Gravimetric methods based on precipitation or volatilization reactions require that the analyte, or some other species in the sample, participate in a chemical reaction producing a change in physical state. For example, in direct precipitation gravime- try, a soluble analyte is converted to an insoluble form that precipitates from solu- tion. In some situations, however, the analyte is already present in a form that may be readily separated from its liquid, gas, or solid matrix. When such a separation is possible, the analyte’s mass can be directly determined with an appropriate balance. In this section the application of particulate gravimetry is briefly considered.