysis were proposed by Noda, [8][9][10][11] and many studies concerning the assignments of the NIR band by using 2D NIR/mid-IR heterospectral correlation spectroscopy have been reported.…”

“…Fermentation monitoring has been investigated using NIR, mid-IR, and Raman spectroscopy because of its importance in several fields, such as food, pharmaceutical, and biological sciences and technologies. 7,[18][19][20][21][22] In our previous work, ethanol fermentation was monitored with the online NIR/mid-IR dual-region spectrometer, and principal-component analysis revealed that the detection of the end-point in the fermentation can be performed by using either transmission NIR and attenuated total reflection (ATR) mid-IR spectra based on the same chemical changes: relative changes in the concentrations of glucose and ethanol. 7 In the present study, time-dependent NIR/mid-IR spectra of the fermentation solution were acquired, and NIR bands assigned to the CH group were detected from the 2D NIR/mid-IR heterospectral correlation spectrum calculated from the obtained spectra.…”