Quantification of trace arsenic in soils by field-portable X-ray fluorescence spectrometry: Considerations for sample preparation and measurement conditions

► Quantitative in situ analysis of trace As (<20 ppm) in soils by FP-XRF. ► Importance of attenuation of measured concentrations by pore water. ► Influence of protective films on analytical results is negligible for As. ► Strong bias demonstrated by in built quantification algorithms in commercial instruments.