Rapid in situ determination of heavy metal concentrations in polluted water via portable XRF: Using Cu and Pb as example

In this research, the effectiveness of using portable X-ray fluorescence (pXRF), with the help of waterproof film, to determine the concentration of the heavy metals Cu and Pb in polluted water was assessed through indoor and field studies. The effects of the thickness of the film and the distance between the instrument and sample were also evaluated. The penetration depth of X-rays in water was found to be between 2 mm and 4 mm, and a water sample of at least 4 mm in depth was thus suggested. The minimum detectable concentration for Cu was ca. 21 ppm and ca. 28 ppm for Pb. Based on the indoor study, the pXRF results were found to be comparable with the certified concentrations of prepared solutions (R² > 0.99 for both Cu and Pb). The field pXRF readings also showed a good linear correlation with the corresponding laboratory results (R² > 0.95 for Cu). The calibration formula derived from indoor analysis was used to correct the field pXRF results and effectively improved the accuracy. Consequently, pXRF has the potential to be applied to the analysis of polluted waters with relatively high concentrations (e.g., >20-30 ppm Cu), which would benefit the in situ monitoring of water pollution caused by heavy metals.