Determination of trace element concentrations in organic materials of "intermediate-thickness" via portable X-ray fluorescence spectrometry

This research explored the feasibility of using portable X-ray fluorescence (pXRF) spectrometry to quantify Fe, Cu, Zn, and As concentrations in dried and ground organic materials (fungi, vegetation, and animal tissues) with intermediate thickness. The experimental results indicated that pXRF determined concentrations of 39 organic samples (calibration set) with intermediate thickness decreased with increasing sample mass per unit area (also known as surface density or mass thickness) in a power function. The derived mass-correction model allows for correcting the matrix effect caused by analyzing samples with intermediate thickness and for predicting pXRF determined concentrations for infinitely-thick samples. Then a simple linear regression (SLR) model was established based on the linear relationship between the pXRF and inductively coupled plasma mass spectroscopy (ICP-MS) determined concentrations of the organic samples. The SLR model allows for matrix effect correction caused by analyzing organic materials using pXRF soil mode and predicting the ICP-MS concentrations. The mass-correction and SLR calibration models were employed to predict the ICP-MS based trace element concentrations of 10 other organic samples of intermediate thickness (validation samples). The validation results were very good for Zn and As, and acceptable for Fe and Cu. The relative errors (REs) of the predicted Zn, As, Fe, and Cu concentrations were <18%, <22%, <34%, and <30%, respectively. Thus, pXRF shows strong potential for determining the trace element concentration in organic materials of intermediate thickness. The use of pXRF provides an appealing compromise between data quality and analytical time, and a potential alternative to laboratory analysis techniques such as ICP-MS.