Our laboratory is equipped with two Mettler Toledo XP-6 microbalances and one Mettler Toledo XP2U ultrabalance. The maximum weight capacity of the XP-6 is 6 g, although most of our filters weigh around 50 mg. The quoted readability of XP-6 balance is 0.001 mg. The Gravimetric Mass Sampling is completed in the Sample Handling Lab by AQRC staff. Samples are measured during the pre-processing and post-processing where they are then sent for analysis.