AUTHOR=Dai Shengyun , Pan Xiaoning , Ma Lijuan , Huang Xingguo , Du Chenzhao , Qiao Yanjiang , Wu Zhisheng 

TITLE=Discovery of the Linear Region of Near Infrared Diffuse Reflectance Spectra Using the Kubelka-Munk Theory

JOURNAL=Frontiers in Chemistry

VOLUME=6

YEAR=2018

URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2018.00154

DOI=10.3389/fchem.2018.00154

ISSN=2296-2646

ABSTRACT=<p>Particle size is of great importance for the quantitative model of the NIR diffuse reflectance. In this paper, the effect of sample particle size on the measurement of harpagoside in <italic>Radix Scrophulariae</italic> powder by near infrared diffuse (NIR) reflectance spectroscopy was explored. High-performance liquid chromatography (HPLC) was employed as a reference method to construct the quantitative particle size model. Several spectral preprocessing methods were compared, and particle size models obtained by different preprocessing methods for establishing the partial least-squares (PLS) models of harpagoside. Data showed that the particle size distribution of 125–150 μm for <italic>Radix Scrophulariae</italic> exhibited the best prediction ability with <inline-formula><mml:math id="M1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mrow><mml:mtext>R</mml:mtext></mml:mrow><mml:mrow><mml:mtext>pre</mml:mtext></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msubsup></mml:math></inline-formula> = 0.9513, RMSEP = 0.1029 mg·g<sup>−1</sup>, and RPD = 4.78. For the hybrid granularity calibration model, the particle size distribution of 90–180 μm exhibited the best prediction ability with <inline-formula><mml:math id="M2" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mrow><mml:mtext>R</mml:mtext></mml:mrow><mml:mrow><mml:mtext>pre</mml:mtext></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msubsup></mml:math></inline-formula> = 0.8919, RMSEP = 0.1632 mg·g<sup>−1</sup>, and RPD = 3.09. Furthermore, the Kubelka-Munk theory was used to relate the absorption coefficient <italic>k</italic> (concentration-dependent) and scatter coefficient <italic>s</italic> (particle size-dependent). The scatter coefficient <italic>s</italic> was calculated based on the Kubelka-Munk theory to study the changes of <italic>s</italic> after being mathematically preprocessed. A linear relationship was observed between <italic>k</italic>/<italic>s</italic> and absorption <italic>A</italic> within a certain range and the value for <italic>k</italic>/<italic>s</italic> was &gt;4. According to this relationship, the model was more accurately constructed with the particle size distribution of 90–180 μm when <italic>s</italic> was kept constant or in a small linear region. This region provided a good reference for the linear modeling of diffuse reflectance spectroscopy. To establish a diffuse reflectance NIR model, further accurate assessment should be obtained in advance for a precise linear model.</p>