Last week with a Niton XL5 (30 s soil mode), I saw Pb and As reading 15–25% high in clay-rich tailings at about 10% moisture compared to 3051A/6020 ICP-MS, which makes rapid risk screening tricky. Has anyone settled on a field workflow that keeps numbers defensible — Compton normalization, quick desiccant drying to <5% moisture, or routine checks with SRM 2711a — without turning the day into a drying line?
I quit chasing Compton and just “weigh–dry–weigh 10 g” in a vented 32 mm cup with a 12 V food dehydrator (8–12 min to <5% moisture), then scale the wet pXRF result by the mass‑loss factor; on an XL5 this has pulled Pb/As in clayey tailings to within about 10% of 3051A — if the clay films the Prolene, toss the cup and rerun.
And quick example: XL5 30 s soil. ‘Wet/dry pair’ + Compton linear correction, anchored to 2711a https://www-s.nist.gov/srmors/view_detail.cfm?srm=2711a; clays still nudge Pb/As.
I get Pb/As much closer to 6020 by fixing geometry: I pack 32 mm cups to a set mass and height with a 3D‑printed plunger and add a 2 mm boric acid backer so the film stays flat, then run the XL5 30 s soil mode; that took the about 15–25% high bias in about 10% moisture clays down to about 5–8% for me. Small caveat, @OP: if the tailings are sandy the over‑pack can under‑read Pb, so I back off the tamp and do a quick hourly check on one site composite rather than leaning on Compton — “film flatness beats Compton in wet clays.”.