WASP and EnACT are UK proficiency-testing programmes for the analysis of air monitoring samples. Since the scheme's inception WASP has offered metals spiked onto filters at occupational levels. More recently, realistic filter samples such as welding fume have been introduced into the scheme. The development of a new CEN measurement method for metals in ambient air has highlighted the need for new filter-based QC materials. A multiport air sampler was used to collect large batches of near identical air filters from the ambient air. Representative filters were digested and analysed for As, Cd, Ni and Pb using ICP-MS and by TXRF. Results obtained were cross-checked against filters analysed by INAA and PIXE. It is shown that this sampler can produce batches of filters with an intra-batch precision of typically better than 10 %, which may be sufficient for use in future QA/QC initiatives involving the EnACT scheme.