The assessment of a method for measurements and lead quantification in air particulate matter using total reflection X-ray fluorescence spectrometers

This paper presents the assessment of a direct method to measure and analyse Pb in air particulate matter (PM) collected on polytetrafluoroethylene (PTFE) filtering membranes prepared by the SMART STORE® procedure. The suitability of grazing incidence X-ray fluorescence technique is verified on a set of continuous and conformal thin film samples created by atomic layer deposition. Different scans changing the angles of incidence are performed and the fluorescence intensity of thin films on PTFE substrate compared with that obtained by similar thin films deposited on Si wafer substrates. The effects of sample preparation, constraints, and limitations of the experimental setup are discussed. The results obtained by three commercial total reflection X-ray fluorescence spectrometers, equipped with Mo or Rh X-ray tubes, are compared. Reference samples with different Pb content are used to define the best measurement conditions, corresponding to the maximum fluorescence intensity. The precision is evaluated in terms of relative standard deviation of the net intensity, taking into account the homogeneity of the PM samples and hardware contributions to the errors. The calibration curves are built on the basis of mono- and multi-elemental Pb loaded PTFE reference samples. The analytical parameters, namely linear calibration and determination range, limits of detection, and quantification, are determined.