Using hand-held X-ray fluorescence spectrometry for quick analysis of organic amendments

Abstract

The determination of heavy metals in organic amendments, such as compost, manure, biofertilizer, and sludge, generally involves the digestion of samples with aqua regia, and the determination of those in the solution using various techniques. Hand-held X-ray fluorescence (pXRF) has many advantages in relation to traditional analytical techniques. However, pXRF determines the total elemental content and, until now, its use for the analysis of organic amendments has been limited. The objective of this work is the calibration of a pXRF instrument to determine the aqua regia-soluble elemental contents directly in solid samples of organic amendments. In this way, we will avoid the digestion step and the use of other more laborious and slower laboratory techniques. A training set of samples corresponding to the MARSEP-WEPAL (Wageningen evaluating programs for analytical laboratories) program was used for obtaining calibration functions that allow the prediction of the aqua regia-soluble contents from the pXRF readings of total contents. The calibration functions (obtained by multiple linear regression) allowed the quantitative determination of the aqua regia-soluble contents of Fe, K, P, S, Zn, Cu, Pb, Sr, Cr, and Mn, as well as the organic matter content and a semi-quantitative assessment of Al, Ca, V, Ba, Ni, and As contents. For each target element, additionally to their own pXRF readings, the readings of Si, Fe, Al, Ca, K, or S were used as correction factors and introduced in the multiple linear equations, indicating that the calibrations functions found are truly based on the chemical composition of the sample matrix. This study will allow a fast, cheap, and reliable field analysis of organic amendments and of other biomass-based materials. In this way, immediate analysis can be made in the field that would allow, for example, adapting the application to the characteristics of specific batches or discarding non-compliant batches. More complete information on this work can be obtained from López et al. (2019).