Our Whatman glass microfiber filter papers in grade 934-AH RTU have been pre-washed, dried (or ignited), cooled, desiccated and weighed, which eliminates the pre-treating steps that are otherwise required by the US EPA Laboratory Standard Method 2540 parts C, D, and E. These glass microfiber filter papers also have fine particle retention of 1.5 µm at high flow rates to process heavy, turbid samples.