title: Buoyancy-corrected gravimetric analysis of lightly loaded filters.
abstract: Numerous sources of uncertainty are associated with the gravimetric analysis of lightly loaded air filter samples (< 100 microg). The purpose of the study presented here is to investigate the effectiveness and limitations of air buoyancy corrections over experimentally adjusted conditions of temperature (21-25 degrees C) and relative humidity (RH) (16-60% RH). Conditioning (24 hr) and weighing were performed inside the Archimedes M3 environmentally controlled chamber. The measurements were performed using 20 size-fractionated samples of resuspended house dust loaded onto Teflo (PTFE) filters using a Micro-Orifice Uniform Deposit Impactor representing a wide range of mass loading (7.2-3130 microg) and cut sizes (0.056-9.9 microm). By maintaining tight controls on humidity (within 0.5% RH of control setting) throughout pre- and postweighing at each stepwise increase in RH, it was possible to quantify error due to water absorption: 45% of the total mass change due to water absorption occurred between 16 and 50% RH, and 55% occurred between 50 and 60% RH. The buoyancy corrections ranged from -3.5 to +5.8 microg in magnitude and improved relative standard deviation (RSD) from 21.3% (uncorrected) to 5.6% (corrected) for a 7.2 microg sample. It is recommended that protocols for weighing low-mass particle samples (e.g., nanoparticle samples) should include buoyancy corrections and tight temperature/humidity controls. In some cases, conditioning times longer than 24 hr may be warranted.
authors.affiliation: Exposures and Biomonitoring Division, Environmental Health Science and Research Bureau, Health Canada, Ottawa, Ontario, Canada. pat.rasmussen@hc-sc.gc.ca
authors.forename: Pat E
authors.initials: PE
authors.lastname: Rasmussen
authors.forename: H David
authors.initials: HD
authors.lastname: Gardner
authors.forename: Jianjun
authors.initials: J
authors.lastname: Niu
mesh_terms: D000393:Air Pollutants / Q000032:analysis*; D004784:Environmental Monitoring / Q000295:instrumentation*; D004867:Equipment Design; D005374:Filtration / Q000295:instrumentation*; D006813:Humidity; D012680:Sensitivity and Specificity; D013696:Temperature
chemical_list: D000393:Air Pollutants