X-Ray Fluorescence Method for Direct–on–Filter quantification of Airborne Particulate Metals using a Handheld Analyzer

Abstract

The expansion of industrial sectors dependent on welding processes has intensified concerns regarding occupational exposure to metal and metal oxide aerosols. This study presents a direct-on-filter method for quantifying airborne particulate metals using a handheld X-ray fluorescence (XRF) analyzer for exposure assessment purposes. An evaluation of a commonly employed calibration technique utilizing commercial calibration filters was conducted. A new, simplified calibration approach including spiking filters with Certified Reference Material (CRM) solutions was also developed, which is cost-effective and relatively easy to implement. Calibration curves were established employing single-element commercial calibration polycarbonate (PC) filters and both single- and multi-element in-house calibration mixed cellulose ester (MCE) filters, across a range of mass loadings. The analyzer demonstrated excellent linearity (R² ≥ 0.994) and detection limits in the range of 0.03 – 0.35 μg cm^-2 (or 0.82 to 9.55 μg m^-3 assuming a 15-minute sampling time on a 37-mm-diameter filter with a 2 L min^-1 sampling flow rate) for Cr, Mn, Fe, Co, Ni, Zn, As, and Pb, which are adequate for identifying these metals at concentrations relevant to OSHA, Cal/OSHA regulatory thresholds, and most NIOSH exposure limits. Bland-Altman analysis revealed that multi-element calibration resulted in reduced bias and more precise limits of agreement referencing established laboratory techniques. Although the analyzer can detect exposure limits for metals such as Mn, Fe, and Cr (II)/(III), challenges remain for elements like As and Cr (VI), which have lower permissible exposure limits. The non-destructive nature, rapid analysis time, and portability of handheld XRF render it an effective onsite or in-field method, allowing prompt decision making. The method can also be used as a screening method to complement more advanced Inductively Coupled Plasma – Mass Spectrometry (ICP-MS) or Optical Emission Spectroscopy (ICP-OES) methods.