Portable X-ray Fluorescence Analysis of Organic Amendments: A Review

Portable XRF spectrometry (pXRF) has recently undergone significant technological improvements and is being applied in a wide range of studies. Despite pXRF advantages, this technique has rarely been used to characterize organic amendments and residues. This article reviews those studies undertaken to date in which pXRF is used to characterize these products. Published studies show that pXRF correctly measures elements such as Fe, Pb, Zn, Mn, Ca, and K but gives conflicting results for elements such as Cr, Ni, and As. Among the reasons that may cause the low performance of the technique with certain elements or under certain measurement conditions would be the inadequacy of the analytical comparison procedures used (i.e., digestion with aqua regia), the lack of knowledge of the interfering effects of organic matter, and sample moisture on the XRF signals and the need for a standardized protocol for performing the measurements. However, the speed and low cost of the procedure forecast a greater future use of this technique, especially in cooperation with other fast spectroscopic techniques based on near-infrared (NIRS) or mid-infrared (MIR) spectroscopies. Chemometric procedures based on one or more of these techniques will allow the prediction of elements below the detection limit of pXRF instruments (Cd, Hg), or other properties of organic amendments (organic matter, N, electrical conductivity, cation exchange capacity).