An X-ray fluorescence method for direct-on-filter quantification of airborne particulate metals using a handheld analyzer

Abstract

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. A calibration technique that employs commercial calibration filters was evaluated. A new, simplified calibration approach that involved spiking filters with Certified Reference Material (CRM) containing single and multiple elements was also developed; it is a cost-effective and relatively easy method to implement. Calibration curves were constructed using single-element commercially available calibration filters and a set of calibration filters generated in-house across a wide range of mass loadings. The XRF 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 filter, at 2 L min⁻¹ sampling flow rate) for Cr, Mn, Fe, Co, Ni, Zn, As, and Pb. These detection limits are adequate to address most occupational exposure limits. Bland–Altman analysis revealed that multi-element calibration resulted in reduced bias and better precision when compared to Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES) measurements. The non-destructive nature, rapid analysis time, and portability of handheld XRF make it an effective onsite or in-field method, allowing prompt decision-making. The method can also be used as a screening or laboratory method to complement more advanced Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) or ICP-OES methods.