Effect of soil moisture and its correction method for quantitative analysis of hazardous metals in polluted soil for the on‐site XRF analysis

We investigated the effects of soil moisture and its correction method for on‐site XRF analysis of hazardous metals in polluted soil. A wet soil sample was prepared by exposing the water mist generated from the ultrasonic humidifier to dry soil for 0–95 min to reach the soil water content to 0–30 mass%. Calibration curves of six hazardous metals (Cr, As, Se, Cd, Hg, and Pb) measured from the soil certified reference materials JSAC 0461 to 0466 were compared with the water content changed from 0 to 30 mass%. The inclinations of calibration curves of six metals decreased with the increase of the water content. In addition, the XRF intensities of six metals decreased about 15%–20% by adding the water in 30 mass%. It was revealed that the soil moisture effect is caused by two factors as a decrease of the amount of analyte in the XRF generating area, and a change in the sample matrix due to increase of water contents. Thus, a new correction method using the combination between Compton scattered X‐rays and the water contents was applied to overcome the soil moisture effect. Applying the proposed correction method, calibration curves of six metals with different water content gave identical inclinations of calibration curves. The analytical results of chromium in the geochemical reference sample were in good agreement with the standard value even with increased water content.