Improving the Linearity of Infrared Diffuse Reflection Spectroscopy Data for Quantitative Analysis:  An Application in Quantifying Organophosphorus Contamination in Soil

Abstract

Diffuse reflection data are presented for ethyl methylphosphonate in a fine Utah dirt sample as a model system for organophosphate-contaminated soil. The data revealed a chemometric artifact when the spectra were represented in Kubelka-Munk units that manifests as a linear dependence of spectral peak height on variations in the observed baseline position (i.e., the position of the observed transmission intensity where no absorption features occur in the sample spectrum). We believe that this artifact is the result of the mathematical process by which the raw data are converted into Kubelka-Munk units, and we developed a numerical strategy for compensating for the observed effect and restoring chemometric precision to the diffuse reflection data for quantitative analysis while retaining the benefits of linear calibration afforded by the Kubelka-Munk approach. We validated our Kubelka-Munk correction strategy by repeating the experiment using a simpler system--pure caffeine in potassium bromide. The numerical preprocessing includes conventional multiplicative scatter correction coupled with a baseline offset correction that facilitates the use of quantitative diffuse reflection data in the Kubelka-Munk formalism for the quantitation of contaminants in a complex soil matrix, but is also applicable to more fundamental diffuse reflection quantitative analysis experiments.

Organically Modified Silicas on Metal Nanowires

“…All spectra were plotted in absorbance units, thus avoiding baseline offset errors of the Kubelka−Munk transformation. (52) Vapor-phase water features were subtracted from the spectra using the OPUS atmospheric compensation function. The CO 2 mode centered at ∼2350 cm −1 was mathematically removed, a one point baseline offset was applied at ∼3900 cm −1 , and the Si−O−Si peak centered at ∼1150 cm −1 was normalized to an absorbance value of one to improve visualization.…”

Heterogeneous oxidation of sulfur dioxide by ozone on the surface of sodium chloride and its mixtures with other components

“…Both the absorbance [ Vogt and Finlayson‐Pitts , 1994; Ullerstam et al , 2002] and Kubelka‐Munk (K‐M) function [ Tsai and Kuo , 2006; Averett and Griffiths , 2006] integrated over the ( υ 3 ) region can be used to quantify the surface products. The K‐M method is known to vary with baseline position error that give rise to unacceptable uncertainty levels in quantitative experiments [ Samuels et al , 2006]. Hence the surface products of the SO 2 reactions on NaCl particles in this study were quantified using the integrated absorbance.…”

Heterogeneous chemistry of monocarboxylic acids on α-Al<sub>2</sub>O<sub>3</sub> at ambient condition

“…Both the absorbance (Vogt and Finlayson-Pitts, 1994;Ullerstam et al, 2002) and Kubelka-Munk 5 (K-M) function (Averet and Griffiths, 2006;Tsai and Kuo, 2006) integrated can be used to quantify the surface products. The K-M method is known to vary with baseline position error that give rise to unacceptable uncertainty levels in quantitative experiments (Samuels et al, 2006). Hence, the surface products of the carboxylic acids react on Al 2 O 3 particles in this study were followed using the integrated absorbance-reaction 10 behavior.…”