Xrf Analysis of Harmful Metals Collected onto Filters as Thin Layers from Workplace Air: Inter-laboratory Exercise

An inter-laboratory exercise has been carried out to evaluate the analytical performance of Method for Determining Hazardous Substances: MDHS 91 for determining Metals and metalloids in workplace air by X-ray fluorescence spectrometry, published by the Health and Safety Executive, United Kingdom. Sets of prepared filter standards were used to “transport” a master calibration established on an X-ray spectrometer at the Health and Safety Laboratory (HSL) to a wide range of makes and types of X-ray spectrometers in over 20 participant laboratories. By subsequent analysis of test filter samples prepared by collection of particulate fume generated from ferrous and non-ferrous alloys, it has been demonstrated that both wavelength-dispersive and high resolution energy-dispersive instruments produced results for masses of most toxic elements of interest to occupational hygiene which were mostly (p>0.75) within 10% or 2μg, and nearly always (p>0.9) within 20% or 3μg, of masses previously determined at HSL. Exceptions were elements measured using analytical lines yielding low X-ray count rates /μg – arsenic (As Kβ), tin (Sn Kα) and antimony (Sb Kα). However, even for these elements, over half (p>0.55) of the masses reported were within 10% and nearly all (p>0.9) were within 20% of masses previously determined, provided these were in excess of 15 μg. It was not possible on the basis of the exercise to make generalisations about the performance of energy-dispersive instruments using Peltier-cooled detectors, because such instruments were poorly represented and because such detectors vary so widely in their sensitivities and energy resolving powers. Nevertheless, it was shown that MDHS 91, is applicable to a range of X-ray fluorescence spectrometers, including wavelength dispersive instruments, energy-dispersive instruments and those using radiation source excitation.