Uncertainty Evaluation for Quantification of Low Amount of Benzo[a]Pyrene: Law of Propagation of Uncertainty and Monte Carlo Method for Propagation of Distributions

Law of Propagation of Uncertainty (LPU) and Monte Carlo (MC) method for propagation of probability distributions were used for uncertainty evaluation of low amount of benzo[a]pyrene (BaP). BaP is usually chosen as a marker of Polycyclic Aromatic Hydrocarbons, which are a class of persistent organic micropollutants particularly dangerous for their toxicity and ubiquity. Following the procedure developed at INRiM [4], glass fiber filters, commonly used for the sampling of airborne particulate matter, were spiked with a suitable certified reference material. The spiked filters were then extracted twice by Soxhlet in order to obtain two samples each having different mass fractions of BaP. Such mass fractions were quantified by means of a gas-chromatograph coupled with a mass spectrometer by using perdeuterated BaP as internal standard. In order to investigate the difference in the uncertainties evaluated by LPU and MC methods at the limit of quantification (LOQ) of the analytical procedure, a hypothetical value of BaP mass fraction much lower than the experimental ones was also considered. The results outlined that the two methods applied to the sample containing the highest amount of BaP gave very similar coverage intervals. Instead, at the lower mass, LPU tended to provide larger uncertainty than the MC method. For the case close to LOQ, LPU led to an unphysical coverage interval (spreading over negative values), whereas MC method still produced reliable results.