Maximizing data quality in the gravimetric analysis of personal exposure sample filters
The weighing of particle sampler filters has always been plagued by problems in the weighing environment: hu-midity, temperature, drafts, vibration, and electrostatic charges on the filters. These are particularly critical for samples with small mass collections, such as those en-countered in personal exposure monitoring for PM 2.5 . While modern electronic balances offer substantial reduc-tions in the effects of temperature and vibration, these balances are still sensitive to factors such as thermal drafts and zero shifts from tilting. Drafts may be controlled through room ventilation modifications, and zero drift can be eliminated by computer-assisted data collection algorithms. A less well-understood influence is static charge, which is often controlled with a simple radioac-tive neutralizer. Although radioactive neutralizers are ef-fective, their effectiveness decays rapidly with time, and their use may be objectionable for nontechnical reasons. We have analyzed a number of environmental factors in-fluencing gravimetric microbalance operations and have developed methods to minimize or eliminate them.