Light Scattering and Light Absorbance Separated by Extended Multiplicative Signal Correction. Application to Near-Infrared Transmission Analysis of Powder Mixtures

Abstract

The extended multiplicative signal correction (EMSC) preprocessing method allows a separation of physical light-scattering effects from chemical (vibrational) light absorbance effects in spectra from, for example, powders or turbid solutions. It is here applied to diffuse near infrared transmission (NIT) spectra of mixtures of wheat gluten (protein) and starch (carbohydrate) powders, linearized by conventional log(1/T). Without any correction for uncontrolled light scattering variation between the powder samples, these absorbance spectra could give reasonable predictions of the analyte (gluten), but only when using multivariate calibration with a much more complex model than expected. Standard MSC preprocessing did not work for these data at all; it removed too much analyte information. However, the EMSC preprocessing yielded powder spectra that obeyed Beer's Law more or less as if they had been obtained from transparent liquid solutions, apparently by isolating the chemical light absorption from additive, multiplicative, and wavelength-dependent effects of uncontrolled light-scattering variations. The model-based EMSC and its converse, the extended inverted signal correction (EISC), gave rather complete descriptions of the diffuse absorbance spectra and virtually indistinguishable performance in the calibration set and the test set of samples.

Minimising contributions from scattering in infrared spectra by means of an integrating sphere

“…7,15,[17][18] In the past, there have been multiple attempts to understand the nature of the spectral changes associated with scattering and to develop physical models to separate absorption and scattering effects in the IR spectra. [6][7][8]15,19 The models developed in these studies have been incorporated into computer algorithms to minimise scattering effects in contaminated IR absorption spectra. For example, Bassan et al applied the van de Hulst approximation 8 and in a subsequent study an improved model with the full Mie scattering formalism for separating scattering and pure absorption contributions from experimental IR spectra 22 .…”

“…In electromagnetism the extinction is convenient to calculate because it corresponds to the interference between the incident and forward scattered light (=0°, is the scattering angle). 19 Equations (5) and (6) are equivalent because I 0 () =I T () + I Ext (). Absorption and scattering are not independent from each other: Absorption and scattering are optical processes that are intertwined via the complex index of refraction of the sample under study (see equation (4)).…”

Fourier transform infrared microspectroscopy reveals unique phenotypes for human embryonic and induced pluripotent stem cell lines and their progeny

“…Here, spectra were converted to their second derivatives using a SavitskyGolay algorithm using 9 smoothing points in order to minimize baseline effects and to resolve spectral components that would otherwise be overlapping in the underivatised spectra. Normalisation was performed using Extended Multiplicative Signal Correction [26] using the following spectral ranges : 3050-2800 cm À1 , 1770-1730 cm À1 , 1470-900 cm À1 , as these ranges contain biological bands and therefore provided the best possibility of discrimination between different sample types. The amide I and amide II region were omitted from the analysis as this region is greatly affected by resonant Mie scattering, which may have confounded our interpretation of the spectra [27].…”

Spectral pre and post processing for infrared and Raman spectroscopy of biological tissues and cells

“…In cases where the spectral background cannot be completely eradicated experimentally, background removal is commonly performed, by one of numerous algorithms [40,41] e.g. one automated approach is the implementation of the so-called EMSC (extended multiplicative scatter correction) algorithm, originally developed for IR spectroscopy [42]. Common semi-automated computational methods of background subtraction are the subtraction of a polynomial of certain order [43][44][45].…”