Whatman™. 513-0118EA 438.51 EUR. 513-0118. Membrane Filters for Air Monitoring, Whatman products (Cytiva) Filtros Filtros de membranas. A high-purity, thin PTFE membrane in a sequentially numbered chemically resistant PP support ring for PM 2.5 ambient air monitoring. PM 2.5 membranes have low tare mass for accurate gravimetric determinations.