An extension to “Mid-infrared spectral interpretation of soils: Is it practical or accurate?”

Abstract

This note extends the topic of the performance of ashing soil samples and then using spectral subtraction of diffuse reflectance Fourier transform mid-IR spectroscopy (DRIFTS) of original and ashed samples in highlighting the significance of the organic fraction. It was found that accurately interpreting the ash subtracted spectra (mid-infrared range from 4000cm−1 to 400cm−1) is nearly impossible not only because soil minerals undergo extreme spectral changes from the ashing process but also because inorganic residues from burning soil organic matter (mainly humic substances) also confound the spectra of the mineral fraction. Removing soil organic matter using wet ashing methods with H2O2, NaOCl, or Na2S2O8 is associated with inaccuracies in spectra interpretation from organic remains (uncompleted organic matter removal) and spectral changes of minerals from wet ashing processes. Accordingly, with the current techniques of dry and wet ashing it is impossible to accurately interpret the ash subtracted spectra of soil samples.