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: humidity, temperature, drafts, vibration, and electrostatic charges on the filters. These are particularly critical for samples with small mass collections, such as those encountered in personal exposure monitoring for PM2.5. While modern electronic balances offer substantial reductions 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 radioactive neutralizer. Although radioactive neutralizers are effective, their effectiveness decays rapidly with time, and their use may be objectionable for nontechnical reasons. We have analyzed a number of environmental factors influencing gravimetric microbalance operations and have developed methods to minimize or eliminate them.