Determination of sulfur in soil and plant media using wavelength dispersive X-ray fluorescence spectrometry as a tool for assessment of chemical spills

Sulfuric acid, a highly corrosive substance with a high risk of accidental spills, is important worldwide as a raw material in chemical production. This research aims to develop the best analytical method to determine sulfur contents from the accidental spill sites of sulfuric acid. Wavelength dispersive X-ray fluorescence (WDXRF) spectrometry was selected because of its suitability for mass solid samples and calibration standards were prepared to fit the spill conditions. When the calibration standards were prepared by a solution spiking method, the sulfur concentration showed large differences, especially at the 5.0 wt.% as sulfur standard, for which a concentration of only 4.40 wt.% was detected using inductively coupled plasma-atomic emission spectrometry (ICP-AES) analysis. Therefore, the method of reagent addition to the base material was selected in this study. Natural soil and purchased cellulose powder were used as the base material and calcium sulfate as the reagent. The instrument conditions, such as tube current, generator voltage, and measuring time, were tested with two instruments from different manufacturers and were subsequently optimized. The detectable concentration range of sulfur in this research was 0.001-23.6 wt.% in soil media and 0.002-4.0 wt.% in plant media. When six samples from the spilled site were analyzed, the results of WDXRF spectrometry showed 80-117% recovery compared with those from ICP-AES after microwave-assisted acid digestion as reference values.