Determination of metals, matalloids and non-volatile ions in airborne particulate matter by a new two-step sequential leaching procedure. Part B: Validation on equivalent real samples.

Due to the lack of proper standard materials for airborne particulate matter collected on filters, a validation scheme was developed, which is here described, to the aim of testing the application of leaching procedures performing both ions and elemental determinations on real samples of airborne particulate matter collected on filters. The scheme has been developed on a two-step leaching method (extraction in acetate buffer and acid dissolution of residue) previously developed by authors and consists of two series of tests to be run on n pairs of equivalent parallel samples filter-collected. The first series of tests aims to assess on real samples the equivalence between results obtained by the tested procedure with those obtained by the EMEP ions extraction and the EN 12341 standard methods, whereas the second aims to evaluate the reproducibility of analytical results of elemental determination in the leached and dissolved fractions; in the latter case data reliability is also evaluated as a function of the environment-intrinsic variability of real samples. To avoid errors due to sampling differences data from filter pairs were standardized both by gravimetric determination of loaded filters, according to the EN 12341 standard and by the rate [SO42-]A/[SO42-]B, where [SO42-] indicate the soluble sulphate concentration in the extract; in the latter case values improved for all elements and in both fractions. Results of equivalence with standard methods and reproducibility tests are evaluated as mean relative percentage differences (%) and percentage elements recoveries (R%). The application of the validation scheme to the two-step leaching method is here discussed for non-volatile ions and for 17 elements detected on 22 pairs of low-volume collected PM10 samples on Teflon filters.