Why both MIR and XRF for LiaB analysis

The alpha (MIR) and XRF instruments are two different methodologies of analysis that are complementary and not overlapping: x-ray fluorescence (XRF) is an elemental method, measuring the elemental composition of material. Due to the intrinsic characteristics of the methods, light elements such as B, C, N cannot be detected. Alpha instrument measuring diffuse reflectance spectroscopy in the middle infrared (MIR) range (600 – 4000 cm-1) is a molecular method, measuring the light absorbance of specific molecules such as C- O, N-O, H-O, C-H, among others.

They  have  been  designed  to  work  together  in  the  analysis  of  different  soil  elements  because  their complementarity enhances the strength and reduces the weakness of the properties’ predictions of such heterogeneous  and  complex  media  as  soil.  Though  each  instrument  may  work  separately,  there  are expected  differences  in  accuracy  for  each  case  due  to  the  prediction  capacity.  For  example,  the  MIR (alpha)  uses  an  indirect  prediction  model  through  proxies  such  as  clay  content,  organic  material,  to analyse the total elements while XRF uses direct prediction.

Because of the direct measurement of total elements used by the XRF, the XRF comes in to complement on the strength of the predictions in addition to elements whose predictions are not strong for the alpha instrument. For example, XRF is more accurate  in  the  analysis  of  the  total  P  than  the  alpha. This makes a complete LIAB a highbred of measurement and prediction. Therefore, the fusion approach of the two instruments is highly recommended for increased accuracy.