Maximizing data quality in the gravimetric analysis of personal exposure sample filters

The weighing of particle sampler filters has always been plagued by problem s in the weighing environment: humidity, temperature, drafts, vibration, an d 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 subs tantial reductions in the effects of temperature and vibration, these balan ces are still sensitive to factors such as thermal drafts and zero shifts f rom tilting. Drafts may be controlled through room ventilation modification s, and zero drift can be eliminated by computer-assisted data collection al gorithms. A less well-understood influence is static charge, which is often controlled with a simple radioactive neutralizer. Although radioactive neu tralizers 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 opera tions and have developed methods to minimize or eliminate them.