34242

2D NIR-MIR correlation spectroscopy - a useful tool to augment the interpretation of NIR spectra

Tine Ringsted 1 ; Sune Vestergaard Lund Dupont 2 ; Jacob Ramsay 2 ; Søren Rud Keiding 2 ; Søren Balling Engelsen 3
Favorite this paper

The idea of two-dimensional (2D) correlation spectroscopy was first proposed by Noda in 1986 and further developed into generalized 2D correlation spectroscopy.[1] The technique can be used to augment the interpretation of overlapping peaks by mapping samples that are modulated systematically (e.g. the samples vary in temperature or the chemical reaction time). The spectra can then be visualized in plots showing how the wavelength variables covary (in the synchronous plot) and change during the systematic modulation (in the asynchronous plot). Barton and co-workers developed a similar technique. Here the correlation coefficients between near- and mid-infrared spectra are mapped in order to show how the fundamental molecular vibrations in the mid-infrared (MIR) region relates with the overtones and combination bands observed in the near-infrared (NIR).[2] Since the interpretation of MIR spectra is much simpler – the interpretation of the NIR spectra can be significantly augmented by analyzing the 2D NIR-MIR correlation plots of the spectral variables.
This work will present a new software tool for 2D NIR-MIR and demonstrate its use on two cereal applications namely (1) bread staling of white wheat bread and (2) barley phenotype characterization.[3] The bread staling experiment was conducted with an experimental design consisting of 6 different types of bread and simultaneous texture profile analysis (hardness measurement), NIR and MIR measurements performed at 3 hours, 9 hours, 1, 2, 4, and 7 days after baking using three replicates. The NIR spectra were collected in the range between 1100-2500 nm using a NIR systems spectrometer model 6500 (NIR systems, Inc., Silver Springs, USA) in reflectance mode and the MIR spectra were collected in the range 4000-400 cm-1 using a Bomem Arid-Zone MB100 FT-IR (Bomem, Quebec, Canada) interferometer equipped with an attenuated total reflectance (ATR) unit. In the case of the barley phenotype characterization 5 different barley genotypes (in 70 replicates) were measured in the NIR overtone region (2235-2381 nm) using an experimental transmission setup and the MIR measurements were recorded with the same Bomem instrument as used in the bread measurements.
This study presents generalized 2D correlation analysis and 2D NIR-MIR correlation spectra of the bread crump staling process. Moreover, previous studies have investigated the NIR spectra of barley and found an information rich area from 2260-2380 nm but these spectra have not yet been assigned. [3] This study provides a thorough assignment of the overtone spectra by using 2D MIR-NIR correlation spectroscopy.

References
[1] I. Noda, Generalized 2-dimensional correlation method applicable to infrared, raman, and other types of spectroscopy, Applied spectroscopy (1993), 47, 1329-1336.
[2] F.E. Barton II, D.S Himmelsbach, J.H. Duckworth & M.J. Smith, Two-dimensional vibration spectroscopy: correlation of mid- and near-infrared regions, Applied Spectroscopy (1992) 46, 420–429.
[3] H.F. Seefeldt, A. Blennow, B.P. Møller, B. Wollenweber & S.B. Engelsen, Accumulation of mixed linkage (1→3)(1→4)-D-β-glucan during grain filling in barley - A vibrational spectroscopy study, Journal of Cereal Science (2009), 49(1), 24-31.