According to EN 71-3:2013 (E) method, the sample is filtered through a 0.45 or 0.22 μm syringe filter.    However, certain small particles, such as cloudy solutions or colored filtrates, may pass through these 0.45μm or 0.22μm filters.    This can lead to inaccurate migration measurements in some cases, as the measurements include not only migrating elements, but also some elements chemically adsorbed on suspended particles.
If this occurs, re-filter the solution using a syringe filter with a aperture of 0.02μm.    If re-filtration is not possible, the migration and separation steps are repeated and filtration is finally performed using a filter with a pore size of 0.02 μm.