Abstract
Detecting clandestine, intermittent release of heavy metal pollution into natural and man-made water ways is challenging. Conventional chemical methods are both labor intensive and expensive. A recent approach combining ion-exchange resins with the capabilities of X-ray fluorescence core scanners (XRF-CS) therefore is of great interest. In short, ion-exchange resin is deployed in the water using small sachets, the resin is then collected, dried, filled into sample holders and scanned using XRF-CS. Ion-exchange resins take up heavy metals in proportion to the concentration in the ambient water, with a correlation coefficient (R2) between concentration and XRF-CS counts better than 0.96 for most elements. However, a number of parameters influence the measurements. Different drying methods introduce differences in the XRF counts because of lattice bound water, resin shrinkage, and disaggregation of the resin particles. Furthermore, the newly developed sample carrier, which was constructed using 3D printed polymers, contains trace amounts of elements that may influence the sample measurements through edge effects and secondary fluorescence. In the tested sample carrier materials, substantial levels of Cr, Fe, Co, and Zn were detected, while Ca, Ti, Ni, Cu, Ga showed variable levels. Ba, Tl and Bi show very low levels, and Pb is only of importance in the PLA carrier. It is therefore necessary to streamline the analysis-process to ensure that the variations in sample treatment and drying and filling methods are minimized. It is also recommended that only spectra from the center of the compartments are used for the evaluation to avoid edge effects caused by secondary fluorescence of metals in the compartment walls. Although the technique of using ion-exchange resin sachets and XRF-CS analysis is only semi-quantitative, it is a cost effective and fast way to monitor large areas for environmental pollution, and the new sample carrier greatly contributes to make the process faster and less error prone.
Highlights
In the 1990’s, the growing number of long, marine and lacustrine sedimentary records retrieved for paleoclimatic research highlighted the need for fast and non-destructive analytical methods
The sachets were collected, rinsed and dried, and the resin was placed in purpose-built cuvettes that could be lined up and scanned with the XRF core scanner
We evaluate the potential effects of different sample carrier materials, the influence of matrix effects when scanning ion exchange resins that largely consist of XRF transparent elements, and how different methods of drying the resin after deployment affect the signal
Summary
In the 1990’s, the growing number of long, marine and lacustrine sedimentary records retrieved for paleoclimatic research highlighted the need for fast and non-destructive analytical methods. The technical solutions differ between the three main players (Avaatech, Geotek, and Itrax), the basic principle remains the same: a split sediment core is shifted relative to an X-ray source, and a detector reads the X-ray fluorescence emitted from the sediment surface This technique is inherently semi-quantitative at best, but it allows for an extremely fast assessment of downcore variations in elements typically ranging from Mg/Al to U; analyses that would take weeks to months using conventional geochemical methods can be obtained within hours. The sachets were collected, rinsed and dried, and the resin was placed in purpose-built cuvettes that could be lined up and scanned with the XRF core scanner This allowed a large area to be assessed, and contamination hotspots related to industries scattered around the farmland could be visualized using geographical information systems. We evaluate the potential effects of different sample carrier materials, the influence of matrix effects when scanning ion exchange resins that largely consist of XRF transparent elements, and how different methods of drying the resin after deployment affect the signal
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